mcb keeps blowing on lighting

[Wayne Hudson]

Hello sparks
I was at a Job earlier today,the customers upstairs lights would not turn on due to the 6A mcb operating so it's a short circuit so I disconnected the supply to the first light the supply disconnected from consumer unit ,then did a insulation resistance which came out clear tried the mcb without any connection it stayed on.so connected the supply at consumer unit and left the other end not connected to anything it stayed on so connected the loop out and switch live it all come back on for 2 poxy minutes then it would come back on .I had to leave disconnected and will be returning back tommorow . Any suggestions would be extremely grateful
Thanks

 

[Hawk81]

You will just have to keep breaking the circuit down and testing it until you find it. Has any work been done recently? Anyone tried changing a light fitting ect? Banging in nails? Screwing up picture hooks etc?

 

[davesparks]

Use the logical process with appropriate testing to find the fault.
Repair the fault.
Replace the MCB at your expense as you are likely to have damaged it by repeatedly closing it onto a fault.

Or

Employ the services of an electrician

 

[Knobhead]

You claim to have 2330 level 3 nvq/AM2 /17th edition and your method of fault finding is to keep closing the MCB.

By the time you find the fault the MCB will be toast. That’s if the house hasn’t burnt down first.

 

[Farmelectrics]

basic fault finding this split the circut do your dead testing not trying mcb each time i would gather it will be simple to find

 

[tazz]

Dead testing is the basics of any fault finding, or even a new installation......start by breaking the circuit down until the fault is found. Instead of hit and missing with the mcb.

 

[Darkwood]

Not sure what to really say here tbh, this is your standard testing for a fault set-up and basic at that. I'd expect a trainee to ask a question like this but not someone who carries your qualifications.

Qualifications aside have you any practical experience in fault finding and when you did your apprenticeship were you not shown and/or taught how to, as Tony points out closing the protective device repeatedly onto the fault as part of your testing procedure shows you really don't know what your doing, use your meters they are there to safely identify the fault without you damaging your protective device or sending multiple mains transients into the network and upsetting other users on the same sub-station.

 

[Richard Burns]

From what you describe you have not mentioned closing any switches when IR testing, so this sounds like a good palce to start since if the fault is (as is likely) at a light fitting and the switch is open then the fault will not show up.
Similarly if there are two way lights swap the switches while testing.

 

[Clive P]

Hi,

As Richard says , check the strappers on the 2 way. Had one a while ago at my brothers, tested fine, switched the 2 way; screw through the strapper and earth!

Regards.

 

[Knobhead]

Any reports of house fires around Faversham? (Where ever Faversham is).

 

[Geordie Spark]

Any reports of house fires around Faversham? (Where ever Faversham is).

It's nowhere near Yorkshire Tony, so you wouldn't know! :laugh:

 

[GMES]

It's pretty much been covered by the Guys already so just learn to fault find with your test equipment and leave the Bang test alone.

 

[Knobhead]

There’s always copper links, they usually finds the fault. Probably blow a hole in the ceiling but at least you’ll know where the fault was.







Was being the operative word.

 

[Knobhead]

It's nowhere near Yorkshire Tony, so you wouldn't know! :laugh:

Yorkshire doesn’t exist as far as I’m concerned.

 

[Baker1988]

Yorkshire doesn’t exist as far as I’m concerned.

Yorkshire is awesome especially east Yorkshire haha

 

[micknew]

Hello sparks
I was at a Job earlier today,the customers upstairs lights would not turn on due to the 6A mcb operating so it's a short circuit so I disconnected the supply to the first light the supply disconnected from consumer unit ,then did a insulation resistance which came out clear tried the mcb without any connection it stayed on.so connected the supply at consumer unit and left the other end not connected to anything it stayed on so connected the loop out and switch live it all come back on for 2 poxy minutes then it would come back on .I had to leave disconnected and will be returning back tommorow . Any suggestions would be extremely grateful
Thanks

You shouldn't have left it on for 2 poxy minutes, you should know that as a professional electrician.
It gets worst, sorry if that offends, not lol.

 

[Darkwood]

Yorkshire doesn’t exist as far as I’m concerned.

Herhmmm!!!! Its the preverbial Gods country but been an Atheist all I have as input is; 'there is Yorkshire and then there is the rest of the world'...... How very dare you :boxing_smiley:

 

[Knobhead]

 

[Geordie Spark]

I see your new medication is still at the experimental stage Tony.

Never mind though - you may win a prize at Crufts next year.

Every cloud etc. .......

 

[Wayne Hudson]

Thanks for most of the replys it ended up being a squished cable in the loft from a walk board on to and the c/u was not up to date to the 17 th edition 7671 so replaced with rcbos.tested dead and live test all performed and passed and certified and logged on to building control .so there won't be any house fires reported from Faversham .I thought I was on a site where I could talk to people in confidence without having the **** taken .I was wrong with my fault finding procedure I shouldn't of tried the mcb with a fault in the circuit but before I left I made sure it was all completely 100% safe hasn't any of yous been on a job and had to leave it and come back the next day with a clearer head obviously not cos you are all pefect.so thanks for your input keep it up north a .

 

[davesparks]

If I have a fault like that I will normally work until I have at least found it and made any temporary repairs necessary to get the lights back on. But then I am not afraid to work past 'finishing time' and will happily work as late as the client wishes me to in order to get a job done.

