15th Ed. Reg Query

[securespark]

I know the 15th is no longer applicable, but was intrigued by the wording of these regs*:

Installations which are part of a TN system

413-9 The protective devices shall be of one or more of the following types:

- overcurrent protective devices,
- residual current devices.

provided that where the neutral and the protective functions are combined in one conductor (PEN conductor) a residual current device shall not be used.

Installations which are part of a TT system

413-12 The protective devices shall be of one or more of the following types:


- residual current devices,
- overcurrent protective devices.

NOTE - Residual current devices are preferred.


413-9 Does that mean you cannot use an RCD on a PME supply?
413-12 No overcurrent devices on a TT supply?



* Yes, I'm a fad sucker who reads old regs in his spare time...

 

[ban-all-sheds]

Protection against what?

And CNE refers to the installation, not the supply.

 

[securespark]

1. Indirect Contact

2. Where does it say that?

 

[PBC_1966]

To protection against what is section 413 referring? It sounds as though it's specifically related to earth-fault protection rather than overload.

And there's nothing wrong with using an RCD where the supply has, as some point, a combined neutral/earth; it's that they must be completely separate on the load side of the device.

 

[stillp]

The prohibition was, I believe, against reliance on an RCD as the sole means of protection against indirect contact.

 

[ericmark]

provided that where the neutral and the protective functions are combined in one conductor (PEN conductor) a residual current device shall not be used.

This is the line in question I would have written "provided that where the neutral and the protective functions are combined in one conductor (PEN conductor) a residual current device shall not be used before splitting. Or some other phrase to show there were referring to where combined and not after the split. I know now they are only combined before the DNO head, but I remember working in Algeria in 1980 where the Turkish electrician who lived in Holland seemed to consider there was no problem combining and splitting earth and neutral where ever he liked.

I find the "To a previous edition" always causes problems as often we don't have a copy of that previous edition to refer to. There is of course a huge difference between "a previous editions of wiring regulations" and "a previous editions of BS7671".

I looked at the wording of BS7671:2008 over RCD protection, and I could see nothing which separated LV and ELV, clearly you simply can't buy a RCD to work with 12 VDC so we all realise it does not refer to ELV, but there is nothing to say that. In 20 years time looking back we may have RCD's which work on 12 VDC so we would maybe question BS7671:2008 meaning.