RCD`s on a TT System (With a slight twist)

[Colport]

Good evening all, could some of you share your opinions on the following please ......

A friend has recently purchased a bungalow which currently has the Consumer Unit and Supply head in a rather tatty lean-to on the side of the property. It`s a TT system (with the nice old bakealite 500mA earth trip) and the local supply company have told us a TN-C-S connection is out of the question.

Ideally he would like to reposition the Consumer Unit to the opposite side of the property but on the inside this time (Supply authority have given an estimate of

 

[Zeespark]

You would have to install a Switch Fuse unit no further than 3 meters from the DNO's equipment. This can be done with tails. From the Switch Fuse, run an SWA submain into your new board.

AndyGuinness

 

[Evans Electric]

Sounds alright to me , I wonder if you need the 100mA delayed trip to be honest .

I've just done a similar job with an overhead TT incomer > The Eon guys agreed they could PME it in the meter cupboard after checking the Ze however, so I took the rod out . They connected the meter, and a 100A DP isol . I had already fitted an 80A KMF and meter tails from there to the C/U .

 

[Manator]

The smoke alarms do not require a separate way in the CU, you could have them connected to the most used lighting circuit, so that the loss of power on that circuit would be quickly noticed. All final circuits should be protected by RCD, more so in domestics and TT.

 

[Zeespark]

Manator, I was having a look on the Kidde smoke detectors website. It said that smokes should go onto their own circuit (I disagree with this), so what can one do? trust their best judgement? Sorry if it appears that I have hijacked the thread.

AndyGuinness

 

[Manator]

Strangely first and foremost you should wire anything to the instructions given by the manufacturer, unfortunately as we are all aware the instructions are not updated in line with best practice guides and the wiring regulations in general.

If they insist on a separate circuit, that is how you should wire them, because if, by any chance they fail to operate, the manufacturer can claim that they were not installed as per their instructions.

I am sure most manufacturers have received a letter by now asking to clarify their instructions in relationship with being in line with the requirements.

 

[batty]

I prefer to have them on there own circuit there are a lot of things on lighting circuits that can affect them just my opinion though.

 

[Colport]

Thanks all, I had a couple of years out of the game and been back in the sparks lark for about 2 years now, despite undertaking and passing the 17th last year the company I work for rarely get involved with any domestic installations hence the questions posed above.

Manator I agree with your statements but someone had recently told me that under no circumstances should smoke detectors be fed via a 30mA RCD .... as the cables to the smokes would not be flushed in walls I thought the 100mA time delay RCD at the incomer could be used to provide the protection to this circuit?

Manator/Andy ....... I spent almost 2 years undertaking periodic tests on MOD married quarters properties where almost every house had a dedicated circuit supplying 2 smoke detectors ...... In 90% of the properties tested the MCB supplying the smokes was already switched off when we arrived. Once the internal PP9 batteries had run down the detectors emitted a lovely beep about once every 5 minutes so all the tennants got wise, removed the batteries and switched off the MCB`s !!!!! I`ve always been a believer that the smokes should be on the local lighting circuits to prevent the above happening.

 

[Manator]

The problem or myth about 30mA RCD's for smokes comes from the theory that if the RCD trips it takes out the protection value of the smokes. This is of course a bit of nonsense, because with battery backup, and the dreaded beep, it will soon become apparent that something is wrong.

The 100mA RCD is for protection of the building under large fault currents, and is for fire protection mainly, and would not prevent a shock capable of at least muscle contraction, or worse. 30mA is the norm for protection against harm, or life.

As for MOD properties, we all know how resourceful our armed forces are, I bet most of them never even waited for the beeps to annoy them.

 

[steptoe]

sounds good to me,

Deke, he needs the 100mA TD as he is using a mc switch fuse (to accommodate the SWA presumably).

personally I would have the smokes along with the local lighting circuit, that way if it trips out it quickly becomes apparent.

 

[kme]

Concur with Steptoe & Manator - I`d have the smokes with a lighting cct., too.

 

[ProDave]

Good evening all, could some of you share your opinions on the following please ......Ideally he would like to reposition the Consumer Unit to the opposite side of the property but on the inside this time (Supply authority have given an estimate of

 

[Badger]

who needs the dno when you can just get a pair of these bad boys opcorn :coat :^O :^O

View attachment 1296

 

[steptoe]

we wont ask what you use them for,

did you get them from Apache then?????? :slap

 

[Manator]

I have some gloves like that :^O

They are not anything like your Marigolds!