supply setup

[RMS]

Hi,

i was at a job today and the and the suppliers cable entry was located outside the property in an enclosure. In the enclosure was the main fuse and tails which the live was wired through a 100A double pole isolator but the neutral went straight into a tail block, the out going cable was a 16mm² two core armoured that went under the ground and to the consumer unit in the house. The armourings were used as the earth and were just made off into a MET where a 16mm² earth connected to the PME earth terminal.

Can anyone see any problems with only isolating the live and not the neutral?

thanks RMS.

 

[securespark]

No.

Next question?

 

[RMS]

I would have thought the isolation to the whole installation would have had to be double pole. (both live conductors)

maybe i'm wrong but thought i would get it checked out.

Thanks

 

[securespark]

No, I've seen many isolators installed by recs on pme installs that leave the neutral unswitched.

Maybe something to do with the neutral on pme also being the earth...

 

[JohnD]

It is equivalent to pulling the fuse on an installation without a switch.

 

[securespark]

Indeed. That too!

 

[Spark123]

From GN2
(3.5)
.....Regulation 476-01-03 specifically requires the interruption of both the phase and neutral conductors by the main isolating switch at the origin of supply to a household (domestic) or similar installation which is intended for operation by an electrically unskilled person.....

 

[RMS]

From GN2
(3.5)
.....Regulation 476-01-03 specifically requires the interruption of both the phase and neutral conductors by the main isolating switch at the origin of supply to a household (domestic) or similar installation which is intended for operation by an electrically unskilled person.....

Thanks Spark123

 

[SparkyMarky]

From GN2
(3.5)
.....Regulation 476-01-03 specifically requires the interruption of both the phase and neutral conductors by the main isolating switch at the origin of supply to a household (domestic) or similar installation which is intended for operation by an electrically unskilled person.....

But surely the "main isolating switch" for "operation by an electrically unskilled person" would be the main switch (presumably labelled as such) on the consumer unit inside the house, and not the isolator outside the property?

 

[Spark123]

I was in two minds myself, although do you agree the origin of supply will be outside in the meter box?

 

[RMS]

I have no doubts that the origin of the supply is the outside meter box and access is required by the consumer to access the electricity card, but wether or not this main switch is intended to be operated by the electrically unskilled person is debatable?

 

[Spark123]

I suppose it could depend on who would use it and the reason, if it were to be used in an emergency to kill the power to the entire installation would it be an electrically skilled person?

 

[plugwash]

.....Regulation 476-01-03 specifically requires the interruption of both the phase and neutral conductors by the main isolating switch at the origin of supply to a household (domestic) or similar installation which is intended for operation by an electrically unskilled person.....

i presume this is why some recs mark the isolator as "for contractors use only" but in any case the recs are under absoloutly no obligation to follow BS7671 so its rather beside the point.

actually twisted as it may sound i don't think the recs are allowed to have any isolators in the neutral they supply because rec neutrals are often CNE cores i guess it was considered safer to simply ban putting isolators in them than to risk a core that could be isolated being used as a CNE core by mistake.

 

[Job_n_knock]

Modern digital domestic meters have 2 terminal covers on them. This is so that Contractors can isolate and rewire the tails. Where outside meters are used, some supply authorities require a double pole isolator where the tails enter the building.

 

[RMS]

Modern digital domestic meters have 2 terminal covers on them. This is so that Contractors can isolate and rewire the tails. Where outside meters are used, some supply authorities require a double pole isolator where the tails enter the building.

but should the double pole isolator be used to isolate both live and neutral conductors to the installation?

that is the question