Help please!!

[SparkyAndGeorge]

Hi guys, I would very much appreciate some advice here!! Basically was called to a school, every time they clicked the light switch, the RCD in the CU tripped. Meggered the circuit L to E over 299 ohms, E to N, over 299 ohms, but L to N 0.01 ohms. This is correct on a lighting circuit with fluorescent fittings. R1, R2 values all good. This leads me to the conclusion that one of the flo. fittings has become faulty (possibly a small amount of current leaking through to the cpc inside the fitting? But if that was the case, wouldnt that show up on the megger test? When i disconnected the cpc from the CU on that circuit, the lights stayed on! How is the best way to discover the faulty fitting? A lot of head scratching going on today!!!! Any help greatly appreciated, thank you guys.

 

[Flanders]

Start in the middle disconnect half the lights see if lights trip out if they do work closer to DB if it does not trip work further away from light until you find the culprit

 

[davesparks]

Your post reads as though you disconnected the cpc and then made the circuit live, with a known fault on it!

If I have read it wrong then I apologise, but if I have read it correctly then I strongly suggest you pack up your tools and find a new career.

 

[camerabloke]

Shouldn't IR flouries either

 

[Pete999]

What is "I megered the circuit do you mean I carried out an Insulation resistance test? R1 R2 values all good?? not sure what you mean? As Dave said give it up until you understand what you are doing

 

[telectrix]

Your post reads as though you disconnected the cpc and then made the circuit live, with a known fault on it!

If I have read it wrong then I apologise, but if I have read it correctly then I strongly suggest you pack up your tools and find a new career.

sometimes the bold approach can work. it's not as if he left the circuit with no cpc.

my query is... how many florries on the circuit? cumulative leakage could be the problem.

 

[SparkyAndGeorge]

sometimes the bold approach can work. it's not as if he left the circuit with no cpc.

my query is... how many florries on the circuit? cumulative leakage could be the problem.

yeah exactly, especially when time is against you. I did all the usual pre work checks etc and was the only one around. Anyways, not here to explain myself to some 'know it all'. There are 8 florries on the circuit, looks like theyre slightly dated now.

To the guy who said:

What is "I megered the circuit do you mean I carried out an Insulation resistance test? R1 R2 values all good?? not sure what you mean? As Dave said give it up until you understand what you are doing

You are very well aware of the slang in the industry so yes to 'megger' means carry out an IR test. And R1 R2 values all meaning there is continuity of the R1 and R2. I think someone else needs to give up till they understand the slang hehehe!!

 

[KAS1]

Oh the joys of Basic fault finding, post No 2 has it nailed, if could even be cable fault between 2 lights who knows lol

 

[bigdavs83]

To continue with the "bold approach" have you tried separating the circuit and continuing from there. Obviously if it holds after then it's more than likely the issue is with the disconnected section of the circuit. Always help to narrow this kind of fault down. Then you can put the "megger" away when finished

 

[SparkyAndGeorge]

Thank you for the sensible suggestions, my friends got a super clamp meter so we will try putting that round the cpc and seeing what amount of earth leakage current we are getting. I will be pressing for a full lighting circuit rewire he he he

 

[davesparks]

sometimes the bold approach can work. it's not as if he left the circuit with no cpc.

my query is... how many florries on the circuit? cumulative leakage could be the problem.

I don't agree, disconnecting the cpc of a faulty circuit then making it live is dangerous.
If there is a fault to earth them disconnecting the cpc will quite possible result in that cpc and everything connected to it becoming live!

I don't understand what you could hope to achieve by doing this that cannot be achieved without creating a dangerous situation. If you want to prove that the fault is on a particular circuit disconnect the L and N.

 

[davesparks]

I will be pressing for a full lighting circuit rewire he he he

Cowboy!

 

[pjcomp]

Switch on it trips. I had that after a light fitting install when the fitting was from a big blue shed and I misinterpreted the minimal colours visible in the wire, seeing the "yellow" as brown and vice versa, hence wired the earth to live and live to earth. Assuming you have a similar miswire, by disconnecting the earth at the CU the earth is no longer carrying the current to the RCD so no trip (I think).

Presumably the school has just started back after the holidays - during holiday maintenance have any of the lights been taken down/replaced, to be reconnected by a caretaker or decorator?

pj

 

[ayjay]

how old are the fluo,s? electronic or old choke ones?

 

[Druncanduncan]

Id be looking along the lines of what ayjay has just mentioned. If the fittings are dated as has been mentioned then chances are they could well be switch start. Ballast quite possibly burned out. Have come across no end of this type of fault