Running Mains & Signal Cables Together

Please post a full description of the signals in the signal cables.

My that was quick,

1 x 240v AC , protected with an RCD

1 x screened twisted pair RS422

2 x 24v DC, plain 2 core 2.5mm^2 cable

3 x HD video cables. (Type 5015F, double screened)

That lot should be reasonably immune from spikes in the 240VAC. Provided the 240VAC cable is screened or has an armour, go for it, though it is best practice to segregate it from the signal cables, crossing them at right angles if possible.

What does the local installation specification say on the topic?

It's not for an installation. It's a temporary umbilical cable for a remote camera platform, on the end of a telescopic crane.

It will be used outdoors, quite likely when it's raining, though both ends will be under covers.

If I used armoured cable it will be too heavy for the crane.

I work in the film industry - there's not a great deal of published specification for what we do!

The AC load will not be great; there won't be a lot of current around. My main concern I guess is health & safety. Quite often we get cables back that have been chopped by a camera dolly wheel. The mains will have an RCD fitted but the power could come from a generator which may not be adequately earthed.

The RCD on the mains is a good idea, regardless of the quality of earthing; it gives a greater level of personal safety to anyone downstream that might come into contact with a fault.

It sounds as though "custom and practice" is the standard. Do post back with the outcome, as it might be of interest to a number of CR4 readers.

Nothing actually wrong here...

The signal cable is twisted to negate electro-magnetic interference/ inductance, so do not untwist the pair in the presence of the power cables.

Unless the sending and receiving electronics make proper use of the twisted pair, the difference will be minimal.

The signals have to be "differential" to gain from a twisted pair.....

My advice to the OP is not to mix the two types, AC on one side of the mast, signals on the other may help......but never together.

Greetings.

Installing the communication cables with a ground sheath grounded at the beginning end of the cables and isolated at the far end should eliminate crossover from the power.

If you have to run all together put some kind of plastic or insulating material between the power and the communication cables.

It would look like a figure 8 when taped or cable tied together.

Covering the whole or part with some kind of bright color will alert people that "whoa there is the cable".

Communication people dealing with non communication people is always a challenge.

This has helped me I hope it can help you.

Have a Great Day,

Oly

I don't have handy access to the texts of more current documents, but in the NAB Engineering Handbook 7th edition:

"If possible, do not run low-level cables near high-voltage lines, avoiding especially long parallel runs of adjacent microphone and ac power cables. When such cables must cross, they should do so at right angles."

I hope that this helps.

You may not have any problems with your situation, but I agree that running the power cables should be on the opposite side of the crane pole from the other low level signal cables. I think that this separation would be considered best engineering practice. If your cables do get mangled, you don't want the 240V line to short through the equipment connected to the low level signal cables.

Thanks everyone for your input.

I forwarded you your comments to the powers that be, but despite the quote from the NAB handbook, they have decided to press on.

I'll use some brightly coloured sheath, that's a good idea.

Similar cable looms we have at the moment function OK so, as surmised here, interference will hopefully not be an issue.

Mike