Consumer Unit Blanking Plates

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It is conceivable that a loose live conductor could come into contact with a metal blanking plate.  Some of the twist-on  types do not make electrical contact with the (earthed / powder-coated) case in which case they thus constitute exposed conductive parts.  This means that they should be individually earthed. But there is no means provided to do do this.  So the question is: does the use of metal CU blanking plates contravene the Wiring Regulations if fitted but not earthed?

The Niglon consumer units that I use have metal blanks to fill the gap when there are spare ways. They fit very tightly and sometimes have to be bashed into place. The cables are normally well behind the front cover and metal blanks. But, theoretically, a live cable could make the front cover live if it is damaged or gets crushed between the cover and consumer unit body. At that point the circuit R.C.D. or M.C.B should automatically disconnect the damaged cable and render the situation safe.

 

Z.

my point is that the blanks are not earthed.  So anyone touching a blank which has a live conductor touching it would receive a shock.  Yes an RCD might provide adequate protection but you are assuming one is fitted.  That is not always the case.  

If the blanks are painted and not earthed they are electrically insulated from the metal earthed cover. If so they can not become live either, as the paint is insulating them. B.S. 7671 does not accept that paint can be used as an insulator but it may well happen in reality. (416.1).If their paint is scratched off and they fortuitously become earthed by being in intimate contact with the front cover then a protective device will operate and disconnect  the fault. If you are really worried then why not file off the paint on the metal blank locating point and on the opposite cover location to earth the blank? Then you have clean metal to metal.

I think that the risk of a single metal blank becoming live is very unlikely indeed.

Z.

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It is conceivable that a loose live conductor could come into contact with a metal blanking plate.  Some of the twist-on  types do not make electrical contact with the (earthed / powder-coated) case in which case they thus constitute exposed conductive parts.  This means that they should be individually earthed. But there is no means provided to do do this.  So the question is: does the use of metal CU blanking plates contravene the Wiring Regulations if fitted but not earthed?

The Niglon consumer units that I use have metal blanks to fill the gap when there are spare ways. They fit very tightly and sometimes have to be bashed into place. The cables are normally well behind the front cover and metal blanks. But, theoretically, a live cable could make the front cover live if it is damaged or gets crushed between the cover and consumer unit body. At that point the circuit R.C.D. or M.C.B should automatically disconnect the damaged cable and render the situation safe.

 

Z.

my point is that the blanks are not earthed.  So anyone touching a blank which has a live conductor touching it would receive a shock.  Yes an RCD might provide adequate protection but you are assuming one is fitted.  That is not always the case.  

If the blanks are painted and not earthed they are electrically insulated from the metal earthed cover. If so they can not become live either, as the paint is insulating them. B.S. 7671 does not accept that paint can be used as an insulator but it may well happen in reality. (416.1).If their paint is scratched off and they fortuitously become earthed by being in intimate contact with the front cover then a protective device will operate and disconnect  the fault. If you are really worried then why not file off the paint on the metal blank locating point and on the opposite cover location to earth the blank? Then you have clean metal to metal.

I think that the risk of a single metal blank becoming live is very unlikely indeed.

Z.