Post subject: Speaker Wiring distance from 240v cables?
Posted: May 27, 2011 10:39 am
Joined: 30 Apr 2010 Posts: 57
Hi, Just a quick query. Is there a distance from 240v to speaker cables that's recommended in wall and roof? Also is it possible to clip the speaker wire on a 45mm beam in the roof if a 240v is running parallel on the opposite side of the beam? Is intersecting at 90 also the best way if I must pass a 240v? Cheers
_________________ __________ Steve & Mel Building the Henley Cooper
Post subject: Re: Speaker Wiring distance from 240v cables?
Posted: May 27, 2011 4:43 pm
Joined: 14 Feb 2011 Posts: 494 Location: Blue Mountains, NSW
I had a quick look at AS/NZS 3000 ("The wiring rules"). It has this to say about Low Voltage (240V) and extra-low voltage systems:
Cables of low voltage circuits and cables of extra-low voltage circuits may be enclosed in the same wiring system only where one of the following arrangements is employed: (a) The low voltage cables shall be of a type providing the equivalent of double insulation. (b) All cables or each conductor of a multi-core cable shall be insulated for the highest voltage present. (c) The low voltage cables shall be installed in a separate compartment of a common cable trunking system having fixed and continuous barriers between compartments.
Although this is primarily referring to conduit/trunking, clause (c) could apply to your scenario of using a beam.
The other document you could use for guidance is the cabling wiring rules, even though you aren't installing communications cable (because that would be illegal), its advice on separation (50mm or a barrier between cables, 150mm or a barrier between "terminations" ie. the back of power point and the back of a speaker plate) is probably a good starting point.
If you have to cross a 240v cable, and both cables are crossing on top of a truss or some other location where it may be stepped on you may want to consider enclosing the speaker cable in a short run of conduit to provide additional physical protection. It would pretty extreme damage that broke through both layers of insulation on the 240V cable and the insulation of the speaker cable, but look at what happened with the insulation scheme!
Both of these documents are concerned with safety (preventing 240V from ending up on the speaker/comms cables if one is pierced by a screw/nail for example), not performance.
The performance concern is whether you will get mains "hum" on your speaker lines. For lines running in parallel or crossing at 90 deg, I would think you are unlikely to get noticeable noise on a speaker cable if you maintain 45-50mm separation, although I guess it depends on how long the parallel run is and the current in the 240V cable.
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