Discuss Type of 3 Phase supply cable? in the Commercial Electrical Advice area at ElectriciansForums.net

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R

richlj

Hi,
Iv found a 3 phase supply cable in the basement of a restaurant.
It had been plastered over and I'm curious if this type of cable is legal.
It had been installed a long time ago but is Red, Yellow and blue phase colours, it obviously has pvc covering over the copper, then half of the circumference has steel armouring used as the neutral then another layer of pvc.
There were no warning signs, it entered the basement about 400mm below the ceiling and went diagonally up beneath the plaster to about 150mm below ceiling and ran beneath plaster horizontally for about 10 metres. What would happen if someone was seriously hurt from potentially drilling through this cable? Who would be at fault? It was below plaster but everything else in the room is clearly surface mounted. Would this cable have met standards when it was installed?
Thanks very much
 
Are you sure it wasn't split concentric cable?
Half of the outer ring of wires are insulated copper neutral and the other half are earth (can't remember if copper or steel)
 
horiz. at 150mm from celing is just within safe zone, but buried diagonally up a wall is deffo a no no.
 
Are you sure it wasn't split concentric cable?
Half of the outer ring of wires are insulated copper neutral and the other half are earth (can't remember if copper or steel)
Im pretty sure, is it possible to have a half concentric cable or something and it being a tncs system?
 
Unless it turns out it is armoured after all.

Is this an incoming supply cable or is it part of the installation?
Yeah this is the feed to the installation so its not protected by RCD therefore surely not allowed to be buried even if it is within the safe zone?
 
not if installed prior to 2008, when 522.6.101 was introduced. once, on a new tear's day, i drilled through a lead sheathed incomer buried behind the front door architrave. expecting a huge bill from DNO when they sent 2 wagons with 6 men out on bank holiday rate, was pleasantly surprised to be told that DNO would stand the cost of digging up and reinstating driveway and jointing a new length of about 10m, as " cable should not have been there anyway".apparantly it was originally surface and the builder who moved the door decided to bury it there.
 
I think it is just a funny shape, my friend has pictures I'm waiting on but I'm almost certain its only half. I really doubt its acceptable even within the safe zone as it can't be RCD protected. I understand that reg is only recent but I think it may have been put under the plaster after 2008?? There is no signage either but I'm curious is that cable acceptable even surface mounted?
 
Yeah this is the feed to the installation so its not protected by RCD therefore surely not allowed to be buried even if it is within the safe zone?

Are you saying it's the DNO's cable?

If so how did you get to see its internal construction?

And to the best of my knowledge if it is DNO property it cannot be buried without their expressed permission.
 
Ok so have you actually seen the cable yourself?

I think you will find it is going to be either split concentric for a TNS service or a concentric cable for a TNCS service.

Bearing in mind that if it is a concentric cable they normally gather the outer strands together and pull them to one side as a bundle. This could give the impression that they are only around half of the cable.

Either way if the cutout is in such a condition that you can see that much of the cable the DNO out to fix it.
 
It is split concentric but the neutral cores are like a 0.75mm core, would that be classed as mechanical protection? and my mistake also they have been installed after 2008.
 
So it's TNS then not TNCS?

It is a DNO cable and they operate under different rules, BS7671 is largely irrelevant to them. The ESQCR is a statutory regulation which the DNO have to adhere to.

I think you are going to need to call the DNO out to fix this bad termination aswell as dealing with it being buried in the wall
 
yeah sorry its a tns. Yeah thats why I'v posted it on here as I'm not familiar of anything outside BS7671 hoping someone with previous experience of supply cables and regs would be able to help, but thanks very much for your help, Iv already arranged the termination to be sorted.
 
There you go, it's as simple as that. The DNOs cable is the DNOs problem, if you suspect something is wrong you call them out to deal with it.

I'm curious as to what is wrong with the termination? Do you have any pictures?
 
It had been installed a long time ago but is Red, Yellow and blue phase colours, it obviously has pvc covering over the copper, then half of the circumference has steel armouring used as the neutral then another layer of pvc.




This description doesn't sound like a TN-S ''Split Concentric'' to me, ...it sounds like a concentric TNC-S. The so called steel armouring is probably tinned copper, though i've never seen bare tinned neutral copper conductors in this cable type, others here may have....
 
My best guess on it is that it is split concentric with black insulated neutrals which haven't been noticed. Bearing in mind the op didn't see it but is working on 2nd hand info. And he only saw it through a bad termination apparently, not sure what he means by that though.
 
If it’s a DNO 3Ph TN-C-S supply it will be concentric wavecon.

As for as for safe zones, RCD’s, etc. It’s got nothing to do with you or BS7671 so leave it alone.
 
My best guess on it is that it is split concentric with black insulated neutrals which haven't been noticed. Bearing in mind the op didn't see it but is working on 2nd hand info. And he only saw it through a bad termination apparently, not sure what he means by that though.

Not from the way the Opening post has been written it's not second hand info!! As far as i can see, the OP has little to no idea what he's looking at...lol!!
 

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