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So we have this machine at work, a strapping machine, and it has a long power lead which is left loose on the ground, and it's getting gradually destroyed - accident waiting to happen.

I know that there are fire hazard risks associated with coiling wire, but I don't know how to work out how much you can coil with virtually no risk.

I would prefer that we don't permanently shorten the cable, because it may come in handy to have it long in the future, and we'd have to raise engineering tickets etc... major hassle for what I suspect is a non-issue under these conditions.

Please help! Let me know what other info might be pertinent.

  • Rated Power: 5A
  • Volt/Hz: 230/50
  • Cable length: Around 3m
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  • \$\begingroup\$ So, how many engineering tickets might need to be raised if someone tripped over it and, due to the wear on the cable, it exposed a live terminal and the tripping person also got electrocuted. Have you heard of this modern day thing called "risk analysis". If you don't do it then someone at your works must surely do it. Get in touch with them. \$\endgroup\$ – Andy aka Jan 19 '18 at 16:03
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    \$\begingroup\$ Coiled or not, the cable needs to be protected from damage. Why can't you use the extra length to move it out of the way of whatever is damaging it? \$\endgroup\$ – Dave Tweed Jan 19 '18 at 17:00
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    \$\begingroup\$ Just talk to OSHA or your local fire warden, they'll be more than happy to take care of it \$\endgroup\$ – Voltage Spike Jan 21 '18 at 6:05
  • \$\begingroup\$ The cable gauge is relevant here. \$\endgroup\$ – Dmitry Grigoryev Jan 22 '18 at 11:32
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The hazard with coiled power cables is they can't dissipate heat as effectively because it's exposed to less air.

It's especially an issue for long cables since some layers of the spool are exposed to no air at all, instead being surrounded by more hot wire.

Fortunately 3 meters is not very long, and you will not need a very tight coil to take up that length. So I'd say a safe guess would be:

  • Coil it loosely, so there is only one layer of coiling.
  • Derate the the maximum current by 50%. This will be a 4x reduction in heat generated, since power is proportional to the square of current. So be sure the attached equipment will not draw more than 2.5 amps. To really be sure of that, add a circuit breaker or fuse.
  • Be sure there is ample airflow around the cable. Don't coil it inside a small cabinet or in a wall, for example.

Of course I can't take responsibility if this starts a fire anyway. The cable will get warm before it catches fire, so if after running the equipment for a while you notice the cable getting noticeably warm, it's probably time for a thicker cable, or a shorter one that doesn't need to be coiled.

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  • \$\begingroup\$ Also, transformer effect. \$\endgroup\$ – Ian Bland Jan 19 '18 at 16:40
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    \$\begingroup\$ Transformer effect is relatively small, as Live and Neutral currents largely cancel out. Or if they don't, you have bigger problems. \$\endgroup\$ – Brian Drummond Jan 19 '18 at 17:09
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Is 3m a typo? I can't believe it is real or the question is not really an issue if you are not coiling the wire REALLY tight and already approaching the maximum rated current for the wire.

A 30m cable for a 3m span would be a different story.

There are ways to alleviate that issue, but since all of them reduce the safety of the system, the only real answer to this is to properly wire it up in the first place.

Have an appropriate outlet installed where the power is needed, or buy the required length of suitable cable and the appropriate end connectors so the cable can be routed safely to where it needs to go.

Besides, minimizing the cable length will improve the performance of whatever you are powering.

"Accident waiting to happen" should be all you need to know to justify the expense.

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Cable is current-rated assuming it's laid straight out, by itself.

Coiling the cable means that it has other heat producing things next to it, so will get hotter. Heat softens insulation, and a lot of heat could cause it to burn.

The heat produced by cable is proportional to the current squared. If a cable is carrying half its rated current, it will be generating 25% of the heat it's been designed to dissipate. If you coil the cable 4 times, then the coil will be generating the same heat per unit length as a single cable at full current. While it will run cooler than a single cable, as the diameter of a bundle of 4 cables is larger than a single one, it's not safe to estimate how many extra times the cable could be coiled.

You need to know the actual current consumption of the machine, and the rated current for the cable. You can coil the cable that ratio squared. It's not clear from your question what the 5A refers to. It will be safe to work from the rated current or the fuse rating of the machine, as these tend to be more than the actual consumption, an actual measurement may well be more favourable. If you don't know the rating of the cable, it tends to be 10A/mm2 for cables up to about 1.5mm2.

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