Question on Square D-QO panel

stoichiometry · July 2011

Hello there,

What is your experience with square D-QO outdoor panel as a combiner box?

Here are details:
-I have six 205 W evergreen 12V panels - [I'm saving money to add an additional two]
-3 strings of 2 connected to give 24V nominally.
-I want to take the three lines [Tray cable wiring] and run them into a square D-QO panel. From there, I would run them into a "main breaker" and Ground fault 63A breaker [ugh ... but required per NEC] before connecting to the charge controller.

Regarding the combiner box, I probably have two options: (1) I can do this outside under my solar panel rack, or (2) I can run the tray cable wires from the strings 10 feet into my 'powershed' and combine them in a QO indoor panel. For cost reasons, I'm considering doing this *outside* but I generally don't trust any electrical connections made 'outside'.

What is your experience with QO outdoor panel boxes? Do they hold up? Are they good and watertight?

Thanks for any insight.
MS

Vic · July 2011

Re: Question on Square D-QO panel

This post has been sitting here for some time ...

So, will add a comment or two. I have not used QO parts as ANY part of a DC system, altho, the Breakers are rated for DC up to 48 V nominal system voltages, and to about 50 or 60 Amps Breakers, I forget.

Have used Square D QO panels in sheltered outdoor locations, and they do fine. In general, I do like Square D products (now a Schneider company).

You probably do not want a WATERPROOF outdoor enclosure. Bet the normal QO box is type 3R -- called "raintight", which is really a box that protects the guts from direct rain, and drains any wind-blown rain, and allows any condensation to drain, or evaporate.

As you probably know, 3R boxes are usually rated for vertical installation, and some will allow mounting flat to a sloped roof, of a certain slope. For example, many of the Outback and MidNite combiners are rated for mounting flat to a sloped roof with pitches of 14-or-more degrees.

Have not looked up the spec for NEMA Type 3R boxes. This slope spec may be in that category, such that all 3T boxes must meet that spec ... Will look later.

QO is a neat solution, especially because they can often be found locally, and they are a bit less expensive than an OB or MN combiner giblets. However, these real combiners use breakers which have screw terminals for BOTH the common BusBar, AND the wire from the PV string. I have not been a great fan of push-on common busses, but they are the norm for consumer-grade AC panels, and also for many light/medium commercial MSB equipment, in my limited experience, and opinion.

Good Luck, Vic

Dave Angelini · July 2011

Re: Question on Square D-QO panel

Along with the previous the type QOU is a little better with set screws for both contacts as oposed to relying on the bus/mounting system for one terminal. The breaker sits on a DIN rail and if outdoors with DC it will be better over the long haul than type QO.

Vic · July 2011

Re: Question on Square D-QO panel

Hi Dave,

Yes, do use QOUs here, but they are EXPENSIVE, compared to MN DIN-Rail DC and AC Breakers.

The QOU do have an advantage of directly fitting into Trace ACCBs, as that is the breaker for which they were designed.

Think that the QO breakers are about $8, or so for a single. IIRC, the QOUs are $25-30 for a single, and around $50-60 for a double.

The MN-marketed CBI breakers are dirt cheap as DC and AC types.

Just MHO, Get Trackin', Vic

stoichiometry · July 2011

Re: Question on Square D-QO panel

Vic,

Thanks! I sincerely appreciate you sharing your time and experience. When digging around, I found that QO boxes were approved for low voltage DC. I figured it was a good way to make a combiner box. I am running 11.5 Amps DC at 24V (nominal), so I figured it was ok . I can find the parts at any local store and probably even at the two big box super hardware stores.

It'll be mounted vertically (my panels are on a ground mounted pole), so I don't expect much problem from rain.

Do you think for an application such as mine that MN combiners are better? I'm hesitant to spend a ton of money here, esp if the QO works 'perfectly fine'. I can buy the outdoor combiner and breakers for what it'll cost me to ship a MN combiner.

BTW - This question might be naive, but I have limited experience with DC. Would a 15A or 20A breaker be better for my 11.5 Amp DC line?

Kindly,
MS

"QO is a neat solution, especially because they can often be found locally, and they are a bit less expensive than an OB or MN combiner giblets. However, these real combiners use breakers which have screw terminals for BOTH the common BusBar, AND the wire from the PV string. I have not been a great fan of push-on common busses, but they are the norm for consumer-grade AC panels, and also for many light/medium commercial MSB equipment, in my limited experience, and opinion."

BB. · July 2011

Re: Question on Square D-QO panel

NEC (and circuit/breaker design) requires a minimum of 1.25x your maximum continuous current--Or you will trip your fuse/breakers over time (at 100% rated current, a breaker will trip in minutes to hours--depending on lots of variables).

If this is a solar array, 1.25x to 1.56 Isc would be the area I would aim for the breaker.

