Earth-Leakage breakers??

[Mustang]

Hello everyone,

Just wondering is an Earth leakage circuit breaker exactly the same as an RCD? The reason I ask is that I heard someone mention once that Earth leakage circuit breakers do not work very well. Maybe I heard wrong?

 

[Guest123]

Hi.

Depends if you are referring to an Voltage Operated Earth Leakage Citcuit Breaker (VOELCB), usually black in colour with a yellow test button on. These things are now obsolete and most I come across dont work anyway.

Bit different to todays RCD's.

 

[slocm3105]

What they probably meant was the voltage operated earth leakage circuit breakers. I've seen a couple of different types of these, the main ones being a black standalone switch with a big yellow test button on it. I have also seen big grey oines with a longer yellow test button(again a standalone unit).

Basically these types of circuit breaker were written out of regs by the IEE at around 1985 I believe because it provides "no real protection to persons".

Hope this helps, maybe someone has a couple of pictures .

EDIT: Ah i see Lenny just posted as i've been writing this

 

[Deleted member 9648]

An RCD works on an imbalance in the line and neutral current passing through the device. ie if there is a current of 10a on the live there will be a 10a in the neutral as well unless there is a leakage to earth. In a voltage operated earth leakage device the earth conductor for the installation passes through a coil in the device and in the event of earth leakage the magnetic field generated by the coil is detected. As lenny says they are no longer an acceptable means of protection and often fail to trip.

 

[solo2771]

Purpose
Many electrical installations have a relatively high earth impedance. This may be due to the use of a local earth rod (TT systems), or to dry local ground conditions.
These installations are dangerous and a safety risk if a live to earth fault current flows. Because earth impedance is high:

1. not enough current exists to trip a fuse or circuit breaker, so the condition persists uncleared indefinitely
2. the high impedance earth cannot keep the voltage of all exposed metal to a safe voltage, all such metalwork may rise to close to live conductor voltage.

These dangers can be drastically reduced by the use of an ELCB or Residual-current device (RCD).
The ELCB makes such installations much safer by cutting the power if these dangerous conditions occur. This approach to electrical safety is called EEBAD. In Britain EEBAD domestic installations became standard in the 1950s.
In non-technical terms if a person touches something, typically a metal part on faulty electrical equipment, which is at a significant voltage relative to the earth, electrical current will flow through him/her to the earth. The current that flows is too small to trip an electrical fuse which could disconnect the electricity supply, but can be enough to kill. An ELCB detects even a small current to earth (Earth Leakage) and disconnects the equipment (Circuit Breaker).
[edit] History

ELCBs were mainly used on TT earthing systems. Nowadays, ELCBs have been mostly replaced by Residual-current devices (RCDs). However many ELCBs are still in use.
Early ELCBs responded to sine wave fault currents, but not to rectified fault current. Over time, filtering against nuisance trips has also improved. Early ELCBs thus offer a little less safety and higher risk of nuisance trip. The ability to distinguish between a fault condition and non-risk conditions is called discrimination.
ELCB manufacturers include: Legrand,Havells, ABB, Siemens AG, Areva T&D, TELEMECANIQUE, Orion Italia, Crabtree, MEM.

 

[Mustang]

Thankyou to you all for all the useful information. Now i know! Cheers

 

[DNS1]

Depends if you are referring to an Voltage Operated Earth Leakage Citcuit Breaker (VOELCB), usually black in colour with a yellow test button on. These things are now obsolete and most I come across dont work anyway.

Sorry to revive such an old thread chaps, but just encountered this today... Looks basically like a main isolator (at the very least it works as one, yay!) but the trip button doesn't work.

TT system, but currently unprotected by RCD (16th Edition board, quite nicely installed). Planning on ignoring the ELCB and just fitting a 100mA RCD incommer. Any thoughts?

 

[Knobhead]

You've got a ready made on load isolator. If the supply company fit one it will be off load.

Just make sure the earthing is up to scratch.

 

[DNS1]

I'm assuming the ELCB doesn't actually operate at all, would it be sensible to back it up with a new RCD, or does the current setup comply with the 16th Edition? Don't know when RCD protection for all circuits on TT became a requirement

 

[Guest123]

I'm assuming the ELCB doesn't actually operate at all, would it be sensible to back it up with a new RCD, or does the current setup comply with the 16th Edition? Don't know when RCD protection for all circuits on TT became a requirement

Since FOREVER!!

The requirement for RCD protection on TT systems always has been there, due to the Ra more often than not being way above the values needed for earth fault protection to be provided by fuses/MCB's.

Think about it, the max Zs for a 32A B type is 1.44ohms in BS7671, the majority of TT systems are 50ohms plus......so under earth fault conditions, the fuse/MCB will not disconnect.

IMO a TT system should have a 100mA TD RCD upfront with additonal 30mA RCD protection offered as required.

 

[DNS1]

Thanks for the help guys

 

[Dorsetspark]

"I'm assuming the ELCB doesn't actually operate at all,"

... why assume? Why not test it and see it it meets trip times?
ELCBs may be old but most I see on TT installations still meet disc. times and work fine, depite being 20+ years old, including the ELCBs in my own house. If it's a VOELCB however, then yes it needs replacing, as these often fail(ed) to operate due to parallel paths diverting the fault current and therefore not tripping.

VOELCBs are usually long and rectangular, ELCBs are usually square and grey, including the test button.

 

[DNS1]

Thanks again.

Definitely looks like a VOELCB. I'm assuming it doesn't operate as the test button is completely dead itself.

I'll check it's trip times anyway.

 

[spark 68]

Thanks again.

Definitely looks like a VOELCB. I'm assuming it doesn't operate as the test button is completely dead itself.

I'll check it's trip times anyway.

If it is a VOELCB then you won't be able to test it with a conventional RCD tester/MFT, as modern RCD's/RCBO's are current opererated, VOELCB's as their name suggests are Voltage operated.

 

[Dorsetspark]

The other thing about the more recent ELCBs is they will say "Controlling L.H. Ways only" on the front - unmistakable.
Pic is of VOELCB - as mentioned above, if it's one of these, don't tinker, just replace!
The other thing to check is the soundness of the earth rod and cable, and to check the Ra/Ze. Last time I found one of these, I followed the earth cable into the garden, round the shed, into the blackberry bushes, and found it connected to a 12" long piece of 15mm copper pipe via a crocodile clip...Ze was a respectable 60 odd Ohms though .