Dead Short

[Electroglow]

hello.

thoughts please....

today we have 2nd fixed a lighting circuit. all ok until we connected the 4 way switches... and suddenly 230V goes down earth...

any way one of the 3 cores has a dead short on it about 0.45ohms. me thinks a screw.

property has been plastered and painting and they don't want any more mess.

now.... i have explained we need to replace the cable or find exactly where the fault is and join extend ect.

but if i disconnect the earth from both ends and put them in a block. this then means that cable will have no earth.

but at every point there is a contuinous path to earth from switches and fittings.

so there for what would you do.... ????

i know the best thing would be to replace the cable but you know how it is

 

[Sidewinder]

Sort it correctly & back charge the culprit!

 

[Marvo]

You must replace or repair the cable. The other options you have in mind are not safe/bordering on downright dangerous..

 

[Electroglow]

umm not really down right dangerous..... if i leave a note at each switch and in the CU.

what else can i do if the client doesn't want their wall ripped to peieces

 

[steptoe]

umm not really down right dangerous..... if i leave a note at each switch and in the CU.

what else can i do if the client doesn't want their wall ripped to peieces

are you being serious?

you want to disconnect the earth and leave a note, and you think that would be OK?

:shakehead

 

[steptoe]

umm not really down right dangerous..... if i leave a note at each switch and in the CU.

what else can i do if the client doesn't want their wall ripped to peieces

refuse to energise due to someone else damaging the cable and leaving it dangerous.

 

[Electroglow]

ok just to check... i no I'm correct in saying that if i have a short of 0.4ish ohms then it MUST be a screw

230 down earth with both ends disconnected... it a good short as well

 

[Apache]

ok just to check... i no I'm correct in saying that if i have a short of 0.4ish ohms then it MUST be a screw

230 down earth with both ends disconnected... it a good short as well

Could be a crushed cable, any number of things. Find the fault and then you will know.

 

[steptoe]

ok just to check... i no I'm correct in saying that if i have a short of 0.4ish ohms then it MUST be a screw

230 down earth with both ends disconnected... it a good short as well

as Apache says, until you find the actual fault then you cant be sure what it is,

and it shouldnt actually take you very long to find it as you know the cable route already.

simply find the fault and fix it.

either do it properly or untie your horse.

 

[SPECIAL LOCATION]

hello.

thoughts please....

today we have 2nd fixed a lighting circuit. all ok until we connected the 4 way switches... and suddenly 230V goes down earth...

any way one of the 3 cores has a dead short on it about 0.45ohms. me thinks a screw.

property has been plastered and painting and they don't want any more mess.

now.... i have explained we need to replace the cable or find exactly where the fault is and join extend ect.

but if i disconnect the earth from both ends and put them in a block. this then means that cable will have no earth.

but at every point there is a contuinous path to earth from switches and fittings.

so there for what would you do.... ????

i know the best thing would be to replace the cable but you know how it is

Lets look at the facts......

a live conductor and an uninsulated protective conductor are making contact somewhere at less than 0.5ohms.......

So disconnecting the terminated ends of the said cable....

WHICH STILL LEAVES...

a live conductor and an uninsulated protective conductor making contact somewhere at less than 0.5ohms.......

So when the live conductor goes 230v..

we now also have an uninsulated bare conductor running the length of the cable at 230v as well!!!!!

Now put it to the vote:-

Q1/ Safe OR Unsafe ????

Q2/ Cowboy OR DIY OR Electrician ????

May be best to ring an electrician to give the customer a safe installation !

:shakehead :shakehead

 

[Sharpend]

Why is it that modern electricians are happy to bow to the customers every whim? As stated the cable is now dangerous, you TELL the customer it's dangerous and will not be energised until it is made safe, either through repair/replacement or disconnection.

Get some back bone, safety rules not the customer. Would they be happy to have a gas pipe with a pin hole in it? Or a car with leaking brakes?

I'm so fed up with hearing lame excuses of why something shouldn't be fixed that is dangerous/unsafe, because the customer doesn't want the hassle. If the friggin customer knows best why did they employ the services of a so called professional?

Either do the job properly or don't do it at all.

It seems to me that the trade, if that's what it can be called, is being over run by people who have little understanding of the basic principles of being an electrician, but believe they can make a better than average wage.

 

[Barx]

Lets say it is a screw, and said screw is still in place. You disconnect cpc at both ends and walk away...

You then also leave a Live screw hanging out the wall or in a floorboard for someone to stand on.

