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Earthing back-boxes (patresses)

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Earthing back-boxes (patresses)

Postby RogerS » 06 Feb 2018, 17:05

Anyone know what the current regs say ? Just that I noticed my electrician hasn't done this in the kitchen when he did the second fix for me.
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Re: Earthing back-boxes (patresses)

Postby HappyHacker » 06 Feb 2018, 18:45

It is not a requirement if at least one of the lugs of the metal backbox is fixed (normally there is one fixed and one sliding). The backbox is then earthed via the metal fixing screw and the earthed metal around the fixing hole on the accessory. It used to be considered mandatory many years ago and has become considered to be good practice but there is a lot of debate among electricians if it is good practice or just a hangover from old regulations. It is not necessary on plastic boxes although some have an earthing connection.
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Re: Earthing back-boxes (patresses)

Postby RogerS » 06 Feb 2018, 18:48

HappyHacker wrote:It is not a requirement if at least one of the lugs of the metal backbox is fixed (normally there is one fixed and one sliding). The backbox is then earthed via the metal fixing screw and the earthed metal around the fixing hole on the accessory. It used to be considered mandatory many years ago and has become considered to be good practice but there is a lot of debate among electricians if it is good practice or just a hangover from old regulations. It is not necessary on plastic boxes although some have an earthing connection.



Thanks Kevin...that's saved me a lot of unnecessary work.
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Re: Earthing back-boxes (patresses)

Postby oddsocks » 06 Feb 2018, 18:58

I attended a 17th Edition electrical training course a few years ago (when the green book was valid, just before the new amendment was issued). The instructor always insisted that we earthed the metal backbox, but as Happyhacker has said, its not mandated (if one lug is fixed) but it was considered 'belt and braces'. His argument was that if someone had a loose line wire and removed the socket outlet to paint behind etc there was a small chance the line/live wire would come out and touch the backbox...which would not then be earthed as the screws were removed/loose.

The other point he emphasised was that the ring or spur earth wire had to be terminated directly on the socket outlet and then a separate one run to the backbox .....the main cable earth was never directly terminated on the backbox first (surprisingly quite a few on the course did that on day 1!).

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Re: Earthing back-boxes (patresses)

Postby RogerS » 06 Feb 2018, 19:28

The other thing that my electrician pointed out was that, on a ring, to put the two earths into the two separate earth connectors on the socket.
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Re: Earthing back-boxes (patresses)

Postby HappyHacker » 07 Feb 2018, 10:43

oddsocks wrote: The instructor always insisted that we earthed the metal backbox, but as Happyhacker has said, its not mandated (if one lug is fixed) but it was considered 'belt and braces'. His argument was that if someone had a loose line wire and removed the socket outlet to paint behind etc there was a small chance the line/live wire would come out and touch the backbox...which would not then be earthed as the screws were removed/loose.

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I have used exactly the same argument about why a fly lead should be connected to the backbox. I am usually shot down in flames when I am told that we should not be taking the accessories off when the circuit is live as the first and second rule of electrics are "don't work live"! Having said that I have on occasions been left embarrassed when taking a socket off when the circuit is live and I am left with the socket in my hand and a bunch of loose live cables in the wall and the occasional big bang.

The third rule is that if you need to work live you need to re-read rule one and two.

When installing accessories I always out a flylead on but it is force of habit as I started on the 14th edition which was a long time ago.

I know there are jobs that require working live but there is a lot of PPE and strict safety procedures involved also some testing need to be done live but the powers that be are trying to reduce that.
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Re: Earthing back-boxes (patresses)

Postby RogerS » 07 Feb 2018, 10:59

So what about light switch back boxes ? Presumably they do need to be earthed ?

Digressing slightly I'll always remember watching my mates' father mending old valve monochrome TVs just with his finger. He'd stick a digit on, say, the pentode, get a belt and say 'That's OK'...then progress through the set until he found one electrode that didn't feel right !
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Re: Earthing back-boxes (patresses)

Postby HappyHacker » 07 Feb 2018, 14:06

Light switches do not normally have an earth (or neutral) termination so it is usual to terminate the earth conductor on the metal backbox.

While trying to fix a valve TV, many years ago, I inadvertently touched the anode of a valve. I woke up on the other side of the room! I became far more cautious after that.
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