Battery to Inverter Wire Gauge for EG4 Kit

Dinobot248 · Aug 8, 2023

First newbie question and more to come.

I am looking at the Off-Grid EG4 System Kit.

✔ 2 x UL 1741 Standard EG4 6.5kW Off-Grid Inverters | 6500EX-48 - Split Phase Optional Output [120/240V]
✔ 6 x 5.12kWh EG4 UL Listed Lithium Batteries - 5 Year Warranty (10 year warranty with EG4-LL!)
✔ Pre-Assembled EG4 Enclosed Battery Rack | 6 Slot (GF1511052)
✔ 2 x Nader 60v 200Amp DC Breaker
✔ 2 x IMO PV DC Disconnect Switch
✔ 2 x ( 1 AWG ) 84 Inch Battery to Inverter Cables

Are the 1 AWG battery to inverter cables limiting the system? According to various wire AWG charts, 1 AWG wire can transmit max of 119A. I understand that temperature will impact the max amps, but lets keep this simple.

I can see on Will's DIY mobile solar power site, he list / recommends the 2/0 cable for his 48v system parts list and this has max transmission at 190A.

Rough / newbie calculation is using the existing kit supplies, 119A x 48v = 5700 watts. For two EG4 units, it would be 11,400 watts. This is obviously less than the 13,000 watts for the combined system. Am I missing anything??

Madco · Aug 8, 2023

Your questions lead to at least a few topics of heated debate on this forum!

As the battery rack has bus bars, I'll focus on the wiring from those to the 200A breakers. The nameplate full load amperage on the EG4-6500 is 158.3A. That is at 48V and some here have argued that the input voltage with the Li batteries will be higher and hence the current will be lower but the nameplate rating is what governs. The NEC requires the wiring to be sized for 158.3A * 1.25, or 198A.

If the wiring is installed in "free air", then #1 copper with 75C insulation will work. It is actually a couple of amps shy of the requirement, but close. A couple of problems pop up though. First, I don't believe 75C insulation is sufficient. The discharged air where these conductors land on the inverter come very close to that temperature when my 6500s are heavily
loaded and supplied with near maximum PV input. With insufficiently rated insulation, you'll very likely have insulation failure at the inverter terminals. Second, I have never seen any installations where the wire was installed in a "free air" condition. As a result, I recommend not using the free air ampacity tables. I also don't know what type of insulation SS supplies on the #1 wire. BTW, the inverter manual specifies 2/0 wire for the inverter input - much larger than the #1.

That puts us on the ampacity tables for no more than three conductors (current carrying) in a raceway. That table indicates with 90C wire, 2/0 copper has an ampacity of 195A - still a little shy of the required 198 but again pretty close. Interesting that this aggrees with the manual's specification on input wire gauge!

So, my recommendation would be to run 2/0 copper, rated at 90C. from the bus bars in the rack to the 200A breakers and then on into the inverter.

I would use 2/0 welding cable rated at 105C, because it is much easier to work with than say THHN. If you're subject to inspection though, you might fail if the welding cable does not have the insulation type marked along the cable!

A lot of folks here will point out that if the runs are short (low voltage drop), you can use smaller wire than the NEC requires. While that works in practice and might be OK practically, there is nothing in the NEC that allows for smaller wire than indicated in ampacity tables-small voltage drop cannot justify smaller wire. Larger wire is allowed to lessen voltage drop but the process doesn't go the other way!

Dinobot248 · Aug 8, 2023

Thanks. That was very helpful.

I will get the 2/0 cables.

Browse · Aug 8, 2023

I run the #1 AWG 7 ft cables supplied by Signature Solar between my rack and the inverter. I sent them an e-mail last week requesting the specs for that particular wire but they haven't responded yet. The wire itself is branded "Infinitiflex" 600V 105C: