Xantrex XW60 CC MPPT any feedback Yet ?

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Now, now, Niel... There is obviously a huge difference in how lightning behaves between when it strikes those wires that come in though the electric meter (or the TV antenna, or vent pipes, or phone lines, or cable TV, nearby trees, etc.) vs those wires that come in from solar panels...

I haven't figured out the difference yet--but obviously there is.

Honestly though, I have found that "Grounding" has become a religion among many engineers and others... Sometimes, when dealing with a "true believer", there is nothing you can say that will change their minds.

Its almost as though that Faraday never invented the Faraday Cage and showed that when everything is at equal potential, it is impossible to see a voltage difference anywhere (example of why all the ground leads should be wired together for common equipment/use).

-Bill

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Henry / SG,

I think the baton of verbosity has been passed!

So, based on your success in dealing with FSEC, have you considered working directly with Wiles to address the NEC 690 "problems"?

Regards,
Jim / crewzer

P.S. You're right about my (lack of) understanding of the innards of the controllers. I'm not an electronics design engineer. I long ago studied both EE and ME, but eventually ended up earning my degrees is Biz Admin and Eng'g Mgmt. If anything, I'm more of an applications engineer than a design engineer.

Solar Guppy

Re: Xantrex XW60 CC MPPT any feedback Yet ?

FSEC was preventing me ( really all FL residents ) from getting a 20K rebate, a good incentive to get that worked around :roll:

Others much longer in this field and much better connected have failed on the NEC thing so I'll pass on another personal mission

Back to my normal writing mode

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Fair enough. But, despite the apparent disagreement, I find this to be an interesting discussion, so let's consider this from another perspective.

Stipulating that the NEC 690 approach is flawed to one extent or another, what should be an acceptable approach to system configuration? Would it be OK to connect a 3,600 W STC array of UL-listed modules to a UL-listed 60 A controller and a 48 V battery bank and let 'er rip?

Might it be one thing to do that in a "mild" environment such as, oh, Florida, but then derate the system by some factor (ala 690-7 temperature correction factors) for more "extreme" environmental calculations?

Hmmm....
Jim / crewzer

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Yep,

There is no reason to derate the charge controller's available power input via the NEC. As long as the device's specifications (max voltage, max available current limited by solar panel output and/or current interrupter device) are met too... At this point, I am going to assume a modern MPPT controller design. I don't know the details of the PWM controllers to know if they have a current limit (and it probably depends on a manufacturer and model basis).

The output current/voltage of the controller is limited by design (just like a computer power supply is limited by design--and believe it or not, one of the limiting options for a computer power supply is to "crowbar" the output--yep, put a dead short on the output if its output voltage is exceeded... Crowbars are perfectly OK because the power supply will current limit--or even fold back to near zero current--and in any case, because lots of current at near zero volts produces little heat and consumes little power from the input).

As long as the input current/voltage does not exceed the charge controller's specification (for normal Listed/Recognized equpment) its ability to safely manage device internal shorts and opens without catastrophic failures--either from internal failures or failures at the inputs from the solar panels.

Perhaps, that is the confusion here... We are typing about a wide variety of devices and capabilities here, but more or less, have been focusing on NEC connections to Grid Tie Inverters (not smaller PWM battery systems).

Older equipment and other designs that don't have to meet the same requirements very well could die if exposed to "over-sized" solar panels as they may not have the internal feedback control to limit output current/power.

And those inverters which have full control over their outputs (max current and voltage) and are designed to never exceed (under normal operation) the rated input current/power. And the inverters are designed and tested to "fail safely" (fail safely is my term--it drove my regulatory engineer nuts because they never want to say if anything fails safely--they just want to say it meets requirements--and there was even a rewrite in an older UL spec. that removed a statement in a later versions that talked about the safety of devices test under that code).

Just like the average computer power supply or inverter. You can connect any load to the device, but it will limit the total power through the device based on its specifications... And it does not matter what its available input current is (except in terms of upstream wiring/current interrupt ratings).

-Bill

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Actually, I've been semi-automatically focusing on off-grid systems.

OK... but, allowing for the "60 A" controller's input voltage limit (~140 Voc), what should be the limit for the array's STC power spec?

Regards,
Jim / cewzer

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

And that is a very good question Jim (not being sarcastic).

There should be a spec. somewhere in the Xantrex documentation that talks about the maximum circuit rating that it can be connected too...

From the Xantrex GT 3.0 specifications (PDF), they list two ratings...

Maximum input is 22 amps (240 VAC connection) and Isc of array at 24 amps...

600 volts * 22 amps = 13,200 watt "solar array" for a 3kW inverter...

