Tails to second consumer unit

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I was hoping someone could clarify this for me. I have two consumer units. From the meter, 16mm tails go to an isolation switch and then to a Henley block that divides to one consumer unit close to the metre and one eleven metres away, again with 16mm cable. Both consumer units have a 100amp switch. I understand that the tails should be 25mm. For the second unit, am I correct in thinking that either the cable should be armoured (and presumably 25mm) or unarmoured but with a time delayed rcd? Also there is an isolation switch after the meter before the Henley blocks, do I need a second isolation switch after the tails divide for the second consumer unit? I ask because I have had conflicting advice from different electricians and I want the set up to be safe but not "over engineered" as it were.
 
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I was hoping someone could clarify this for me. I have two consumer units. From the meter, 16mm tails go to an isolation switch and then to a Henley block that divides to one consumer unit close to the metre and one eleven metres away, again with 16mm cable. Both consumer units have a 100amp switch. I understand that the tails should be 25mm.
Not necessarily. It depends on the rating of the main fuse and the design current.

For the second unit, am I correct in thinking that either the cable should be armoured (and presumably 25mm)
Only if they are concealed less than 50mm. from the surface and you don't want to protect with an RCD or a mechanical method.

or unarmoured but with a time delayed rcd?
NO.
They will require 30mA RCD protection if concealed less than 50mm. from the surface and not armoured or otherwise protected.

Also there is an isolation switch after the meter before the Henley blocks, do I need a second isolation switch after the tails divide for the second consumer unit? I ask because I have had conflicting advice from different electricians and I want the set up to be safe but not "over engineered" as it were.
No, not required and not advisable.
There must be ONE means of isolating the whole installation.
Addition separate switches could present a hazard.
 
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PBoD is correct about the fuse (I missed that).

In view of what is required for isolation, would people replace the single isolator with switch fuse?
 
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Thanks for the replies guys. The cable lies secured to ceiling joists and the attic will be converted hence it will likely be within 50mm of surface.

The incoming supply has a 100amp fuse without a switch. The isolator is an rccd green on red off device which I think edf fitted. Would metal trunking meet the requirement for protection or would I be better off with rcd protection? Thanks again.
 
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The cable lies secured to ceiling joists and the attic will be converted hence it will likely be within 50mm of surface.
Ok. Will you have to fit larger joists for conversion?

The incoming supply has a 100amp fuse
Are you certain?
It could well be, but there may be a label stating a 100A maximum.
This does not mean the fuse is.

The isolator is an rccd green on red off device which I think edf fitted.
Can we have a picture? RCCB?

Would metal trunking meet the requirement for protection
Not trunking - some steel plate to stop screws/nails.

or would I be better off with rcd protection?
It's not advisable to have the whole supply vulnerable to one bulb blowing.
 
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Ok. Will you have to fit larger joists for conversion?


Are you certain?
It could well be, but there may be a label stating a 100A maximum.
This does not mean the fuse is.


Can we have a picture? RCCB?


Not trunking - some steel plate to stop screws/nails.


It's not advisable to have the whole supply vulnerable to one bulb blowing.

Thanks again for replying.

You are of course correct, it is rccb 63a 240v trip 30ma

House fuse (looks old and its a 60s bungalow) just says 100a 415v

There will be new trusses laid on top of a built up wall plate so all cables/pipes will go in the gap above ceiling joists and below floor joists - if that makes sense.

I will organise a pic. Thanks again.
 
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You are of course correct, it is rccb 63a 240v trip 30ma
and where exactly is this fitted?
House fuse (looks old and its a 60s bungalow) just says 100a 415v
. Really need to know what the fuse has on it, but you should not attempt that.
There will be new trusses laid on top of a built up wall plate so all cables/pipes will go in the gap between ceiling joists and above floor joists - if that makes sense.
Only makes sense if the tails are either 50mm or greater from bottom of timbers or mechanically protected. This would be either by armoured cable or by armoured plate.
 
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Thanks for your reply.

It goes incoming mains>distribution company fuse>meter>rccb isolator>Henley blocks then divides to the consumer units.

Distribution company fuse is 100a written on the fuse itself. I won't pull it as that would be foolhardy and the seal is intact.

I'm thinking from the posts above that the isolator should have 100a switch fuse and the cable should be 25mm either armoured or armour protected which would make it safe?
 
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What do the two CU load number circuits and types. Find odd that a RCCB rated at 63A would be protecting two CUs that could possibly overload the RCCB current rating.
 
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As above the rating of the fuse, will be printed on the fuse. What is stated on the fuse carrier, can be misleading. But don't rule it out.
 
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Thanks guys,

Consumer unit switch - bg cusw100 in=100a 230v/400v

The distribution company fuse amp is imprinted in the plastic not labelled - to all appearances I could snip the security seal and tug it out were I so inclined! I guess to see the actual fuse you would have to remove it as you say.
 
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The distribution company fuse amp is imprinted in the plastic not labelled
That is the maximum current for which it is rated - as is the 100A on the switch.

They are both quite happy with less.

to all appearances I could snip the security seal and tug it out were I so inclined! I guess to see the actual fuse you would have to remove it as you say.
NO.
 

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