Outback FP2 Wiring Problem

Anawa · February 2015

I recently puchased a pre-wired Outback FP2 integrated system panel with 2- 3648 FVX's and 2- FM 80's. This past I Saturday as I was connecting the "factory" supplied charge controller wiring, I discovered the cable to be #6awg. For the FM80, Outback recommends a "minimum" of #4awg and suggests that #2awg is preferred. I have not yet contacted the equipment vendor (sponsor of this forum) to advise them of the problem. Before I do that, I would like some feedback from members of the forum.

First some specifics: this is an off-grid install. The total array is 4,590 watts (18 ea - 255 watt Kyocera's). The array is split into 2 - 2,295 watt to each of the FM80's. The battery bank is 804 Ah forklift's. The generator is 8.5 kW.

The system 2,295 wattage is less than the maximum voltage rating for the FM80, as well as, for the FM60 (4000 and 3000 respectively). Note: Outback recommends #6awg for the FM60.

My concerns are that; the #6awg is probably acceptable for this particular application, right now, but could I be limited in expansion of the system in the future? What would be some of the unintended consequences?

Also, what would be an appropriate response from the vendor for the error on their part? I'm not too excited about having to completely re-wire a "factory wired" system even if all the parts and pieces were furnished. Those boxes make for a pretty tight fit!

Comments appreciated.

Thanks
Anawa

BB. · February 2015

Hi Anawa,

Is this a 48 volt system?

I do not work for NAWS (Moderators here are purely volunteers). When I designed computer systems (including power), we could use "lighter gauge" cables inside enclosures because the cables are short and good air ventilation (little voltage drop, and little heat generated from "short jumpers"). Inside UL/NRTL Listed equipment, NEC deratings do not have to apply.

What size circuit breaker (if any) is wired into the system? 80 or 100 amps? For example, in marine (engine room use) use, you can use 6 AWG cable up to 102-120 amps:

http://www.boatus.com/boattech/articles/choosing-cables-and-terminals.asp

However, if you have any questions, please contact NAWS directly. Generally, they do not monitor this forum for business related questions (we are all volunteers here and not connected with NAWS in any way other than they kindly host the forum).

-Bill

Photowhit · February 2015

I suspect it was wired at Outback, Though I/we might not understand what wiring you are describing as you were connecting it? is this internal to the integrated panel?

gww1 · February 2015

I used 6 awg from the dc breaker to the fm80 cc with a 2820watt solar aray. I used 2/0 from the breaker box to the battery bus. It was a very short run to the cc from the dc breaker box and I have seen no ill affects. I tried to follow the insulation guide. I have the fp2dc set up. I think that is the correct model with out looking it up.

I give this for imfomation not to claim it is correct.
gww

PS the 2/0 from the dc breaker to the battery buss carries two charge controllers with 2820 watts each.

Anawa · February 2015

Thanks all for the replies.

The #6 awg wiring referenced is internal to the pre-wired panel (short runs), it is a 48 volt system, and the DC breaker is only 80 amps. If the system was configured at Outback, or by one of it's distributors, I probably do not have much to be concerned about. However, I am perplexed that a manufacturer would recommend something different for customers than they do themselves. Perhaps the up-graded customer recommendations help ensure a level of safety for the equipment warranty. I will now follow-up with the vendor to find out more about this issue and post the results.

I am now faced with another wiring decision. What gauge cable should I use from my combiner box to the controllers (neg) and the DC disconnect (pos)? Fortunately, the runs are very short (less than 30"), located in an enclosed and weather tight room adjacent to my dwelling, and just above the pre-wired panel. It does not make a lot of sense to use #4 awg (as recommended) when the circuit is continued via the #6 awg. Besides, I have some #6 awg available to make the connection and would not have to spend anymore $'s.

BB. · February 2015

What are the Vmp-array and the Imp-array ratings for the circuit?

-Bill

Anawa · February 2015

The panel: Vmp: 30.4 volts, Imp: 8.39 amps. Panels are 3 series, 6 strings (18 total). For each controller: Vmp = 91.2, Imp = 25.17 (2,295 watts).

This is the current configuration. Not sure if I will add to the system.

Anawa

BB. · February 2015

Using a voltage drop calculator...

http://www.calculator.net/voltage-drop-calculator.html

6 awg wire for 3 feet one way run and 25 amps:

Voltage drop: 0.059
Voltage drop percentage: 0.065%
Voltage at the end: 90.941

No drop at all... Current rating:

25 amps * 1.25 NEC derating = 31.25 amp minimum circuit
25 amps * 1.25 * 1.25 NEC double solar derating = 39 amp minimum circuit

Using NEC Table:

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

6 AWG looks OK (note, the real NEC code has temperature/conduit fill/etc. deratings)... I am not an electrician.

-Bill

Anawa · February 2015

Thanks BB

Anawa

Outback FP2 Wiring Problem

Comments

Categories