Mixing TT and TNCS supply systems

[catdog1121]

Yes. Currently we have no other options

My thinking is that it's more a question of when than "if"

Can you show a link of where it says you have to have a TNCS if doing a rewire... First I have every heard of this...

 

[catdog1121]

We only have a reliable solution if all 3 phases are present

the current signle phase options are not really a solution

I think the DNOs should implement PEN fault disconnection as they have access to all phases easily, but that would require more cost

Don't some EV car chargers have PEN fault detection? I think there is also a standalone system that can detect PEN fault..

I cant see any DNO ever implementing a PEN fault disconnection as that would cost them money, I think the next edition of wiring regs will have all sorts of fancy earthing because the DNO's no longer want to provide a reliable earth so cant see them will to accept responsibility to disconnect a PEN fault.

 

[LastManOnline]

Can you show a link of where it says you have to have a TNCS if doing a rewire... First I have every heard of this...

The DNO (ESB) will only provide you with a TNCS supply. On coming across a TT supply, a REC (registered electrical contractor) is obliged to issue a "Notice of Hazard" to the homeowner, alerting them of the requirement to upgrade to TNCS. No exceptions are allowed.
On the most recent "Safe Electric" newsletter, they doubled down on this by stating that metal sheds may not be connected to a converted TT supply (see March 2021 newsletter under "faq, s" on page 12, I think).

 

[LastManOnline]

I thought the ROI now mandated double-pole MCB as the main incomer switch,

It's an 80 amp DP isolator.

so I presume the 'neutralising link' is at the supply head, and not in the CU?

Correct

 

[catdog1121]

The DNO (ESB) will only provide you with a TNCS supply. On coming across a TT supply, a REC (registered electrical contractor) is obliged to issue a "Notice of Hazard" to the homeowner, alerting them of the requirement to upgrade to TNCS. No exceptions are allowed.
On the most recent "Safe Electric" newsletter, they doubled down on this by stating that metal sheds may not be connected to a converted TT supply (see March 2021 newsletter under "faq, s" on page 12, I think).

Agh ok your in Ireland....

 

[Mikegh]

It's an 80 amp DP isolator.

If there's a main overcurrent protective device upstream in the cabinet

 

[pc1966]

On coming across a TT supply, a REC (registered electrical contractor) is obliged to issue a "Notice of Hazard" to the homeowner, alerting them of the requirement to upgrade to TNCS. No exceptions are allowed.

Has the nature of the hazard been described?

Is it this very issue of TT'd homes returning open PEN current via another's neutralising link?

 

[LastManOnline]

Has the nature of the hazard been described?

The description of the hazard would simply be termed as the home being "un-neutralised".

Is it this very issue of TT'd homes returning open PEN current via another's neutralising link?

Yes. That's one issue. But main issue is the gradual disappearance of the metallic network that was deemed essential for a sustainable TT system.

 

[marcuswareham]

These systems only disconnect the supply if the L - N voltage is outside of range of 207v - 253v it is still very possible to have a PEN fault with a dangerous voltage present on all exposed metal work and these devices would be non the wiser, therefore they do not protection against PEN faults in everycase

Other products have a device which senses any current flowing on the CPC, these require a person or animal to receive a shock for a very short duration in order for them to disconnect in a PEN fault scenario

So as yet we do not really have a satisfactory single phase PEN fault detection/protection device

 

[Mikegh]

These systems only disconnect the supply if the L - N voltage is outside of range of 207v - 253v it is still very possible to have a PEN fault with a dangerous voltage present on all exposed metal work and these devices would be non the wiser, therefore they do not protection against PEN faults in everycase

Other products have a device which senses any current flowing on the CPC, these require a person or animal to receive a shock for a very short duration in order for them to disconnect in a PEN fault scenario

So as yet we do not really have a satisfactory single phase PEN fault detection/protection device

A protective device that requires a person to receive a shock

Hmm


Not sure I like the sound of that