Consumer Unit Blanking Plates

Qbit: 
 

Chris Pearson: 

If a compact / miniature rcbo is used, the line and neutral are both quite close to the front panel At installation, human error in making live conductor connections could result in one of them touching (unpainted) Blanking plate when front cover is replaced. I realise that I am dealing with relatively low probabilities but the aim is to ensure fail safe.  For example, for the same reason, great care is taken to ensure that socket fronts and boxes are earthed.  I see no difference for consumer unit fronts.  The case itself is earthed / protected but unpainted blanking plates are exposed, conductive and unearthed.  I am questioning why some manufacturers supply uninsulated bare metal blanking plates.  I suggest that plates should either be made of non-conductive material or they should be designed in such a way to assure that they make full and reliable contact with the case (a simple screw would suffice).

Having looked for a Niglon B.S. reference for its metal consumer units I only found references to the protective devices inside and nothing for the complete assembly.

I wouldn't have time to individually earth each metal blanking plate. 

I don't think that R.C.B.O. final cables will be able to touch the metal blanking plates normally hidden in the bowls of the enclosure.

If you are that worried then just over-sleeve the final conductors, and check for terminal tightness. Give the conductors a final gentle tug to confirm correct termination and terminal grip.

Has there ever been a report of a live metal blanking plate causing shock or injury?

Z.

Zoomup: 
 

 

 

If you are that worried then just over-sleeve the final conductors, and check for terminal tightness. Give the conductors a final gentle tug to confirm correct termination and terminal grip.

 

Has there ever been a report of a live metal blanking plate causing shock or injury?

 

Z

it’s not me I’m concerned about because I am aware of the potential hazard

Qbit: 
If a compact / miniature rcbo is used, the line and neutral are both quite close to the front panel …

If the job is done properly, I don't see why any conductor should become detached.

If the line conductor becomes detached, there is nothing to worry about. If the neutral becomes detached and just touches the plate and nothing else, there will probably be sufficiently good contact to activate ADS, but if not, as soon as somebody touches the floating blanking plate, the RCBO will trip.

I think that you are worrying about a non-existent problem.

I just checked a recent Wylex CU. There was no continuity from the front panel fixing screws (which are earthed) to the metal blanking strips, nor to the exposed metal hinges of the front lid.

Wylex insist on metal blanking strips to maintain the non-combustible rating, but as mentioned earlier, it's not obvious why a “dummy” MCB made from the same material as a standard MCB is not suitable when when real MCBs are.

For example, for the same reason, great care is taken to ensure that socket fronts and boxes are earthed. 

So long as one of the metal box fixing lugs is fixed, ie not the adjustable side, there is no requirement to “tail back” from the socket-outlet to the metal box.

Regards

BOD

And to confuse matters some clip on front covers for sockets are not earthed either…

Now, if we accept a metal CU on TT without an all insulated RCD before it (and I do not like it but many do) then we are assuming the live wire off that makes something live without ADS, condition is rare enough to be acceptable. So the same folk should be happy with that.

It would be better if the CU makers masked off the paint on the back where the clips go, but in many designs the whole front relies on a screw heads on paint to earth it anyway.

Mike.

In the real world I see far more consumer units with the blanks missing altogether than with metal blanks.

Chris Pearson

Precisely: the fixed lug is used to earth the box via the screws.  Any metal front at risk will be earthed by the screw and/or internal design connection.  I.e. significant effort to ’deadfront’.  

Conduit box lids, adaptable box lids and trunking lids all come to mind.

Sparkingchip: 
 

Conduit box lids, adaptable box lids and trunking lids all come to mind.

a, Metal box, metal lid, metal screws……no problem.

b, Metal box, metal lid, metal screws……….no problem.

c, Painted metal trunking…erm…don't the cover fixings scrape off the paint of the trunking when tightened?

Most trunking that I have installed has been galvanized.

A previous discussion…..

IET Forums - Earthing of trunking lid containing non-sheathed cables (theiet.org)

Z.