Gauge for negative DC wire

[VagabondDK]

I would like to mount some external flood-lights on a motorhome with a 12V DC system. I may need to install new wires to make sure they are sufficiently thick.

Someone told me that the negative wire in a 12V DC system can be very thin, but I haven't been able to find any information on this, and it sounds rather strange to me.

Is this complete nonsense? Should the negative and positive wires always have the same gauge / thickness? Or can the negative wire be thinner by some ratio?

I suppose an alternative solution would be to connect the negative wire to the chassis, so I don't have to run a thick negative wire all the way through the motorhome, right?

Thanks!

 

[acropolis22]

I bought a sort of mini wiring loom sold as specific for wiring up USB and 12V cigar sockets. The red had an inline fuse, and the black cable was indeed a lighter gauge. It does seem odd though, although I have little electrical knowledge. Is it because you don't have the same current flowing back to negative as it has been consumed by the device?

 

[Gromett]

I would like to mount some external flood-lights on a motorhome with a 12V DC system. I may need to install new wires to make sure they are sufficiently thick.

Someone told me that the negative wire in a 12V DC system can be very thin, but I haven't been able to find any information on this, and it sounds rather strange to me.

Is this complete nonsense? Should the negative and positive wires always have the same gauge / thickness? Or can the negative wire be thinner by some ratio?

I suppose an alternative solution would be to connect the negative wire to the chassis, so I don't have to run a thick negative wire all the way through the motorhome, right?

Thanks!

In general that it BS. both wires need to be the same size. HOWEVER.
If the ground wire only has to go an extremely short distance to the chassis whilst the live has to travel many meters there can be a size difference as losses in the cables are defined by I²R With R being the resistance of the cable which is affected by length. So in theory a shorter cable can be thinner and carry the same amount of current with the same losses.

In practice though, Always use the same size cable.

 

[Gromett]

I bought a sort of mini wiring loom sold as specific for wiring up USB and 12V cigar sockets. The red had an inline fuse, and the black cable was indeed a lighter gauge. It does seem odd though, although I have little electrical knowledge. Is it because you don't have the same current flowing back to negative as it has been consumed by the device?

You do have the same current flowing back. Current is not consumed by the device.

Think of it like a watermill. The water flowing past the mill turns it (does work) but is not consumed in the process. Hope that helps.

As for your device. The insulation may be thicker on the live? You need to look at the copper. A negative line being chaffed away tends not to be so problematic in a car. A live getting chaffed is a serious fire hazard. So the insulation may be thicker for this reason.