Voltage reduced to zero when load is applied.


Postby Masheded » Tue Aug 03, 2010 9:24 pm

Ok here goes,

Whilst doing some diy at a friends house i hit a mains cable feeding the 1st floor lights (i know, no need to say it). The fuse box is of 1960 manufacture if not earlier, and is the sort that takes the bacolite fuse cartridges using fuse wire. I must stress now that i have no electrical knowledge, and other than removing and replacing electical furniture whilst plastering etc i do not intend to undertake any works myself, and would give this advice to anyone with-out training. With that out of the way, i have removed the plaster around the cable and have exposed the damaged section. I have joined the cable using a certified junction box from my local hardware store (the round type), as i feel this is within my capabilities. The cable in question was running to/from a light a switch. It has 4 cores (incl earth). In general, the cable through-out the house is pvc, but it has been added to here and there over the years resulting in a very complex mish mash of cable. I then replaced the fuse wire in the main fuse box which was blown. I turned the lights on and..nothing. 1 light on the 1st floor and 3 lights ont the 2nd floor dont work. As far as i can tell, everything is as it was. I have replaced the bulbs with new bulbs and still nothing. I have checked the light sockets with a neon screwdriver, and they show voltage, but when i turn them on...nothing. I have done all i am prepared to do, and am calling a sparky to take a look. My question is, how serious an amount of damage could have been caused? Is it possible that other cables further on are damaged, or is it likley to be the fuse box damaged. To be fair he needs a new 1 anyway, and i have just plastered 2nd floor, so rerunning the whole loom will be a nightmare.
Please advise with some idea of the cost if poss.
Thanks in advance
Masheded
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Postby ericmark » Wed Aug 04, 2010 5:51 pm

With some of the old type rewireable fuses it is easy to break the wire inside the tube. When the fuse blows it can leave a coating which is enough to conduct a very small amount of power enough to light a neon.

The round junction boxes are not suitable for use inside a wall. You need maintenance free type.

Three core and earth means likely part of a two way switch and it should not affect other lights.

The problem is not the damage you have caused but if the regulations will allow reconnection of the circuit. It is an odd situation but we are not allowed to make a property uninhabitable so does not matter what we find on an inspection we can't just turn off the power. Same applies with gas. To turn off the power the council would need contacting and some alternative accommodation would need finding. However where the power is already off we can't power up where it may be dangerous so where the installation is sub standard it may need bringing up to standard first.

Old fuse boxes often have asbestosis and the old option is to change whole box.

As a result to try to guess on costs is very hard. I would say this is one of those times to claim on your insurance.
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Postby NETTY » Fri Aug 06, 2010 11:20 am

From your discription you are not realy checking that you have 240v across the live and the neutral. If you infact have 240v on the live conductor and the light is still not comming on, then you have lost the neutral connection.
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Postby Masheded » Wed Aug 11, 2010 2:08 am

Thanks guys...

Ive had 2 sparkys look at it now, theyve tested it for free (gentlemen) and walked away. They have said its such a confusing set up, to test it all could take a couple of days to work out what goes where, and it still could be somthing else, and i got the impression its "one of those jobs" sigh. Looks like its a rewire for these lights and the ball ache it entails. To anybody reading these posts, i say this:

if i had of used the proper metal/pipe/wire detecting apparatus before i drilled this hole, not only would i not be writing this now, but i wouldnt have risked the ability to ever write again. Luckily i was using a high quality makita "cordless" drill, which i understand its a lot easier to kill yourself with, especially when your dealing with the kind of property i am. This is a mistake i will never be repeating. Even though i adhered to the so called "safe" perimiters around entry/exits and cielings, i still paid for not making simple checks.
Unless you did it yourself..question and check. This has cost me, but luckily it was only time and money.

Thanks eric and netty.
Ill let you know how i get on.
Atb
Mash
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Postby ericmark » Wed Aug 11, 2010 4:32 pm

Sorry to hear of your problem but we all make mistakes.

I was installing a new fridge freezer that needed a water supply. The loo was just above it so tapped together two hack saw blades with a spacer and started to cut a pair of cuts ready to knock out the plaster between them.

I went through the cable going between the original light switch and one in kitchen extension I had not even thought that anyone would take the wires horizontal between the two without any capping. But that is allowed with regulations.

I was lucky that all electrics in my house are protected by earth leakage at 30ma but although less than 40ms in length it still hurt. Mainly my pride.
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