12v Lights tripping the MCD

Qwerty?

I'm having trouble with two lights that I'm fitting in the landing. Thye both have 12 20w bulbs, and each have a built in transformer. I've had one up and running, without problem, for months, but when I went to add the second one, it'll trip the MCD after a switching the lights on and off a few times. I've tried wiring the light in another room (which is on the same circuit), without problems. So i'm baffled. Anyone any ideas what the problem could be?

Thanks

Q?

Edited:- MCD's instead of RCD's

charlie@w.d

RCD's are usually for sockets. maybe u mean a normal 10amp MCB.
those electronic transformers are well known to trip rcd's, they put out a lot of interference.
The other thing is it could be that the cable could possibly be faulty and u are getting leakage to earth.

Qwerty?

Sorry Charlie meant MCB's.

Originally, we had put up two of these lights, but discovered that the screw of the casing had pierced a transformer wire, so assumed this was the problem. We sent that light back, and waited months to get a replacement, now the same problem, without the pierced wire.

charlie@w.d wrote:

The other thing is it could be that the cable could possibly be faulty and u are getting leakage to earth.

Which cable are you refering to?

Would a 16a MCD make any difference? The fact that I tried the light on the same circuit in the other room without problem, seems to suggest the MCD is ok. Think it's time to get my electrician back:(

charlie@w.d

i'd say its the start up load on both the transformers is causing the mcb to trip. when both of them are turned on at the same time the transformers for a few milliseconds take a surge which could trip the mcb.
the reason the lights both work on the same circuit is because you arent turning them on at the same time, when u turn both them on at exactly the same time they will trip.
A type c 10 amp m.c.b. will probably work
A 16 amp m.c.b. would probably work too

there are other sparkys here too im wondering what their thoughts are on this

Qwerty?

Thanks Charlie. I'll try the 16amp. I did try turning the two of them on at the same time with both switches to see if this tripped the MCB, but I suppose a split second could make all the difference.

Hope this works, cos I'm getting sick of putting this transformer up and down (you wouldn't believe the weight of them), and it's over the stairwell to make it even more fun.

charlie@w.d

lol i understand your torment, i hope it works for u and make sure u turn off the main switch before changing a mcb and remember there is still a live cable in the consumer unit so just treat everything as live just to be on the extra safe side, u probably no all this anyway.
let me know how u got on

FX Meister

Your lighting circuit is on a 10amp MCB for a reason, the cable is only rated to take 10 amps. If you change it for a 16 amp MCB you are removing the protection for the cable. The MCB is there to protect the cable.

dr.bollocko

Ex-nay on the MCD-nae on Oards-bay because of the ourt-case-kay.

charlie@w.d

FX Meister wrote:

Your lighting circuit is on a 10amp MCB for a reason, the cable is only rated to take 10 amps. If you change it for a 16 amp MCB you are removing the protection for the cable. The MCB is there to protect the cable.

yeah but he is only gettin a surge of power for a few milliseconds which trips the sensitive mcb.
type c 10 amp mcb would of course be safer

Qwerty?

They didn't have a C10, but suggested a D10 which seems to have done the trick. Have to fix the light to the ceiling before I insert all the bulbs, but it's working without problems with 2 bulbs.

Thanks for your help Charlie.

Sparky

I was going to suggest D10 as it is motor rated to take the surge.
C10 is only intended in commercial buildings

Solair

I was just reading this thread and was somewhat alarmed to see someone suggesting that a 10amp MCB should be replaced by a 16amp MCB to prevent tripping.

The MCB, like a fuse, protects the house's internal wiring from overloading. The breaker's rating was choosen by the electrician who originally designed your home's electrical system to be appropriate for the gauge of cable used in lighting circuits.

If you just put in a higher rated MCB, you're just over riding the overload protection and put your home at risk of fire.

I would also think that should you have a fire, that you could have difficulty claiming against your home insurance.

Also, the letter code on the MCB refers to a curve of how it behaves under certain fault conditions. Most domestic MCBs will trip quite quickly to prevent fire, damage to property or people. It's not a great idea to downgrade this ability to trip.

If you have nuisance tripping, you've simply got an overloaded circuit and would really need to look at getting your power from another source.

A 12V transformer can be connected to a normal power (socket) circuit via a plug+socket or via a fused spur unit.
Sockets are typically fed by a 20A radial in Ireland (rather than a 32A ring as in the UK)
We're a little more european in that regard.

Also, when working with any circuit, it's worth baring in mind that the neutrals are not necessarily sitting at 0V. Depending on the earthing arrangement in your home the neutral may or may not be referenced to earth.
Most homes thesedays are "Neutralised" i.e. connected to a TN-C supply i.e. the ESB neutral is connected to earth. In some areas, depending on a whole variety of factors.. age of installation, age of local distribution network and even the type of rock in the ground, you could be connected to a TT supply. In such a setup, your house's earths are simply connected to local earth rods

charlie@w.d

1.5 t+e has a rating of about 20 amps, god your been way over dramatic on the seriously dangerous, u no the problems transformers cause when firstly switched on they take a surge of power for a nanosecond, if it takes more than 10 amps the cable will not blow up it wouldnt even get luke warm. he used a type d 10 amp mcb anyway
what have neutrals got to do with his question? he was just wondering about 2 lights that were trippin his breaker!!

Sparky

I wonder does each fitting have a toroidal tranny in them?

It's a hell of a lot of VA between the two of them, so the result was normal.

Copper

The only problem with changing from a B10 to a D10 is your max allowable earth loop impedance is 4 times smaller, so you must have an earth loop equivalent as though the circuit was protected by a B40. In most houses the earth loop probably won't be adequate.

Type D are mainly used for large industrial transformers, they aren't very sensitive to faults, a C10 would be safer.

Solair

The neutrals comment was just because I know someone who was rather badly injured while working on a consumer unit and assumed the netural to be zero volts.