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Installing IWB


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Hello people.


I am a theatre technician who has been approached from my local college who wants to install some IWB's.


1. One of these would be suspended from a box beam, so in my experience I have always seen this by using box steel or angle, and clamping the beam with studding either side. However is this a correct method? (As long as the threaded rod is correct spec etc..)


2. I intend on installing it myself as I have done a fair bit of rigging bars in theatres and am more than confident it will be safe (In fact it will probably be better than the last bar a 'company' put in!) - Can I just confirm that so long as I get a company to load test the bar, and give it its certificate, there is nothing wrong with this?


3. As I am not an electrician, I intend of buying IWB's with socapex connections on the end (as there is loads available on the market) and runnig socapex out to them. The run is not in any special air circulation void or anything; but today I was told I cannot use socapex for a permanant install. I find this hard to believe, as it is everywhere in theatres I work at, but can any of you people shed light on this?


Many, MANY thanks for your help!!!



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To the best of my knowledge it isn't banned under the current version of the regs. In years gone by the iee wiring regulations prohibited the installation of a flexible cable longer than 2 metres. Many electricians (me included) will stick to this in most regular installations, and I think the general consensus is that it is bad practice in most situations.


Personally I wouldn't use soca or recommend it, but I wouldn't have any concern about it being used as long as it is installed in accordance with BS:7671.

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In years gone by the iee wiring regulations prohibited the installation of a flexible cable longer than 2 metres.

IIRC that went out when the 16th edition was published in 1991.


I had a very heated argument with the site foreman of a large London based contractor about the subject when he refused to wire a system in flex to my spec. The end result was a new site foreman.

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Thanks people...


Just out of interest...


Any particular reason you wouldnt recommend it?


Whats socapex done to you ?!?! ** laughs out loud **


Also, the reason I am using this method is to avoid using an electrician. I mean, I'm a theatre technician but not an electrician, and I screw socapex in all the time, to bars and dimmers alike etc, as do all technicians I know!! So, surely this can be done without an electrician ?!



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From BS 7671 (the wiring 'regulations') section 521.9


Use of flexible cables or cords


521.9.2 A flexible cable or cord shall be used for fixed wiring only where the relevant provisions of the Regulations are met.


In other words, as long as you use the same care in selecting and installing the flexible cable as you would in using a different wiring system there is nothing to stop you using it and to say otherwise is just plain wrong.


It really is about time the electrical contracting industry caught up with the real world.


The main things to watch are...


cable length vs cable size (volts drop and earthing)

bend radius around corners

mechanical protection

fixing to the structure



And to answer your other original questions...


1) Yes, stud of the right size (usually M10 or M12) is perfectly acceptable. It's used like that in hundreds of IWB installs everywhere.


2) You don't *need* to get the bar tested although you then have no way to prove it's load capacity unless you go the structural engineer route and get someone to do some sums. Either route is acceptable, either route will give you an independent figure you can stick on a label to indicate SWL.


3) As above.

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The regs USED to prohibit the use of flexibles (including socapex and similar products) as a substitute for fixed wiring.

As others post, this is no longer the case, and subject to the usual caveats about electrics, it should be fine.

If the future use and loading is unknown it might be advisable to use 2.5mm.


It could be argued that the PERMANENT use of multicore constitutes an installation, and should therefore be done by an electrician. IMHO this is being unduly pedantic.

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Thanks people.


I will indeed make sure the cable is fixed and protected and run etc... in accordance...


And to be honest, the most each socapex would have to deal with is 6 1k's.... or 6 source fours (juniors even)

but I agree, 2.5mm gives me more scope.


To be honest the college in question has never, ever had any of its IWB's tested to date, and it was only when I pushed them to get it done that they wanted to do it! In fact, they are still using bars held up by M8 bolts, into wooden batterns (3in x 2in) bolted onto a beam! (Needless to say I recommended it was replaced!)


Great work people. Much apped.



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