3rd Year apprentice looking for help

[ApprenticeSparky]

Hi there, basically the shed out our back garden was wired by someone else about 6-7 years ago and now for some reason keeps tripping the ELCB, I checked the wiring in the sockets, spur and light and it all seems grand, the SWA coming in also seems grand, the only things plugged in are the freezer and the dryer but the dryer is only plugged in when its been used, I plugged the freezer out last night and it went again, any one know wat it could be ???

Need to get it fixed before the old man loses his hair

 

[Taylortwocities]

So, with nothing plugged in the RCD still trips?

Where is the RCD in relation to the shed. Is it in the shed, or is it in the house?

If its in the shed, do you have a mini fusebox with it in?
Are there separate MCBs for sockets and lighting?

Do you have an insulation tester (eg Megger)?

 

[ApprenticeSparky]

So, with nothing plugged in the RCD still trips?
Where is the RCD in relation to the shed. Is it in the shed, or is it in the house?

If its in the shed, do you have a mini fusebox with it in?
Are there separate MCBs for sockets and lighting?

Do you have an insulation tester (eg Megger)?

I have just been told te dryer was plugged in when it went,

The RCD is on the main ( and only ) board in the house, I don't have a megger unfortunately

Will I plug everything out and see if it goes again ? ? ?

 

[Spark123]

You could do, it would be more professional to Insulation Resistance test the wiring to check it is sound tho.
Can you borrow an IR tester from college/work?
Having a single RCD as a main switch is a PITA!

 

[ApprenticeSparky]

right but to be honest I've never used a megger before so how would I go about testing the circuit and how do i understand the readings

 

[londonboy]

Try unplugging everything first, 80% of jobs like this is due to something plugged in!

 

[Spark123]

Have your lecturer go through it with you, basically unplug everything, isolate and disconnect the L&N at the consumer unit, IR test @ 500v between L&E and N&E.
You can check between L&N but if there is anything connected it can show as a fault.
The readings should be above 5M ohms, if they are lower there is a fault and means you need to break the system down and check.

 

[Taylortwocities]

I have just been told te dryer was plugged in when it went,

The RCD is on the main ( and only ) board in the house,

So it could be the dryer but that RCD protects other circuits in the house. What makes you think it is the shed? it could be the dishwasher, or the cooker.

Using the proper test gear makes this sort of thing a lot easier. Without its just a matter of trial and error.

First off, isolate the shed circuit completely. Disconnect the live & neutral - don't forget that RCDs trip on an earth fault on either L&N.

If your RCD still trips then you don't need to worry about the shed!

 

[ApprenticeSparky]

Well whenthe RCD trips the only breaker that goes down is the mcb thats for the shed, when all other mcb's are on ALL SOCKETS in the house work, when the shed breaker is down the ONLY sockets that dont work are the one in the shed,

the rcd just tripped there now again with nothing plugged in ...

 

[bloxy]

tripping the ELCB,

Is it a VO ELCB covering the whole installation or an RCD on the board?

If the MCB trips it's an over current fault, if it is a VO ELCB then the fault is phase to earth somewhere in the shed wiring.

If it is an RCD then there could be phase to neutral short giving the ove rcurrent fault plus a phase to earth or neutral to earth causing the RCD to trip.

Anyone put a nail through a cable?

 

[electronicsuk]

Well whenthe RCD trips the only breaker that goes down is the mcb thats for the shed, when all other mcb's are on ALL SOCKETS in the house work, when the shed breaker is down the ONLY sockets that dont work are the one in the shed,

the rcd just tripped there now again with nothing plugged in ...

If you're in your third year and think that an MCB tripping is a mere small leakage fault, and you intend to fix it without having any test equipment, perhaps you're in the wrong trade?

Just to confirm, both the main RCD and the MCB for the shed are tripping at the same time? This would suggest you have a short or near short-circuit between L and E.

 

[ericmark]

When current leaks to earth rather than going down the correct path there are two ways to test.

The static test with an insulation tester (mega) is the norm and this will highlight most installation faults but measuring the ma leakage is better for any appliance which has relays or other switches which could disconnect the faulty part when not connected to power.

The fault is much more likely to be an appliance than the main installation so since you are likely to have access to tools of trade I would "PAT" test the two items and look at ma leakage. And a manual "PAT" tester is best as you can run the appliance longer.

One I had was a freezer with fault on auto de-frost and with those sort of faults only way to test is with mega and with some dismantling of appliance.

As third year you should be by now well versed in using test equipment to teach over this format is not really a safe practice. I would ask in the college and get them to show you.

 

[electronicsuk]

The fault is much more likely to be an appliance than the main installation so since you are likely to have access to tools of trade I would "PAT" test the two items and look at ma leakage. And a manual "PAT" tester is best as you can run the appliance longer.

the rcd just tripped there now again with nothing plugged in ...

 

[bloxy]

The fault is much more likely to be an appliance than the main installation

You would think so but he said it tripped with nothing plugged in.

 

[securespark]

I have to agree with Uncle Eric. I find it somewhat surprising to hear you are in your third year and you are not trained to use an IR tester.

How do you manage when you are out in the field or in the college workshop?