Acceptable method to bond earths in a plastic junction box

[P6Jax]

Hi All

Wiring a junction box - Is this considered an acceptable method of bonding the earths? Soldered banjo, clipped short and clamped to the inside of the enclosure with the gland nut. Photo attached.

Untitled

• P6Jax
• 20 Jun 2013
• 1

Alternatives are:

1/ Piranha / p-nut / lynx nut (expensive on bigger jobs)
2/ Clamp banjo between two nuts on inside (not enough thread)
3/ Traditional banjo on outside with screw through (ruins IP rating, possible plastic deformation over time)
4/ Use an earth clamp bar http://www.tlc-direct.co.uk/Products/WKEC308.html (only good if swa glands are on the same side, no other downside)

Problems with the photographed method - zinc plated nut may degrade over time, reducing the integrity of the bond. Can't seem to find slim brass ones easily.

Comments / opinions please - specifically, what is the PROPER method, before piranha nuts existed.

Thanks

 

[bernardgreen]

If I had soldered those earth connections I would have wrapped and compressed the end of the tag around the wire to make a mechanical joint before soldering.
( solder weakens, degrades over time ).

Also loop the wire rather than cutting it at each banjo.

 

[P6Jax]

If I had soldered those earth connections I would have wrapped and compressed the end of the tag around the wire to make a mechanical joint before soldering.
( solder weakens, degrades over time ).

Also loop the wire rather than cutting it at each banjo.

Thanks. I agree that solder can weaken over time under certain circumstances. ( see: http://www.ami.ac.uk/courses/topics/0154_fsj/ ). This is a very large surface area of soldered contact, which is in a static installation. Thermal cycling will be a factor but given the size of the joint, insignificant, given a proper, clean, impurity free solder joint.

Back to the original question (and assuming I had looped this round the banjo hole) - Is this an acceptable method and if not - what is the best method and why?

 

[EFLImpudence]

Alternatives are:
2/ Clamp banjo between two nuts on inside (not enough thread)

Shouldn't your soldered banjo be fitted like that?

Connections should be mechanically and electrically sound before soldering.

 

[P6Jax]

Alternatives are:
2/ Clamp banjo between two nuts on inside (not enough thread)

Shouldn't your soldered banjo be fitted like that?

Connections should be mechanically and electrically sound before soldering.

Yes, between two (BRASS) nuts would be much better. This is why I am asking, because there is no clear guidance or consensus as to what is acceptable or not. And there are plenty of examples on the web / this forum that I would not be happy with too....

Whether the banjo is soldered first, provided it is not stressed when fitted, why would that be a problem?

Do you have a preferred method?

 

[ericmark]

Job looks a good one but when one asked if acceptable the question is always by whom.

The banjo rings do vary from make to make and some are easier to manipulate easier then others. In the main I have managed to use a brass bolt somewhere to make a connection or run the earth around the outside of the box.

The usual compromise is between being water tight and making a good earth connection but I have found it is hard to get a plastic box not to warp with the fitting of SWA glands so unlikely the box will be any better than IPX4 and often either a drain or filling with a re-enterable compound is required.

So I see little point in going to all the work of manufacturing a special using solder like you show. Small hole in bottom with earth wire entering the box and banjos linked on outside is more common.

The proper job

cost about £1.50 each and what you have to consider is if it's worth all the hassle of soldering for the money saved.

Some boxes do come with "Earth Continuity Plate"

may be better if you made some for your boxes if your really into DIY.

 

[Spark123]

I don't see an issue with soldering the connection as such, have done it myself before where space is an issue and before piranha locknuts were easily available.
I still reckon though that the banjo should be between two locknuts as the PVC plastic can compress creating a poor connection.

 

[P6Jax]

Thanks for the comments. It seems the conclusion is, in order of best to worse for normal plastic enclosures:

1/ Earth clamp / bar if both on one side.
2/ Piranha nuts
3/ Banjo between two brass (not galvanized) nuts

Not a good idea / discouraged: Using plated parts or dissimilar metals for continuity, contacts that rely on the compression against the plastic housing. See comments below for more comments about this

I will go with Piranha nuts throughout. IMO it would be nice to have a SWA gland made with a flat section and a threaded hole on the thread, so that you can screw directly to it.

Hope that this encourages better practice among installs in the future.

 

[ericmark]

I do remember when working with ExII that there were things with a earth wire built in which went before the box (since had to use special fibre washer) but I would guess these cost more than the more common Piranha nuts.

I hatted them as because the plastic box was threaded you had to fit the gland into the box then cable into the gland and marking the gland was a real crime so had to make sure correct spanners. All flats matching even though it would all then be hidden with a shroud.

Ali plate was inside the box with brass nut and I suppose it should not get wet inside the box. Although still worked when drizzle was coming down. Mainly for trace heating so likely they would be warm.

 

[Spark123]

What is the issue with galvanized locknuts, bar their size?

If there was a problem with brass and galvanized steel then I doubt the gland suppliers would provide them in a gland pack!!

 

[P6Jax]

Spark123: you raise a good point. A potential argument could be that they are dissimilar metals and you'll get a slight corrosion / oxide of the zinc. Two arguments against this could be:

1/ It's inside an IP rated enclosure, so any tarnishing will be minimal.
2/ The armour of the cable is galvanized - so it will be at least as good as that!

Regarding the junction box and compressing against it - I'm not sure that's going to be a problem either. It's made from a high grade polycarbonate http://www.spelsberg.com/no_cache/product-sheet/an/49040201/Productsheet.pdf, and with the additional 'o'-ring seals on the glands, adds a controlled compression over time.

Would anyone not be happy with the original photograph? With ericmark's question regarding 'by whom' - to be signed off for Part P by a sparky or a building regs officer.

 

[Spark123]

The only bit I wouldn't be happy with is the metal being compressed onto plastic.

 

[P6Jax]

The only bit I wouldn't be happy with is the metal being compressed onto plastic.

I've been thinking about this - surely this is exactly the same issue as if the banjo was on the outside of the enclosure (compressed directly onto the plastic i.e. the prescribed / normal method)? It would also suffer the additional exterior weathering, ruining some of the continuity.

 

[P6Jax]

Changed them to pirahna nuts anyway...

Untitled

• P6Jax
• 24 Jun 2013
• 1

 

[JohnW2]

I've been thinking about this - surely this is exactly the same issue as if the banjo was on the outside of the enclosure (compressed directly onto the plastic i.e. the prescribed / normal method)? It would also suffer the additional exterior weathering, ruining some of the continuity.

What you were missing is that, whilst what you describe is the 'standard method' for a metal enclosure, it is theoretically not the "prescribed/normal" method with a plastic enclosure. With a plastic enclosure, one is meant to either use a Piranha nut (as you have now done) or have a banjo inside the enclosure between two back nuts. Having said that, I've often (when neither Piranhas nor extra back nuts were not to hand!) sandwiched banjos between a locknut and plastic enclosure, and have never yet come across one which became significantly loose.

Kind Regards, John