Bending a supply cable

An electrician said that these back boards for service cut-outs and meters are known to present problems to builders and plasterers who require access behind them. The DNO is often reluctant to temporarily remove the board and leave what was attached to it hanging free although it's what most plasterers want in order to do their work.


The electrician has admitted to removing a few back boards before, which involve having to pull the big fuse to be on the safe side as the cover on the meter has to be removed to access its mounting screws. He said that the real danger is the supply cable snapping a conductor or short circuiting inside the service head which is no longer physically supported.

Without seeing it, the advice has to be 'it is not wise.' Just because it has been done once or twice and nothing went wrong, does not mean it will always be so.


Yes it may be possible to suspend the board from ropes from the ceiling and  swing it forward an inch or two, if there is a long length of cable than can gently curve, but not in the general case.


Or put another way, only proceed, when everyone involved  fully understands and is happy with exactly what process will need to be invoked for each possible bad outcome.

How much arc flash PPE clothing is the plaster intending to wear for example ? I bet it is not even on his RADAR. It should be !


A very credible example of a bad outcome would be if say the cable kinks too sharply instead of a graceful curve,  and the lead sheath cracks at the point where it leaves the floor, or if the backboard is not separable from the wall  in the way expected and it drops at a sharp angle, damaging the cable.  In such a case, once the cable has been damaged, fire or not, given the length and diameter of a joint for that sort of cable,  it probably means digging up the grounds outside to bury a joint, and then routing a new service cable into the building.


Now the 10 mins of plastering starts to look expensive, but at least you get a week or two with the power off to do it.


When PILC is first installed the paper is oily, and that gives the turns of paper the ability to slide over one another, and the  whole cable has a well defined minimum bend radius of a few feet.

The oil also provides a degree of self healing against pinhole failure of the insulation, as it fills any small holes and joints/tears in the paper.

In cellars it is not unknown for the oil to seep out the end, and the reverse is true it that a cable high up may lose some or all of the oil as it drains down, especially with high load cycling making it warm and cold. The upshot is that an old cable is not always as safe to flex as a new one, though it may well be perfectly fine for years if unmoved. There is a reason the DNO cable jointers are a lot more careful than the meter swappers.



In summary there is a very good reason why the wall behind the meter board is often bare block work, or very crummy original plaster. I suggest the customer gets used to the idea, and lets go of the idea of plastering behind it. Fill up to the edges instead.


Mike.

The service head is a whopping great Henley Series 8 with 3 fuses but only a live and a neutral cable emerging from the outlet terminals.


I'm unsure whether it's 3 phase inside or if the Series 8 was chosen because it's an optimal physical fit onto the supply cable.

I am still rather mystified by the wish to replaster behind the board.

One question: If this happens in front of you https://www.youtube.com/watch?v=6hpE5LYj-CY, will it be survivable? It should give a rough idea of the flash that may happen if the service cable / cutout fails. 


Edit: In real life, the fire will probably last for several seconds. 


Regards,


Alan.

I've seen enough of these safety videos to know that if it all comes on top its not going to end well. Seriously get your customer  to understand its just not worth the risk just for a bit of plaster no one will even see.i think there's a reason why intake rooms are usually a bit mingy

I have advised the plasterer to discuss it with the DNO. I told him do not bend the supply cable because of potential metal fatigue.


A concern I have with a service head that is hanging free is that it could be accidentally knocked and something inside short circuits. The likelihood of it being knocked is significantly increased if a plastering float is swishing around behind it!