I should also add to my post and others' comments, that SAE rated and
welding cables are not NEC legal for building wiring. That used to be a
common bust by the AHJ, and as others have pointed out: Cobra Xflex,
Arctic, etc are all UL listed building cable. Its got to have something
listed on the NEC chart such as RHH, RHW, THHN, THWN etc.
Ray Walters
Remote Solar
303 505-8760
On 8/12/20 1:25 PM, Ray wrote:
Also, welding and automotive cables use totally different rating
systems like SAE, that are much more liberal than NEC. For instance,
golf carts are traditionally wired with #6 battery cables, and can see
a continuous draw of 125 A and surges to 200. We would never do that
by NEC, but the cables just get warm to the touch in golf carts.
Ray Walters
Remote Solar
303 505-8760
On 8/11/20 6:04 PM, Kent Osterberg wrote:
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, peter...@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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