Neutral/Earth leakage

[Couleddie]

A few weeks back I was adding some sockets to my ring main (yes, I only have one). I isolated the circuit but left the RCD on to keep a couple of radials powered up. When I came to doing the connections on the sockets the neutral and earth inadvertently touched and this tripped the RCD.

I can understand the theory behind what is happening but I could do to know why and whether it's an issue I need to get sorted. Something's not right.

I really think I should know the answer to this so i'm preparing to feel extremely embarrassed for being a bit daft Blushing

 

[Barx]

An RCD WOULD trip if neutral and earth touch. An RCD works by monitoring the phase and neutral for differences (under normal use neutral current = phase current) If the neutral and phase currents are different then some leakage is present and so something is wrong......trip goes the RCD. So, if neutral is leaking (touching in this case) to earth then more current is flowing through neutral then phase and so your RCD tripped.

Hope that makes sense.

 

[Andy™]

when you turn an MCB off it doesnt disconnect neutral. if it touches earth, some current uses earth, bypassing RCD, tripping it

 

[Couleddie]

Thanks. Should've known that. The brain's having a day off - it couldn't get into work because of the snow.

 

[batty]

Quite often will not trip on PME supplies but be careful with single module Rcbo's as they have a solid neutral if there is another RCD downstream.

Batty

 

[beemer]

Quite often will not trip on PME supplies but be careful with single module Rcbo's as they have a solid neutral if there is another RCD downstream.Batty

What do you mean by a SOLID neutral, Batty?

 

[batty]

What do you mean by a SOLID neutral, Batty?

Neutral is connected through Rcbo and even with switch off is still connected hence cannot be used on certain installs ie caravan parks, jettys etc.

Batty

 

[Andy™]

What do you mean by a SOLID neutral, Batty?

its only single pole. neutral only passes through RCBO so it can detect an imbalance. unlike RCD's, its not switched

 

[SLIPSHOD & SLAPDASH]

Neutral is connected through Rcbo and even with switch off is still connected hence cannot be used on certain installs ie caravan parks, jettys etc.Batty

What about a caravan in a jetty :x

 

[Apache]

What about a caravan in a jetty :x

better than on the narrow lanes near me

 

[SPECIAL LOCATION]

An RCD WOULD trip if neutral and earth touch. An RCD works by monitoring the phase and neutral for differences (under normal use neutral current = phase current) If the neutral and phase currents are different then some leakage is present and so something is wrong......trip goes the RCD. So, if neutral is leaking (touching in this case) to earth then more current is flowing through neutral then phase and so your RCD tripped.Hope that makes sense.

Assume thats a phase neutral reverse typo!

Just to correct it for any others reading...

If neutral and earth touching,

less current will be flowing though neutral than phase.

e.g. if N and E were the same resistance back to supply transformer, would be just two parallel resistors.. divide current equally.

so if 6a up phase to load then... (N & E touch)

3a though N and 3a though E back to supply transformer.

less though N because some of it is going through the earth path,

neutral cannot generate more current than was coming in though the supply line.