Current op Earth leakage Circuit Breaker

[normacman]

My house has overhead L & N Supply with TT Earthing, an Electrician put in a new Consumer unit for me with 30ma RCD and Mcbs but the old MEM COELCB
that was in use with the old Fusebox remained, this incidentally is rated @40A. 30ma Trip
as i have now built an extension to the house and need to upgrade the CU, and have RCBOs fitted
My Question is this, Do I still need the stand alone MEM COELCB which Does seem to work, but the test button does not,
Or will the Electrician remove this

 

[stuart569]

What do yo mean when you say it still works?You still get power?That doesn't mean it works as it should

 

[stuart569]

And no you will not need your standalone elcb! A new 100ma rcd would probably be best.With time delay for discrimination

 

[Octopus]

Do you actually need another RCD in front of the CU? Maybe not. It would be handy to understand the distance from the suppliers head to the CU, the route of the tails and whether the CU is metal or insulated.

 

[Engineer54]

Do you actually need another RCD in front of the CU? Maybe not. It would be handy to understand the distance from the suppliers head to the CU, the route of the tails and whether the CU is metal or insulated.

A somewhat wise thing to have, when the earthing system is TT and your relying on RCD device as your sole means of earth fault protection. The up front 100mA S type RCD would then act as additional protection, whereas any 30mA RCD or RCBO downstream are ''Required'' protection.

 

[normacman]

Hi Stuart
It Still works in that it has tripped out a couple of times when the RCD in the consumer unit has tripped,but as I said the Test button has no effect
By fitting a 100ma Rcd I assume you mean in the Consumer Unit Instead of a switch Isolator when used with RCBOs
Thanks for taking the time to reply,
normac

 

[telectrix]

you could replace the old unit with a 100mA delayed RCD.before the CU. this can then also serve as an isolator for the CU

 

[normacman]

Thanks for that one telectrix I will go with that, plus Split load consumer unit with RCBOs i think,
Regards
Normacman

 

[Octopus]

Thanks for that one telectrix I will go with that, plus Split load consumer unit with RCBOs i think,
Regards
Normacman

In your first post you indicated that you would be using an electrician, now you're saying "I will go with that" - please remember that a CU change is notifiable work and that theres a lot more to than simply simply replacing the existing unit.

 

[normacman]

Murdoch
Yes i will be employing an Electrician to carry out the work as i have not the Qualifications and the time to do it myself, Although I have a City& Guilds in Electrical Installation,
I realize that this is no longer sufficient,
The Idea of seeking advice is so that I can have input on my Installation and not sound like some dumb --- householder ready to part with wads more cash,
as I have done so on the Extension Build
Regards,
Normacman

 

[malcolmsanford]

My house has overhead L & N Supply with TT Earthing, an Electrician put in a new Consumer unit for me with 30ma RCD and Mcbs but the old MEM COELCB
that was in use with the old Fusebox remained, this incidentally is rated @40A. 30ma Trip
as i have now built an extension to the house and need to upgrade the CU, and have RCBOs fitted
My Question is this, Do I still need the stand alone MEM COELCB which Does seem to work, but the test button does not,
Or will the Electrician remove this

Bit confused here you have a new CU installed and the electrician has kept the 100mA COELCB in, as I assumed he either thought it would give you discrimination or he as installed a metal clad CU.

If it was for discrimination then as you have found out it was wrong, if it was because he installed a metal clad CU then it works as it is protecting that CU. It is also in line with the regulations as it is not giving you that discrimination between the RCDs and the reg it contravenes is 531.2.9

As these ELCB are no longer recognized in the regs they should be replaced and to be honest I would have thought it would have been easier for him to remove it, and fit an insulated 30mA dual split board or RCBO's. Sometimes the old Voltage operated ELCB are kept as an isolator for the installation, but to be honest if your one is rated only 40amps it's basically very small for a modern installation where you could have showers or cookers. Though it is not affording overload protection at 40amps it is going to mechanically deteriorate if it's overloaded.