Also, most newer/larger panels have a Series Protective Fuse rating--which is exactly what you are supposed to use (for code). You, most likely, will not find any standard main panel branch circuit breakers at the smaller SPF ratings.

-Bill

stoichiometry · July 2011

Re: Question on Square D-QO panel

BB. wrote: »

NEC (and circuit/breaker design) requires a minimum of 1.25x your maximum continuous current--Or you will trip your fuse/breakers over time (at 100% rated current, a breaker will trip in minutes to hours--depending on lots of variables).

If this is a solar array, 1.25x to 1.56 Isc would be the area I would aim for the breaker.

Also, most newer/larger panels have a Series Protective Fuse rating--which is exactly what you are supposed to use (for code). You, most likely, will not find any standard main panel branch circuit breakers at the smaller SPF ratings.

-Bill

Bill,

Thanks. Two follow-up questions:
(1) so 11.45Amps on label as Max current x 1.25 =14.5 Amps. I was going to upsize to 15, but then I didn't know if it was wise to go 20 Amp QO breaker. I've never worked with DC, and I know there is no zero point as there is in AC. Perhaps the extra 5 Amps would be wise because of enhanced power on colder days?

(2) The SPF rating is 20A. This is what I am supposed to use?

I guess I answered my own question -- I am to use a 20A breaker, correct?

Cheers,
M

BB. · July 2011

Re: Question on Square D-QO panel

M,

You got it!

I am after "safe and reliable" power... Running too small of fuse/breaker is a pain with false trips. Too big--Fire is even a bigger pain.

-Bill

stoichiometry · July 2011

Re: Question on Square D-QO panel

Thanks Bill! I appreciate the help!!

BTW - Any experience with QO panels/breakers as a combiner box? I think it should be ok. As protection after the combiner, I will have a regular (midnite solar) 60A breaker (PV input disconnect) in line with a 63A midnite solar GF breaker before the charge controller.

Cheers,
Matt

BB. · July 2011

Re: Question on Square D-QO panel

Personally, I would keep sun and rain off of the box (under cover, drip loops, etc.). I do not have any experience with DC on these guys, and little AC experience with them.

Regarding the DC Ground Fault system as suggested by NEC (National Electric Code)--I believe it is dangerous and causes way more safety hazards (fire and shock) than it fixes... The "system" requires a 1 amp fuse/breaker between DC Ground and Earth/Frame ground. Not a good idea at all for a Ground Referenced System.

I have attached a PDF document (sorry, very quickly written) of my (personal) position on the issue.

As always, don't trust everything (anything

:roll:) you read on the Internet. Do your own research and reach your own decisions.

-Bill

Vic · July 2011

Re: Question on Square D-QO panel

I have not used the QO box/breakers as a combiner, but, probably would do fine, with the cautions BB Bill noted. Some on this Forum do use them as DC distribution panels, at the very least.

And, about six months ago seemed that the local HD was discontinuing the QO line, but just the other day, noticed that they are back at HD, so do agree that it is a benefit to be able to buy locally. If the Isc of the panel is as you noted as Max current, then seems that the 15 amp breaker would be the one to choose, and that size is common as an AC breaker.

Good Luck with your project. Vic

BB. · July 2011

Re: Question on Square D-QO panel

Note the Series Protection Fuse mfg rating for Matt's panels is 20 amps--so the 20 breaker is the appropriate choice here.

-Bill

Vic · July 2011

Re: Question on Square D-QO panel

OK BB Bill,

Sorry, I stand corrected ...

20 Amp Breaker it is. Thanks, Vic

stoichiometry · July 2011

Re: Question on Square D-QO panel

Bill,

I've *very* little experience with DC. So forgive my naive questions:

(1) So the following is *not* recommended, per your information below:
http://www.midnitesolar.com/pdfs/Small_DC_MPPT_system.pdf

I figured it would prevent a fire if something happened to the charge controller.

(2) Specifically, then what do you suggest on smallish systems?

Kindly,
Matt

BB. wrote: »

Personally, I would keep sun and rain off of the box (under cover, drip loops, etc.). I do not have any experience with DC on these guys, and little AC experience with them.

Regarding the DC Ground Fault system as suggested by NEC (National Electric Code)--I believe it is dangerous and causes way more safety hazards (fire and shock) than it fixes... The "system" requires a 1 amp fuse/breaker between DC Ground and Earth/Frame ground. Not a good idea at all for a Ground Referenced System.

I have attached a PDF document (sorry, very quickly written) of my (personal) position on the issue.

As always, don't trust everything (anything:roll:) you read on the Internet. Do your own research and reach your own decisions.

-Bill

BB. · July 2011

Re: Question on Square D-QO panel

One of the causes of fire in solar panels is when a poor connection is made--and the available current/voltage cause the point to overheat. At times, that overheating can cause an arc to occur. With DC, very low voltages (down to ~12-15 volt range) can sustain arcs very easily.

