Sub CU

[JohnW2]

With this setup all of the heating can be isolated simply and easily to the uninitiated - simple to understand.

Indeed - but, as I said, exactly the same regardless of how the heating CU is fed.

The system also has a main switch as well, so all is off in the house. Could have both CUs off Henley blocks and a separate mainswitch for both, which produces messiness with three units on the wall.

What 'third unit' are you talking about - the Henley block, perhaps, or are you thinking about having a 'whole house isolator' as well as the main switches in each CU?

Kind Regards, John

 

[SUNRAY]

I had an issue at the beginning of last year with one of my rental properties, there is a teleswitch? controlling power to 1/2 of the CU. I had a change of managing agents whoe produced documentation from one of the bodies (I guess I can get hold of this info) which specifically stated the whole flat had to be on a single point of isolation.
Unfortunately the agents asked DNO to quote to fit an isolator in the external meter box and it came out close to £1K and after that there was no route back for me.
Initially it looked like the only way of doing this was a 3 or 4 pole isolator. at the same time as replacing the 40++ year old CU to add RCD.
Luckily for me the tails (buried in the wall) came to a henley block beside the CU then 'L' went back to the teleswitch in the meter box and backto the CU. By careful positioning of the new CU I was able to get the 4 tails to reach. So that the feed to teleswitch came off the load side of main switch.

 

[JohnW2]

... I had a change of managing agents whoe produced documentation from one of the bodies (I guess I can get hold of this info) which specifically stated the whole flat had to be on a single point of isolation.

There is a regulation in BS7671 which can be take to mean that there has to be single means of isolation of the supply to an entire "installation".

However, as you will have seen above, BS7671's definition of an "installation" is so vague that those who so desire can argue that all the "electrical goings on" within a dwelling do not comprise just one "installation" but, in fact, two or more "installations" - in which case I suppose that having separate isolators for each of those "installations" would be acceptable. Make of all that what you will!

Kind Regard, John

 

[SUNRAY]

I've trawled through emails and found the message

The salient copy and paste from that email which has been quoted from NICEIC:

a single device to safely and securely isolate all poles of the electrical supply to the property in an emergency in a single operation

What does need to be born in mind is this is specifically related to a rental property, if that makes any difference, and i don't know if this was from a general relaese or a reply to a request for information.

 

[EFLImpudence]

NICEIC don't make the rules.

The emboldened text of your quote does not sound like the language of the wiring regulations, especially the use of the word property in such a case.
It cannot be a requirement to have a single device to isolate every property.

There are no wiring regulations exclusively for rental properties.

 

[SUNRAY]

NICEIC don't make the rules.

The emboldened text of your quote does not sound like the language of the wiring regulations, especially the use of the word property in such a case.
It cannot be a requirement to have a single device to isolate every property.

There are no wiring regulations exclusively for rental properties.

I beliieve I agree with everything in your reply.

 

[JohnW2]

... that email which has been quoted from NICEIC:

EFLI has said it all - NICEIC do not make 'the rules'

The one thing to be said about the wording of that NICEIC statement is that, in contrast with the confusion BS7671 has created by it's useless ('non') definition of "an installation", NICEIC are at least very clear in saying "all poles of the electrical supply to the property" - which clearly applies to 'all electricity going into the property' regardless of how many "installations" Risteard may believe the property to have!

Kind Regards, John

 

[boringoldcodger]

Just to live down to my moniker:

Certain about what?

following on from:

Just to be 100% certain, what's the maximum demand of the heaters?

My guess is that Chivers was trying to check the 63A RCD would be correct.

 

[Risteard]

I didn't make the claim about numbers of installations - the IET did in their Guidance Notes. They explicitly state that there does not need to be a switch which isolates all of these together. That is their opinion on it. I simply reported that to you.

As for firefighters a fireman's switch is different to these isolators and can be operated from outside the building so isn't really relevant.

 

[SUNRAY]

And to throw in another spanner...
What is the definition of a property?
In the situation that particular flat is in, there are 22 flats within the one building, of which 5 or 6 on the ground floor have their own external door and those on the first and second floors are accessed via a pair of communal doors and stairs. The free hold documents refer to it as '...part of property formally known as...' & '...property known as...'.
During the refurbishment, agent change and CU change I did wonder if the quoted words referred to the property per se or extend to the property as a whole.
If the later, may God help us make those changes.

 

[AndyPRK]

The way I see it, is that a fireman needs to go into an burning building, but doesn't want to get a shock from wires handing from the ceiling, as he goes in (while someone outside sprays water in thru the roof)

He either wants to turn the supply off from outside (I guess they pull DNO fuses?) or be able to turn 1 switch off in the hall way ?
What he doesn't want is a second CU upstairs or at the back extension that he doesn't know about.

If 2 CU's are next to each other, it's common sense I would think, to turn both off. Adding a 3rd (Main) switch next to them isn't helpful.

However if one switch isolates front/back/upstairs from one location, then that is helpful

 

[scousespark]

There will be electric heating in each room, seven of them. A new CU is being installed for the whole flat. The idea is to have a sub CU off the main CU holding only the mcbs for the electric heating, so the heating is all in one unit. On the main CU, is an 63A RCD feeding the sub CU OK?

To answer your question, you need to know the total load (as Chivers) asked in one of the early replies. When you know this, you can start to design the circuit. As this is a new CU, for a rental property, I would say this is not a job for a DIYER.

 

[hard-work]

To answer your question, you need to know the total load (as Chivers) asked in one of the early replies. When you know this, you can start to design the circuit. As this is a new CU, for a rental property, I would say this is not a job for a DIYER.

Firstly, it will not be DIYed. Secondly, I was after comments regarding a sub CU. Thirdly, the loading is not in question, not an issue, all in hand.

 

[scousespark]

Firstly, it will not be DIYed. Secondly, I was after comments regarding a sub CU. Thirdly, the loading is not in question, not an issue, all in hand.

I only suggested this as not a DIY job, because it is relatively complicated.

You asked if a 63A RCD was suitable, but the thread does not have the load. If you have 7 500 watt heaters, your load is under 16 amps. If they are 3 kilowatt heaters, the load is over 91 amps. As well as the RCD you need to consider the Size of the MCB.