Ground floor lighting trips out mcb

Biggy · Dec 27, 2018

Hi everyone,

My first post but straight in with a couple of issues.

I'll start with a 6amp MCB that keeps tripping out relating to ground floor lights.
For your info:

There is 10 x 3w led recessed lights in Kitchen, 8 x 3w led recessed lights ,plus a main central Led light (approx 100watt equivalent ) in the room next to the kitchen and then the same amount of lights and Main central light in the Back room. I would say the combined wattage including two outside lights (40watt each) will be around 480w so let's call it 500watt on the ground floor.

From my understanding a 60w bulb draws around 0.5amp so in effect 30 of the 60w bulbs (around 1800watt combined ) would require a 15amp breaker which would be comfortable, so based on this theory is the 6amp MCB actually overload on 500watts on Ground floor and this tripping the breaker .

The breaker does not trip immediately as can take 5-10mins sometimes longer, and in some instances it has tripped even when ground floor lights have been OFF.

The joist spaces have all been insulated with rockwool if this makes any difference as I want to eliminate any possibility before I start questioning my electrician who advises that maybe I should fit a 15amp breaker in as he feels 6amp is less power for 30 odd lights .

Can anyone shed LIGHT on this

I'll come to the second issue after I can get a solution to this.

Sorry for the lengthy explanation but I know there's nothing more frustrating than not arming knowledgeable people will full info and expecting solutions. Hope I've not missed anything out.

Hope to get a few responses and guidance as I have basic understanding of electrics.

Thanks

telectrix · Dec 27, 2018

your estimate of 1800 watts equates to 7.5 A. however, not all lights will be on at the same time. so a 6A MCB is fine. even with 7.5A, the 6A MCB will not trip in my lifetime. and a 60watt lamp draws according to P = VI. or I=P/V, so I = 60/240 = 0.25A.

littlespark · Dec 27, 2018

I think you may have your sums wrong.
6 amp breaker at a nominal 230v will take 230 x 6 which is 1380 Watts.
Sounds like you don’t have that much.

If it’s tripping without any lights on, then it sounds more like a short circuit than an overload situation.

Your electrician should test the circuit with his test equipment.

Replacing a 6A MCB with a 16A is the modern equivalent of replacing fuse wire with a nail.

telectrix · Dec 27, 2018

[ElectriciansForums.net] Ground floor lighting trips out mcb

Biggy · Dec 27, 2018

OK so I definitely have nowhere near 1380watts so 6amp should be fine from what I gather.

The electrician used his friend to come and certify it off and does this mean there is a possibility the certificate has just been issued without really having a proper test done to check.
Is there anything I can check myself to eliminate any basic problems first ?

Should I stop him from putting a 15amp breaker in then ?

Thanks

Toneyz · Dec 27, 2018

Biggy said:
The breaker does not trip immediately as can take 5-10mins sometimes longer, and in some instances it has tripped even when ground floor lights have been OFF.

Based upon the above I would recommend an electrician does an insulation resistance test you have either a short circuit or earth fault.

Biggy · Dec 27, 2018

I have the domestic electrical installation certificate . Is there anywhere on this I can check what I need to look for with what he has written down ?

camerabloke · Dec 27, 2018

Outside lights check for water ingress. Have you had any work done lately. Hung pictures put a shelf up etc?

littlespark · Dec 27, 2018

The problem could be with so many LED lamps, he’s maybe tested it with the switches off, to protect the lamps from the test voltage.
However if there’s a fault after the switch, he’s missed it.

The other question is.... are you sure it is an mcb? It might be an RCBO... trips off under a different type of fault.
Can you photograph the mcb in question and post it to the thread here?

You could scan in the certificate and post it here, but you would have to block out any identifying information of you or your electrician (or his friend)

Toneyz · Dec 27, 2018

Why do I get the feeling that the whole story has not been posted that said and put aside, you have told us the full loading the fact that it is tripping out after a short time and the circuit breaker is 6A.
Is this a new or newly rewired circuit?
What is tripping out the 6A circuit breaker RCBO or RCD (photo would be helpful)
As posted if it is tripping out with no lights switched on some testing needs to take place.

