New RCD Query

[JohnD]

I have an RCD in my garage (which is integral to the house, but I plug in my lawnmower and car vac there) in its own enclosure.

I test it occasionally, and had no trouble fitting a new one when the original failed to trip. However, I recently noticed that RCDs in manufacturers catalogues now show an additional thin wire, as well as the pair of big terminals top and bottom. I am familar with how RCDs work, with a tracer coil wrapped round the two conductors that does not develop any voltage unless there is an imbalance in current carried.

Is there some new feature of RCDs that I ought to understand? What is this wire for?

 

[andy]

functional earth. more used on RCBO's. not sure why it needs it tho

 

[Adam_151]

Don't quote me on this, but I think its to enable it still function in the case of a disconnected neutral supply.

Like andy says, never seen an RCD like this, only RCBOs

 

[NuttallsSpark]

MEM RCDs have the earth link on them, must admit unsure of the real purpose, maybe more reliable or sensitive maybe

 

[andy]

AFAIK, its something to do with detecting a dead neutral and it trippin. possibly because RCBO's are single pole?

 

[JohnD]

NuttallsSpark is right, it was MEMs that I was looking at. I thought it might just be that I'd got a new MEM catalogue and technology had moved on and left me behind? My current MK and previous Crabtree didn't have this thin wire (It's not an RCBO, but a 2-pole RCD, and is in its own insulated enclosure so no earth in there at the moment.)