MPPT80 -> XW PDP wire gauge verification?

ThirstyRoss

If I'm wiring a Conext MPPT80-600 charge controller to the Conext power distribution panel (w/ Conext XW inverter), what wire gauge is needed for the battery connection?

If I look at a voltage drop calculator it seems to imply that #3 would be required (60V, 80A, 3metres), does that seem right? 

If that is correct, does that mean for an MPPT100 you would need #2?

Thanks for any advice!

mike95490

practically speaking, you only need wire gauge large enough to handle the power your array generates.
 over sizing brings with it issues like needing larger conduit to carry the larger wire, cost of larger wire, difficulty bending and managing the install.

ThirstyRoss

mike95490 said:

practically speaking, you only need wire gauge large enough to handle the power your array generates.
 over sizing brings with it issues like needing larger conduit to carry the larger wire, cost of larger wire, difficulty bending and managing the install.

Thanks Mike!  The charge controller(s) will be somewhat over-provisioned to account for less solar energy in the wintertime, so we would see the maximum power out of the unit...I guess #3/#2 it is.

BB.

Using a voltage drop calculator--For a 12 volt bank, 0.1 to 0.2 volts max drop from controller to battery bus suggested... 48 volt bus would be 0.4 to 0.8 volts max drop.

For 10 feet, 3 AWG, 80 amps we get:

https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.6465&voltage=60&phase=ac&noofconductor=1&distance=10&distanceunit=feet&amperes=80&x=81&y=26
Voltage drop: 0.32
Voltage drop percentage: 0.53%
Voltage at the end: 59.68

So, from the voltage drop of view, you could go with a lighter awg... #4 AWG would be:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.8152&voltage=60&phase=ac&noofconductor=1&distance=10&distanceunit=feet&amperes=80&x=61&y=23
Voltage drop: 0.40
Voltage drop percentage: 0.66%
Voltage at the end: 59.6

Basic NEC chart:
https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

You could use #4 with "better" (higher temp) insulation and get 95 Amps (note--The "real" NEC code has all sorts of conduit fill, ambient temperature, etc. deratings).

Personally, I like to suggest that wiring used to charge battery banks be derated by 0.8 (or 1/0.8 = 1.25x) for the NEC "continuous current derating... Basically, wiring that runs for "hours" at rated capacity should be derated (run cooler):

• 80 amps * 1.25 NEC derating for wiring/breakers/fuses = 100 Amp rated branch circuit wiring and breaker/fuses...

In North America, our "typical" fuses and breakers are rated to blow at 100% of rated load (can take minutes or even hours), and not blow at 80% of rated current... So picking a heavier wiring+breaker can save the hassles (false trips) down the road.

-Bill

mike95490

BB. said:

.............................

• 80 amps * 1.25 NEC derating for wiring/breakers/fuses = 100 Amp rated branch circuit wiring and breaker/fuses...

In North America, our "typical" fuses and breakers are rated to blow at 100% of rated load (can take minutes or even hours), and not blow at 80% of rated current... So picking a heavier wiring+breaker can save the hassles (false trips) down the road.

The issue of a thermal style breaker slowly cooking off all day, is why I like the
Carling C-Series hydraulic/magnetic circuit breakers that Midnight Solar has: ( and the NAWS store carries )
http://www.midnitesolar.com/pdfs/breakers_11x17.jpg
 

ThirstyRoss

Thanks @BB.

I hadn't seen that NEC wire chart before, very helpful, cheers!

Dave Angelini

If you use the Schneider PDP and it's breakers #4 is fine and #6 is what most would do. Why do you need 10 feet? It should be a 6 inch run. Also this is in free air and not even in a tray and certainly not in conduit, really #6 is all that is needed and #4 might be needed depending on the wire type. For offgrid where the device does hit the peak all day like a grid app, this can be relaxed to #6.

Is cable tray considered free air?

The term "free air" is not defined in the NEC but is usually applied to conductors that are not installed in cable assemblies or raceways. ... If the conductors are in a cable tray then 392.80 applies.Apr 4, 2017

Dave Angelini

Mike, none of those breakers will fit properly in an XW PDP by Schneider. They also are not listed for XW if an inspector was looking.

 I am not saying the right one from Midnite is bad just not listed and will not fit properly without modification.

The Schneider PDP is fit with 60, 80, 100, and now 125 adc for the Mppt-100-600vdc

ThirstyRoss

Dave Angelini said:

If you use the Schneider PDP and it's breakers #4 is fine and #6 is what most would do. Why do you need 10 feet? It should be a 6 inch run. Also this is in free air and not even in a tray and certainly not in conduit, really #6 is all that is needed and #4 might be needed depending on the wire type. For offgrid where the device does hit the peak all day like a grid app, this can be relaxed to #6.

Is cable tray considered free air?

The term "free air" is not defined in the NEC but is usually applied to conductors that are not installed in cable assemblies or raceways. ... If the conductors are in a cable tray then 392.80 applies.Apr 4, 2017

@Dave Angelini , thanks.

This particular MPPT charger is not abutting the XW PDP (added on after initial system install).  It would be difficult to shift all existing kit to accommodate new charger in the "ideal" position (to the right of the PDP).  I'll admit, 10' was probably overstating it, but erring on the side of caution.  I'm not sure 6" of wire will even get you out of the PDP from the battery breaker, so assume you were exaggerating there for dramatic effect 

Thanks again for the input.

Dave Angelini

Probably a foot or so, if the Mppt were on the right side of the PDP. And also add the 125% over rule to the breaker.

mike95490

I was pointing out breakers (hydraulic/magnetic circuit breakers) that are not subject to thermal heating and tripping too slow or nuisance tripping & some of which are rated for 150VDC

Dave Angelini

Yea I should read more and type less   The OP here needs 600vdc for sure, and he knows it!