ELCB's?

[JohnnyG]

I was round someone's house yesterday and had a look at their installation, as you do.
The house was built @1980, original electrics still & they've got an ELCB (which the owner calls the 'lifesaver') between the meter & CU, 'protecting' the whole TNC-S system, there's no earthing to it, just the L/N.
He's having the CU replaced soon & I'll fit an isolator in place of the ELCB but just wondered how these things work, do they measure the difference in volts or resistance or is there some other trickery going on?

 

[LoveRocket]

It's just an RCCB - ie an RCD. If there's no earth connection then it must be current operated (which is good). If everything's hunky-dory, there will be the same current on L as there is on N - if there's an earth fault then there will be an imbalance, the RCCB detects this and shuts off the supply.

 

[Paul_C]

You can tell the other type of ELCB - the voltage-operated type - by the fact that it has two separate terminals for earth connections. One connects to the earth reference electrode, the other connects to the installation's earthing system.

The voltage-operated ELCB then just works on the principle that it trips when the voltage on the installation's earthing system exceeds a certain level relative to true earth (50V being the limit at which the ELCB must trip).

 

[PrinceofDarkness]

JohnnyG: Are you confident in your ability to fit an isolator (and goodness knows what else) given that you clearly have difficutly recognising types of earth trip and understanding their method of operation?

There are many RCDs with the marking 'ELCB'. The term ELCB simply mean an 'earth trip' - it certainly doesn't imply that it's a FVOD type.


Lucia

 

[JohnnyG]

I've fitted a few isolators (and goodness knows what else) and that ability has no relevance to my lack of understanding of a defunct protective device.
Go troll somewhere else, sweetheart.

 

[PrinceofDarkness]

I'll move on when it suits me to do so, Johnnyboy. In the meantime you'll just have to tolerate me - or better still, avoid me if you have such an 'attitude'. In time, you might come to realise that I'm not actually a 'troll'...........

At least you've learned from this post that you need to brush-up on your knowledge of ELCBs, current operated and voltage operated. So, that's not such a bad thing, is it dear?


Lucia.

 

[JohnnyG]

JohnnyGirl actually, love.
I asked here as I didn't know about ELCB's in the first place, hence my question, thanks to those who've helped in that respect.
I don't care what you do or when you move on really, your type of help is of no use to me :shrug:

 

[PrinceofDarkness]

I'm sorry that you feel that way Johnny. I hope that you'll come to realise that I don't mean to cause you any offence and that we'll learn to tolerate each other eventually.

You really shouldn't take offence at such a simple question - rather, you should acknowledge the true meaning of it.



Lucia.

 

[JohnnyG]

Don't feel sorry, I couldn't care less and doubt that I'll remember you in the morning anyway so there's little chance of future tolerance unless you're able to actually add anything of value to a question I ask.

Edit: No offence taken by the way, or meant...

 

[PrinceofDarkness]

So we have an understanding then? I don't mind if you forget about it tomorrow. But I trust that you'll try to swot up on ELCB's, because that's what this, your thread, is about - and you might benefit from doing so........

I shan't be returning to this particular thread( troll that I am) - unless provoked to do so by another member ..........

Lucia.

 

[flameport]

They work by comparing the current in the two wires (L&N). Normally thes are equal. If a fault to earth occurs within the installation, some of the current will not return via the wiring, the device detects this imbalance and cuts off the supply.

He's having the CU replaced soon & I'll fit an isolator in place of the ELCB

A separate isolator is not required - the new consumer unit will contain one. The supply tails should go straight from the meter into the consumer unit.

 

[JohnnyG]

They work by comparing the current in the two wires (L&N). Normally thes are equal. If a fault to earth occurs within the installation, some of the current will not return via the wiring, the device detects this imbalance and cuts off the supply.

He's having the CU replaced soon & I'll fit an isolator in place of the ELCB

A separate isolator is not required - the new consumer unit will contain one. The supply tails should go straight from the meter into the consumer unit.

Cool, so the ones not directly connected to earth are basic RCD's then?

I realise an isolator is not required but as the current meter tails won't reach the new CU when the ELCB is removed it seems an easy way to extend them

 

[flameport]

Cool, so the ones not directly connected to earth are basic RCD's then?

Yes.

The other type are voltage operated and will have 2 earth connections as well as the L&N in/out. These trip when the voltage on the earth wire from the installation rises above 50v. They are obsolete and should be replaced, as they only work properly when there is a single earth connection (parallel earth paths via gas/water will significantly reduce their effectiveness), and they don't work at all where the fault is via some other route (such as a person being in contact with a live conductor).

 

[Taylortwocities]

I realise an isolator is not required but as the current meter tails won't reach the new CU when the ELCB is removed it seems an easy way to extend them

That's just plain lazy. Install new tails.
In any event, I will bet that the tails provided for a 1980 house will not meet today's requirements for a TNC-S installation.

 

[Paul_C]

They are obsolete and should be replaced, as they only work properly when there is a single earth connection (parallel earth paths via gas/water will significantly reduce their effectiveness)

The key point with the voltage-operated ELCB is that the reference electrode must be outside the resistance gradient area of any other earth connection. It doesn't matter if there are multiple parallel earth paths on the "F" terminal side of the ELCB (via bonded water pipes, structural metalwork etc.), just so long as the electrode on the "E" side of the coil is outside of their influence.

It's when earth electrodes on the frame side overlap the gradient area of the reference electrode that the ELCB is desensitized.