Joining Armoured Cable together.

[psd99]

Hi guys,

I got my wiring done recently and one of the circuits is dedicated to my garage which is like 25 metres away from the RCD unit.

Irritatingly The RCD for the garage trips and then it will not turn back on again causing all of the right hand side of the RCD to trip. First I thought it was rain water somewhere but...

I suspect the problem is when I was turfing my garden I remember slightly nicking the armoured cable and that might be causing the trip. I think two of the cables are touching each other and causing the trip.

So it looks like I am going to have to dig up some of my turf to get to this cable and patch the cable up.

but how exactly do I re-join armoured cable together? What type of unit/box do I need that I can keep underground permanently?

Links to products would be good or names. Thanks.

 

[psd99]

so the problem I got right is how will I know exactly which type of cable I have?>

i.e 2.5mm 2 core or
4mm 3 core

what does the core bit mean just like live, neutral and earth?

 

[psd99]

thanks for the reply

I think I shall have to dig up the ground and work out where this cable is damaged it just has to be the problem.

what type of crimping tool would work? Same one as RJ45?

 

[psd99]

it also might also be written on the cable? so 2 core is 2 little cables and 3 core is 3?

I might need to actually join this up twice and buy additional cable as it will not be long enough to rejoin.

 

[psd99]

interesting replies

what happened was I was using a sharp spade and it did nick the cable
I suspect that the wires were visible inside. I know i should have taped it at the time. I wish I had.
Everything worked fine before the turf but since then it doesn't go on or just trips randomly.

I can't work out what else the problem could be, you're probably right in asking a sparky to come out but money is tight right now.

One suggestion from my friend was to temporarily run another cable from the RCD to my garage and see if that works.

If that does work then 100% I know it is the cable but I still do not know 100% exactly WHERE the fault on the 25 metre cable is! I believe the cable is damaged very close to the garage from memory within a few metres.

 

[psd99]

thanks for the reply guys that helps...

the RCD works for the garage today bizarrely

I find it hard to believe you've nicked an armoured core with a spade, are you sure it's armoured?

I'm pretty sure it is armoured. It is quite tough cable and black in colour

The steel armouring of an SWA cable should be earthed anyway. However, that steel armouring going to ground should not cause the RCD to trip, as the RCD detects an imbalance in the live/neutral phases. What is happening on the earth doesn't matter, except in that current goes there when it's not going over the neutral.

For you to have nicked an actual L/N/E conductor, I wonder if you actually have NYY (non armoured, not suitable for burial) cable not SWA.

It could also be that the RCD tripping is unrelated to this cable. Heating elements for example (cookers, sandwich makers, immersion heaters) tend to cause RCDs to trip when they are close to failure, and RCDs tend to get more sensitive as they age.

RCBOs make it much easier to fault find than an RCD covering multiple circuits.

I just find it strange how everything was good before I did the turfing. What is RCBO?

I join swa cables every day at work.

If you trust me and provide postage ill send you a resin jointing kit we use on mains cables hey are designed to be buried in the footway

Just disconnect the armoured from the consumer unit and see if the RCD stays in / doesn't trip.

If it is the cable, then the only real option is a resin torpedo joint, as stated above, but it's not an easy job for a layman and it might be easier to get a man in or relay the cable.

Just find the damage and cut it out. Hopefully there will be enough slack to rejoin the cores and earth bonding (armour) if not you may need to bridge joint a piece in between.

Thanks I might need two of these though? I will take you up on your kind offer very soon I guess I will PM you in trust thanks man certainly helps. Just trying to locate exactly which cable this is.

If the cable is armoured can you see if the metal sheathing has been earthed?

My suspicion is it has, and you have nicked the outer plastic and opened the now earthed metal sheathing to the elements.This just needs a waterproof repair as you haven't compromised the main cable just created a bridge between the metal sheathing and the outside world, which has probably quickly become damp and is conducting to earth.

If you have somehow managed to cut clean through the outer plastic, metal sheathing and some of the inner wires with one spade cut, which seems dubious as the point of this cable is to protect vs exactly that scenario, then IMO easier to just lay a new line time.

I will need to dig the ground up to see the cable first.. hopefully soon.

I'm hoping your suspicion is correct and I will just need some electrical tape. what do you reckon? only way of working this out is digging the ground up.

 

[psd99]

Just disconnect the armoured from the consumer unit and see if the RCD stays in / doesn't trip.

If it is the cable, then the only real option is a resin torpedo joint, as stated above, but it's not an easy job for a layman and it might be easier to get a man in or relay the cable.

but with the cable connected + the RCD switch ON for the the 'garage' switch on the RCD that does not seem to work for the whole right hand side
when I turn the garage off everything is okay.

- by removing this cable what do I prove?

 

[psd99]

the cable has writing on it
19069.0 2016

trying to work out what that means.....

