Question on TT main RCD

[067256]

Hi there,
Have installed a new circuit for a bathroom heater (3Kw)
TT system, old style wlyex rewirable DB. Earth rod reading 126 ohms, so ok with that. Bonding fine.
Main RCD on incomer did not trip out when tested...its 1 of those old style crabtree 60a ones with a yellow test button. Shall i replace with a 100Ma or 30Ma?
Just a bit concerned that when i have fitted the new RCD it may pick up 'other faults'
Thanks.

 

[trev]

Was this for a client or for your own home?
Are you a spark?

 

[Engineer54]

It's not an RCD, it's a VOELB, and should always be replaced with a RCD device, they weren't very reliable when new!! Oh, and an Ra of 126 ohms in real life isn't OK!! lol!!!

 

[Guest123]

Was there a mA rating on the existing RCD as it sounds like it may be a VOELCB, or possibly a very early ELCB. How did you test it...what settings etc??

Your new bathroom circuit will require 30mA RCD protection but, you cant leave the rest of the house unprotected if the existing RCD is faulty as this is a dangerous condition.

An upfront RCD is by no means ideal but, is better than nothing

 

[067256]

for a client.....recently qualified sparks.

 

[067256]

No Ma rating on the RCD or VOELCB. Tested at 30Ma and 100Ma 1x and 5x....each time my megger tester came up with 'check'
Manual test button on device does not work either. I have installed an RCD spur outside the bathroom to feed the heater.
Yes, the other circuits do not now seem protected due to faulty device. Thought reading up to 200 Ohm was acceptable????
What would you advice as main incoming protection?

 

[robsparky1975]

an rcd test on a voltage operated earth leakage circuit breaker will not work(voelcb)as mentioned above,they are recommended to be replaced as soon as you see one as they are not proven to work and have been discontinued since 1978(from memory)id fit a 30ma although not ideal as said better than what is there.

 

[trev]

Think back to those courses you recently completed mate. What do you think is the best course of action for you to take?

 

[Guest123]

Right,

First things first, the install in that house is TOTALLY UNSAFE!!!!! THE EFLI IS WAY TOO HIGH to enable the 3036's to operate under fault conditions hence the reliance on the VOELCB/RCD.

If this device is faulty, there is no protection at all!!!!

Is the MPB adequate, did you check this???

Recommend a CU upgrade in the first instance, if they are not keen, you will have to install an upfront RCD AS A MINIMUM

You cannot leave the install like that, end of.

 

[robsparky1975]

anything over 100 ohms is deemed to be unstable(niceic state this).id recommend that for future reference check what you are adding to,saves you some grief from the client and if anything needs upgrading beforehand however minor the works you are supposed to do then its beneficial for yourself and the clients installation.

 

[trev]

Well I was trying to be gentle with the lad

 

[Guest123]

Well I was trying to be gentle with the lad

Gentle, it's a potentially lethal condition!!!

 

[trev]

I know, and in my opinion he should not be doing it. But as he is newly qualified, or so he claims, the information should be fresh in his mind and he should have come to this conclusion without our input.

 

[067256]

TOTALLY AGREE in the first instance.
I shall replace the main crabtree device with a new 63a 30Ma RCD. Appreciate the advice as i didnt realise that VOELCB dont work with test equipment. Can i also address the issue with a high ohms reading on the earth spike by replacing it?
Thought OSG states reading up to 200 Ohm is ok for TT???

 

[trev]

Most single rod systems using the twigs they sell as reliable earths are pretty much worthless get your hands on some 5/8" couplable rods so you can drive deep because the top layer of soil freezes and dries out seasonally making any meaningful Ra value difficult to achieve. Although your current Ra is within the limit of 200 ohms it's unstable and can quite easily be lowered to a value which will actually offer some protection