Or at minimum operation voltage of ~200 volts DC (round numbers) that would be:

200 volts * 22 amps = 4.4 kW PTC rated panels.

The maximum input wire size is either 6 or 4 awg--which certainly exceeds the 24 Amp maximum Isc--so that, from my guess, would be the result of Design/UL (and possibly NEC) limitations of the input "chamber" for the Xantrex GT... Technically, one could probably wave hands and argue that a 22-24 amp branch circuit breaker on a 1 MW solar array would also meet NRTL requirements too (my guess anyway)...

Jim, I have to go right know--so I will have to take some time and look up the new Xantrex product line. I did a quick post on the Xantrex GT 3.0 because I am familiar with that unit (installed at my home).

-Bill

Now, we can also start asking which xx Imp / xx Isc it is? STC, PTC, -40C/F, +77F, or Isc*125%*125% or whatever too...

nigtomdaw

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Well Ive enjoyed and understood a little of this and Im better off for it.

However Im going to start a new thread extolling the usefullness of Xantrex Sizing Tool that Ive just visited. Good Bit of Kit !:cool:

boB

Re: Xantrex XW60 CC MPPT any feedback Yet ?

crewzer wrote: »

Actually, I've been semi-automatically focusing on off-grid systems.

OK... but, allowing for the "60 A" controller's input voltage limit (~140 Voc), what should be the limit for the array's STC power spec?
Regards,
Jim / cewzer

If the controllers' output current limit is working properly, the input current will be limited to no more than the output current. There may be some overshoot though that lets the input (and output) current go high for a few moments.

I wouldn't (personally) have a problem hooking up a 10,000 Watt array to the input of an MPPT controller, except it would be a waste of money a lot of times (but certainly not always up here in Washington AC). A regular PWM controller (C40 etc) would have very high peak currents though, but average or RMS current would be limited to the output current.

How about a failsafe PV array shading current limit thingie operated by a linear actuator that shades the "too-big" array when the sun is shining too much to limit current ? New product.

boB

nigtomdaw

Re: Xantrex XW60 CC MPPT any feedback Yet ?

I think Wallace and Gromit have one close to production:p

Do you boys get Wallace and Gromit ?

nigtomdaw

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Sorry for being flippant...............................but boBo makes complete sense of this hi tech NEC UL mumbo jumbo.................if a unit can self limit to 60 amp output,,, like the Mx and Xw can it therefore will regulate its imput draw........John Wiles back to basic O Level School for U ! ..Whats O Level in NA terms...High School?



Wow sorted is is this what BB said a few pages ago...... I maybe think so !

Ralph Day

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Have seen a few Wallace and Grommit films. What great actors. Fancy a bit of cheese?

Rlaph

nigtomdaw

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Since this thread is so off topic..........................................yum,yum:p

niel

Re: Xantrex XW60 CC MPPT any feedback Yet ?

is that boBo or boBeye? related to popeye?
bb, what wiles proposed isn't even close to a faraday shield and you don't put the leads through to the area to be protected, but rather around. we aren't just talking emp here either as a full strike may have a slightly less impact when the ground lead does not enter the home and a true faraday shield would not enter the home to be a faraday shield for the home. i did email wiles on the subject of the grounding and he addressed it halfarsed by soon creating that garbage ruling. i do know what i'm talking about on this area of subject matter. i would rather have no ground at all than to do what wiles proposed and sg knows how i feel about grounding being important as i've discussed it before with him and for me to say i'd rather go with no ground than his (cough) ruling says much.

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Niel,

I was referring the the Faraday Shield in terms that for everything that is at the same potential, there is no "problem" with arcing/high currents/etc...

However, by referencing different parts of a system (household wiring in this example) to different ground/circuit potentials--all bets are off.

I have gotten pretty good shocks by touching to ground references separated by ~100' (>60VAC) (was a dolphin exhibit and lots of water pumps, salt water, and bay fill).

Of course, Ground Loops and high frequency effects (light lightning), do have various strange things that they can do and cause problems... It is not really an easy problem to address--and it is even harder to test different grounding systems (G*d--please strike here at 8am Monday...).

-Bill

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

boB wrote: »

If the controllers' output current limit is working properly, the input current will be limited to no more than the output current. There may be some overshoot though that lets the input (and output) current go high for a few moments.

I wouldn't (personally) have a problem hooking up a 10,000 Watt array to the input of an MPPT controller, except it would be a waste of money a lot of times (but certainly not always up here in Washington AC). A regular PWM controller (C40 etc) would have very high peak currents though, but average or RMS current would be limited to the output current.

