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[Brightspark2]

So as an example if i was asked to add a garage supply to an existing installation where the main consumer unit does not have sufficient ways i would have to......
A) ask the d.n.o to attend one day never to isolate the supply at the head.
B) Install a main switch in a metal enclosure after the meter before splitting the supply at the henley.
C) Charge the client again for another s/fuse unit to protect the supply to the garage.
D) Charge the client again for another board within the garage which also has another d/pole main switch within.

In total we have now put in 3 points of isolation for a garage!!
TBH i can't see the point of this switch between the meter and henley. Both boards have their own isolation. With a single board your isolator still does not isolate the supply upstream. Putting an isolator before the henley block still does not kill the supply upstream of it.

Well when your adding the Henley blocks to split the tails you'd install a isolator before that. Your making it out to be a big thing. You've already got the supply off to split the tails haven't you?. So just add an isolator too.

For example It gives an ordinary person a quick and simple way of isolating the installation in an emergency etc.

I don't know why your mentioning the supply up stream, are you getting mixed up. IF there is one consumer unit then the main switch in that is fine, if 2 consumer units then there needs to be one point of isolation, as is the discussion. So an isolator would be fitted.

 

[hightower]

My interpretation of 537.1.4 is that there should be one point of isolation for the installation.

A main switch at the origin.

The double pole switches in the consumer unit are the main switch for that consumer unit but then there must be a main switch for the installation. As I interpret it.

Although probably not best practice table 53.4 (old regs, might have changed under BYB, only have old regs at work digitally - wish I could find a digital BYB pdf....) specifies that a BS 88 series fuse can be used for isolation, so wouldn't this technically be your main point of isolation for both boards?

As I said, not best practice surely, but an install as such would still comply?

EDIT 1: (Except in a TT install where isolation requires disconnection of both line and neutral?)

EDIT 2:


537.1.3 Each installation shall have provision for disconnection from the supply.
Where the distributor provides a means of disconnection complying with Chapter 53 at the origin of the installation
and agrees that it may be used as the means of isolation for the part of the installation between the origin and the
main linked switch or circuit-breaker required by Regulation 537.1.4, the requirement for isolation and switching of
that part of the installation is satisfied.

 

[Brightspark2]

Although probably not best practice table 53.4 (old regs, might have changed under BYB, only have old regs at work digitally - wish I could find a digital BYB pdf....) specifies that a BS 88 series fuse can be used for isolation, so wouldn't this technically be your main point of isolation for both boards?

As I said, not best practice surely, but an install as such would still comply?

(Except in a TT install where isolation requires disconnection of both line and neutral?)

Needs to isolate both live conductors IE line and neutral.

 

[Risteard]

My interpretation of 537.1.4 is that there should be one point of isolation for the installation.

A main switch at the origin.

The double pole switches in the consumer unit are the main switch for that consumer unit but then there must be a main switch for the installation. As I interpret it.

Be that as it may IET guidance (in the Guidance Notes) specifically states that if there are multiple distribution boards it may be taken to be more than one installation, and therefore no overarching isolator is necessary.

So at best it is debateable whether a main main switch is required in front of the sub main switches.

 

[hightower]

Needs to isolate both live conductors IE line and neutral.

Only in a TT install. Only the line in a TN as I gather?

 

[Risteard]

Only in a TT install. Only the line in a TN as I gather?

In a domestic TN installation all live conductors must be interrupted.

 

[hightower]

In a domestic TN installation all live conductors must be interrupted.

Could you point me to the regulation for this as I'm struggling to see where it says that? Thanks

 

[Risteard]

Could you point me to the regulation for this as I'm struggling to see where it says that? Thanks

Haven't the good book on me at present but if you read it it is clearly stated that for a domestic premises all live conductors must be interrupted. That is why domestic distribution boards come with double pole main switches regardless of earthing arrangement.

 

[hightower]

haven't the good book on me at present but if you read it it is clearly stated that for a domestic premises all live conductors must be interrupted. That is why domestic distribution boards come with double pole main switches regardless of earthing arrangement.

duplicate - deleted

 

[hightower]

Haven't the good book on me at present but if you read it it is clearly stated that for a domestic premises all live conductors must be interrupted. That is why domestic distribution boards come with double pole main switches regardless of earthing arrangement.

Just read it in the OSG - very first point in there. It seems I was getting crossed wires between single-phase and three-phase then.

EDIT: Also Reg 537.1.4:

A main switch intended for operation by ordinary persons, e.g. of a household or similar installation, shall interrupt
both live conductors of a single-phase supply.

I think I was stumbling at "well an ordinary person wouldn't pull a supply fuse so it's fine to be single pole" because the CU isolation is at each CU, and the main isolation (for a spark, not an ordinary person) would be the supply fuse.

Ignore me, getting in a tizz over nowt.

 

[Deleted member 26818]

In many instances if there are two supplies, the second supply is intended for emergencies where the first supply has stopped.
Having an isolator which disconnected both supplies could actually be a danger.

 

[UKMeterman]

So how would the single point of isolation be applied to this E7 install, note the suppliers seals on the henley blocks and the contactor. This may be partially due to the contactor coil feed being unmetered.

 

[Octopus]

So how would the single point of isolation be applied to this E7 install, note the suppliers seals on the henley blocks and the contactor. This may be partially due to the contactor coil feed being unmetered. View attachment 31148

Precisely why these interpretations that a DP switch are needed are misleading.

If some body is going to dabble with the electricity and they don't have the knowledge or competence to ensure that the correct circuit(s) are isolated then they shouldn't be doing it.

Just saying.

 

[davesparks]

So how would the single point of isolation be applied to this E7 install, note the suppliers seals on the henley blocks and the contactor. This may be partially due to the contactor coil feed being unmetered. View attachment 31148

By installing a 4 pole main switch