SWA failure.

[defadog]

Having removed the faulty junction as discussed in previous thread I wanted some advice on bast approach to rectification.
As discussed, 16m swa goes from hose to garage to shed. Garage about 60m as the cable runs...no voltage drop at all. But at the now open wires, measured with no load, meter reads 199 L to E, 150 L to N. This suggests a neutral fault?
I temporarily protected the bare cable in a waterproof box (power is off but just to be sure!). When I opened the box to put the CAT signal generator on, there was water in it...can only have come from the cable itself.
I mentoined in previous thread that conductors were green, even between the strands in the core. So water has got in. I assume it is from the destryoeed joint, and about 2m beyond this point the land rises steeply. Is it likely this water damage will be restricted to one spot, and would itcause the 10K resistance I measured?
Current plan to dig out at this point, cut cable and test again...or am I wasting my time and new cable required? Any advise welcome at this point!

 

[DetlefSchmitz]

But at the now open wires, measured with no load, meter reads 199 L to E, 150 L to N. This suggests a neutral fault?

If those are volts, and you think the other end is powered, then at least two wires are open circuit. As I said before, to see what is really there you need a lower impedance at the meter. Comparing stray voltages has no future.

 

[conny]

Water can travel uphill as well as down hill due to capillary action. This is particularly true if the cable is stranded wires.
I'd stop all the faffing and run a new cable in, making sure you keep both ends sealed until you are ready to terminate them.

 

[bernardgreen]

Is it likely this water damage will be restricted to one spot,

If there is water in the cable then replace the whole length.

to see what is really there you need a lower impedance at the meter.

A quick and simple way to create a ( relatively ) safe low impedance across meter probes is a 230 volt incandescent lamp in a holder with insulated croc clips to clip on the points being measured. A ten watt lamp is adequate.

 

[JohnW2]

Water can travel uphill as well as down hill due to osmosis.

I don't see how osmosis can come into it - I suspect you're thinking of 'capillary action', which can certainly allow water to travel uphill in situations such as you describe.

Kind Regards, John

 

[defadog]

Thanks for the hint on the incandescent lamp. Will test again. As for replacement..it has only failed recently...and I suspect that the culprit is a sycamore that would not have been there when the cable was laid. Traced the cable this am - passes within 2 feet of it. So I will try one more inspection about 5m uphill (steep uphill at that) from the tree...if that fails, will lay a new cable. Will let you know what I find.

 

[RF Lighting]

It definitely sounds like you have a failed joint. I hope you can find it. I’d be interested to see it whether the cable is salvageable or not.

 

[conny]

I don't see how osmosis can come into it - I suspect you're thinking of 'capillary action', which can certainly allow water to travel uphill in situations such as you describe.

Kind Regards, John

You are quite right John. Must have had a brain seizure. LOL

 

[EFLImpudence]

Perhaps it was osmosis.

 

[chivers67]

If you know someone who has a time-domain reflectometer (TDR) it might pin point if there's another joint or issue?

 

[dannyboi2003]

I think the issue is more likely at the garage end where the cable to the garage has been spliced into to supply the former pump house, or does the supply cable for the pump house originate from within the garage (fed from garage consumer unit)? Reading your previous post its a little unclear which. If its been spliced underground from the garage feed i would find that splice and asses its condition. If the previous splice is anything to go by that will likely be your issue. They may not have cut the garage feed to splice into it which is why you still have working power there, however if its compromised it needs sorting as it will only be a matter of time before it starts tripping/blowing fuses at the house end.

 

[defadog]

Therein lies an issue. The splice is located, but my guess is that the house to pumphouse was the original run, then garage spliced in, then shed. Given that garage supply is sound, I am loathe to dig up the join...it is under a path and rockery! I also noticecthat garage and pumphose cable is 16mm...shed splice was small three core, and clearly original joint was broken to add it.
As for TDR...sounds like something out of doctor who!
I will investigate and let you know what I find.

 

[dannyboi2003]

Let us know how you get on, we all love an ending to the story even if it’s not a good one. By all means dig by the tree but I suspect the issue lies at the splice to the garage and if you want to restore power to the shed fixing that splice will be your only solution. If you’re lucky you may be able to cut back the SWA from the failed splice back to good cable, fit a straight through splice with a proper Y splice For the garage and you should be back in business. Look forward to the update

 

[defadog]

Tested with inandescent lamp..not good. 200v L-E, 70v L-N. Tried 5m uphill. Good news, cable clean and bright, no evidence of moisture, bad news, same result. So I guess dannyboy is right..need to expose the splice. Will probably take me a week to get to it! Sigh!

 

[defadog]

Ok, think I might have found the problem...