1 amp CO ELCB

[mattg4321]

Came across what I'm pretty sure was a current operated Crabtree ELCB today. Just had a search on here and a google and haven't found a lot. Annoyingly I didn't take a picture as I thought they would be more common than they evidently are! Pretty sure its the first I've seen in the 15 years I've been doing this.

It looked similar to the usual voltage operated ELCB we all often come across except it was a fair bit wider. Had the switch with a yellow button below and when you took the cover off it exposed some sort of large sense coil with the line and neutral running through. Rated 60A and said 1A on the side which I assume is tripping current. Tested with my MFT on 1000mA and it didn't trip but it did trip on high current EFLI tests.

Anyone?

 

[Andy-1960]

ELCB's are all current operated and the coil you saw would have been the core balanced CT that looks for the current imbalance.
The current flowing out should equal what comes back on the neutral, any imbalance detected therefore must be flowing to earth. The amount of current allowed to flow to earth before the device trips is dictated by the rating of the device, in this case 1000mA.
Would this have been on a TT system by any chance?

 

[Richard Burns]

I cannot see any reason for any voltage operated breaker to mention any current other than a maximum loading so therefore it must be a current operated breaker. However if it is so old it may well not work properly.
They normally say on them current operated earth leakage circuit breaker at that sort of age to separate them from the voltage operated earth leakage circuit breakers.

 

[mattg4321]

ELCB's are all current operated and the coil you saw would have been the core balanced CT that looks for the current imbalance.
The current flowing out should equal what comes back on the neutral, any imbalance detected therefore must be flowing to earth. The amount of current allowed to flow to earth before the device trips is dictated by the rating of the device, in this case 1000mA.
Would this have been on a TT system by any chance?

I'm willing to be proved otherwise, but I always thought most of the ELCB's I've come across have been voltage operated - 50v on the earth rings a bell. I thought what I found was very unusual and annoyingly I can't find any pictures of one online!

What's even more unusual is it's an old TN-S supply. Why a 1000mA ELCB (I guess essentially RCD) was fitted is another good question.

 

[mattg4321]

I cannot see any reason for any voltage operated breaker to mention any current other than a maximum loading so therefore it must be a current operated breaker. However if it is so old it may well not work properly.
They normally say on them current operated earth leakage circuit breaker at that sort of age to separate them from the voltage operated earth leakage circuit breakers.

1A is a pretty high current imbalance by modern domestic regulations though! It didn't specifically say whether or not it was current or voltage operated, but the only markings were crabtree, 60A, 240V and 1A.

 

[mattg4321]

Just found one mentioned on another forum.

 

[Richard Burns]

Seeing the picture reminded me of this one I found at a customers this one was 500mA and did work, it was from around 1970 ish.

View attachment 35890

 

[Andy-1960]

I'm willing to be proved otherwise, but I always thought most of the ELCB's I've come across have been voltage operated - 50v on the earth rings a bell. I thought what I found was very unusual and annoyingly I can't find any pictures of one online!

What's even more unusual is it's an old TN-S supply. Why a 1000mA ELCB (I guess essentially RCD) was fitted is another good question.

If it was voltage operated why would it have a rating in mA?

 

[freddo]

1A is a pretty high current imbalance by modern domestic regulations though! It didn't specifically say whether or not it was current or voltage operated, but the only markings were crabtree, 60A, 240V and 1A.

The 1Amp ones are quite common around here on TT installations, remember it will have been installed to provide fault protection and nothing else. It will be current operated.

 

[HandySparks]

ELCB's are all current operated...

Most of the old (30 years +) Crabtree and Chilton ELCBs are 'voltage' operated. The coil is in series with the earthing conductor and they trip when the voltage across the coil reaches about 50V (as mattg says).

If it was voltage operated why would it have a rating in mA?

mattg's one is differential current operated, which is more unusual for a device of this age and style (but universal now).

 

[Andy-1960]

Loving these forums, I have never come across a voltage operated ELCB, but good to know they exist. You live and learn, thanks Handy

 

[PEG]

Most of the old (30 years +) Crabtree and Chilton ELCBs are 'voltage' operated. The coil is in series with the earthing conductor and they trip when the voltage across the coil reaches about 50V (as mattg says).



mattg's one is differential current operated, which is more unusual for a device of this age and style (but universal now).

If the coil is in series with the earthing conductor,operation relies on a fault current taking that path.

Any fault path,taking another,possibly even better route,will not be sensed.

During the 70's and 80's,several unfortunates,found this out the hard way,whilst mowing the garden with their new Black and Deckers.

 

[mattg4321]

Seeing the picture reminded me of this one I found at a customers this one was 500mA and did work, it was from around 1970 ish.

View attachment 35890

Does anyone know what BS number these conform to? Are they still recognised in the regs?

If one was doing an EICR on a TT system and one of these was used for fault protection, is this acceptable? (assuming it tests ok of course)

 

[Richard Burns]

Presumably they would still come under BS4293 but this did not come out until 1983 and I am not sure of an earlier standard, though here must have been one.
If they are still functional and are providing fault protection then they should be acceptable, though the age of them may mean they have suffered over time if not then they are OK, they often trip very fast as there is no particular control on the timing of tripping.

 

[westward10]

BS842:1965