 

[psd99]

that is all I can see

I'm going to open the junction box on the inside of the garage and show y'all a picture of what that looks like when I get a chance.

 

[psd99]

I think it is 3 core too

these are my mundane attempts at pics such a shame what they did to photoshop so using tinpic now which is as useless as some people I know!

is the 6mm the circumference around the wire?

 

[psd99]

photobucket I meant*

it seems they've put the earth together with either live or neutral not sure why
I wish I paid more attention to this when I got the wiring done in the whole house.

 

[psd99]

what was your theory again?

I was hoping you'd look at that and see something glaringly obvious like it's not been earthed that is your problem right there. shame.

got to be nicked slightly underground and needs repairing.

 

[psd99]

theory that shielding is earthed and is nicked and causing your problems, its still possible its earthed at the other end but unlikely one end would be and the other not imo

worth just checking the other end as well I guess, you should never rule out a loose wire etc before you start digging!

so basically open the whole RCD and check whether on the RCD side the earth wire is connected in the same way?

If it Is NOT the same, then what shall I do? (rather check first this than dig up my lovely turf)

 

[psd99]

ok thanks

I will check the RCD first, I bet it is wired the same way.

 

[psd99]

It wouldn't work if that was the case. If you look closely the wire that has been wrapped in earth tape (grey core), and your neutral go to different points. I thought the same as you at first glance but that is not the case.

so basically the earth wire connects to nowhere!

 

[psd99]

Thats the nastyiest looking way to terminate an armourd cable ive ever seen!

If you have a volt meter disconnect the cable (both ends) and check the resistance of all the cores to earth one by one. And then check them all to the armour one by one. And if you still dont find anything check between eachother

We test with a megger at work (500/1000v) to earth but you should hopefully be able to see if someings fubar with a normal meter.

And yes 6mm is the conductor size, will be 1.5mm armour.

Where are you located out of interest?

cheers mate sent you a message in trust.

 

[psd99]

hi well the electricity in the garage has been okay last few days
even when it rained so heavy!

I find this a strange situation

actually the installation for this wire could have been a lot worse.

I was in a situation where there was so much works going on and little things like this got missed out
I actually had a lot of paving/turf that I would do myself almost 6 months later, therefore wherever this cable was did not make a difference to me at the time.

Anyways I don't know what I'm going to do yet but thinking of digging some of the turf up next time it won't turn on to see if the cable has been nicked or not in a place I suspect it has happened.

 

[psd99]

Where exactly is that jointbox?

It looks to me it's open to the elements and certainly not IP rated. I wouldn't be suprised if the amount of crap and debris within that JB is causing a low insulation resistance between the cores which will most certainly trip a RCD out.

Either way, as said above, it's a proper mickey mouse installation.

I will clean the junction box out tonight properly.

just found it weird how everything was good before the turfing now not so great (except all this week when the circuit started to work)

 

[psd99]

So, there are a number of devices in your consumer unit.

MCBs: Each circuit has an MCB - Miniature Circuit Breaker. This has a curve type (A, B, C etc, usually B Curve for home) and an Amp rating (e.g. rings on 32A, etc). It will trip out if too much current passes through the live.

RCD: Commonly twice the width of the above, has a test button on it, and measures the balance in the live vs the neutral. A difference over the rated allowance (usually 30mA) between live and neutral, and it trips. Has a test button on it. Effectively, this device is looking for the same current going out of live to be coming back in via neutral. If some current is going elsewhere (down the earth, through your leg, whatever) it trips. These usually cover multiple MCBs, and, crucially, any leakage will cause them to trip. So for example, you might think "it must be the garage, because even when all the other MCBs are off it still trips" but even if you've turned an MCB off, that's only isolated the live for that circuit. So some device with a short between neutral and earth that is currently completely unpowered on a circuit that is off, could still cause the RCD to trip.

RCBO: RCBOs combine the functions of an RCD with an MCB, and are the width of an MCB. They are newer and more expensive (£30 each rather than £3-4 each) but by having an RCD for each circuit, a fault only takes out that circuit and doesn't leave you sat in the dark.

Personally I like to have RCBOs on everything, it makes things much easier.

In any case, as long as the live and neutral are intact, what you have or have not done to the earth is irrelevant and won't trip the RCD. The RCD will only trip if there is a difference of current going out the live vs coming back in the neutral. Nicking the SWA cable and exposing the armour (which should be earthed, but isn't in your image, although might be at the other end) CANNOT have caused the RCD to trip, unless you hit it so badly that you went through the armour.

Thanks that is good to know

the main purpose of getting electricity to the garage is for the fridge that I will put in there eventually.

so what is your theory in all of this?

 

[psd99]

yes that is possible

well I got the electrician on the phone earlier he is going to check this out
hopefully he will troubleshoot this and see if he can work out why that trips! Let's see!