fused spur and faults

[lockhes]

hi everyone

if i had a fault on an outside socket and the fused spur was switched off inside what controls outside socket would it still trip the rcd

hope that makes sense

 

[chris gray]

your right.
and wayne was defo not gna give up on that

 

[WayneL]

You're just too argumentative

 

[chris gray]

ive had some real bad beats on the poker tables tonight is all matey

 

[lockhes]

woah opened up a can of worms here then lol

right i have a switched fused spur off the ring wheich feeds a outside socket

now if this fused spur was switched off and i had a fault on outside socket would it trip

are all switched fused spurs double pole if so im guessing you cant as your breaking line and neutral conections and only the cpc will still goto the socket

if single pole it would only break the line so if i had a fault between neutral earth it would still trip even if switched off id of thought


its like when u cut through a cable when breakers off but rcds on it detects an inbalance and trips rcd



does that sound right lol

 

[chris gray]

correct

 

[WayneL]

woah opened up a can of worms here then lol

right i have a switched fused spur off the ring wheich feeds a outside socket

now if this fused spur was switched off and i had a fault on outside socket would it trip No



if single pole it would only break the line so if i had a fault between neutral earth it would still trip even if switched off id of thought

does that sound right lol

Not a chance! You need a circuit for current to flow to your outside socket - with line disconnected (switched off) you have no circuit, so no current

its like when u cut through a cable when breakers off but rcds on it detects an inbalance and trips rcd

This, also, would not happen

 

[eddielarge]

Not a chance! You need a circuit for current to flow to your outside socket - with line disconnected (switched off) you have no circuit, so no current



This, also, would not happen

Wayne have i read this right ,, u are saying that if you cut through a cable that has the mcd turned off but is still connected at the board,, it wont trip,,

If so you are totally wrong as the RCD will trip ..

 

[pennywise]

If you only break the live conductor ie turn it off at the breaker or single pole devise and it's RCD protected then you touch the earth down to the neutral of that circuit the RCD will trip.

 

[eddielarge]

If you only break the live conductor ie turn it off at the breaker or single pole devise and it's RCD protected then you touch the earth down to the neutral of that circuit the RCD will trip.

That what i was trying to say

 

[WayneL]

If, on the RCD side of the board, you have the MCB for a circuit, (say your ring final), open (off) - you could connect the neutral and earth of that circuit together in a choc bloc and it isn't gonna trip the RCD!

You really need to read up on how a circuit operates and how an RCD operates.


If you don't believe me, try it

 

[pennywise]

If, on the RCD side of the board, you have the MCB for a circuit, (say your ring final), open (off) - you could connect the neutral and earth of that circuit together in a choc bloc and it isn't gonna trip the RCD!

You really need to read up on how a circuit operates and how an RCD operates.


If you don't believe me, try it

So your saying to disconnect the neutrals and CPCs of that circuit from their respective bars and put them in block and this won't trip the RCD? when I said to touch the earth down to neutral I meant at the end of that circuit not in the board.

 

[WayneL]

So your saying to disconnect the neutrals and CPCs of that circuit from their respective bars and put them in block and this won't trip the RCD? when I said to touch the earth down to neutral I meant at the end of that circuit not in the board.

No, I mean connect them together at the end of the circuit - (eg. the Ops outside socket)

The only time it would trip the RCD is if enough current was flowing from other loads(circuits) on the same RCD - and some of this current flowed up the neutral of the fault circuit and down to earth (parallel path).
This would obviously depend on impedances of cables etc.

But if no other circuit was under significant load, then, as I said, it's not possible for a neutral/earth fault on an isolated circuit to trip the RCD.

If you only break the live conductor ie turn it off at the breaker or single pole devise and it's RCD protected then you touch the earth down to the neutral of that circuit the RCD will trip.

If this were true then we would all be in danger whenever we worked on an isolated circuit - because, what do you do - open MCB on circuit, then test L-N, L-E, N-E with your voltage indicator - all clear and off to work you go

But, if the neutral is gonna leak enough current to earth to trip the RCD, then we're in trouble

 

[pennywise]

Yes you are correct but nine times out of ten every other circuit is on and is leaking a slight current down the neutral, we are talking real world situations not text book scenarios and i wouldn't have disputed what you said if I hadn't interpreted the OP situation as a real world problem.

 

[WayneL]

Reading back over everything, I'm beginning to think I might have got hold of the wrong end of the stick with regards what was being asked.

I was thinking more in single circuit scenario - where if the MCB is off - that circuit is dead and can't possibly trip an RCD.

it's clearer now that in certain circumstances a neutral/earth fault could cause a problem for the whole installation.

That's the good thing about these discussions - it gets you thinking

 

[pennywise]

No problem M8 I thought we we're at slightly crossed purposes