Multicores for AC loads

[spider147]

Hi. I've been party to a discussion today concerning the use of mulicores for running AC power between distribution boards, rather than running singles or flex. Basically, an electrician can see the space and time saving benefits, but others are not so sure of the electrical implications (differing currents in cores, safety etc)

For instance, is it common, or allowable to pass mains voltage sockets, lighting, fans, entertainment etc (low'ish loads) along the same sheathed multicore cable- obviously rated accordingly?

What about earthing arrangements?

Many thanks for your thoughts.

[Tim B]

It's not common in small craft as far as I know, but that's probably due the effort of breaking out a circuit quite regularly on small craft. It's quicker and easier just to bundle all the AC cables with wire ties as required.

The multicore cable itself is regularly used in the theatre and entertainment business, for running six lights from a single pack of dimmers. There are several varieties, but "Socapex" is one of the more common. I'm not aware that there are any particular limitations, except an increased core size for maximum load, due to the increased heating effects.

The usage is really dictated by the need. Is it necessary to control several circuits from a central location? and is that location sufficiently far away to make multicore worth using?

The other use is to save space or reduce trip-hazards, and that may be important.

Cheers,

Tim B.

[DaveJ]

The problem with AC is that it continually produces EMI fields around it, which can cause interferance with the other cores running in the same multicore. Lets say you have some AC device (laptop) in the cabin, and you run a multi core from the gen down the back, and in the multicore you are also have wired up a running light. It is possible when the AC device is being using, that some EMI can get into the running light circuit and make it glow dimmly.

[gonzo]

It doesn't make any difference if you buy the wires already bundled or ir you make the bundle yourself. A laptop uses very little power and would not make a light glow. Only very high amperage devices would produce a strong enough magnetic field to do that. For example a large electrical motor. The earth wire (green) will be sized for the current rating of the multiconductor.

[DaveJ]

Originally Posted by gonzo

It doesn't make any difference if you buy the wires already bundled or ir you make the bundle yourself. A laptop uses very little power and would not make a light glow. Only very high amperage devices would produce a strong enough magnetic field to do that. For example a large electrical motor. The earth wire (green) will be sized for the current rating of the multiconductor.

Maybe laptop is a bad example, lets say a fridge or a fan, they aren't high current (like winches) but enough to caused induced EMF into the multicore bundle.

[gonzo]

A bundle of pair conductors is basically the same as a multicore.

[DaveJ]

Originally Posted by gonzo

A bundle of pair conductors is basically the same as a multicore.

Yep, execpt for the fact that in a multicore the distance of the conductors are alot closer together, which increases the effectivity of the induced EMF.

Something else i thought of after my last post was lets say you have a peice of sensative equipment running of a 12Vdc(~14.4Vdc when engines running) line that is running next to your AC line and that AC line is at 115Vac or heavens forbid 240Vac. Because of the closeness of the conductors you could have a 10% injection of the AC waveform over the DC line. That means your 14.4Vdc or line will peak at nearly 20Vdc (115Vac) or 26Vdc (240Vac) 50 times a minute.

[gonzo]

High and low voltage cables should never be run together.

[Mark Cat]

The term I use for the multi-conductor AC distribution cable with a dedicated sheath (covering) is AC boat cable. Meaning, for US 60Hz single phase 120VAC a cable will have three conductors, Hot (Ungrounded, Black), Neutral (Grounded, White), and Ground (Grounding, Green), routed in a single cable, flat or round cross section, with a plastic jacket.

The requirement from ABYC and IEEE 45 - 2002, is to minimize loop area formed by the Hot and Neutral. The best way to do this is to use multi-conductor. Multi-conductor is available in very large AWG through Naval wire manufacturers and suppliers.

Mark