Acceptable method to bond earths in a plastic junction box

[P6Jax]

Thanks for the comments. Whilst at Alton towers a couple of weeks ago, I noticed that all of the plastic enclosures on rides had banjos on the outside. Some where mounted on rails, which would be subject to vibration... I guess this is just the way it is. I suppose if there is an earth core too, then only one of the ends would need to be in good contact for the armour to be earthed.

I'll post photos of a wired box in situ when I'm doing the install for newcomers benefit.

 

[JohnW2]

Thanks for the comments. Whilst at Alton towers a couple of weeks ago, I noticed that all of the plastic enclosures on rides had banjos on the outside. Some where mounted on rails, which would be subject to vibration...

As I said, despite the theoretical considerations, I'm personally not convinced that tightening the banjo against a hard plastic box is really a problem. People happily do it with aluminium boxes (e.g. see this forum's wiki on SWA glands), and I'm not convinced that a soft metal, like aluminium, represents any less of a 'problem' than does a hard plastic. I'm certainly sure that it's a fairly common practice, even in my limited experience of such things.

Kind Regards, John.

 

[Iggifer]

im not a fan of using the armour as a CPC, regardless of whether it not it satisfies the andiabatic equation or not. Obviously I'll connect the armour to the cpc, but where possible, but I'll use cable with a core for the cpc

 

[JohnW2]

im not a fan of using the armour as a CPC, regardless of whether it not it satisfies the andiabatic equation or not. Obviously I'll connect the armour to the cpc, but where possible, but I'll use cable with a core for the cpc

Same here. In fact, I've very rarely used armour as the only CPC. However, I suppose that even if one is only using the armour as armour, one still wants the connection between it and the CPC to be good and reliable.

Kind Regards, John

 

[DaftPunk]

Why waste your money on an extra copper core when you've already got a perfectly good CPC provided by the armour?

 

[JohnW2]

Why waste your money on an extra copper core when you've already got a perfectly good CPC provided by the armour?

Speaking personally, if I were totally confident about the electrical connection to armour afforded by a gland, then I probably wouldn't.

Kind Regards, John

 

[Spark123]

As I said, despite the theoretical considerations, I'm personally not convinced that tightening the banjo against a hard plastic box is really a problem. People happily do it with aluminium boxes (e.g. see this forum's wiki on SWA glands), and I'm not convinced that a soft metal, like aluminium, represents any less of a 'problem' than does a hard plastic. I'm certainly sure that it's a fairly common practice, even in my limited experience of such things.

Kind Regards, John.

It isn't hard plastic as seen in the pic on the OP, it is soft plastic! If it was hard plastic then it would probably shatter when tightening to it or drilling.

Aluminium is fine.

 

[Spark123]

Why waste your money on an extra copper core when you've already got a perfectly good CPC provided by the armour?

I don't see the point either, but then again I can undercut them price wise .
I served most of my apprenticeship with large-ish 3 phase stuff, I have not yet come across 5 core 3p + n + e properly coloured SWA cable, I suppose you can get them at a premium tho.

 

[JohnW2]

It isn't hard plastic as seen in the pic on the OP, it is soft plastic! If it was hard plastic then it would probably shatter when tightening to it or drilling. Aluminium is fine.

I reckon that's quibbling - I wasn't talking about brittle plastic. Aluminium is easy to squash.

As I've said, although I do use a pair of backnuts if I have them to hand, FWIW, I've never seen a problem due to tightening onto a plastic box - whether one calls the plastic soft or hard.

Kind Regards, John

 

[RF Lighting]

Why waste your money on an extra copper core when you've already got a perfectly good CPC provided by the armour?

I don't see the point either, but then again I can undercut them price wise .
I served most of my apprenticeship with large-ish 3 phase stuff, I have not yet come across 5 core 3p + n + e properly coloured SWA cable, I suppose you can get them at a premium tho.

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• RF Lighting
• 2 May 2013
• 2

Complete waste of money though.

My local wholesaler doesn't stock two core armoured, and it ends up being cheaper to use 3 core than order in the correct cable. Really annoys me.

 

[P6Jax]

Here's what I'm both happy with and going with for the future. I would rather do a as close to faultless job as I can, if anybody ever looks at it in the future.

I've used stainless screws on the tabs and tightened them just so the enclosure has a fraction of movement against the wall, to prevent distorting the enclosure (and seal!) in case the surface isn't level. I'm going to put a smear of non-petroleum based grease around the enclosure seal and glands once its all tightened up as an additional seal. Comments?

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• P6Jax
• 25 Jun 2013
• 1

 

[RF Lighting]

Personally I would link across the glands for continuity, but not connect them to the CPC at the joint.

Also I would drill a 4mm drain hole in the bottom of the back of the box, so if any water or condensation does get in to the box, it can get back out again.

Apart from that though, looks like you've done a really good job of it. Well done.

 

[Spark123]

It isn't hard plastic as seen in the pic on the OP, it is soft plastic! If it was hard plastic then it would probably shatter when tightening to it or drilling. Aluminium is fine.

I reckon that's quibbling - I wasn't talking about brittle plastic. Aluminium is easy to squash.

As I've said, although I do use a pair of backnuts if I have them to hand, FWIW, I've never seen a problem due to tightening onto a plastic box - whether one calls the plastic soft or hard.

Kind Regards, John

I have come across a number of loose joins where metal vs soft plastic so it isn't a quibble, not come across a problem ally one yet.

 

[Spark123]

Personally I would link across the glands for continuity, but not connect them to the CPC at the joint.

Also I would drill a 4mm drain hole in the bottom of the back of the box, so if any water or condensation does get in to the box, it can get back out again.

Apart from that though, looks like you've done a really good job of it. Well done.

I don't see an issue with cross bonding at an intermediate joint with bog standard mains stuff, with signal cables it could be an issue tho. Wether it is or isn't doesn't really matter in the above case, but is looking good, better than some professional jobs!!

 

[JohnW2]

I have come across a number of loose joins where metal vs soft plastic so it isn't a quibble, not come across a problem ally one yet.

Fair enough - you've undoubtedly seen a lot more than I have. Maybe I've just been lucky in what I've seen!

Kind Regards, John