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.

 

[Engineer54]

coupled together.

Good to hear that, it wasn't clear in your earlier post!! lol!! So why was it hard, was you using a hammer?? You daft fool ...lol!! A good SDS drill should have made things much easier, you can purchase the driving tool to fit an SDS, or make one up yourself!! So did you link the existing earth rod to your new driven system as i suggested?? I tend to forget to mention that it is Always good to install a concrete or heavy Plastic earth pit over the rod and connection. One, it protects the connection and secondly the rod position doesn't get lost over time...

But well done, an Ra of 42ohms is darned better than 126 ohms, and it will keep improving over the next year or two as the ground consolidates around the rod. Don't be too surprised to see as much as a 10 to 15% improvement, it'll certainly be a sub 40 ohms figure anyway!!

 

[Knobhead]

067256

I just re-read you OP, if you look in to how a VOELB works you will find that your statement “bonding fine” couldn’t be further from the truth. I’m not having a dig at you because a lot of electricians have never come across these units. It’s mainly us old farts that have.

Taken from Wiki

Voltage-operated ELCBs were introduced in the early 20th century, and provided a major advance in safety for mains electrical supplies with inadequate earth impedance. V-ELCBs have been in widespread use since then, and many are still in operation but are no longer installed in new construction. A voltage-operated ELCB detects a rise in potential between the protected interconnected metalwork (equipment frames, conduits, enclosures) and a distant isolated earth reference electrode. They operate at a detected potential of around 50 volts to open a main breaker and isolate the supply from the protected premises. [SUP][2][/SUP]
A voltage-operated ELCB has a second terminal for connecting to the remote reference earth connection.
The earth circuit is modified when an ELCB is used; the connection to the earth rod is passed through the ELCB by connecting to its two earth terminals. One terminal goes to the installation earth CPC (circuit [[Power system protection |protective]] conductor, aka earth wire), and the other to the earth rod (or sometimes other type of earth connection).
Disadvantages of the voltage-operated ELCB are the requirement for a second connection, and the possibility that any additional connection to earth on the protected system can disable the detector.

As you can see the bonding can disable the VOECB

 

[067256]

Engineer54,
Experience, experience, experience.....in years to come i will laugh about it.
Will get myself a driving tool!! No doubt i will be doing this again sometime.

 

[Jonesy83]

just a question

my perants had 1 of these before i replaced their cu and i removed this and replaced with a 100dp isolator i was told i could of left it in for an isolator

now was he rite or wrong

 

[trev]

Your parents had what mate?

 

[Jonesy83]

elcb before the consumer unit

 

[trev]

Ahh yeah right sorry I blame my mid life crisis hehe. As long as you installed the correct means of protection when you did away with the VOELCB then yes it was right