[RE-wrenches] Ampacity Ratings for Different Conductors

[Kent Osterberg]

Peter,

The 210-amp rating is probably for a 105°C insulation temperature in 
free air. For comparison, #2 THHN (90°C) copper in free air is rated for 
190 amps. Not sure that it makes sense to use a free-air rating in a 
small closed box.  For outside use a temperature de-rating for ambient 
temperature, maybe around -10%, should be included too.

It looks like Cotek recommends a minimum cable size of 1/0, so out of 
fear of starving the inverter of enough voltage, I wouldn't use any smaller.

Kent Osterberg
Blue Mountain Solar

On 8/11/2020 3:18 PM, petertor at pobox.com wrote:
> I have been designing a off-grid system that can fit in an 
> outside-accessible compartment with an approximate 24" square 
> footprint and space above about 18" - 24".
>
> I am using two Battle Born LiFePO4 batteries rated at 24 V / 50 Ah, a 
> Cotek pure sine wave inverter with an output power of 4,000 VA , a 
> MorningStar TS-MPPT-60 charge controller, a Victron BMV-712 "coulomb 
> counter" and a Battle Born surge limiter CL500.
>
> The current limiter limits the current to 120 continuous, and 200 A 
> for 30 sec.
>
> I have been able to fit everything in and I am designing the cabling, 
> and here is my problem.
>
> I have one vendor that recommends Ancor brand Tinned Marine Grade 
> Battery Cable. It is "resistant to salt water, battery acid, oil, 
> gasoline, heat, abrasion and ultra-violet radiation. Exceeds UL 1426, 
> ABYC and US Coast Guard Charter boat (CFR Title 46) standards. Highest 
> quality ultra-flexible (Type 3) tinned copper stranding. Vinyl 
> insulation. -50 deg-C to 105 deg-C." 2 AWG is composed of 665 ea 30 
> AWG stands.
>
> The same vendor has "welding cable" with an EPDM insulation rated at 
> 600 V, water/chemical/grease/abrasion resistant, -50 deg-C to 105 
> deg-C, "marine grade". Not UL listed. 624 ea 30 AWG strands.
>
> Roughly comparable pricing.
>
> They claim both 2 AWG cables are rated at 210 A. Not sure if this is 
> continuous duty or whether I should derate this for what will be 
> continuous duty.
>
> This is new territory for me, and any help would be appreciated.
>
> Peter T. Parrish, Ph.D.
> President, California Solar Engineering
>
>
>
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