Need Help Calculating Breaker Sizes For an Off-Grid System

[SunnyIAV]

Greetings,

I am upgrading an off-grid system and I would sincerely appreciate some input.

(4) FLA Trojan SPRE 12 225 = 48 V

DC Disconnect /Load Enclosure: Midnite MNDC

Inverter: COTEK SD2500-148 2500 Watt 48 Volt Pure Sine Wave Hardwire Inverter

I would like to get some help figuring out inverter breaker, cable and inline fuse size.

The Cotek manual recommends a 90 amp inline fuse and 4 AWG cable < 6ft. Bigger cable can be used for longer distance to avoid reducing inverter performance. I didn't want to post a link to the manual to avoid making the moderator's job harder.

What would be the best breaker choice between the following Midnite panel breakers: MNEDC90, MNEDC100 or MNDC125? Midnite breakers are reported to be rated for 100% continuous duty.

The breaker opening in my MNDC enclosure is 1.5 " wide, but I can always create an adapter to make either one of those breakers fit since they are smaller.

The wiring (under 6ft) from battery to inverter will be as follow:

Pos battery post - inline fuse near battery - breaker - inverter

Neg battery post - 500A, 50 MV DC Shunt - inverter

I would prefer to use a cable bigger than 4 AWG, if possible.What is the maximum size cable (THW) and corresponding inline fuse I could safely use based on that configuration?

Bonus - There will be no code or inspector to worry about, however being safe is a priority.

Thanks for reading, and possibly commenting.

Harry

[Mike90250]

Wire size determines the maximum breaker size
4ga wire is good for 70A
if you need 90A, you need #2 wire, to do it safely

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

[SunnyIAV]

Thank you for replying Mike. By looking at the NEC table in the link, 4 ga corresponds to 85 A and # 2 = 115 A. I looked at the column for THW wire. Did the wire sizes you provided include derating?

I am not exactly sure what I need, I would like to know the safest size wire I could use with matching fuses and breakers. The manual provides information based on 1 inline fuse between battery and inverter, but it doesn't take consideration of the additional breaker I will have in the DC enclosure. I have attached some of the specs , if that would help.

Thank you

Cotek_SD500_48V.jpg

[NewBostonConst]

You will also have to worry about going to big and the wire not fitting in where the connection is made.

[SunnyIAV]

Thank you for replying. The inverter post can take a 2/0 lug without a problem. Strangely enough two 2/0 compression lugs were included inside the inverter box

[SunEagle]

Wire size determines the maximum breaker size
4ga wire is good for 70A
if you need 90A, you need #2 wire, to do it safely

https://lugsdirect.com/WireCurrentAm...ble-301-16.htm

Just for clarification that chart is for wires inside a raceway or direct burial. If they are being run in open air they can handle more amps then what the chart shows. There is another NEC chart for open air wire runs but for some reason I can't find it now but the #2 wire is definitely safer then the #4.