Also why was the 'upgrade' to RCBOs required? Did the client request this be carried out after you had carefully talked them through this? I'm sure you didn't just sell it to them as bring a necessary upgrade because the regulations say you have to, because as we all know that's not true!

 

[Geordie Spark]

Thanks for most of the replys it ended up being a squished cable in the loft from a walk board on to and the c/u was not up to date to the 17 th edition 7671 so replaced with rcbos.tested dead and live test all performed and passed and certified and logged on to building control .so there won't be any house fires reported from Faversham .I thought I was on a site where I could talk to people in confidence without having the **** taken .I was wrong with my fault finding procedure I shouldn't of tried the mcb with a fault in the circuit but before I left I made sure it was all completely 100% safe hasn't any of yous been on a job and had to leave it and come back the next day with a clearer head obviously not cos you are all pefect.so thanks for your input keep it up north a .

Good lad - well done!!

We had every faith in your ability and knew you would get there in the end!!

Now just get a towel and dry behind your ears and then grow a thicker skin.

 

[Silly Sausage]

you are all perfect.so thanks for your input keep it up north a .

It's a burden we've learnt to shoulder over many years.
Any future problems, don't hesitate to ask!

 

[SparkyJoe]

Thanks for most of the replys it ended up being a squished cable in the loft from a walk board on to and the c/u was not up to date to the 17 th edition 7671 so replaced with rcbos.tested dead and live test all performed and passed and certified and logged on to building control .so there won't be any house fires reported from Faversham .I thought I was on a site where I could talk to people in confidence without having the **** taken .I was wrong with my fault finding procedure I shouldn't of tried the mcb with a fault in the circuit but before I left I made sure it was all completely 100% safe hasn't any of yous been on a job and had to leave it and come back the next day with a clearer head obviously not cos you are all pefect.so thanks for your input keep it up north a .

Went to fix a fault, and managed to persuade customer to upgrade a perfectly fine DB to the "17th edition". well done.

 

[Badged01]

Oooooh, this forum can get so catty to the newbies .........

 

[Wayne Hudson]

I explained to the customer about the difference between rcbos and 17th edition d/b and the customer agreed on the rcbos.on the old d/b all the lighting was not protected a shed supply and cooker supply also was not protected by 30mA rcd .Any cables buried less 50mm has to be protectected by a 30mA rcd or rcbo,tt earthing arrangement zs=8.69 ohms thanks to all

 

[telectrix]

nothing wrong with explaining the advantages of upgrading the CU and letting customer make an informed decision, as long as you don't do a BG , telling them the old CU is illegal and dangerous.

 

[Wayne Hudson]

nothing wrong with explaining the advantages of upgrading the CU and letting customer make an informed decision, as long as you don't do a BG , telling them the old CU is illegal and dangerous.

So a 16 th edition c/u is perfectly safe then on a tt earth arrangement ??? What about the earth fault loop impedance being to high to provide the correct disconnection on the circuits not protected by a 30mA rcd ??

 

[Engineer54]

So a 16 th edition c/u is perfectly safe then on a tt earth arrangement ??? What about the earth fault loop impedance being to high to provide the correct disconnection on the circuits not protected by a 30mA rcd ??

Well it met compliance with the Reg's for far more years than it hasn't!!

Also, are you aware that SP RCBO's are NOT recommended for TT system earthing? They need to be either SP + N RCBO's or DP RCBO's!!

 

[Bobster]

Well it met compliance with the Reg's for far more years than it hasn't!!

Also, are you aware that SP RCBO's are NOT recommended for TT system earthing? They need to be either SP + N RCBO's or DP RCBO's!!

Schneider RCBOs explicitly state, they should not be used on TT or IT systems.

 

[Knobhead]

It would be interesting to know what has been fitted.

The trouble nowadays is RCBO’s being peddled as the instant cure all for all ills. A lot more effort should be made so that people understand the shortcoming of SP RCBO’s.

 

[Wayne Hudson]

It would be interesting to know what has been fitted.

The trouble nowadays is RCBO’s being peddled as the instant cure all for all ills. A lot more effort should be made so that people understand the shortcoming of SP RCBO’s.

Explain then, I fitted proteus sp rcbo 30mA, I always thought that rcbos are the best protection to have in domestic due to it being less disruptive to other circuits if a fault occured. I'm sure your gonna have a lot to say about this

 

[Bobster]

N - E faults are not cleared.

 

[SPARTYKUS]

Ive just bought a double pole RCBO. Thats the size of an MCB also.

just to have a look at it.

i suspect its like the French ones I've seen in mobile homes

 

[Geordie Spark]

Explain then, I fitted proteus sp rcbo 30mA, I always thought that rcbos are the best protection to have in domestic due to it being less disruptive to other circuits if a fault occured. I'm sure your gonna have a lot to say about this

Lose the attitude bonny lad. You're WELL out of your depth and it's showing!

 

[Wayne Hudson]

Is that a regulation in bs 7671 that sp rcbos are not recommended on a tt system if so what page number is it

 

[Wayne Hudson]

You didn't explain about the sp rcbos on a tt system

 

[urbanmonkey]

Single pole rcbo will operate in the event of an N-E fault but will not clear it, I'm sure you can how this can be a problem. Split board with 2x 30ma RCDs will cover all circuits and disconnect both L+N on the affected circuit in the event of a fault.

 

[Geordie Spark]

You didn't explain about the sp rcbos on a tt system

Sorry - I was away connecting a gas pipe to a Combi boiler.

 

[trev]

Sorry - I was bypassing my gas meter

Fixed that Fatha