# Confusion with voltage rating when sizing wire gauges

This is a conceptual question. I mean I have a confusion about voltage rating of a wire. So I want to ask with an example:

Above 80V DC power supply will power the load which needs around 80V voltage and sinks 1A current. The one-way length of the wire L is 20m. I want/tolerate 1% voltage drop between the power supply and the load. So to size a suitable wire I do the following:

One way voltage drop ΔV tolerated is:

ΔV = 0.5×80×0.01

This ΔV is for L one-way distance, so to calculate Ω/m:

ΔV = R_wire(Ω/m)×L×I

R_wire(Ω/m) = ΔV/(L×I)

R_wire(Ω/m) = 0.4/(20*1)

R_wire(Ω/m) = 0.02 Ω/m

So I go to this table and find out the corresponding AWG for a 0.02 Ω/m wire.

In this case the table shows it as 24.

Imagine I use the following AWG 24 cable: https://www.velleman.eu/products/view/?id=18950

In the specs, max current 4.3A which is great for my purpose.

But how about "max. voltage: 60 V" in the specs?

Does that mean I cannot use this wire for this application?

I thought what matters for heat was current. Is my sizing method correct?

Is that 60V max voltage applied across the wire without a load?

• The voltage rating applies more to the insulation than the wire.
– JRE
Jun 6, 2017 at 13:30
• What does that mean pictorially? Jun 6, 2017 at 13:32
• It means that the size of the conductor says nothing about the voltage it is meant to be used with. I use AWG30 wire for 10kV Jun 6, 2017 at 13:33
• Extrapolate to the extreme. A cable without insulation has no Voltage rating. It can still conduct, etc etc, but there can be a shock hazard if it touches anything else. Jun 6, 2017 at 13:35
• It means the insulation isn't guaranteed to insulate if the voltage between the wire and something else is more than 60V.
– JRE
Jun 6, 2017 at 13:35

Voltage rating applies to the insulation, but there are subtleties.

On very low voltage (like 12V), pretty much any insulation thick enough to stick to the wire will do. On higher voltages, insulation thickness and material type really matters.

For example, the wire you link is a hookup wire for low voltage electronics. In this use case, you want thin insulation, because this makes the wire more flexible, and practical to use. This explains the very low 60V rating. It will be inadequate for your 80 volts.

If the wire is exposed (for example, it runs on the floor and people could walk on it) or if it is exposed to vibrations or chemicals, then of course this has to be taken into account too. Insulation will need to be rated for this.

In your use case, I would use simple 2-conductor lamp cord. It is cheap, readily available, inconspicuous, and robust.

EDIT:

For a 20m run it will most likely be mounted on walls or at least attached to something, so check regulations in your area for things like electrical conduits, etc.

For example, your hookup wire would only be allowed inside an enclosure. Here, as a general rule, wires with hazardous voltage are not allowed to be apparent, which means they have to be inside a conduit, for example:

If it can be touched, walked on, etc, then it has to be a cable. In the above photo, if the wires were cables instead, the T-junction could be omitted, with cables visible. In this case, the conduits would be used more as a convenient way to bunch up the cables and mount them on the wall.

• So in my case If I wire the wire's insulation(at a point on insulation between 80V+ and the load) to ground I will have a problem since the potential difference will be more than 60V? Jun 6, 2017 at 14:03
• @user134429 - yes. The wire manufacturer is saying that if there is more than 60V measured between the wire conductor and any other conductor which rests against the wire insulation (like a metal box or another wire), then they don't guarantee that the insulation will hold up and actually insulate. You probably cannot safely use this 60V rated wire in your 80V application. Jun 6, 2017 at 14:08
• someone wrote in the comments "I use AWG30 wire for 10kV". Isn't that risky as well? If the insulation is not rated for 10kV. Jun 6, 2017 at 14:11
• @user134429 - Yes, it's risky. Actually, it's asking for trouble. But, since the insulation has nothing to do with wire gauge, it is simple enough to look for wire whose insulation is rated for 10kV. Jun 6, 2017 at 14:19