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?

 

[telectrix]

could be a sign that the cable has broken down and after a few months of service will finally die. might be an idea to IR all the core and armour, see if there's low insulation resistance. if it's just 1 core down, you still got 3 to play with.

 

[Darkwood]

It depends, do you need all 4 cores and is the outer sheath damaged at all, does the cable pass its Insulation tests as it could be a warning sign of a progressive problem, can you confirm is earthed up and give you a good ELI reading, lastly is there an rcd covering this cable?

Bugger tel' beat me again ... Hmmmph same advice though!

Tel'!!!! is that someone at yer door, maybe i can get a post in edgeways

 

[Engineer54]

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?

If you have conducted all the tests suggested above, and this yellow core is definitely broken then Yes, you will need to change this cable. You can bet your bottom dollar that the sheath has been compromised. Probably by a sharp stone or other sharp debris, going through the sheath and between the armouring strands on into the conductor(s), it will also mean the SWA will be corroding away. So eventually you won't have any CPC protecting this cable.

Easiest way to check this, is to disconnect this cables SWA glands at both ends from any earth contact and conduct a sheath test!! Achieving any reading on the test, will indicate the sheath has been compromised, and replacement will be required!!

 

[Farmelectrics]

if the other 3 cores are ok and you just need single phase then as long as swa tests ok then yes make sure you gland swa both ends then you have internal earth aswell as external earth ie the armour

 

[telectrix]

b&q have your answer.....

 

[Octopus]

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?

Why is a 4 core being used?

 

[ackbarthestar]

b&q have your answer.....

Good grief - Its a foot operated Gardeners screwdriver !

 

[ackbarthestar]

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?

Firstly, establish exactly what each core does, or not, and when it last worked if it ever did in the first place.

That should tell you when the gardener last visited, or not.

Secondly, establish whether or not there is continuity on each core and armour

Thirdly, establish whether there is a high IR between all the cores and armour when disconnected at each end.

If the cable has been damaged it is likely to show up pretty quickly.

I had this type of fault last year, 4-core 16mm2 supplying a garden office using only 3 cores with no armour bonding was repaired by a plumber who jack hammered through the cable when laying a water pipe. poorly jointed with a torpedo , then subsequently failed after a couple of years.
Found at least 4 joints in the run where the builder was attempting to be artistic. So I decided to run a new 6mm2 3 core cable.

 

[Guest111]

b&q have your answer.....

that ones broken,someones cut the lead off lol

 

[Engineer54]

Firstly, establish exactly what each core does, or not, and when it last worked if it ever did in the first place.

That should tell you when the gardener last visited, or not.

Secondly, establish whether or not there is continuity on each core and armour

Thirdly, establish whether there is a high IR between all the cores and armour when disconnected at each end.

If the cable has been damaged it is likely to show up pretty quickly.

I had this type of fault last year, 4-core 16mm2 supplying a garden office using only 3 cores with no armour bonding was repaired by a plumber who jack hammered through the cable when laying a water pipe. poorly jointed with a torpedo , then subsequently failed after a couple of years.
Found at least 4 joints in the run where the builder was attempting to be artistic. So I decided to run a new 6mm2 3 core cable.

If the sheath is proved damaged via a sheath test and a core is proven open circuit, then this cable is a dead duck in the water...lol!!!

 

[oldtimer]

Why is a 4 core being used?

Because thats all the spark could get out of his work lol

Anyway make sure you are testing this end to end ie no junction box under the floor also and sorry to bang on about this but more info required ie I take the 4 cores are red,yellow,blue and black plus what is the yellow being used for

 

[ackbarthestar]

If the sheath is proved damaged via a sheath test and a core is proven open circuit, then this cable is a dead duck in the water...lol!!!

You've got me there, what is a sheath test?

We are not talking Durex here are we ?

Let me see..... a 50V AC Ohmmeter generating 25A ?

 

[Engineer54]

A very simple test between the SWA and earth!! The earth can be via a test spike into the soil or any earthed metal work... Obviously any reading between the isolated SWA and earth will indicate that the PVC outer sheath has been compromised /damaged!! The simple test can be performed with a low ohm meter (my prevalence) or IR tester....

 

[ackbarthestar]

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.

If the cable installation was likely to be costly, then you could consider a Murry Loop Test. which would then identify the position of the fault along the run.

 

[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........

 

[ackbarthestar]

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.

I recon that its unlikely to be a broken yellow core in the cable but disconnected at one of the terminals somewhere,

Light blue touch paper and stand well back ......... Whoosh