Current ratings for cable

[Trevor Rymell]

Dear All

If a certain type of cable has a max current rating of 4.5A and a voltage rating of 1500VAC, is there a formula for calculating the max continuous current at other voltages?

Regards

Trevor

 

[awright]

cable ratings

Current and voltage ratings of insulated wire are unrelated. The current rating is a function of the cross-sectional area of the wire. The voltage rating is an indication of the type, thickness, and quality of the insulation surrounding the conductor.

The cable you cite can be used with any current up to a maximum of 4.5 amps at any voltage up to 1500VAC. There is no trade-off of one for the other.

Have fun.

awright

 

[stevez]

You have to be careful when looking at things like "capacity" because there are likely to be conditions that go along with the stated capacity. In the case of wire temperature can often be an issue. An uninsulated conductor in free air can carry quite a bit of current before it melts or otherwise fails. Add some insulation, put it in a conduit or bundle it with other conductors and it's a different story. The insulation holds some of the heat in and at some point the insulation will melt or degrade.

I have a table open that shows the allowable ampacity of various wires and various conditions - all based on an ambient temp of 30 deg C. A single insulated 14 AWG wire can carry anywhere from 15 to 45 amps depending on number of conductors, insulation type, multiple conductors, etc.

I know this doesn't really answer your question but if you intend to push the limits it sounds like a little more info is required. Note also that voltage drop has not been addressed and the ampacity presumes your system can tolerate the resulting voltage drop and power loss.

 

[Trevor Rymell]

Awright, Stevez

Thanks for the replies. I was just a bit confused. I'm doing some rewiring on a motorcycle and figured this type should be ok.

The cable I have is a general purpose hookup wire 24/.2mm (24 strands, .20 mm dia each strand) and the manufacturer quotes a max current of 4.5amps.

Vehicle Wiring Products

**broken link removed**

in the UK sell a 16 /.2mm which they rate at 11amps. I just wondered why the big difference when mine has more copper strands.

Cheers

Trevor

 

[Nigel Goodwin]

Awright, Stevez

Thanks for the replies. I was just a bit confused. I'm doing some rewiring on a motorcycle and figured this type should be ok.

The cable I have is a general purpose hookup wire 24/.2mm (24 strands, .20 mm dia each strand) and the manufacturer quotes a max current of 4.5amps.

Vehicle Wiring Products

**broken link removed**

in the UK sell a 16 /.2mm which they rate at 11amps. I just wondered why the big difference when mine has more copper strands.

It depends mainly on the heat dissipation of the cable, the thicker insulation on the high voltage cable will prevent heat loss - so the thinner insulation cable can stand more current as it gets rid of heat faster.

 

[awright]

Wire

Trevor, at least in the U.S., wire is sized by guage, and for a given wire guage, the number of strands does not affect the current carrying capacity ("ampacity" in the electrical trade). Is wire sold by mm diameter in the U.K.?

Yes, it is a bit strange that your wire with the larger number of .2mm. strands has a higher ampacity, but the difference could reflect the intended application and temperature rating of the insulation. In particular, if what you are describing as general purpose hookup wire is intended for non-vehicular uses, it may have insulation that is rated at very low temperature. Some ordinary "hookup wire" has amazingly low temperature tolerance and will melt back when you solder the wire. Such wire would be totally unsuited to vehicular applications.

Speaking of solder, in general, PROPERLY crimped, high-quality crimped connectors are more reliable than soldered connections for vehicular use with vibration exposure. A soldered joint can provide such rigid support for the wire that it will be more subject to fatigue failure right at the end of the solder joint if it is subjected to continuous vibration. That is also a good reason to use cable ties liberally to minimize flexing of the wire joints.

In addition to temperature rating, insulation on wire intended for vehicular applications should be tolerant of sunlight (depending upon the styling of your bike) and oil and gas exposure. For motorcycle wiring you would also want abrasion and fatigue resistance, especially if you ride a Harley. (Sorry, as a BMW K75 and R65 rider, I couldn't resist that.)

Considering the implications of an electrical problem in your bike on the road and the relatively small amount of wire in even a complex, modern motorcycle, I think you should get the highest grade wire available and be sure it is intended for vehicular wiring. Pay the extra price and consider it a road insurance premium.

Have fun.

awright

 

[pietjepuck]

Hi awright,
I have worked for a US company in south-america and had to get used to using tables for calculating wire sizes.
In Europe this is not necessary.Wires are sold in square millimeters.For instance for general power wiring in homes 1.5 and 2.5 square millimeters are used.For use in conduits the rule is simply 5 A per square mm.