**** tt query ****

[Sav]

Hi everyone,
hope your all having a good weekend !!

This is from a job that I WAS about to do and would like some advise from you all.

1/ Customer has had a consumer unit fitted about 4- 5 years ago in his house. Its a wylex mcb board witha 100amp main switch and serving 5-6 circuits.

2/ He had a new boiler installed on Friday and the boiler man said " you got no earths mate " !!!
This is where I got the "emergency call" from the customer, whilst I was at another job. I quickly went round, just to have a quick look, and from what I can see, the consumer unit is under the stairs and just below the floor boards there is an earth spike in the ground and 25mm earth from the spike to the board . TT system i say....but the board has no RCD protection at all. I told him thats a problem, especially on a TT sytem.

His builder who was there at the time replied " No thats fine mate, a lot of these old boards dont have an RCD, as its before the regs came into place . I've earthed all the pipes, so its fine " !!

Now, the customer thinks that I want to get money off him for a new board and has given me the elbow in favour of his builder friends advise !!!!

Was I right about the RCD protection, or is the installation ok if there ever was an earth fault ???

Thanks for reading this and best regards to you all,

Sav

 

[Guest123]

You were absolutely right mate.......hers a post I just wrote in reply to another thread.


Ok, as a very basic description of the issue of no RCD protection on a TT system.

Basically every fuse or circuit breaker has a job of disconnecting the supply within a specified time before fault voltages reach a dangerous level to touch.

Every fuse/circuit breaker has a maximum earth fault loop impedance value (the rough maximum is 7.5 ohms for a lighting circuit breaker) to which it will achieve this disconnection time. In a TT system the earth fault loop impedance is too high (usually between 50 and 200ohms) for the fuse/circuit breaker to achieve this disconnection time so we must provide additional earth fault protection with an RCD.

Without the presence of this RCD a fault voltage has the potential to reach a level above the accepted safe limit and NOT cause the fuse/circuit breaker to operate in the required time, in some instances not at all therefore the fault voltage will "sit" on any metallic parts of the installation and any main service pipework with the potential of transferring to YOU should you come into contact with the metalwork.

 

[bugsy]

Sav take a copy of the regs round to the builder in the pressence of the home owner and show him !
I hate these cocky builders who know it all makes my blood boil

 

[Sav]

Thanks guys for your sound advise.
It makes my blood boil too, especially when your trying to help someone.
I HATE these type of "know it all" builders.

I will call him tomorrow and read out what Lenny has said.....and then translate that to builders language for his mate !!!!!

Thanks again for all your help,
Best regards,
Sav

 

[acat]

Bob the Builder strikes again, if he belongs to any competent person schemes for builders ask them what the fees are for builders to become experts in the electrical field. You might also like to let building control know about this expert


Chris