Cable Size

Buford T Justice

Hi Guys

Need to pull some cable into my van to run a 12V fridge. Rekon the cable should be rated for 30 - 40 amps. What size cable would I need, if max rating was between 30 & 40? Distance isn't an issue. Looking at about 3 meters max

Davy

Are you sure its going to be pulling that much?

That would want 10sq if it was the case

sparks24

jaysus some fridge! whats the wattage?

Buford T Justice

Just looking there. Its 95 watt over 12V so somewhere in the region of 8 amps.

Trouble is, its blown a 20A fuse. Runs fine on a 25A, but the cable is warm when its under load, so I'm concerned its underrated for the load. Cable iirc is rated for 25A

Want to make sure if I'm going to the hassle of uprating the cable that I future proof it if you know what I mean, hence the suggestion of 30 - 40A cable.

2011

Fingers McGee wrote: »

Just looking there. Its 95 watt over 12V so somewhere in the region of 8 amps.

95/12 =7.9 so yes about 8 amps

I take it that 95W is written on the unit?

Trouble is, its blown a 20A fuse. Runs fine on a 25A

That would be due to the high starting current of the compressor in the fridge. It would be at least 3 times the full load current (of 8 amps).

the cable is warm when its under load, so I'm concerned its underrated for the load.

If it is only 3 m go for a monster cable, as Robbie says a 10 sq. will do 40 A no problem.

What you need to watch is how you terminate. Ensure that terminations are very tight and use lugs.

Buford T Justice

2011 wrote: »

95/12 =7.9 so yes about 8 amps

I take it that 95W is written on the unit?



That would be due to the high starting current of the compressor in the fridge. It would be at least 3 times the full load current (of 8 amps).



If it is only 3 m go for a monster cable, as Robbie says a 10 sq. will do 40 A no problem.

What you need to watch is how you terminate. Ensure that terminations are very tight and use lugs.

Not sure if it will fit into the terminals on the back of the fridge though. What was originally in the unit when I got it was something like 3^2 I think, but it was automotive stranded cable.

2011

Fingers McGee wrote: »

Not sure if it will fit into the terminals on the back of the fridge though.

If you have a large cable but only small terminals the solution is simple, use a pin lugs such as these:




The important thing is quality connections, and a cable that is large enough for the load. I would agree with you that stranded cable is best, it reduces the chances of a break from work hardening.

Bruthal

Fingers McGee wrote: »

Just looking there. Its 95 watt over 12V so somewhere in the region of 8 amps.

Trouble is, its blown a 20A fuse. Runs fine on a 25A, but the cable is warm when its under load, so I'm concerned its underrated for the load. Cable iirc is rated for 25A

Want to make sure if I'm going to the hassle of uprating the cable that I future proof it if you know what I mean, hence the suggestion of 30 - 40A cable.

Its hard to see 8 amps warming any cable over 1.5 square. At 12 volts you have to make sure you have good connections though, as its bad connections that can get very hot and cause the cables to feel warm through conduction of heat.

Buford T Justice

robbie7730 wrote: »

Its hard to see 8 amps warming any cable over 1.5 square. At 12 volts you have to make sure you have good connections though, as its bad connections that can get very hot and cause the cables to feel warm through conduction of heat.

All connections are solid. They are all crimped spades, crimped with the correct tools. Not sure if i mentioned it, but the cable was warm, but not hot.

You could feel the heat in the fuse holder too. Standard size blade fuse holder in a chassis mount.

What diameter should the cable be for 1.5sq. I can measure it with a calipers to see what i have.
I'd rather use stranded cable if at all possible, as the solid cores have a tendency to wiggle loose from terminals due to vibrations from the road. (so I've been told, but I'd bow to the experience of others here)

Bruthal

Fingers McGee wrote: »

All connections are solid. They are all crimped spades, crimped with the correct tools. Not sure if i mentioned it, but the cable was warm, but not hot.

You could feel the heat in the fuse holder too. Standard size blade fuse holder in a chassis mount.

What diameter should the cable be for 1.5sq. I can measure it with a calipers to see what i have.

PI x Radius square is area so Radius (R)= (Square root of (Area/PI)= a fraction under 0.7 so diameter is 1.4mm(slightly below 1.4) according to that, which should be right for a solid core.

I'd rather use stranded cable if at all possible, as the solid cores have a tendency to wiggle loose from terminals due to vibrations from the road. (so I've been told, but I'd bow to the experience of others here)

Stranded is better for that without any doubt, as it does not transfer vibration near as much as solid cores, it also has a slightly higher capacity as well for equal sizes the more strands there are.

A bit of sylflex might be good for it. If its easy to get these days, but 2.5 should be more than enough for that even with 25 amp fuses in a van.

2011

Fingers McGee wrote: »

All connections are solid. They are all crimped spades, crimped with the correct tools.

Good.

You could feel the heat in the fuse holder too. Standard size blade fuse holder in a chassis mount.

Perhaps you should look at a higher quality fuse holder.
Remember,
Heat = current ^2 x resistance

Therefore the closer you get the resistance to zero, the less heat

What diameter should the cable be for 1.5sq. I can measure it with a calipers to see what i have.

Area = π r^2

⇒ r = √(Area/π)

r = √(1.5/3.142)
= 0.7

But the diameter, = 2 x r

So I would expect the diameter of the conductor (if it were a solid core) to be about 1.4mm

As your cable is stranded allow a little more.

I'd rather use stranded cable if at all possible, as the solid cores have a tendency to wiggle loose from terminals due to vibrations from the road.

Also you should not crimp a solid core copper cable!

BTW I love your thread on the camper van!

2011

I see we crossed posts Robbie!

Bruthal

2011 wrote: »

I see we crossed posts Robbie!

The same answer as well. whats goin on:D

We even mentioned its right for a solid core,,, madness...

2011

robbie7730 wrote: »

The same answer as well. whats goin on:D

We even mentioned its right for a solid core,,, madness...

I said it before Robbie, "great minds think alike!!!!" :D:D

beanie10

How old is the fridge, could be knackered and be pulling too much current.

Bruthal

The only real way they would pull too much current is if the compressor is stuck, or not running up to speed properly. That can happen alright, but the fridge wont be working then most likely.

A multimeter might be worth putting on it in amps mode. If you wanted to avoid the starting current just run the fridge through a switch and connect the probes into the switch, then switch the switch off and the current will be shown on the meter while its up and running.

2011

How old is the fridge, could be knackered and be pulling too much current.

I see nothing to indicate that the fridge is faulty.

8A full load current for a 95 watt fridge that has a compressor with a starting current in excess of 20 A. It all sounds good to me.

Bruthal

Me either, it would be obvious enough to any owner if a compressor is not running right, not obvious its the compressor faulty, but that something is wrong.

Buford T Justice

Thanks for the help guys. Yeah, there nothing wrong with the fridge, it works well on all methods, 12V, GAS and 240.

I think I just didn't put in heavy enough cable when i was running cable in the van.

I didn't think at the time to find out what wattage the fridge was and future proof......:rolleyes:

I'll be changing it for heavier cable and using a maxi fuse holder instead of the standard size ones. The van is becoming my pride and joy at this stage so I don't want to have anything half assed in it, if you know what i mean. With the bigger fuse holder i'm hoping it won't heat up as much as the one thats there.