Two questions - safe zone overlap and double socket earthing

15 Jul 2007
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West Midlands
United Kingdom
Safe zone overlap - is it considered safe to route an additional spur (off existing ring socket) horizontally to the corner of the wall (ie. within the safe zone for said socket), then chop the cable around the inside corner and into a socket less than 150mm from said corner - ie. through two different safe zones - it seems to me like it will be obvious enough to anyone in future where the wiring runs (provided they are bright enough to take the cover off the sockets and have a look see where the ring is!) - plus the buried cable will be in the safe zone for the new socket upto the corner anyway.... - I'm guessing that the real question is - is it ok to bury a cable around a corner!

I assume that the 150mm is to the edge of the new socket anyway, as after this point it ceases to be a buried cable without protection (provided by the edge of the box)?

Double socket earthing - what is the purpose of having the two earth terminals? Is it because of a requirement to have an earth per outlet? Or is it intended that one earth from each side of the ring be terminated into each - therefore ensuring that the earth remains connected to the socket if one wire comes out? Am I worrying unnecessarily about this one? Just want to make it as safe as physically possible, whilst complying with the requirement to have all provided earth terminals connected.
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Yes, it's ok for cables to go around corners.

If it weren't we'd have problems! :rolleyes:

Also the safe zone that passes across/through the said socket is 150mm wide.
So you don't need to concern yourself with the edge as such.

Regarding the two earth terms in some sockets now (not all).
I believe it's to do with the earth not causing problems with PCs. But I forget the actual detail.
Sure someone can put me right.
If you have a socket on each wall, these create two zones horizontally to the sockets anyway, regardless of the 150mm internal wall zones. So, yes, you can run a cable horizontally from one socket to another, around a corner.

As for the earthing terminals, most socket manufacturers now provide two earth terminals on the sockets. In normal circumstances you can use either one, or both. They are intended for use on circuits (computers mainly) which have been wired for high integrity earthing, where the earth conductors are all individually terminated at all accessories and consumer unit. The reason being, as you have said, that if one earth falls out, every socket will still have a means of earthing, and as such, the earth will not rise in volts due to the higher than normal leakage current.
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Ah, so the extra earth terminal is only provided for systems with high leakage current - makes sense, I've had a whack off a pc power supply in the past (this is what I do for a living!) I kinda answered my own first question, but wanted to reassure myself that it was ok to chase around a corner horizontally!

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