fault on lights

[paul b b]

hello chaps,

looking at a job today, light would not work, i thought the dimmer had broke so changed it to normal switch, stuck tester on and got 24V. went to another switch and got 135v.

i saw a few loose floor boards so riped them up and found a JB, tested there and got 240 across loop in L & N and 24v L-SL.

i found another JB touched it and it went bang. looked a bit more and it was a mess so recomended to rewire downstars lights (

 

[sparkytim]

Hi Paul

Sounds like you may have had a high resistence connection at some point or things were not wired correctly, if lights are wired in series then can give this sort of test result.

Not sure what you mean by MEC?

 

[paul b b]

Main earth conductor

sorry tim, in series? please explane, its been a long day

 

[sparkytim]

Know how you feel mate.

If someone has incorrectly wired the lights so that the L runs from a switch to a light then the N from that light is wired to feed the L of the next light then these 2 lights are in series. This can happen with the loop in method where the switch wire gets mixed up with a Nuetral.

 

[paul b b]

ahhh ok, so this could give strange voltage readings then?

does the price sound ok?

 

[sparkytim]

Its your call

If its twin and earth and tests ok after you have sorted connections then

it may not need rewire just a re do of terminations as required

If you rewire then will it need RCD? all additional cost and what about switch drops, are they in conduit or will walls need disturbing?

 

[paul b b]

its all a bit of a mess to be honest, walls are lath and plaster and should be able to ust existing as draw cables, oh well hes acepted now and wants me to start tomorrow lol

rcd in place mains water right next to meter

EDIT: forgot to say IR test L N-E 12 m ohms

and lots of singles

 

[Ian Speirs]

Hi paul, sometimes when you test for voltage and your reference, usually the earth wire in the back box, might not actually be connected at the other end which will give you false readings. :coffee

 

[paul b b]

Hi paul, sometimes when you test for voltage and your reference, usually the earth wire in the back box, might not actually be connected at the other end which will give you false readings. :coffee

sorry ian i dont follow.... why would an earth cable mess around with a voltage reading?

 

[Ian Speirs]

if the earth is not connected to the earthing system, i.e. the twin and earth is exposed at the light switch, but say is broken in the jb or light pendant. if you test between the live in the switch and the earth cable then dependeing on the length of the cable your reading will differ to that of a trure (connected) earth. it would be like testing between the live and the cable insulation. it would not show 230v. Not great at explaining but hope this helps.

 

[paul b b]

sorry, are you saying to test between live and earth? but this would trip the rcd

 

[Evans Electric]

I was thinking much the same as Ian , as he says, if the earth wire is not connected you will get all sorts of nightmares. You say you got 24v between L-SL . How did you test at the switches for voltage L-E or was there a N there?

Redo that dodgey JB ,sounds like someone has been messing , they don't tell you .

Your main earth , there is no size 8mm , you must have 6 or 10mm2 Both are too small anyway so upgrade to 16mm2 .

 

[paul b b]

i tested at switch SL-L

light on 24v

light off 8v

just seems all wrong, i'm also worried about putting mu name to something that is dodgy

 

[steptoe]

Main earth conductorsorry tim, in series? please explane, its been a long day

NO such thing

sorry, are you saying to test between live and earth? but this would trip the rcd

Not using a suitable resistance meter, ie, a normal voltage indicator.

I was thinking much the same as Ian , as he says, if the earth wire is not connected you will get all sorts of nightmares. You say you got 24v between L-SL . How did you test at the switches for voltage L-E or was there a N there? Redo that dodgey JB ,sounds like someone has been messing , they don't tell you .

Your main earth , there is no size 8mm , you must have 6 or 10mm2 Both are too small anyway so upgrade to 16mm2 .

you should know better.! Wet Fish

 

[paul b b]

earth must be 6mm then,

do i have to do this? its a right ******

 

[maccarooni]

I was thinking much the same as Ian , as he says, if the earth wire is not connected you will get all sorts of nightmares. You say you got 24v between L-SL . How did you test at the switches for voltage L-E or was there a N there? Redo that dodgey JB ,sounds like someone has been messing , they don't tell you .

Your main earth , there is no size 8mm , you must have 6 or 10mm2 Both are too small anyway so upgrade to 16mm2 .

Maybe some ones cut the earth in half......Lenghtways LOL:red card

 

[paul b b]

NO such thingNot using a suitable resistance meter, ie, a normal voltage indicator.

you should know better.! Wet Fish

so if i stick my megger on to the Volt setting and test between L-E the rcd would not trip? sorry for being dumb! i'm tired

 

[Ian Speirs]

i tested at switch SL-Llight on 24v

light off 8v

just seems all wrong, i'm also worried about putting mu name to something that is dodgy

If you are putting one probe of your voltage tester on the live conductor at the light switch and the other probe on the switched live in the light switch, then there will be virtually no differance in potential as you are testing the same conductor. your tester measures the potential voltage between test probes. if you touch both probes on the same busbar conducing 230v it would read 0v or there abouts.

 

[Ian Speirs]

so if i stick my megger on to the Volt setting and test between L-E the rcd would not trip? sorry for being dumb! i'm tired

nope, it will not trip mate,

 

[paul b b]

thanks chaps, guy was not happy when he saw dodgy Jbs and wanst it rewired now anyway.

i was just wondering why the funny results.

i see what your saying ian, light in sitting room has given up anyway so nice job for tomorrow.

thanks again