My last 'non Amd 3' CU Install.

[HandySparks]

Thanks, I also hadn't spotted that, I'll fix it for them when we go to finish off.

At the other end of the supply the have just fitted piranha nuts and relied on the teeth biting into the metal enclosure to make the connection, which is something I'm in two minds about at the moment.

I'm happy to rely on the teeth biting into the metal enclosure and don't even think that the locking screw is required in this situation if done up nice and snug. This is provided that the cable is properly cleated to eliminate movement and that it's a dry environment, so corrosion at the interface is unlikely.

Here's one I did last week. Continuity between gland and earth bar was confirmed (and actually there's a separate cpc in the cable anyway).




Should raise a couple of other issues, but I don't care!

 

[davesparks]

As far as I can remember the manufacturers instructions stipulate that the grub screw be tightened whatever.

The one issue that I'd pull it up on is the wrong cores being used for N and E.
Yellow (which is now black) has always been used for earth
Blue (which is now grey) has always been used for neutral

 

[HandySparks]

As far as I can remember the manufacturers instructions stipulate that the grub screw be tightened whatever.

The one issue that I'd pull it up on is the wrong cores being used for N and E.
Yellow (which is now black) has always been used for earth
Blue (which is now grey) has always been used for neutral

See, I said that the pic would raise issues.

You may be right about the manufacturer's instructions, but my judgement is that a tight metal to metal joint like that, not subject to vibration or movement, is perfectly OK. After all, everyone's happy with the usual thin nut provided with gland kits, which has no additional locking. I regard the locking screw as only essential where a plastic enclosure forms part of the 'sandwich' which may creep and result in a loose joint.

As far as the cable colours go, yellow may always have been used for earth and blue for neutral (which is now history), but the regs allow me to sleeve black with blue and grey with green/yellow, so I choose to do this (despite what the NICEIC or others may stipulate). If I was installing or extending a three phase cable then, of course, I would comply with Table 51 and Appendix 7 of the BYB.

 

[davesparks]

My concern is the csa of just the points of the teeth making contact, what will happen under fault conditions? In the case of the fuse switch I posted above the incoming side is connected to the 200A busbar so will have an appreciable fault current available.

Blue and yellow are not history, they are still present in many installations.
If you extend a 3 core cable of any type would you join blue to grey and yellow to black?
What about the convention of using the L1 core for live, L2 core for sw live and L3 core for neutral?

 

[HandySparks]

My concern is the csa of just the points of the teeth making contact, what will happen under fault conditions? In the case of the fuse switch I posted above the incoming side is connected to the 200A busbar so will have an appreciable fault current available.

I think that the points of the teeth on the brass nut will be somewhat flattened and biting tightly into the steel of the enclosure. I recon the joint will be as good as the usual banjo, which will only be making metal-to-metal contact in places if looked at at a microscopic level anyway.

Blue and yellow are not history, they are still present in many installations.
If you extend a 3 core cable of any type would you join blue to grey and yellow to black?

If three phase, I follow the regs, L1 brown, L2 black, L3 grey. If working to a design, I'd follow the drawings. If single phase and my own job, I make my own decisions. Unfortunately, the IET haven't seen fit to define what the colour allocation should be when using bn/bk/gy cable in single phase applications. Maybe they should have.

What about the convention of using the L1 core for live, L2 core for sw live and L3 core for neutral?

When they were red, yellow and blue, it made some sense. Moving to brown black and grey....

 

[davesparks]

I think that the points of the teeth on the brass nut will be somewhat flattened and biting tightly into the steel of the enclosure. I recon the joint will be as good as the usual banjo, which will only be making metal-to-metal contact in places if looked at at a microscopic level anyway.

The banjo would be making full contact with the gland and have a flylead attached for the earth.

The piranha nut instructions state that the grub screw should be fitted and a flying earth lead should be fitted

 

[davesparks]

This from the earthingnuts website

 

[Midwest]

You lot should be going to bed at a respectable time!

 

[happysteve]

The last few posts, between Handy- and davesparks, have been very good: reasoned, polite debate, with historical insights and reference to good quality sources (eg manufacturers instructions). You are both a credit to the trade.

 

[HandySparks]

This from the earthingnuts website...

I see that they don't regard the teeth as guaranteeing a good connection to the enclosure every time due to varying paint thicknesses, etc. It's a fair point, although in my defence, I measured the resistance and was happy with the result. Had I thought about it at the time, I might have added a little protective grease to reduce the chances of future corrosion affecting the conductivity of the joint.

