Neutral isolation for TT supply

[Gardner]

Where is neutral isolation required for a TT supply? The way I read it, I need to have isolation on each individual MCB, or does my main DP incomer take care of this?


Isolation of the neutral conductor - Electrical Installation Guide

 

[Gardner]

Because the circuit breaker is not an isolator in this instance - the main switch is.

Even for domestic TN systems all-pole isolation is required, so there is no reason to make a distinction between them and TT systems.

Correct, but I dont see people turning the main switch off to work on an individual circuit. How does anyways when out troubleshooting or repairing?

 

[Risteard]

Correct, but I dont see people turning the main switch off to work on an individual circuit.

That doesn't mean that they shouldn't operate the main switch, however.

 

[Gardner]

That doesn't mean that they shouldn't operate the main switch, however.

Places like France which use 2P MCBs, is this optional or mandated?

 

[Risteard]

Places like France which use 2P MCBs, is this optional or mandated?

I presume it is a requirement, but you need to remember that continental socket outlets aren't always polarised.

 

[Gardner]

I presume it is a requirement, but you need to remember that continental socket outlets aren't always polarised.

The ones in France are since the earth pin forces the schuko plug to go one way.

 

[Risteard]

The ones in France are since the earth pin forces the schuko plug to go one way.

Indeed, but it may be the reason why double pole protective devices were initially used. It may be simply for traditional reasons now.

 

[Gardner]

Indeed, but it may be the reason why double pole protective devices were initially used. It may be simply for traditional reasons now.

I still think the mass us of TT in France might be doing it. The DP MCB acts as isolation for each circuit.

 

[dav1980]

In the case of a circuit on a petrol station fed through single pole mcb... If we need to work on that circuit then we should be locking off the front end / section breaker to disconnect the neutral?

 

[DPG]

I thought petrol stations had a big book of additional regs though (and you can't have TNC-S I believe) - is it covered in these? Daz

 

[dav1980]

I thought petrol stations had a big book of additional regs though (and you can't have TNC-S I believe) - is it covered in these? Daz

Yeah I thought we were on about TT systems which petrol stations are.
Most circuits Are protected by DP RCCBs but I've seen a few sp breakers so I was just curious. No one has ever mentioned needing to isolate the main section breaker if I was to work on a circuit which doesn't have DP isolation.

 

[DPG]

Yeah I thought we were on about TT systems which petrol stations are.
Most circuits Are protected by DP RCCBs but I've seen a few sp breakers so I was just curious. No one has ever mentioned needing to isolate the main section breaker if I was to work on a circuit which doesn't have DP isolation.

Yeah see what you mean, sounds like a fair point. Daz

 

[Gardner]

I thought petrol stations had a big book of additional regs though (and you can't have TNC-S I believe) - is it covered in these? Daz

You would need isolation even more on TT then TN-C-S, because in TN-C-S the neutral is at least referenced to the petrol pumps and structures to some degree. In TT the neutral could have many more volts on it by the time it hits the petrol pump then TN-C-S.