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Can You Join Armoured Cable ????


 
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julea field

from United Kingdom

Joined: 28 Dec 2006
Posts: 11
Location: Hertfordshire,
United Kingdom

PostPosted: Mon Aug 06, 2007 5:44 pm Reply with quote

Hi All you DIY's

New to this, so hope I explain myself OK. We have armoured cable 2 core laid about 27 years ago running underground for 100ft from our house to our garage at the end of the garden.

Last weekend all the power went the garage, no lights and the one and only double socket on the wall was dead. First thought was the MCB on our Protues CU board had tripped, but it hadnít. Then checked the two fuses in the garage on a separate fuse box, not blown either.

Called my stepson who is an electrician albeit he is still in his early days, but has better knowledge than me or my husband. We ask him what the test button on the RCD on the main CU in the house is for, he suggests pressing it to test if the RCD trips, we press it and nothing happens. So he then suggests turning off the main RCD manually then turn all the mcbís off, switch RCD back on and then one by one turn each MCB back on. Well that was a great idea, except the main RCD wouldnít go back on. Anyway I wonít bore you with any more info on that. We came to the conclusion that our 19 year old Protues board needed changing as we were unable to locate a replacement RCD due to its age.

Had an electrician come out last week (not stepson) as he lives in Wales (250 miles away) unfortunately, to fit a new CU. I bought a Moeller split load board and the electrician fitted it knowing we had this fault with the garage circuit. After fitting the new board the main RCD would trip out as soon as the mcb for the garage was turned on ( the mcb for the garage stayed on though). He did a few tests then left saying he didnít have enough time to check it out any further, nor did he have a special tester to check for live power running straight through the cable from end to end. Plus we didnít know where under the floor in house the junction box would be, as the cable size in the garage was different from the size terminating at the CU, so they must be a join in the cable somewhere.

I had a good idea where the join would be and the next day had the carpet and floor boards up. Sure enough there was an old metal JB with the armoured cable going in. Took the lid off and ran various tests, i.e., disconnected all the three wires of the armoured cable from the block connector in the JB, then turned the power back on. Main RCD didnít trip, connected earth an neutral back up, didnít trip, disconnected all 3 wires at garage end and then put the live wire back in at the house end and it tripped. Swapped live & neutral around in JB and it didnít trip, so now we think that somehow the live cable inside the armour has suddenly started to short out to earth.

This cable was disturbed about 5 years when we landscaped the garden, but it was buried again under concrete and has been fine for those last 5 years. The thought that this cable might be faulty is giving me nightmares, there is absolutely no way we can ran another cable in its place. The garden is now concrete slabs and bricks walls and then the last 20ft itís under a concrete car port we built. It would also be very hard to run another cable taking a different route underground, it would have to be above ground which I believe is OK. If we dig up the old cable which is possible for about 10ft , where the cable is running under grass, can we join a new piece of cable if we discover the fault is beyond the cut we make ?????.

Sorry this is so long just need to put you all in the picture.

Why would this fault just develop like that anyway, has anyone else known of armoured cable getting a live fault whilst undisturbed buried in the ground for years. The only other thing that keeps bugging me, but sure itís just a coincidence , is that the night before it went out , we had an extension lead running out the garage running a radio, it started to rain so after 15 mins unplugged the radio and moved it else where. We left the extension lead out in the rain for a further 45 mins before putting it away in the garage. Next day plugged the extension lead in to a car charger then hours later noticed the car charger was off, discovered the 13a fuse in the plug of the extension lead had blown, changed the fuse,plugged car charger back in, it worked for 2 seconds then went off again. This is when I discovered the socket on the garage wall wasnít working and you know the story from there.

So, can we double check the cable is US, if so can we ran another one above ground, or join the old one with new cable if we can find the bad bit to eliminate.

Hope you can help need electric up the garage 24/7. Car battery is now in my kitchen on charge all the time. Its off our car that doesnít really go anywhere, sort of an old classic so the battery needs to be trickle charged all the time.

Thanks all lot for reading all this.

Julea
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Lectrician

from United Kingdom

Joined: 18 Jul 2004
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Location: Devon,
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PostPosted: Mon Aug 06, 2007 5:50 pm Reply with quote

When you turn off the switch in the Consumer Unit in the garage and then try turning on the RCD and MCB at the house, does it them trip?

I would be suprised if it is the cable - it certainly could be, but more than likely it is going to be a fault in the garage causing the RCD to trip.