So, somehow (I do not know the history), someone came up with the idea of placing a ground fault current sense circuit breaker that would be ganged with a second larger breaker to place in the + current conductor from a solar array to a charge controller/GT inverter.

If there was a + to earth ground short somewhere--which could create an arc fault--that small breaker was to trip and open the large array breaker and "do something".

From my paper--I showed that the second large breaker was basically useless and the small "current sense" fuse/breaker was what "stopped" the Arc Fault.

The big breaker stopped the solar charge controller from working--so that was how people would know they have a problem.

Because Solar Panels are current sources (fixed maximum current) vs voltages ("unlimited" current into a short)--Normal fuses/breakers do not work (no over current possible, so no fuse/breaker will trip).

The problem is that lifting the "safety bond/earth ground" connection in a grounded DC system is, simply, unsafe.

So--for the, relatively few, fires that a 1 amp fuse in the negative to earth bond may prevent (and roof based electrical fires are not good)--The overall system is made much unsafe.

I have to go now--but that is the summary of what I was trying to show in that paper.

-Bill

Dave Angelini · July 2011

Re: Question on Square D-QO panel

BB. wrote: »

Personally, I would keep sun and rain off of the box (under cover, drip loops, etc.). I do not have any experience with DC on these guys, and little AC experience with them.

Regarding the DC Ground Fault system as suggested by NEC (National Electric Code)--I believe it is dangerous and causes way more safety hazards (fire and shock) than it fixes... The "system" requires a 1 amp fuse/breaker between DC Ground and Earth/Frame ground. Not a good idea at all for a Ground Referenced System.

I have attached a PDF document (sorry, very quickly written) of my (personal) position on the issue.

As always, don't trust everything (anything:roll:) you read on the Internet. Do your own research and reach your own decisions.

-Bill

I always have a hard time disagreeing with you Bill ! Your off on this one. The GFI if installed correctly makes the system safer and with no loss electrically !
--Dave

n3qik · July 2011

Re: Question on Square D-QO panel

I am using two QO distribution panels. One for the battery bank combiner and the other as a power distribution center. The only problem I did have was using Tandem Single-Pole 20A breakers in the battery combiner box. Tripped one, then later noticed a larger voltage drop with it, compared to the others. I repurpose some of the batteries to other projects, like car and tractor. Now using single pole breakers and have had no problems.

BB. · July 2011

Re: Question on Square D-QO panel

Dave Sparks wrote: »

I always have a hard time disagreeing with you Bill ! Your off on this one. The GFI if installed correctly makes the system safer and with no loss electrically !
--Dave

Dave,

Well, I hate to disagree with you too... But on this one, I believe the DC GFI system is very dangerous...

Just as a thought exercise (rather than rehashing my white paper), what would you think of the safety aspects of a 120/240 North American Split Phase power drop to a home that used a 1 amp fuse between Neutral and Earth Ground to prevent arc faults on the pole drop between one Hot Leg (120 VAC) and Earth Ground/Green Wire/Conduit/Electrical Box bonds.

Yes, such a fuse would break the Hot to Earth connection and "stop the arc"... However, you have now just made the Neutral Hot with 10,000 amp source (pole transformer) and no in-line fuse/breaker for all neutral/ground bond wiring... Plus now the other 120 VAC leg is actually 240 VAC to Earth.

More or less--that is what the DC GFI system, as shipping/installed today is doing with a single fault.

Could a DC GFI system based on a 1 amp breaker/fuse be made "Safe"--Possibly, using double pole breakers on both DC Hot and Return--on all major energy sources (solar panels, battery bank, AC battery chargers, etc.)--But it would be expensive and probably take out the entire DC/AC power system because of a 1 amp fault from DC (or possibly even AC) hot to earth ground anywhere in the system. From my point of view, a major drawback from a system that "protects" for relatively rare DC Hot to Earth arc faults--and does nothing for (I believe--but may be wrong) more common DC Wiring Arc Faults.

Dave (or anyone else), if you wish to have a detailed discussion on way I believe the current DC GFI "solution" to be a major safety issue--I can split this off to its own thread.

-Bill

Dave Angelini · July 2011

Re: Question on Square D-QO panel

Bill,

On this specific case I will not disagree with you. In general however if the GFI is done right in a solar system, it not only protects safety of, say a little kid touching the frame, or a grass/roof fire from staring, it also protects the system. This last aspect is one of the reasons I choose the XW system for many of my clients.

stoichiometry · July 2011

Re: Question on Square D-QO panel

I've decided to try the QO panel and will update you all from time-to-time.

Now to decide on an inverter. [I'll post that separately].

Question on Square D-QO panel

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