Get the boards up and check the cable. Is it in capping / conduit? could you pull the cable up with another drawn in behind it?

However you go about it, please don't just leave it. You putting lives at risk.

 

[ProDave]

+1 to all the above . Find and fix the fault is the ONLY answer.

Presumably it's plasterboard then skimmed? where else would the offending screw come from?

Or is it capping then plaster, in which case YOU might have put the nail through your own cable.

Ask another question. If it was a leaking pipe, what would the plumber do:

a) fix the leak

b) fit a pressure reducing valve so at reduced pressure it didn't leak any more.

If you really really really can't replace it, then are there any options to reconfigure the lighting, i.e make it so the light controlled by the damaged cable was switched from fewer places. the customer might find that preferable to ripping the place apart.

Otherwise think carefully where it is possible to have damaged the cable. It might turn out to be somewhere more accessible like under a floorboard.

 

[SPECIAL LOCATION]

Why is it that modern electricians are happy to bow to the customers every whim? ........

...... Either do the job properly or don't do it at all.

It seems to me that the trade, if that's what it can be called, is being over run by people who have little understanding of the basic principles of being an electrician, but believe they can make a better than average wage.

+1

Its all down to communiaction me thinks...... :|

But then agian... With the customers hat on.... they may say;

• Possible the installers have be negligent not full testing before they get to the point of enegising...?
  
• Could the fault have been spotted earlier?
  
• Is it 100% that the damage was cause by "other trades"?
  
• Has the job been rushed on a low budget or tight deadline??
  

So the contractors should pay for the remedial works!

Were the cables tested after first fix to ensure there was no damaged bits?

We are supposed to install our wiring systems with adequate protection for external influences...

(inc other trades and services)...

reg's 522 pg 123 onward!

:C

 

[kerching]

You know the cable route

IF it is a dead short then it is not rocket science to calculate the resistance to the fault so the fault distance can be calculated.

IF it is not a short of negligible impedance then you have a bit of a problem

IF it was me I would test it with my TDR andd find 'distance to fault' then repair or replace

If client refuses then get them to write to their insurers and explain the situation to them..................then they WILL have problems!

 

[Andy™]

umm not really down right dangerous..... if i leave a note at each switch and in the CU.

what else can i do if the client doesn't want their wall ripped to peieces

so you think leaving an uninsulated conductor live at 230v is not in any way dangerous?

either isolate cable, or fix it

 

[betty swollocks]

I've had this exact situation on an extension

It had been 1st fixed but then the customer decided that he needed three separate switches 2way switching

So even as the boarders and plasterers were doing their bit I ran in 3x3cores+e in

During 2nd fix testing it was shown dead short between 2 cores and earth in two of the new strapper cables

The plastering was finished and the room painted at this point so i told the customer the choices were that

1) the faults were found and repaired

2) the cables were re-ran

3) they forgot about 2way switching

4) we left them as they were, live, in the wall and terminated safely! in each switch box ( just kidding )

After a week of ranting followed at me & the builder before i went back and found the fault

Directly above one switch as the cables entered the roof void a noggin and brace had been added and one screw had trapped/nipped two cables between brace and joist

The builder blamed the roofer the roofer blamed the builder but i felt it was a lack of care as the void/space meant it was actually harder to hit the cables than miss them

Simple cut n join fault luckily found and repaired in an hour thanks to mr wago and his click n shut box

 

[Marvo]

A reading of 0.4 ohms doesn't indicate damage by a screw necessarily as stated already but whatever the cause of the damage something has cut into or deformed the conductors so you no longer know their current carrying capacity and you can't reasonably assume the circuit will be reliable under load (or safe). The cable is no longer viable for several reasons. Please for the sake of yourself and your customer localise & repair the fault or replace the section entirely.

 

[revjames]

I had this on a link between 2 ceiling roses - again house 2nd fixed and painted and decorated. I removed the ceiling rose and gently excavated the plasterboard behing the rose to reveal a bigger hole. I could tell that there was no movement on the cable at all and it must be trapped. Ceiling was supported by metal type battens and board screwed to it. Smashed big hole - took photographs of offending screw into middle of cable, refitted ceiling rose (new location due to now shortened cable. Sent pics to builder and heard no more about it.

 

[Electroglow]

Hello all found the fault today.. Builder has build a stud wall and put a a bit of wood on the cable catching it. I have a pic.

It was a short of 0.08 at one end and 0.49 the other. There for I knew what end to start with. But hey all sorted now. I wasn't ever going to leave it.