How warm should 70mm cable get?

slimf

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Sep 26, 2017
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My powerwall has been running for over a week now and I’ve noticed there is a section of cable between the fuse block and circuit breaker that gets warm when under heavy sustained load.

It’s a 48v system and I use 70mm flexible welding cable and quality Cabec brand crimps - which were double crimped with a hydraulic crimp tool.

When pushing 70-80 amps I notice a small section of both positive and negative get warmer to touch than the rest.
Using a laser temperature meter I found the ‘cold’ parts of the cable at 28 deg C. The warmer parts were at 33 dec C - and perhaps when under the higher end of load 82amp they may have got 3-5 deg warmer than that. Still under 40 deg C.
Ambient today was around 28.

Is this common or have I got some bad crimps?

I also thought maybe the heat was being introduced to the cable from either the fuse block or circuit breaker - but hard to tell?
 

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Roland W

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Oct 9, 2017
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As long you can touch it, its all OK! I am sure the heat is coming from the terminals of the breaker or fuses. Those are typically the weak points of the circuit. 60deg C can be common there. During welding, those cables can reach quite high temperatures. And silicone cables are typically rated beyond 100deg C. A 70mm2 copper cable with a length of 20cm can easily carry 200A. Don't worry.
 

slimf

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From my understanding, 70mm flexible welding cable is good for 310 amps 100% duty cycle.. so it must be either the crimp / terminals generating the heat.
 

OffGridInTheCity

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Dec 15, 2018
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I have a temp probe at one of my 'hot spots' where 4AWG comes into the control box from the Midnite Classic Controllers. When the full 80a are flowing thru the 4AWG (8 feet) - 2 sets in EMT conduit - they routinely reach 50-55C in spring/summer. They feel warm to the touch and seem to be holding up OK at this temp for 1/2 the year.

The chart I use shows 67.4mm 2'rd (e.g. 00) at a max of 283 amps for chassis wiring. The 4AWG above is 21mm 2'rd with chassis amps of 135.... but its running 8 feet within conduit. 300a continuous OR for wire more than a foot long or pairs or within conduit may get hot.

I agree with @RolandW that as long as its only 'warm to the touch' for typical flexible welding cable - then its likely OK. You can always measure the temp under operating conditions and look up the specs for your wire to get a more precise answer.
 
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slimf

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Sep 26, 2017
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Thanks - I was worried as 70 is way short of where I want to be in terms of charging. I figure is 70-80 gets it warm, double that is going to possibly be an issue.

The weird thing is, the rest of the cable run is fine. Its only around the fuse and circuit breaker (and a bit on the cable coming out of the top of the circuit breaker - which goes directly to the inverter). The cable from the fuse to the shunt and battery are all cool.
 

ajw22

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Nov 16, 2018
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Its only around the fuse and circuit breaker (and a bit on the cable coming out of the top of the circuit breaker - which goes directly to the inverter). The cable from the fuse to the shunt and battery are all cool.

The core part of fuses are designed to warm up as current increases, reaching melting temperature as current rises above the fuse rating. Under prolonged load, it's quite normal for the heat to build up and creep along the conductor. Also, warm air rises, so the cables coming out at the top part will be a little warmer.

Very similar with certain types of breakers. But instead of melting, the heating element inside trips the mechanism to throw the switch.
 

slimf

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Sep 26, 2017
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Yep, cool makes sense.
A little unnerving feeling heat thou.
Today was hotter 30’somthing deg C.

the coldest lugs/cable was 30deg C and the warmest around that fuse / breaker was 42 deg. Pulling at the time 75amps for hours.
 
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