How about a failsafe PV array shading current limit thingie operated by a linear actuator that shades the "too-big" array when the sun is shining too much to limit current ? New product.

boB

OK... So, what I'm trying to do is bracket this kettle of fish. Here are the "limits" so far:

1) The NEC 690 specs are too restrictive
2) Input current will be limited to output current
3) There might be some current overshoot (I'll come back to that later)
4) An array that's too large is a wate of money
5) Equipment Voc limits muct be observed
6) Equipment ambient temp specs must be observed

Therefore, as a practical matter, a "60 A" controller should be able to deliver ~60 V x 60 A = 3,600 W all day long. Allowing for "typical" conditions of use, a 90% array derating might be a functional and fair compromise.

Accordingly, it seems the practical maximum array size for a 48 V system with a 60 A controller would be ~4,000 W STC.

Thoughts?

Regards,
Jim / crewzer

niel

Re: Xantrex XW60 CC MPPT any feedback Yet ?

i'll give some input here. before i get started boB should know what he described for a new product is a bull sh#t detector.

1> well that's a bit too general for all of it to be too restrictive, but i'd say there are some definite problems with it. i won't say i am qualified to rewrite it, but there are enough knowledgeable people who do agree some aspects need changed.
2> i suppose so, but why do we need to anyway as controllers are only specialized regulators and like other regulators will usually only take from the source what it needs in the case of too much power up to the limitations the controller allows and given all other parameters are met for fusing or whatever on the input/output? i've never seen any power supplies with these kinds of restrictions and that's with an unlimited (ok nearly unlimited) supply of power available from the grid. on the matter of mppt if you want to reap some of the lost charge power back then a 10 or 15% input current reduction would be warranted, but it is not a safety issue if it's even more current potential than the output of the controller is rated at because it won't pass it all. i suppose there may be some circumstances where it should not exceed a certain point like maybe for shunt type controllers, but even then protection devices are in place.
3> protected so who cares? some surges are normal for many electrical items. where's the hazard in allowing full rated current input, as it has already been certified for, to equal its output rating?
4> not at all true as it is only a waste if it doesn't get to to batteries or loads be it grid tied or not due to insufficient electronics to allow it to pass.
5> common sense here i suppose if you want it to work, but what if they aren't so then what happens?
6> again if you want it to work right you will observe it. again what happens if?

i'm not as into it either as henry or boB would be, but even they don't need a bull sh#t detector when it looks and smells like it with flies all through it and wiles is the one to step into it and claim that it was necessary to have it analysed.

ps you also know that he is supposed to keep people safe and what he did on the grounding issue i feel to be very unsafe, while minimally setting up problems of improper equipment operations or failures due to possible ground loops and voltages where they don't belong.

GreenerPower

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Wow ! I thought this thread was over a couple of days ago. Here are my 2 cents on this subject.
* Electrical/electronics devices should spec. only their operating limits - voltages, currents, tempetarure, ventilation/breathing room ... and when the device fails, for whatever reason, it should fail in a "fire-safe" manner. That's what those UL,CSA, ... certifications are for.
* When these devices are used in a dwelling i.e. connected to a building's wiring structures is where NEC comes in to guarantee that the electrical wiring used are safe from fire hazards and people operating around it are safe from electrical shocks.
* It's the responsibility of the system designer/installer to connect these devices to used them within specs and to guarantee these safety measures and the inpector's responsibility to catch errors in the installation to gurantee safety for people living there.

Well, that was ideal. In practical world, there are potitics and economics involved and the competency of the designer/installers and inspectors.

I have mixed feelings for NEC. I believe the intention was good and has been helpful in the past. Now, the technology advances too fast for the regulatory agencies either to catch up or have enough time to sort out what really needs to be there for home owners in term of fire hazards and personal safety. For designers, manufacturers and techies like us, we feel like NEC is, at places too restrictive, some other places not sufficient enough. For home owners, the only thing they can rely on are these regulations and "good inspectors" to make sure they adhere to the standard for their personal safety. But they are at the mercy of the competency of the designer/installer and the inspectors. Too bad, in this new tech area, there is a huge gap here and some people saw this as opportunity to gain power, make money and jump in to fill this gap with wrong intentions. And there are lawyers to jump in and sue everybody involved - manufacturers, installers, inspectors ... when there is a fire caused by the system. As the end result, everybody plays safe at the expense of the owner. I feel bad when a manufacturer has to cave in for political or economic reasons to get their devices approved.
GP

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

crewzer wrote: »

Therefore, as a practical matter, a "60 A" controller should be able to deliver ~60 V x 60 A = 3,600 W all day long. Allowing for "typical" conditions of use, a 90% array derating might be a functional and fair compromise.

