EICR help

[RF Lighting]

Came across a very bizarre setup this week.

This is a 50A TP&N supply to a submains in a factory.

The 35mm² 3 core R-Y-B SWA on the left of the picture supplies the submain with it's lives, and 16.0mm² 2 core SWA supplies the neutral.

Here's the other end.


There are no slots cut between the glands, and both DBs are steel.

The submains supplies mainly TP machinery, and the neutral current is small, only 4 or 5 amps, but it's still not right.

How would you word this on the repord, how would you code it, and how would you put it right?

 

[ricicle]

Eddy current issues with the armour termination. Steel wire armour should not be used for a single ac conductor. Also you could probably argue about all the conductors of the circuit not being enclosed within the same cable/eathed protection.

Hate to say it - looks like new sub-main time.

 

[Spark123]

Think it falls foul of regulation 521.5 section on electromagnetic effects, 521.8.1
What are you thinking regarding coding Rob, C3?

 

[RF Lighting]

Yeah I was thinking C3. It's not really causing any huge issues as it is, especially with the neutral current being very light, but it's still not right.

I wondered about trying to rearange the armoureds so they are glanded next to each other and either slot the DB steelwork, or bolt some sort of brass glandplate in place of the steel.

I know a new submains would be the best option but £££s

 

[SaladFingers]

That is an odd way of doing it, almsot as if the contractor wanted to use up some cable he already had laying around to maximise profit, or couldn't be bothered to do a proper job.

 

[Spark123]

It still won't comply with the above regulation, the only viable way to do that is to have a 4c cable.

 

[Spark123]

That is an odd way of doing it, almsot as if the contractor wanted to use up some cable he already had laying around to maximise profit, or couldn't be bothered to do a proper job.

Even more odd - the 2c appears to be harmonized and the 3c is old colours, maybe the cable has been removed from a 3p machine and routed to a dis board.

 

[SaladFingers]

That is an odd way of doing it, almsot as if the contractor wanted to use up some cable he already had laying around to maximise profit, or couldn't be bothered to do a proper job.

Even more odd - the 2c appears to be harmonized and the 3c is old colours, maybe the cable has been removed from a 3p machine and routed to a dis board.

Good point, plus the conductors have been doubled up on the neutral to make one adequate csa, they look undersized compared to the 3c, really isn't the best way to be doing things.

 

[JohnW2]

... and either slot the DB steelwork, or ...

I've seen that suggestion on a number of occasions in the past but, as a matter of interest/education, if one does that, does not the (electrical) 'shorting of the slot' by the metal body and/or nut and/or any washer of the gland bring the eddy current problem back into play, even though the ferromagnetic 'cicuit' is broken?

Kind Regards, John

 

[Spark123]

It won't stop the eddys induced into the steel armour hence is a bit pointless.
The cutting two holes together to form a single hole is more for where single core cables enter through separate holes, shouldn't be an issue with a correctly installed SWA.

 

[333rocky333]

You mention mainly Triple pole machinery so maybe the neutral was added at a later date hence the harmonised.

Is it possible to revert it back to a Triple pole board and use the Two core to supply a new single phase board, thats assumiong theres no Tpn loads, however even supplying a smaller Tpn supply for them alone could be cheaper than a new 35mm 4 core

 

[JohnW2]

It won't stop the eddys induced into the steel armour hence is a bit pointless.

True. I hadn't thought about the fact that it's SWA.

The cutting two holes together to form a single hole is more for where single core cables enter through separate holes ....

Yes, that's the usual context of the suggestion - so what's the answer to my question in that situation? Does the electrical 'shorting' (by the gland/nut) across the slot joining the holes facilitate eddy currents around each hole?

Kind Regards, John

 

[ricicle]

Does the electrical 'shorting' (by the gland/nut) across the slot joining the holes facilitate eddy currents around each hole?

Non-ferrous locknuts should be used.

 

[JohnW2]

Does the electrical 'shorting' (by the gland/nut) across the slot joining the holes facilitate eddy currents around each hole?

Non-ferrous locknuts should be used.

Yes, that obviously goes wthout saying - but, as I wrote previously, does not the electrical shorting of the gap (with anything conductive) facilitate some eddy currents, even though the ferromagnetic path is broken?

Kind Regards, John

 

[Spark123]

It will stop the eddys induced into the enclosure plate but doesn't get away from the great big loop formed by the two cables and both of the dis boards so you're only dealing with a small bit of the problem.