Toneyz · Dec 27, 2018

camerabloke said:
Outside lights check for water ingress. Have you had any work done lately. Hung pictures put a shelf up etc?

Very vocal on the forum at last Camerabloke.

camerabloke · Dec 27, 2018

Yes ant. Nice to see you

Toneyz · Dec 27, 2018

Biggy said:
I have the domestic electrical installation certificate . Is there anywhere on this I can check what I need to look for with what he has written down ?

Yes, there are columns referring to installation resistance if not sure post a copy and we can point it out to you.

littlespark · Dec 27, 2018

Just a side note. OP mention recent addition of thermal insulation.
This can decrease the current carrying captivity of the cable, but not to the extent of creating a problem like this.

It can also cause damage to cables by removing and relaying boards to access between the joists.

There can be a dozen or so reasons why this is happening, but I think all the pros on here agree that sticking in a 16A isn’t the answer.

Toneyz · Dec 27, 2018

Going back to your first post are the LED downlights the type with the driver as part of the fitting? as putting insulation over these (unless they are the type designed to take insulation covering) may be overheating the driver and giving a short.

DC-backfrom the past · Dec 28, 2018

as said previously ,,,why would you want to protect with a 16amp mcb.
because its tripping ? if only it was that simple .
this could be a loose connection, it could be a bulb thats faulty, it old be a faulty switch.
too many things , it could be damaged insulation that only causes a problem under certain circumstances.
I suggest you get continuity checked and insulation resistance test.
if that doesn't find the fault take note of the conditions when the fault occurs.
also has there been any recent work done in the house that could affect the wiring ?

Markyd · Dec 28, 2018

Get the sparky who tested it back and tell him to do it properly this time.....

Midwest · Dec 28, 2018

Just another thought; seems a fair bit of led lighting on one circuit, wonder what make & how they are switched?

Biggy · Dec 28, 2018

Thanks a fair few replies overnight, so I'll try answer as best I can.

The rewiring has been brand new throughout the house

The certificate shows a tick box next to "insulation resistance between live conductors" and also to "earth".
Schedule of items tested list has all been ticked .
Single phase prospective fault current is written as 0.99ka.

The led lights are 3w+3w recessed with a transformer with each light.

No bulbs are blown on ground floor (one transformer blown upstairs but that's not on the same circuit )

I have not checked the outside light just yet and it was screwed in a little loose but at the moment I don't have a bulb in it so I will put one in and then check again to see if they are on the same circuit too as maybe I can eliminate water ingress from outside light.

Is there any basic checks I can do myself which could be the reason .
As for the fuse that's tripping on CU, I have the BG 10way unit from screwfix with RCD switches too. The one that's tripping is the 6amp marked ground floor lights .

I will try get a picture up as soon as I figure out how to.

Any suggestions based on info I have now provided.
Thanks

Biggy · Dec 28, 2018

Here is the CU I have and the 5th switch from the left keeps tripping which is my ground lights marked there.

telectrix · Dec 28, 2018

always the possibility of a rogue MCB. is there another 6A on the same RCD?

Biggy · Dec 28, 2018

I don't know if there is a spare I'll check and see if one can be swapped over just to test it. Should I turn all the CU off and do I just pull the breaker out and click back in to test with a different one ?

telectrix · Dec 28, 2018

no. you turn off main switch, then move the circuit wires to a different MCB. if it's on the other RCD, you need to move the N to the appropriate N bar.

a better idea would be to clamp the L coming out the MCB and see what current is flowing. for this you'd need a clamp meter.

DPG · Dec 28, 2018

Biggy said:
I don't know if there is a spare I'll check and see if one can be swapped over just to test it. Should I turn all the CU off and do I just pull the breaker out and click back in to test with a different one ?

I would get a sparky in as soon as you can.

Toneyz · Dec 28, 2018

I think that as long as you have not got a fault to earth and the RCDis not faulty one of the drivers could be faulty due to the reason I gave in post 15 or heat damage causing a L-N at a lampholder. What has thrown me is that you say it sometimes trips when the lights are all off or do you mean when you turn them off. Just to change the MCB to a 16A one is not going to find the problem and could make the installation dangerouse or non compliant with the regs.

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