Accordingly, it seems the practical maximum array size for a 48 V system with a 60 A controller would be ~4,000 W STC.

Any derating of the controller is defined by the manufacturer and "inspected" by the NRTL. They are the ones that should/will define their operating parameters.

Now, when we design the equipment, we too use the NEC to define, rate, and derate the components (like wiring, chemical/sunlight resistance, ambient temperatures, and input connector box volume).

When NEC derates (in general) it is based on the specifications of the components (like wire insulation). And the wire manufacturers design and "certify" their product to meet the NEC requirements (using a NRTL).

Perhaps a bit of the confusion is the chicken and egg appearance of NEC derating wiring, and then buying wire that meets the specifications.

I would guess (since I was not involved in NEC and how new wire types are added to it) that when a new material/feature/compound of wire insulation is created, the inventor/vendor/NRTL work with NEC to define its particular characteristics. So, when NEC says to derate Type XYZ wire by 30% for 40-50C applications, that should have been based on the performance of the insulation that is defined by NEC/NRTL/Mfg.

And those specifications for "raw" components are now defined and approved for field installations via the NEC.

However, that charge controller is not a component. It is a complete device that has been designed/defined/manufactured with a specification sheet. And if it is installed per that specification sheet--then it meets the requirements of UL1950, IEC1950, etc... And NEC should state that all devices will meet the respective NRTL requirements.

Now, what I have seen in years past was checking for the NRTL mark (was originally only the UL mark)--much of this was done during fire inspections by local cities/agencies. And, for example, if the coffee maker in the lunch room was not "UL" marked--the fire marshal could have the device tossed or the business shut down.

Regarding the maximum practical array--that would not be a "code issue" but an installer/owner issue. The NEC/NRTL/Safety question is what is the Maximum Array (voltage/current) that may be safely installed. And under what conditions will those be (circuit interrupters, wire gauge, insulation type, conduit type, etc.).

Generally, if a Mfg. is smart, their requirements for facility wiring terminating into their equipment will meet NEC (wire awg, insulation, box cubic inches, appropriate termination, grounding, protection against prying fingers, markings, voltage/amperage ranges, etc.).

But, in the end, past the input termination box/cord/etc., NEC has pretty much ZERO responsibility/control about how the box is defined, NRTL Listed/Recognized, mfg. inspected, etc.--that is all the responsibility of the NRTL.

So, whether or not that 4,000 kW array connected to a 60 amp charge controller is defined/tested/listed by UL/NRTL under certain specifications. If that is 100% up to 95F, and derate by 1% per degree F rise to 135 F, or whatever, this is done per the NRTL written/controlled standard. Not by NEC.

And if the unit fails if you run it on a 61 volt battery--NEC does not care other than the wiring to the device will not fail "unsafely". And the NRTL does not care one bit about the reliability of the device other than it fail "safely" too. (I have seen times past that Europe has tried to put quality requirements in some of their specifications through the CE process--but I am not sure that will go anywhere--other than may be to provide some standards against which quality/performance could be defined--kind of like STC and PTC for solar arrays today).

-Bill

niel

Re: Xantrex XW60 CC MPPT any feedback Yet ?

yes, you guys got the feel of the whole subject. take for instance wire and connectors as specs for wires and connectors are out there and speced for use in electrical aspects. now with the approval and insistance of the nec i can no longer put a run of say #6 wire and wirenuts from a pv electrical box meeting the spec of the job when involving pvs. no, now you must get special connectors that are only on #10 gauge wire maximally (if you wish to keep your warranty good on the pvs). you must lower the overall voltage drop so now this wire and connector must go into another connector attached to a #10 wire so that it could go into an electrical box so that this may then be wirenutted to a heavier wire. aspects of the industry did this in conjunction with the nec and created a loss where there shouldn't be and a redundancy as just leaving the electrical box there in the first place was the best thing to do. they tried to make it universal and they really can't make it a one size fits all because of there being so many unqualified idiots making connections as it seems to me the nec is being just as bad as any of those unqualified idiots are. basically to make things more plug and play for safety(?) they created another hazard and best of all you still need the same electrical box with all the proper wirenuts and what have you. they should've insisted on creating a universal connector that could have heavier wire that could be wired into the previously existing electrical boxes, but then soon people would've figured out they could skip that step with wirenuts and wire they themselves could provide and elected to say eliminate that box because they think nobody is qualified to make a good electrical connection in it. the redundancy and hypocrisy is that i have to put another box in there with the very connections that should've been on the pv in the first place they deemed me unqualified to make, but that i am qualified to make the connections in this second box.

