Use of flexible cable for installation

rsmck · May 15, 2011

I have a bit of an unusual requirement. I do a lot of work as a theatre technician and am planning on wiring the lighting of our lounge back to a "dimmer pack" to enable "scenes" in much the same way as a Lutron or similar system at a fraction of the cost.

There will be 4 circuits - (ceiling light, 2x 5A sockets for lamps, 2x circuits for wall lights). The dimmer will be protected by a 30mA RCD and each individual circuit is protected by an MCB on the dimmer. The requirements of the 17th edition regarding RCD protection for cables behind walls are satisfied.

Most dimmers have socketed outputs - therefore these (hard wired) sockets and fittings should terminate in plugs beside the dimmer pack - normally theatrical lighting is on HO7RNF cable.

Two questions;

Is it acceptable to use H07RNF TRS cable in place of T&E from the socket / light fitting back to the dimmer (I'm thinking it's not - but please correct me if I'm wrong)

If, as I expect, T&E must be used what would your preferred way be of joining these to flexible tails (I would't put a plug on the end of T&E

) - previously i've seen it done with simple connector blocks in an enclosure but this would be frowned upon under the new regs

Tom Creed · May 15, 2011

H07RNF is fine to use in my opinion - 1.5mm CSA. but you need to have an earth running to all points. so 3 core for SL, N & E

i would recommend through crimps for connecting if you use T&E.

Adam W · May 15, 2011

IMO H07 is fine; as you say you shouldn't put a plugtop on the end of a bit of T&E.
Out of interest what kind of dimmer pack are you using, and why? The 3 way theatrical dimmers I've seen are (from memory) rated around 2.5 kW and above (Strand/Zero 88) which are totally excessive to what you'll be using them for. You can get hard-wired dimmer packs which have a more appropriate rating.

rsmck · May 15, 2011

Thanks Tom, It'd be 3 core 1.5mm H07RNF.. Not least because i've got loads of it lying around... it's also a lot easier to work with then T&E. I think it'd need to be put in conduit of some sort or cap it as well as I seem to remember some issue with rubber and plaster ?

Makes sense though just to run these cables in H07RNF and terminate them on plugs on the dimmer as long as it's permissible

rsmck · May 15, 2011

Dimmer pack will most likely be some small Showtec one with IEC outlets (cheap and readily available) or alternatively an older Anytronics Series 192 (again, have several of them lying around) - yes it's overkill but there won't be much load on them and I already have the kit (or access to it very cheaply) whereas hard-wired "architectural" dimmer packs tend to cost a lot more and most of them use some proprietary protocol rather than simple DMX.

Tom Creed · May 15, 2011

"These cables are designed to provide high flexibility and have the capacity to withstand weather, oils/greases, mechanical and thermal stresses. Applications include handling equipment, mobile power supplies, worksites, stage and audio visual equipment, port areas and dams. Also for use in drainage and water treatment, cold environments and severe industrial environments."
http://------/jDNbKY
i just got the above spec on your cable - not 100 % sure but i don't think conduit it neccessary - just some plastic capping over the top - much cheaper

rsmck · May 15, 2011

Having seen the abuse they suffer on stages I can't imagine a little bit of plaster will do much harm to them to be honest

... still, will do the rest of the house in T&E - otherwise I imagine many years down the line whenever it next changes hands there'll be some very confused homeowner seeing they've got black rubber cable and immediately assume it's old VIR