No earth to smoke detectors.

[Amp David]

Been at a house today doing a pert rewire and new kitchen circuits. Noticed whilst under the floor boards that the smokes have been wired in 3 core flex, using the earth as the interconnect. Is this an acceptable way of doing things? Only reason I can think is that on the back of the detectors it states they are double insulated.

 

[Mr Mark Sparks]

there is a couple of issues
there is a reg somewhere that says a green and yellow cable may not be overmarked and used as a live conductor
and the need to provide an earth in the cable and at the point

 

[Sav]

Even though its flex and the earth is insulated throughout, you MUST never use an earth for a phase/line ( not even if you sleeve it with phase/line).
Its in the regs as well (dont know what page though ).
Hope this helps,
Best regards,
Sav

 

[telectrix]

But, can you sleeve the earth cable blue as neutral? i have seen it stated in this forum that it is ok to use 3 core flex to a bathroom fan

 

[antimatter]

Don't think so because the neutral is a live conductor too!

 

[bugsy]

Flex used as fixed wiring , using the cpc as a live conductor, er hallo!

 

[Sav]

Hi Telectrix,
As animatter said, the neutral is a conductor and so you cannot use the earth for this.
also, as mentioned by Mr MarkSparks, we need to have an earth at the point.

 

[telectrix]

agreed. i always use 3 core+earth. But when will the makers of bathroom fans make them to accept this?

 

[Sintra]

Reg 514.4.2 a protective conductor shall not be oversleeved except if being used as a PEN conductor.

 

[antimatter]

The pen conductor typically occurs between the substation and the entry point into the building, and separated in the service head.

 

[sjm]

When I contacted the NIC helpline and asked whether I could use 3 core flex, with cpc oversleeved as switched live, for an extractor fan (double insulated of coarse) I was told that they could see no reason why not as cpc same conductor size, also this would not require 1 core to be cut out(which they considered was a no no).
Also quote from NIC "you could do a complete rewire using flex if you wanted too".
Reg 514.4.2 states that SINGLE CORE cables that are coloured green/yellow throughout their length shall only be used as a protective conductor and shall not be overmarked.

 

[antimatter]

sjm
Also quote from NIC "you could do a complete rewire using flex if you wanted too".



What is the chaps name that said that?

 

[sjm]

Didn't ask his name, just the question about using flex in fixed installations. If you don't agree with his answer please give reasons, reg numbers etc. I assume that NIC technical helpline is just that, a helpline, and not there to give duff information.

 

[Sintra]

Strange as it may seem flex can be used for the fixed wiring of an installation. Last year we wired a large office block completely in flex apart from the sub mains. Although this installation was overseas it was all designed, installed and tested to BS 7671.

 

[malcolmsanford]

When I contacted the NIC helpline and asked whether I could use 3 core flex, with cpc oversleeved as switched live, for an extractor fan (double insulated of coarse) I was told that they could see no reason why not as cpc same conductor size, also this would not require 1 core to be cut out(which they considered was a no no).
Also quote from NIC "you could do a complete rewire using flex if you wanted too".
Reg 514.4.2 states that SINGLE CORE cables that are coloured green/yellow throughout their length shall only be used as a protective conductor and shall not be overmarked.

In this rare instance have to agree with the NICEIC man if it's not a single core cable and not a bare conductor within a sleeved cable then you can sleeve a yellow/green and use it as a live conductor. What you can't do is use the colour yellow/green as a live conductor.

521.9.1 also prooves him right about the flexible cable. Don't you just hate it when they are right

 

[Mr Mark Sparks]

with regards to the flex issue surely the reason we dont generally use it for whole installations is that its cost prohibitive.?

 

[nickblake]

Find this situation alot with central heating systems , and the hole in my snips shows the reason why it shouldnt be done ,yes it was isolated except for the earth well what i thought was the earth ,this is why multi core cable is made twe or flex

 

[bugsy]

quite agree with all the comments regarding the use of flex and over sleeving and as Sintra states flex is used extensivley in France and Spain for fixed installations, (and here for some modular wiring systems ) then again there's nothing to stop you using a plastic hose pipe instead of PVC conduit, all a question of professional integrity

 

[Amp David]

Thanks for all the input fellas.

Not going to touch the smokes on the job, reason is cost. The customer isn't paying for the smokes to be rewired in 3core & earth, so will be leaving alone. Just make sure I note it on the EIC

 

[rshaw125]

I personally would leave the smoke detectors as they are.

Some would say that it is save but it is an unsatisfactory state, as your smoke detectors are insulated and doesn't offer a risk of shock.

Just inform your customer and note it on your paperwork to cover yourself.

 

[accordfire]

Not ever.

Most smoke detectors have a parking terminal for the CPC. Apart from BS 7671 making clear (as has been pointed out) that the CPC can't ever be used to carry phase, even with over sleeving at terminations - if that flex is ever broken along its length, what is someone going to assume is present on the CPC? Worse, assuming disconnection from supply prior to working, that alleged CPC is then connected to the earth terminals of other circuit devices (as happens, though wrongly), and presto, a potentially "live" building - especially on non 17th installations.

IMHO, it isn't a suitable cable type for smoke detectors in any case. They are there for LIFE safety, typically, and should be treated as such.

Whilst it is still acceptable to use 624x pvc cable for some installations, BS 5839-6 has a clear distinction regarding suitable cable. Anything above a Grade D installation should be in fire resisting cable, and that's mandatory for Grades B and A. All smoke detection in dwellings should be installed to comply with BS 5839-6.

As a rule of thumb, we always use fire resisting cable on any system which has a "central control" or common power supply, and in any situation where there's likely to be a need to identify specifically cable for the fire system, distinct from a general circuit. That's most of them.

 

[antimatter]

Thanks for clearing that up Bill.

Just as I thought.