it was not my asking, but i thought an answer was warranted as some need to realize the nec really isn't just there making sure of our safety. if i may make an analogy here with the car insurance business, i see the nec as an overseeing agency that wants you to buy insurance to insure the insurance and would make such rulings of convenience as to mandate only a certain universal door will be used on all vehicles. this door is now undersized for the truck it is going on so you must now attach the approved door to the proper door with all of the weight of both on the smaller hinges of the smaller universal door. this small extra door creates the hazard in that application and should not be there, but they were too worried for our safety because a few unqualified mechanics weren't installing the right doors properly. let's not forget the probable kickbacks that are being funneled to only use a particular company's door that one size does not safely fit alland done in the name of our safety.

hey boBeye, you should see what my bs detector is doing. off the scale. also note that guys like boB went through much effort and expenses to prove their product works and works safely within specs listed.

now along comes wiles and says hey i'm important too so i'm (image of wiles talking) telling you that's not enough safety margin and screws things up with redundancy and extra expenses, but also insists on some of his own hazards being created. a typical answer from an idiot in charge might be that this is an industry that needs standards for our safety and in the pursuit of this we cannot make everybody happy. keeping everybody happy isn't their job and nobody is safer when the rule maker creates his own hazards. you can't always protect against stupidity and wiles i think has proven this beyond doubt.

blwncrewchief

Re: Xantrex XW60 CC MPPT any feedback Yet ?

I'm no electronics or solar expert but I have dealt with things that are governed/certified by UL,NTRL,NEC,etc for 20 years. This is in the HVAC industry. Everything I have dealt with there is a clear line in the sand on who governs/certifies what. All components/equipment is certified by UL or whoever the agencies that govern that component falls under. NEC ONLY governs the electrical supply, wiring, over current devices, interconnections, etc to MEET the UL or other agencies certification and specifications for that piece of equiptment. This is where I feel the NEC has clearly overstepped the bounds of what they are suppose to do. Many components I deal with have both minimum and maximum specifications and this is where I can clearly see where NEC is wrong by essentially over ridding the UL etc specifications. Best example I can come up with is what if you designed a charge controller that was certified for a minimum input of 50a and a maximum of 60a? Allot of equipment is certified this way by UL and others. Then what would you do???

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

I have to admit that I'm really struggling with this issue.

For example, I don't see how/where the NEC might be exceeding its "authority". All they're doing is setting a design definition for PV current. For example, they say that a (UL-listed) PV module's Isc spec must be increased by 25% (multiplied by 125%) to accommodate a broad range of infrequent but real environmental conditions. Therefore, a controller rated for 60 A can't be connected to an array rated for more than 48 A Isc.

Derating is not new to the NEC. For example, and leaving out all of the "conditions of use" boiler-plate, a wire that's UL-rated for 10 A can only carry 8 A per the NEC. Circuit breakers also usually have similar deratings.

I have to set this aside for a while... my head hurts. Also, now that portions of 690 have been so well shredded, I was hoping that we could collectively develop and defend alternate application "rules. My initial attempt above failed to spur us in that direction.

Regards to all,
Jim / crewzer

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Jim,

Just for clarification, is the 60Amps Charge Controller Input current rating or Output current rating? And what make/model specifically are you referring to?

Because, as an example, the Xantrex GT 3.0 is rated at Imp=22amps and Isc=24 amps (a bit too close together IMHO--unless that is STC rating and it has been taken into account that these panels could be installed in a -40C/F environment--but that should have been taken into account when the panels themselves have been NRTL tagged too)--that at maximum rated voltage Imp gives 13,200 watts of available power for 3kW grid tied inverter.

If, Isc is the concern, then the device should be rated for Imp=60amps, and be "safe" to connect to an array with Isc of (example) =75amps (at a defined temperature--or give the requirements for on-site calculations) or a branch circuit protected by a 75 amp maximum circuit breaker. And the "person" would have the choice to either install Isc=75 amps, or install a 75 amp Circuit Breaker (and associated wiring).

As I added the "marking the UL on the panels too) Isc rating... That kind of gets back to the "problem" with NEC derating the inverter/charge controller...

Should not have NEC derated the solar panel Isc too? I mean, that 8 amp panel be derated to Isc=6.4 amps maximum?

No?--is this because the panel is self regulating (based on the physics of the panel)? Or should this panel have a 8 amp fuse on the output so that we have random trips and that well will teach those inverters not to draw so much power?