Edit: Actually, I bought a small tube of Contralube 770 at Elex a year ago. Looks like it might have been just the stuff for protecting the joint where the paint has been scraped off:
Contralube | Contralube 770

Problem is, it's been sitting on my desk rather than in the van.

 

[Dave OCD]

I think for the minimal additional effort and cost I'd always fit an additional appropriately sized earth lead between gland and earth terminal/bolt within the metal enclosure, it would just give me additional peace of mind.
One of the best products I know of for corrosion protection is ACF50, excellent stuff - although in my case 99% of its usage is on my motorbikes.

 

[davesparks]

I see that they don't regard the teeth as guaranteeing a good connection to the enclosure every time due to varying paint thicknesses, etc. It's a fair point, although in my defence, I measured the resistance and was happy with the result. Had I thought about it at the time, I might have added a little protective grease to reduce the chances of future corrosion affecting the conductivity of the joint.

Edit: Actually, I bought a small tube of Contralube 770 at Elex a year ago. Looks like it might have been just the stuff for protecting the joint where the paint has been scraped off:
Contralube | Contralube 770

Problem is, it's been sitting on my desk rather than in the van.

I have before used the nut the other way round when terminating into unpainted enclosures such as galv trunking and relied on that as an earth connection. Thinking about the example you posted I wouldn't be so concerned as the connection to the armour is there as a bond so theoretically is not required to stand up to fault currents. In the example I posted the armour is the cpc so I am far more concerned about it.

A resistance test is fine but doesn't give a clear picture of what will happen when serious current flows. If I get a chance I'll see about setting up some tests with a decent current source.

Contralube is terribly good, but Vaseline is just as good. A dab of Vaseline on any high current connection can reduce contact resistance and therefore temperature quite a bit. I think it was Tony who posted some actual figures for a busbar connection he improved with a bit of Vaseline

 

[davesparks]

You lot should be going to bed at a respectable time!

If I could actually sleep I would.

My body clock is screwed, I seem to sleep every other night at the moment, if I sleep at all.

 

[Midwest]

Sorry to hear that davesparks, my remark was a flippant reply and wasn't meant as derogatory. Perhaps a break from forums might help?

 

[Gardner]

I'm happy to rely on the teeth biting into the metal enclosure and don't even think that the locking screw is required in this situation if done up nice and snug. This is provided that the cable is properly cleated to eliminate movement and that it's a dry environment, so corrosion at the interface is unlikely.

Here's one I did last week. Continuity between gland and earth bar was confirmed (and actually there's a separate cpc in the cable anyway).

View attachment 31052


Should raise a couple of other issues, but I don't care!

My personal opinion, the only way to earth anything is via full conductor. Ive never felt right with the armor of SWA doing it.

 

[davesparks]

My personal opinion, the only way to earth anything is via full conductor. Ive never felt right with the armor of SWA doing it.

What do you mean by full conductor? If the calculations work out ok then there is no reason not to use the armour in the way it was designed to be used.
Do you also not use steel conduit as an earth?

 

[davesparks]

Sorry to hear that davesparks, my remark was a flippant reply and wasn't meant as derogatory. Perhaps a break from forums might help?

It was taken in the spirit intended and certainly wasn't taken as derogatory, I've always been pretty much nocturnal

A break from working weird and varied hours would help possibly.

 

[Gardner]

What do you mean by full conductor? If the calculations work out ok then there is no reason not to use the armour in the way it was designed to be used.
Do you also not use steel conduit as an earth?

I dislike using the armor as earth, I do not agree with the way its terminated. Id rather the armor be twisted together and terminated under a screw.

As for steal conduit it depends. Sometimes I will pull a separate earth.

 

[davesparks]

I dislike using the armor as earth, I do not agree with the way its terminated. Id rather the armor be twisted together and terminated under a screw.

As for steal conduit it depends. Sometimes I will pull a separate earth.

An armoured gland properly fitted gives a secure connection to every strand of the armour with equal pressure, whereas twisting it together into a screw terminal doesn't give the same equal pressure on every strand.

I don't see what the problem is with using a specially designed and thoroughly tested method of termination?

How do you decide when to pull an early wire into conduit and when not to?

 

[Gardner]

An armoured gland properly fitted gives a secure connection to every strand of the armour with equal pressure, whereas twisting it together into a screw terminal doesn't give the same equal pressure on every strand.

Why do you believe it to be so? Im not saying your wrong, but when done right a screw termination would not be an issue imo.

I don't see what the problem is with using a specially designed and thoroughly tested method of termination?

How do you decide when to pull an early wire into conduit and when not to?

Generally if I feel the conduit could become disconnected inadvertently. But I side toward you on this one.