Discuss Fault finding outside lighting - high tuff cable in the Electrical Forum area at ElectriciansForums.net

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J

jjnr78

Hi all

We have just been to look at a fairly new outside lighting install which is experience nuisance tripping. The installation is actually to a v good standard, but its fairly large, so i though i'd try and do some research before we spend hours pulling it apart. All joints to light fittings are done with surface wiska boxes which are above the ground and the supplies are in swa with external glands. However the fittings are connected using hi tuff cable. In some areas of the install ie around the patio, in walls and bedding, this high tuff is in the ground. Is this cable very permeable? With a little inspection, there doesnt seem to be much moisture in the fittings etc and its separated across a few circuits, but if there is a problem with this cable, it would make sense. Has anyone experienced this before. I have been caught out with using flex in ducts before (ducts filled with water and permeated the flex), so we started using water proof flex used in fountains etc.
Any thought appreciated.
thanks
 
IR readings???? split in half. IR each half. split again. unprotected cable should not be buried. could have been damaged.
 
You do not say what is tripping is it an RCD or an MCB?
They will require different approaches to fault find so I cannot give detailed responses.

Hi Tuff is OK for outside use but not really suitable for direct burial. Then again if it is undisturbed I would not expect it to cause this problem.
I would check if the glands are made off correctly.
Check the loading of the lights compared to the breaker, initial switch on surge may trip a breaker.

Then start testing as Tel says.
 
HI. Yeah, as i said we haven't committed too deeply just yet as i was looking to find out if the wiring system was incorrect. The high tuff is only buried for a very small section. it is however loose laid under decking, so susceptible to the elements. i'm experienced in the practical arts of fault finding, but dont know too much about this high tuff stuff. thanks
 
if undamaged, it's unlikely to be the hi-tuff cable.
 
Sorry. i haven't been there. Here's a little more info:
1 RCBO device protecting 25 1/2 watt led lights; spike lights and surface wall lights.
Every light has been wired back individually to a big IP rated adaptable box and the gland assemblies look good.
There are no joints except that spike lights have been heat shrunk onto the high tuff
The high tuff is buried in a trough for about 20", then loose laid
The feed is clear, but all by one of the 25 loads is measuring as little as zero Mohms IR.
Given the high number this is why we are suspicious that its the cable. Vermin could be the cause, but to chew through 24 out of 25 cables?
With these LEDs loads, there is no heat being pulled through the conductors, so there is never any drying effects.
To replace the cable would be an absolute nightmare.
if this high tuff has a high permeability then it will need to be replaced. this would however lead to more joints as one would have to use swa, which you cannot use to directly connect these fittings. thanks
 
Rcd, mcb, you still need to take lamps and control gear out and get (noseying)

- - - Updated - - -

There's nothing wrong in taking few hours to fix fault if needs be..
 
Thanks guys. i fully appreciate what needs to be done. My question is; has anyone experienced water ingress with high tuff cable?
 
see post #5.
 
first you need to determine if it's the RCBO tripping on overload or earth fault. get a clamp meter on the job and measure the load. then see if there's leakage using earth leakage clamp meter.
 
do insulation resistance test between l+n joined and earth, should give you some idea whats up with the cable...
 
You say 24 of the loads are reading 0 Mohms, however which cores are you measuring between?
Agree with Tel about Hi tuff and finding out if it is high current (line to neutral fault) or high earth leakage (line or neutral to earth fault).
If you test as amlu says then these readings should be high and if so this reduces the likelihood of an earth fault.

If you IR test line to neutral you will get a low reading (and may fry the LEDs).
Is it possible to disconnect the LEDs inside the fitting and so permit a full IR test of the cable (L to N, L to E, N to E)
If you are getting low IR have you tried a continutiy test instead, if this gives you a reading then it is likely that the problem lies there.


If the Hi tuff is heat shrunk onto the spike lights, is this joint 1) buried at all 2) sealed i.e. is it glue lined heat shrink or just heat shrink.
Certainly a cable joint outside,e specially if buried and just sealed with non glue lined heat shrink could well leak.
Can you tell what sort of joint it is through the heat shrink?
 
always split the circuit in half and meggar it, the quickest way IMO, otherwise your chasing ghosts, basic stuff really, I expect a choke or capacitor has melted and shorting out the wires, if the circuit is as large as you say then break it in half.
 
always split the circuit in half and meggar it, the quickest way IMO, otherwise your chasing ghosts, basic stuff really, I expect a choke or capacitor has melted and shorting out the wires, if the circuit is as large as you say then break it in half.

Thanks for all the help. Perhaps i shouldn't have posted at this stage. i'm very experienced in fault finding and therefore know the usual procedures and what an ordeal it'll be to pull everything apart (heat shrunk joints- not easy) and then put back together. There is no over load issue and the testing has been performed L/N to cpc thus far. We are due to return to site soon, but we are very stretched so i was trying to discover whether high tuff was the wrong choice of cable as it allows an ingress of water. i've seen it with other types and we use rubber pond/ fountain flex. this job looks well put together, so my thoughts were to rule out whether the cable was the culprit. I'll batch a few loads and test across all conductors with the loads disconnected and gauge from there.

i do however appreciate the assistance. cheers
 

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