Or, is has it been assumed that the panel output current cannot be managed by NEC (only by UL/NRTL) and so they focused on the unit that self regulates based on actual measured current and voltage?

If the physics of the inverters/controllers was such that you could not "derate" them by cutting down on the number of solar panels--but instead the devices would not work if the exact number of panels required were connected...

Bet that NEC would have just ignored the whole issue--just like they have on the Solar Panel Isc derating today...

I just cruzed through the XW solar charge controller installation chapter (XW installation guide) and:

Array Size:

For PV array sizing guidelines, use the XW Solar Charge Controller PV array sizing tool accessible from www.xantrex.com/support.

Although the Solar Charge Controller can harvest a maximum of 3500 W, the PV array size can be as large as 6720 W (based on 48A×140Vdc=W).
...
Panels rated up to 48 A at 25 °C (77 °F) are recommended to allow for increases in Isc at low panel temperatures and at solar noon. Ensure that the Isc rating under all conditions does not exceed 60 A. A factor of 1.25 is applied to the rated Isc at 25 °C (77 °F) when the panel is colder than -21 °C (70 °F).

But yet, the battery output of the same controller is rated:

Battery Circuit

The DC-rated fuse or circuit breaker between the battery and the XW Solar Charge Controller must have a maximum size of 1.25 × 60 A (the maximum current rating of the XW Solar Charge Controller). That is, the fuse or circuit breaker must be rated equal to or above 75 A.

A bit of confusion in the manual... Maximum would be never exceed 75 amps. Equal or above would mean how high? 80A? 100A? This is where one needs to read the NEC (don't have) and see what it requires (round up? round down? use a higher temperated insulation to allow larger breaker?)

Well... Back on topic, here we have the input connected to a relatively low current source (solar panels) that is designed for 60 amps, limited by panel installation down to 48 amps.

But, we also have the same terminal/box connected to a 60 amp rated minimum circuit--which is really x 125% or 75-80 amp breaker.

Should not the 60 amp output also been derated to 48 amps somehow?

Why could not allow the solar panel input have Isc=60 amps or even Isc>75 amps and protected by a 75-80 amp breaker? Why is derating the only allowed option. The charge controller will not draw more power than it has been designed/approved for by NRTL/UL.

Or could the the Xantrex Solar Panel input be rated for connected to a 75-80 amp capable branch circuit and then use Isc calculation rules and/or a 75-80 amp rated breaker...

This is typical from what I have seen from regulatory agencies sometimes. Focus like a laser on one piece (input solar panel Isc rating for a charge controller/inverter) and completely ignore the implications (derating somehow the solar panels themselves is ignored because it can't be done and is obviously stupid) to ignoring the 8,000lb gorilla (battery bank with tens of thousands of short circuit amperes available).

What is the maximum interruptible current for the 80A, 160 Vdc, Panel Mount, UL/CSA breakers? I bet the short circuit capacity of a 2,000 AmpHour 48 VDC battery bank (max suggested/rated for XW system) could make one of these beakers go up in a cloud of plasma.

-Bill

crewzer

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Bill,

I know you’re trying to help. Your argument appears to be well organized and presented, but my head still hurts. Here are some comments on some particulars that I believe I understand fairly well:

1) I don’t think that PV modules need to be derated. Without intending to be flippant, the CEC already derates PV modules’ power specs, and the NEC already requires “uprating” module voltage (690-7) and current (690.8 ).
2) The “60 A” rating of the TriStar-60 (PWM), MX60 and the XW-60-150 (both MPPT) is the continuous output current rating, subject to ambient temp conditions. It’s also possible to make the MX60 overheat and shutdown by operating it in conditions of high input voltage (i.e., ~114 V) and max output current.
3a) The array size comments you found in the XW manual are the very ones that are to be changed based on SG’s comments early in this thread.
3b) Check the XW’s online sizing tool. It includes a note re the NEC and the 48 A Isc limitation. It’s easy to update web pages these days.
4) The 60 A controllers output circuit breaker would normally be sized at 60 ADC x 125% = 75 A per NEC 690.8(B)(1). However, 690.8(B)(2) provides an exception and allows for an overcurrent device in an assembly listed for continuous operation at 100% of its rating shall be permitted to be utilized at 100% of its rating. OutBack and Midnite Solar both sell DC circuit breakers rated for 100% continuous duty, so it’s OK to use their ~60 A breaker on the output of a 60 A controller. For example, I use MidNite’s 63 ADC 100% duty breaker on the output of my MX60.
5) Part of the reason why an OCD is required on the input of the controller is because of the battery. Note that OCD's are not required between the PV array and the controller/inverter for battery-less utility-interactive installations per NEC 690.9(A).