An RCD trips for a different reason than the MCB, which is why that doesn't trip.
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julea field

from United Kingdom

Joined: 28 Dec 2006
Posts: 11
Location: Hertfordshire,
United Kingdom

PostPosted: Mon Aug 06, 2007 6:36 pm Reply with quote

Thanks for the reply,

The fuse board in the garage was turned off at the time. We then went one step further and disconnected all 3 wires out of the board in the garage, so the armoured cable in the garage was now just in mid air not connected to anything. still trips RCD in House when the garage mcb in truned on. But it doesn't trip when the live & neutral wires are reversed in the JB.
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industryspark

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PostPosted: Mon Aug 06, 2007 7:44 pm Reply with quote

have you tested insulation resistance of the underground cable?

and yes it is possible to joint swa cables
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ricicle

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PostPosted: Mon Aug 06, 2007 7:46 pm Reply with quote

Did your electrician own a horse ?
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industryspark

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PostPosted: Mon Aug 06, 2007 7:58 pm Reply with quote

ricicle wrote

Quote:
Did your electrician own a horse ?


icon_lol.gif icon_lol.gif
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julea field

from United Kingdom

Joined: 28 Dec 2006
Posts: 11
Location: Hertfordshire,
United Kingdom

PostPosted: Mon Aug 06, 2007 8:20 pm Reply with quote

Must look out for sugar lumps in his pockets when he comes round on Wednesday.

I also spoke to my stepson again tonight who asked if this electrician had given me a test certificate for fitting the CU. Well he didn't , isn't that a surprise, perhaps his horse ate it. Or perhaps because the job is not finished he didn't issue one. But there again I didn't say I would call HIM once i had found the JB for the cable , I could have called someone else.

Haven't tested the resistance on the armoured cable ,not sure how to do this and what am I expecting to find from this test please ???.

Thanks again

Julea
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Adam_151

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PostPosted: Mon Aug 06, 2007 10:21 pm Reply with quote

Insulation resistance is a test thats done using a special IR tester which tests at 500v (in your case, [250v and 1000v are also used for different things]) it tests the resistance of the insulation of the connductors to see if its 'down' or not. Generally looking for at least 2meg ohms (in your case).

Unfortunatly as it uses a special tester you probably won't be able to do it, but I'd have thought your electrician would have done so, doesn't take too long (tracking down where the problem is can take a lot longer*)



*and there is special kit for that that can tell you how far along the cable there is a problem, that not even your electrician is likely to have on the van!
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Teahead

from United Kingdom

Joined: 04 Jan 2007
Posts: 37
Location: Huntingdonshire,
United Kingdom

PostPosted: Tue Aug 07, 2007 2:00 pm Reply with quote

Hate to state the obvious, but did you unplug the extension lead that got left out in the rain, or is it still plugged in and soaking wet causing the RCD to trip.

I'm not an electrician so it might not be the cause but i didn't notice you state that the lead had been removed, only that the battery charger is now in the house.

Would an RCD trip if all the wires at the garage end are disconnected? as i thought an RCD measured the difference between the earth and neutral to enable it to work which is why it didn't trip when earth and neutral were joined as this completed the circuit


Last edited by Teahead on Tue Aug 07, 2007 4:27 pm, edited 1 time in total
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CallEdsFirst

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Joined: 17 Apr 2006
Posts: 355
Location: Cambridgeshire,
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PostPosted: Tue Aug 07, 2007 2:38 pm Reply with quote

an RCD measures an imbalance in Live and Neutral. If they are both at "idle", no imbalance! Would an RCD hold if there was no current whatsoever? I suppose it depends on whether it was active/passive. Can you get both versions for CU? Not that I have ever seen!
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Tim 77

from United Kingdom

Joined: 13 Feb 2007
Posts: 565
Location: Nottingham,
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PostPosted: Tue Aug 07, 2007 6:32 pm Reply with quote

julea field wrote:
Must look out for sugar lumps in his pockets when he comes round on Wednesday.



Ask him about Part P tomorrow too, see what he says.
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julea field

from United Kingdom

Joined: 28 Dec 2006
Posts: 11
Location: Hertfordshire,
United Kingdom

PostPosted: Tue Aug 07, 2007 8:40 pm Reply with quote

Teahead

Yes the lead in not plugged in, in fact the extension lead was quite dry the next day when I changed the fuse. The garage end of the armoured cable is currently connected to nothing at all, all three wires have been unscrewed from the fuse board and are just hanging in mid air.

Tim.

I will certainly ask him for a test certificate if he fixes the problem. What would the right question be to ask him about part P. I know it was a change in the law 1st Jan 2005, but what is part P. Is it a test all sparky's had to take and now have a ceritificate to prove they are part p qualified ???.

Thanks for all your help. I'll let you all know the out come tomorrow.

Cheer Julea
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securespark

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PostPosted: Tue Aug 07, 2007 8:50 pm Reply with quote

CallEdsFirst wrote:
an RCD measures an imbalance in Live and Neutral. If they are both at "idle", no imbalance! Would an RCD hold if there was no current whatsoever? I suppose it depends on whether it was active/passive. Can you get both versions for CU? Not that I have ever seen!


IIRC, the early MEM ones used to trip on loss of power.
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