And again...

ericmark";p="2285009 said:
But I have seen many consumer unit changes where 63A RCD's are fitted but it has a 100A incoming fuse. I blame electricians being lazy and since the consumer unit comes fitted with a 63A RCD they continue with that size.

Question now is...

A lot of the "off the shelf" CU's come with a 100A double pole MCB incommer and then proceed with 63A RCD's.

This, according to the logic in this thread would be dangerous as the RCD would be exposed to higher currents than 63A and even higher than 100A whilst waiting for it to trip due to overload.

Plastic melting, fire etc?
 
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I am at the begining of my journey into the world of electrical installations. Would anyone mind explaining (without wishing to hijack the original post) the series of connections from the meter to the Henley Block, where the meter tails are split and then to the CU and in this case to the RCD.

Kind Regards
 
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I am at the begining of my journey into the world of electrical installations. Would anyone mind explaining (without wishing to hijack the original post) the series of connections from the meter to the Henley Block, where the meter tails are split and then to the CU and in this case to the RCD.

Not quite sure what you mean.
You seen to have answered your own question.

Don't forget there are two separate connectors in the block, so -

1 Live in, 2 out,
1 Neutral in, 2 out.
 
A lot of the "off the shelf" CU's come with a 100A double pole MCB incommer and then proceed with 63A RCD's.
Not that I'm aware of - you'll find either a main switch (often 100A rated) or an RCD as an incomer in most off-the-shelf CUs. I've never seen one with an MCB as an incomer.

Kind Regards, John
 
depends on the set up, if you have dual rcd's then 2 no. 63A rccb(rcds) are ok. but by the way you typed it rcds or rccbs are not overcurrent devices. how can can you wait for an rcd to trip with an overcurrent?
 
depends on the set up, if you have dual rcd's then 2 no. 63A rccb(rcds) are ok. but by the way you typed it rcds or rccbs are not overcurrent devices. how can can you wait for an rcd to trip with an overcurrent?
He seems to think that a 100A main switch is an MCB, and is worried that the 100A+ overload/fault current it would pass whilst 'waiting to trip' might damage an in-line 63A RCD.

Kind Regards, John.
 
Just putting it out here becuase it might be relevant, but I've had a call out to loss of power before, when I got there I found a burnt out 100A rated RCD which was 'protected' by a 100A service fuse (outside in a cold meter cabinet). Oh and a heavily overloaded installation!. It seems that there was a persisat minor overload not sufficent to take the fuse out, but was sufficent to slowly cook the RCD. Now I'm not entirely sure that there wasn't anything else at play (there were two such single phase supplies (on same phase) running through the the same 4 pole RCD, so there was almost full load on all poles, something which wouldn't happen on a standard 3phase application)
 
Just putting it out here becuase it might be relevant, but I've had a call out to loss of power before, when I got there I found a burnt out 100A rated RCD which was 'protected' by a 100A service fuse (outside in a cold meter cabinet). Oh and a heavily overloaded installation!.
That presumably is a very common potential problem. Standard domestic installations don't have any OPD between the meter and CU. If installation design is poor and/or diversity does not work out quite how one expected, most domestic CUs have final circuits which, if all nearly fully loaded, would add up to apreciably (or considerably) more than the 'maximum current rating' of the CU incomer, be it a main switch or RCD, quite probably without operating the cutout fuse. Whether or not such degrees of overload would 'burn out' an RCD or main switch is a different matter - I would probably be inclined to suspect a poor connection (were there any signs of localisation of damage to the RCD?).

(there were two such single phase supplies (on same phase) running through the the same 4 pole RCD, so there was almost full load on all poles, something which wouldn't happen on a standard 3phase application)
What do you mean by 'all poles' - you presumably don't mean 'all 4', do you (i.e. two neutrals taken through the RCD)? Does the arrangement you're describing even work (in terms of RCD functionality)?

Kind Regards, John.
 
JohnW2";p="2285886 said:
He seems to think that a 100A main switch is an MCB, and is worried that the 100A+ overload/fault current it would pass whilst 'waiting to trip' might damage an in-line 63A RCD.

Kind Regards, John.

So what you are saying is a double pole Main switch isn't an protective device? I'm pretty sure I've seen old ones trip out, albeit not the DIN rail modern versions.

Its just an Isolating switch with a maximum current rating of 100A, not a protective device with a 100A rated current?
 
So what you are saying is a double pole Main switch isn't an protective device?
Exactly. A switch is a switch, and an overcurrent protective device is an overcurrent protective device.

I'm pretty sure I've seen old ones trip out, albeit not the DIN rail modern versions.
If you have seen such devices (and 100A DP MCBs obvioulsy do exist) then they would be MCBs (or similar), not main switches. I certainly don't think you'll find one in any off-the-shelf CU.

Its just an Isolating switch with a maximum current rating of 100A, not a protective device with a 100A rated current?
Exactly.

Kind Regards, John.
 
I'm pretty sure I've seen old ones trip out, albeit not the DIN rail modern versions.
Not likely or indeed possible.

However, where an older, though not that old, installation has only one RCCB protecting all the circuits then this RCCB may well have been used as the 'Main Switch' as well.
 
I have got a call out in the morning where customer says the switch marked RCCB trips when his shower and hob are on only? my first thought is a combined earth leakage?
 
What do you mean by 'all poles' - you presumably don't mean 'all 4', do you (i.e. two neutrals taken through the RCD)? Does the arrangement you're describing even work (in terms of RCD functionality)?

Kind Regards, John.


4 POLE RCD, two neutrals and two lives passing through it from two SP services (same phase, not 2 different phases, or split phase), But RCD had (from looking at it) cooked from heating on one of the two live poles.

There was a reason it was 1 4 pole and not 2no two pole devices, but thats not really relevant (involved the two neutrals ending up recombined on the load side), but suffice to say it was an installation which had a few fundamental flaws!!!

It worked in terms of RCD functionally, all live conductors passed through the device, but was cooked on from looking at the side, one of the live poles
 

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