My head still hurts…
Regards,
Jim / crewzer

boB

Re: Xantrex XW60 CC MPPT any feedback Yet ?

I believe that the "intent" of this NEC overcurrent ratings stuff is to protect the WIRES from overheating, not the unit itself, which is why the wiring must be sized higher amperage for a given wire temperature.

If 48A is Isc, then you can't have 48A * 140V = 6720 W because that would be comparing apples and moon rocks. They just don't taste the same and can't be had at the same time.

boB

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

crewzer wrote: »

1) I don’t think that PV modules need to be derated. Without intending to be flippant, the CEC already derates PV modules’ power specs, and the NEC already requires “uprating” module voltage (690-7) and current (690.8 ).

CEC derates PV module specs. so that they pay less money for installing the system (and, it is closer to actual output in real life use--not arguing that point). Panels are not derated for any safety issues (i.e., Isc is not increased by CEC, Vmp/Imp is derated for average use).

2) The “60 A” rating of the TriStar-60 (PWM), MX60 and the XW-60-150 (both MPPT) is the continuous output current rating, subject to ambient temp conditions. It’s also possible to make the MX60 overheat and shutdown by operating it in conditions of high input voltage (i.e., ~114 V) and max output current.

Ambient temperature conditions are defined by the manufacturer and "listed" by the NRTL/UL. I have seen equipment that lists 100% power/output/etc. at 70F and derate linearly to 121F. I have seen equipment that is rated at 95F and derated, and I have seen equipment that is rated 100% at 121F... While temperatures inside the unit may have some connection to NEC (input wiring temperatures), derating had nothing to do with the NEC (at least for office and telephone company equipment).

3a) The array size comments you found in the XW manual are the very ones that are to be changed based on SG’s comments early in this thread.

--yea, remembered something like that somewhere here...

3b) Check the XW’s online sizing tool. It includes a note re the NEC and the 48 A Isc limitation. It’s easy to update web pages these days.

Because it was forced by the NEC as amended by our good friend does not mean that it is right.

4) The 60 A controllers output circuit breaker would normally be sized at 60 ADC x 125% = 75 A per NEC 690.8(B)(1). However, 690.8(B)(2) provides an exception and allows for an overcurrent device in an assembly listed for continuous operation at 100% of its rating shall be permitted to be utilized at 100% of its rating. OutBack and Midnite Solar both sell DC circuit breakers rated for 100% continuous duty, so it’s OK to use their ~60 A breaker on the output of a 60 A controller. For example, I use MidNite’s 63 ADC 100% duty breaker on the output of my MX60.

Don't have any issue with that--they have either re-spec'ed a standard device with a lower rating or possibly have made a more precise device that can detect/trip closer to 60 amps...

However, as a question for you--Say I have a 60 amp breaker on a branch circuit. Can I run the circuit at 60 amps or must I populate the branch circuit at no more than 48 amps?

The original intent for the NEC up sizing by 125% of branch wiring installed equipment was to allow for head room for unexpected loads

For example, I could have hardwired (fixed) gym lighting with 60 amps of lamps--but I would still have to rate the branch circuit to be 125% of 60 amps (75/80 amps) to allow for a safety margin. So, even though I could have put a 60 amp rated circuit breaker and run at 100% load--I still would have had to install an 80 amp branch circuit because NEC does not normally allow any branch circuit to be hardwired to 100% of rated load (as I understood the NEC requirements).

By the way ,why is it not allowed for the Inverter/Charge Controller to run at 100% of continuous duty too (as already listed by UL/NRTL's)?

5) Part of the reason why an OCD is required on the input of the controller is because of the battery. Note that OCD's are not required between the PV array and the controller/inverter for battery-less utility-interactive installations per NEC 690.9(A).

Does not make any sense... Solar panels are "batteries"--but they only output power when the sun shines... Whereas a chemical battery only outputs power when the chemistry is still in a "charged" state. No difference to me or the NEC (that I could see).

But my concern that I raised that "so the solar panel can increase its rated short circuit output on cold days by 25%--a single lead acid battery can over drive a 60 amp branch circuit by what--1,000% (100x60amps=6,000 amps)????

Put a 20 100 AH batteries in parallel (for 2,000 AH) and increase the voltage from 12 volts to 48 volts--what is the realistic short circuit potential of that pile of batteries? (pun intended).

Here is was a test made of a 12volt 30AH VLRA battery (PDF file of report). This is not a big battery and one could expect 800-2,000 amps when shorted (depending on test conditions)...

