Earthing metal back boxes.

[DeanoRN]

Hi, i was just after a definitive answer of someone regarding if metal back boxes are to be earthed?

Ive had a look around and can't find a definitive answer, i was told by an experienced electrician i was assisting to earth them, then yesterday i was with another gaining some experience and he said what you earthing them back boxes for? he said don' t bother as when you earth the socket the screws will earth the back box.

so if anyone can clear this up it would be much appreciated.

regards
Deano

 

[Andy-1960]

Earth them, never rely on the screws

 

[Pete999]

Hi, i was just after a definitive answer of someone regarding if metal back boxes are to be earthed?

Ive had a look around and can't find a definitive answer, i was told by an experienced electrician i was assisting to earth them, then yesterday i was with another gaining some experience and he said what you earthing them back boxes for? he said don' t bother as when you earth the socket the screws will earth the back box.

so if anyone can clear this up it would be much appreciated.

regards
Deano

This second guy you spoke to, did he have room on his tool belt for a six shooter? What was his name? Clint the Sparky?

 

[SparkyChick]

I believe the guidance is.... if there is at least one fixed lug, you don't need to earth the back box, but it is good practice to earth it regardless.

 

[Pete999]

I believe the guidance is.... if there is at least one fixed lug, you don't need to earth the back box, but it is good practice to earth it regardless.

I just knew someone would come up with that old excuse, earth the box Mate, not getting at you SC, someone would mention it, just glad it was someone who knew what they were talkng about.

 

[Pete999]

This second guy you spoke to, did he have room on his tool belt for a six shooter? What was his name? Clint the Sparky?

Trouble is Mate they teach this carp at the "be an electrician in 5 week courses" Muppets.

 

[DeanoRN]

thanks for the reply's, i will just carry on and earth it like i was doing before. better safe than sorry.

 

[The Ghost]

I think the only occasion where it is argued to not earth is where there are two fixed lugs. Anyway I always earth the back box, it is no problem to do so why not.

 

[SparkyChick]

The official guidance from the IET on the subject starts in section 9.7 (Pg. 131) of Guidance Note 8.

If you elect to not earth boxes with one fixed lug, you should ensure that the accessory has earthing capabilities at each screw hole. If it doesn't, the one with the earthing must be attached to the fixed lug. Hence, good practice.... earth it

For the two fixed lugs, they say it's not necessary, but once you've seen the state of some back boxes (rust, dust and muck - and in one case I saw recently... half the box had rotted away due to damp)... it's not unreasonable to believe that poor connections could result, so.... earth it

I just knew someone would come up with that old excuse, earth the box Mate, not getting at you SC, someone would mention it, just glad it was someone who knew what they were talkng about.

I know you're not. Just pointing out the guidance as I'm sure this will come up if Deano carries on working with Clint. Especially as there doesn't seem to be any specific regulation that can be quoted to back up the decision to earth. The only one GN8 references is 543.2.7 which relates to using the containment or armour as the CPC.

 

[The Ghost]

If I see a damaged back box I replace it then earth it.

 

[happysteve]

I see since I started typing this out that the question's already been answered, but for the record...

Guidance Note 8 states:

- 2 fixed lugs: "box can be considered adequately earthed through the earthing straps and eyelets of the accessory and the fixing lugs on the box. An earthing tail is not therefore essential although for best practice it is highly desirable."

- 1 fixed, 1 adjustable lug: "...always desirable to provide an earthing tail. However, because some accessories have only one earthing strap and eyelet, it is essential that the earthing eyelet is located at the fixed lug position, otherwise continuation of the CPC will not be maintained and the earthing tail is therefore required to be provided."

- 2 adjustable lugs: "... an earthing tail is essential because these lugs cannot be relied upon for continuation of the CPC to earth the accessory."

 

[SparkyChick]

If I see a damaged back box I replace it then earth it.

That's the plan Customer is very unwell and I didn't want to cause her any hassle. She's going into hospital for an extended period next week and I have a key so I'll be going in and sorting it out along with the faults I found on the RFC so it's all good for when she comes home.

 

[Ian1981]

A metallic DB cover whether 3 phase or single relies on it being earthed when the cover is screwed back.
I believe that the guidance given in gn8 is reasonable and adequate for compliance with earthing exposed conductive parts With regard to socket outlets.

 

[telectrix]

used to be 2 fixed lugs to allow non earthing of back box. an amendment to the 16th, circa 2003 amended this to 1 fixed lug. however i consider it to be good practice to earth the back box with a fly lead and FLICK the IET.

 

[DeanoRN]

Thanks for all the informative replies.

Regards
Deano