SWA continuity

[RobMax]

A 4-core SWA cable laid to supply power to a garden room is not functioning - on doing a continuity check I have established that only 3 of the cores have end to end continuity but the fourth (yellow) reads as an open circuit.

Will this mean a new cable?

 

[Octopus]

What test equipment do you have?

 

[Engineer54]

I think that would depend which end of the SWA is measured to earth, presumably, at the MET? If measured at the 'other end you would be measuring the resistance of the armour.

How's that then?? your testing between totally isolated armouring and earth!! Any reading will indicate that the PVC has been damaged and allowing moisture into the cable. The fact that continuity has been lost on one of the core's indicates severe damage. The cable needs replacing or if at all possible, repair jointing at the damage point...

 

[ackbarthestar]

What test equipment do you have?

Not a Murry Loop tester, that's for sure, although I can get hold of one if need be.

Although its not beyond me to make up a whetstone bridge using basic components.

 

[ackbarthestar]

How's that then?? your testing between totally isolated armouring and earth!! Any reading will indicate that the PVC has been damaged and allowing moisture into the cable. The fact that continuity has been lost on one of the core's indicates severe damage. The cable needs replacing or if at all possible, repair jointing at the damage point...

The OP has not stated that the SWA has not been bonded to the MET. So one would assume, as good installation practice that the SWA is grounded at some point.

 

[Engineer54]

No, .... Read back a bit. I'm saying that to do a sheath test, the SWA needs to be isolated from all earths...lol!!!

 

[Knobhead]

Finding the damaged section is liable to cause more damage going on past experience. Give a couple of lads a pick and shovel each and await the devistation.
Just replace the cable. OK it's the cowards way out, but saves a lot of grief!

 

[yellowvanman]

Surely if the cable was damaged the a protective device would have been tripped - I am assuming that the cable was live at one stage.

 

[ackbarthestar]

Surely if the cable was damaged the a protective device would have been tripped - I am assuming that the cable was live at one stage.

Not necessarily, I've been called out to fix a damaged circuit to find that it had never worked, because when the present owners bought the house never bothered to have an electrical survey done

 

[Knobhead]

We haven't a clue what cores are used and what aren't, as usual the OP hasn't given any information.

Given a broken core the outer serving is liable to be damaged. The sheath test would proove this, but without some input from the OP we may as well give up!

 

[Octopus]

Need more information!!

 

[oldtimer]

Need more information!!

Yep this getting silly and yet again little or no information a lot of guys speculting trying to help out and we will never get to hear the end of it or we might get I sorted it comment

 

[Octopus]

Yep this getting silly and yet again little or no information a lot of guys speculting trying to help out and we will never get to hear the end of it or we might get I sorted it comment

what I find difficult is the fact that the OP was able to isolate the 4 cores and establish that 1 appears "broken". Surely such investigation would also confirm how they are connected, what to and what for!!

 

[RobMax]

Sorry about the delay in responding to your further queries - was called away.

The cores provided a ring circuit with red (live) and black (neutral) with the return being yellow (live) and blue (neutral) with the armour providing CPC. We moved in a couple of months ago and have not used the garden room - I plugged in a fan and it tripped.

On testing the cores and the armour there is continuity in all but the yellow core. I have tested the IR and that is good although not clear - reading 140 mohms - used a Megger MFT.

My thoughts are to convert to a radial and reduce the protective device from a rating of 32A to 16A.

 

[Engineer54]

Sorry about the delay in responding to your further queries - was called away.

The cores provided a ring circuit with red (live) and black (neutral) with the return being yellow (live) and blue (neutral) with the armour providing CPC. We moved in a couple of months ago and have not used the garden room - I plugged in a fan and it tripped.

On testing the cores and the armour there is continuity in all but the yellow core. I have tested the IR and that is good although not clear - reading 140 mohms - used a Megger MFT.

My thoughts are to convert to a radial and reduce the protective device from a rating of 32A to 16A.

That would be pointless, as there must be a reason why you have an open circuit on the yellow core. All indications point to cable damage and if damaged, then your armour CPC isn't going to last too long as it will be corroding away!! Who knows what other damage has been done to this cable??

You will need to replace the affected section of cable, if it's a ring circuit i'm afraid!!!

 

[telectrix]

we.--ell there i was, digging this hole, hole in the ground, so big and round........