100 amp fuse

27 Jul 2008
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United Kingdom
I had to disconnect a fuseboard and fit a temp with 2no TSO's, RCD protected, The earth was poor condition TNS so I advised the house owner have a PME done before the old board was reconnected as there is no RCD protection to the old board, when the PME was fitted a new 100 amp fuse was installed but the old fuseboard main switch has a 60 amp rating, is this a code 1 on the periodic and should they come back out and change the fuse back to a 60 ?
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Code 1 no as it does not in itself present a danger. The danger is only there if there is a second fault. But would be a Code 2.

However if the temp supply was able to be connected to a 100A supply the DNO has done nothing wrong.

As far as they know the fuse board is going to be renewed.

And once disconnected I am uncertain if you can re-connect. This is a problem with many PIR's as we are not allowed to disconnect a domestic supply without ensuring this does not present danger to the occupants and if a DNO wants to disconnect i.e. through non payment there is a procedure that must be strictly followed. The same for GAS the house must be habitable. So you temp disconnect in order to test and you find a fault.

You can't re-connect due to fault found yet you can't leave the house uninhabitable. I would say I am not allowed to switch it back on but neither am I allowed to do anything other than a danger notice to stop the occupier from switching it back on.

In your case main question is who reconnected the old fuse box?

And second once supply is physical removed rather than just switched off can you re-instate a system which does not comply to 17th Edition.

In the same way as one can continue to used a 13A plug without the insulation on the pins to stop fingers touching them but you can't re-fit a plug of that type I would think the same rules go for anything else which is physical removed and I would consider you can only re-fit to regulations.

This is my opinion and I would be interested to hear what others have to say as I am not sure of what is or is not allowed on this one.
My first question would be...

How do you know that it's a 100A fuse??? Just because the fuse holder says 100A does not mean that it's got a 100A fitted!!

My second question is..

What size are the tails??

And thirdly

What is the estimated maximum demand of the installation??

However if it is 100A you could fit a switch fuse in the tails!
I dont know what fuse is inside but should I cut the seal take it to bits and have a look ? surely they should not miss label fuses, I dont take the fuse out on all my periodics and check, if there is no label then I put limited, the fuse holder etc etc is all brand new.

The tails are 16mm

Its a large 3 bed house

The temp board was a 2 way RCD rated at 63 amps, so does that mean the board will come out replace it ?

I did sort advice from my part p scheme, whether or not I could reconnect the old board, (the board stayed in place, only the tails were disconnected) they said yes I could providing the earth reading was safe when I tested it

I think I will leave it off and fix a warning label,
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well if the tails are only 16's then you can't have a 100A, can you? If it was me, I'd check the main fuse, otherwise how can you cert that the tails are protected and/or main switch load is OK?
well if the tails are only 16's then you can't have a 100A, can you?

Not and comply with BS7671, no... but the risk of such an arrangement is quite low on an average domestic (think about what size cable you probably have comming into the cutout)
Ive just spoke to the guy who installed the PME and they informed me that they only do a 100 amp fuse, and are starting to use 80 amp on new buildings, obviously I cant use the old fuseboard !!
If it was me, I'd check the main fuse,

Very true and I do if i'm not sure and teh seal is already missing ;)

I did this on a recent upgrade and was very surprised to find that there was no way to open the DNO's fuse carrier. It had a sort of crimped over rivet so you could not get to the fuse itself :cry:
The fuse carrier had no label to indicate the value.
Now, three weeks (and 8 phone calls) later, i am still waiting for the DNO to tell me what their fuse value is :rolleyes:
I made an enquiry a few months ago and was told that I definately had a 100A fuse. By co-incidence a few weeks ago the dno came because my meter board had rotted away.

The guy said 'that's only big enough for a 60A fuse' and was proved correct. He (hinted at and) received a cup of tea and fitted a 100A holder and fuse before he left.

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