Coiling an electrical lead

[Scott]

Could someone remind me: is it dangerous to coil the lead for Christmas tree lights? I know in general any electrical cord should be fully unwound but is this a factor where low currents are involved?

[Roger Mills]

Depends on the cable. If you're running a cable near its current limit, it shouldn't be coiled but if (say) you're putting 1 amp or less through a cable capable of carrying 13 amps, it doesn't really matter.

[Scott]

It's a very thin cable energised at 24 Volts so I suppose the current is multiplied by 10. Safer not to coil it up I suppose in case it heats up?

[chop]

Better to feel if it heats up and coil it if it doesn't.

[John Rumm]

LED lights or incandescent?

[Harry Bloomfield Esq]

It's a matter of how well they can dissipate heat, the actual coiling makes no difference, if the coil is loose, with air able to easily circulate around the cable to cool it. What cause is the heat, is how closely the current flow, is to the current rating of the cable.

[Scott]

Maybe I am completely misunderstanding this but I thought the coil created an electromagnet and this was the concern.

[Scott]

See my post to Harry but I may be mistaken here.

[Harry Bloomfield Esq]

Many do believe that, but it is wrong. The electromagnet (inductance) heating only happens, where there is a single core, looped through a ferrous metal. Where there is both L and N in one cable (flow and return) they cancel each other out, which is why they can get away with metal cable reels.

[chop]

Yes you did.

No.

[Scott]

I was discombobulated.

[ARW]

I do believe that John Ward made a video of this "inductance" with live and neutral though different holes into ferrous metal and was unable to create hardly heat at all - even with a 100A load.

[ARW]

Energised at 24V

So that is a 24V supply

What does the PSU that supplies the lights say?

Something like 24VA? so that is one amp.

[Chris Green]

If it's 24v it's almost certainly DC anyway so inductance is irrelevant.

[Scott]

6VA. I assume this means a current of 0.25 amps. To go back to Roger's comment, I have no idea what the cable is capable of carrying. Does this mean I should not create a coil just in case or will it never be an issue for 0.25 amps?

[chop]

Any normal cable can handle that fine without getting even warm.

No, any coil will be fine. Coil away.

[Scott]

Can the term 'VA' be used for DC? I thought it applied to AC systems.

[mm0fmf]

VA and Watts are the same in a DC circui, the real power and apparent power is the same. In AC circuits voltage and current are not necessarily in phase so VA is the apparent power and the real power will be less depending on the circuit and the waveform.

[The Natural Philosopher]

The coiling is of course what makes the difference in its ability to dissipate heat....

watts per square cm etc etc. coiling reduces thee number of square cm of the overall volume of air being heated.

[The Natural Philosopher]

? Jesus Wept!