TT System RCD / ELCB?

[owls]

Does anyone know anything about the old ELCB (or is it ELCD??) units, they were the fore runners to RCD's i believe.

I'm about to replace a consumer unit which is running on a TT earthing system (which at present doesn't have any earth!) and i wondered if i could use the existing ELCB in place of a 100A 100ma RCD as the main isolater?

My plan was to use a 100A 100mA isolater feeding the CU then use a split load board with a 30mA to protect the sockets etc. I'm a little reluctant to use a 30mA as the main incomer as it'll be a nightmare for nuisance trips.

Thanks

 

[JohnD]

We don't know what the regulations and standards are in the British Virgin Islands.

 

[owls]

We don't know what the regulations and standards are in the British Virgin Islands.

I just came back

 

[JohnD]

I think you'd do best to use a new unit. Are you trying to save money?

Do you know how old the old one is? Have you tested and timed it at different leakages?

Is it Voltage operated or Current operated?

 

[owls]

I think you'd do best to use a new unit. Are you trying to save money?

Do you know how old the old one is? Have you tested and timed it at different leakages?

Is it Voltage operated or Current operated?

I was just a little puzzled by it.

I going to replace it anyway, i didn't get a chance to test it but as i hadn't seen one before i figured i'd ask on here.

Thanks for the reply

 

[Jaymack]

In the UK, these require to be replaced by RCD's under the new regulations to BS7671. Read all about it: -

The term Earth leakage circuit breaker (ELCB) is often incorrectly used to describe its modern counterpart the Residual-current device (RCD).
An earth leakage circuit breaker (ELCB) is a device with two earth terminals used to directly detect currents leaking to earth from an installation and cut the power. They were mainly used on TT earthing systems before RCDs became common. They have been almost totally replaced by RCDs (except in very old installations) due to a number of problems.

They cannot detect earth faults that do not go through the earthing system.

They do not allow a system to be easily split into multiple sections with independent fault protection, due to the fact that earthing systems are usually bonded to things like pipework.

They may be tripped by external voltages on something connected to the earthing system such as metal pipes, a TN-S earth or a TN-C-S combined neutral and earth.

They introduce additional resistance and an additional point of failure into the earthing system.

Jaymack

 

[plugwash]

that may be one interpretation of the jargon but there were i belive some "current operated elcbs" which are essentially the same as modern RCDs

 

[Spark123]

Agree with plugwash, there were two types of ELCB.
Bit of info here: iee wiring matters

 

[Lectrician]

Many new RCD's are termed ELCB's

It is the voltage operated types that are obsolete and dangerous.

Try for a PME upgrade - what DNO area are you?

 

[Jaymack]

Many new RCD's are termed ELCB's

By whom?, where do see this in BS7671?

It is the voltage operated types that are obsolete and dangerous.

One reason that they are, is due to the fact that they require a connection to earth to operate, Sometimes seen in older TT installations as the man said, can you give any others.

Try for a PME upgrade - what DNO area are you?

He's in the british virgin islands, next door to Blackpool?

Jaymack

 

[Lectrician]

I never said BS7671, and am fully aware of the definitions with in BS7671 thanks. Many manufacturers still refer to a range of EARTH LEAKAGE CIRCUIT BEAKERS in their range - Including RCD's and RCBO's etc. One well known manufacturer is Crabtree.


A current operated ELCB would still be, in effect, an RCD.


Yes, a voltage operated ELCB was very common on TT's, and very often the two poles where used to isolate the live only on a peak/off peak install.


The problem with the voltage operated type is as they look for voltage on the earth conductor (two terminals, one to rod, one to CU), they take no account of faults to mother earth via pipework, metal structures, or people!


People often confuse a voltage operated ELCB with a DC sense RCD - as they both have connections to earth. However, a voltage operated ELCB will (commonly) have a 2.5/4mm earth from CU connection to the F terminal, and the same size cable from the E terminal to a ROD. A DC sence RCD was a simple small white or cream fly lead to connect to the earth bar.

 

[securespark]

You need a S type 100mA (min) on TT supply, then 30mA on the socket outlets, otherwise there is no discrimination between the two.

 

[securespark]

He's in the british virgin islands, next door to Blackpool?

He's back in the UK now.

 

[JohnD]

I don't think he tells the truth.

 

[owls]

You need a S type 100mA (min) on TT supply, then 30mA on the socket outlets, otherwise there is no discrimination between the two.

Sorry for any confusion, i'm not actually in the BVI's!!! Just went there on a wonderful holiday a couple of months ago and put the location to it for a laugh...sorry if it caused confusion