So, for a 48 VDC 2,000 AH system--we could extrapolate short circuit current of:

48v/12v * 2,000AH/30AH * (800-2,000 amps) = 213,000-533,000 amps available...

My question about the ratings of the 60-80 amp circuit breakers was not about the 100% or 125% rated trip current--but the interrupt cabability of the breakers...

A normal "home" AC main panel circuit breaker is rated to interrupt 10,000 amps (because of the design of the pole transformer).

That is the interrupt capability of the typical DC breaker used in these "NEC" spec'ed Solar systems on the battery side?

Again, I am hardly concerned with all of the ajidija that is wrapping us around the 60a/48a derating on the solar PV side (this is just a "questionable" NEC interpretation that costs extra money)... that is nothing compared with the currents available from the battery banks as defined here (which is a real safety issue)...

My head still hurts…
Regards,
Jim / crewzer

Hope you feel better soon Jim!

-Bill

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

boB wrote: »

I believe that the "intent" of this NEC overcurrent ratings stuff is to protect the WIRES from overheating, not the unit itself, which is why the wiring must be sized higher amperage for a given wire temperature.

If 48A is Isc, then you can't have 48A * 140V = 6720 W because that would be comparing apples and moon rocks. They just don't taste the same and can't be had at the same time.

boB

I agree with boB on the first statment (can't get in trouble with agreeing with an expert--can you )

The second paragraph sort of explains why I think NEC is all wet on the issue... The MPPT charge controller can certainly output 672 amps into a 10 volt ("dead") 12 volt battery bank based on a 6,720 watt panel (on a cold day-- see note)... So even derating this by 25% doesn't change the output current to any where near 60 amps maximum.

So this just limits the input current--and they could have chosen wire awg/insulation/packing ratio/ambient temperatures to support 60 amps on the input + 125% branch circuit rating buffer with no problem at all...

In fact, I can argue that since the "cold" Isc is higher, then the cold Isc ambient temperatures are lower... So what does NEC (up) rate a branch circuit with an ambient of 0 degrees F? Seems to me the colder weather should support higher short circuit currents as the system cools. And once the panels warm up to 77F--then can used the standard ambient temperature ratings of the wiring--Right? :cool:

-Bill

Note: I realize that the 60 amp MPPT controller will not output more than 60 amps unless there is a weired falure... And no failure on earth would allow it to output 10x is rated current in any fault condition (this is different than a shorted output stage where a battery can certainly output 10,000x rated current back into the inverter if installed incorrectly or an interrupt device fails).

blwncrewchief

Re: Xantrex XW60 CC MPPT any feedback Yet ?

Ahhh the fun of code discussions:p I hope everyone is just using this as a good constructive discussion. BTW, I specifically did not say the NEC had overstepped its authority as I am not aware of what authority the NEC in and to its self really has at all by my definition of authority. As far as my little world is concerned, as a end user or installer, the NEC only produces guidelines which may or may not be enforced upon me. My state has only adopted the 2002 NEC, my local county has adopted the 2005 NEC and has added to/changed some of that, and one city in the county has adopted the 2008 NEC So I can do the same job in three different places with in 5 miles and fall under three possibly different sets of codes:grr And as my local inspector told me, the only interpretation I need to follow is his as he is the "authority having jurisdiction" I do not know how it applies to a equipment manufacturer?

BB.

Re: Xantrex XW60 CC MPPT any feedback Yet ?

blwncrewchief wrote: »

And as my local inspector told me, the only interpretation I need to follow is his as he is the "authority having jurisdiction" I do not know how it applies to a equipment manufacturer?

And the local inspector has no legal liability for his interpretations--as far as I know--which isn't very far (or even lack of performing his/her duty--as was found decades ago by some condo owners in the town I grew up in where it appeared the inspector never even bothered to inspect the grading/compacting/foundations for a 10-20 unit development and the foundations began failing only a few years later).

And, from what I could tell--as a designer/mfg--it only applies in that we get the "mark" and how we do it is our (and our NRTL's) business.

-Bill

boB

Re: Xantrex XW60 CC MPPT any feedback Yet ?

If the AHJ doesn't approve of your installation, the two main options are to educate the AHJ and/or go to her/his supervisor. Both of those usually work if everything is REALLY OK. Sometimes you will want to leave a screw loose or something that the inspector can find easily to make them feel good.
Then, sometimes they just find little stuff (but important) that needs attention and all will be good after it has been taken care of.

However, the AHJ has the authority NOT to sign off your system.

One decent NEC resource BTW, is www.mikeholt.com He has a good site, interesting newsletter and forum etc. but it is rarely about PV. Sometimes it is.

boB