Electrician upped lighting MCB to 20A

joebre

Yes they are.

It's just that I did not know how to convert to Amps.

When it used trip, there would be nothing on circuit as I would not have gone up to bedroom.

Joe

fishdog

It's just that I did not know how to convert to Amps.

Devide total watts by 230 = Amps

I dont think it is over loaded. I would bet it is a fault to earth or between earth and neutral.

It could well be that there is just too much on it.

I would not think so, remember:
1000 watts = 4.35 amps

Steve

Ok, sort of a scientific approach...

20 No. 10W 12V on traffo on landing = 200W = 0.909A = 7.2A inrush
10 No. 10W 12V = 100W = 0.45/a = 3.6A inrush
2 No. 240V 40W = 0.36A
3 No. 12V 50W = 0.68A
2 No. 240V 40W = 0.36A

so.. if all other lights except the landing were on it would be 1.85A which is nothing in the grand scheme of things, adding a 7.2A inrush should definitely not trip a B10 breaker. This would again point me towards a dodgy mcb...
OK, I know I'll get slated for this but it's worth a try... turn everything on and give the breaker a rap of your knuckle and see does this cause it to trip... if it does then maybe my theory is correct and the breaker is just too sensitive and needs replacing...

joebre

Could try that, but at the moment there is a B20 fitted!!

fishdog

0.909A = 7.2A inrush

I dont know how you are arriving at 7.2 A (other than multiplying by 7.92 !).
But I see your point is that there is an initial surge, which is correct. This is normal for many electrical loads and the load here is very small. A 10B type should have no problem dealing with small transients such as this as you correctly stated.

This would again point me towards a dodgy mcb...

This is possible, but I would not think so. Just from over 20 years experience this has never been a problem for me. However it is easy to rule out and there is no harm trying it out.

turn everything on and give the breaker a rap of your knuckle and see does this cause it to trip...

This will tell you nothing. Measure the current with a grip on ammeter and swap it for another 10A B type MCB and you will quickly know a lot more!

JOHNPT

How do u calculate the inrush current? In what circumstances would you have to take account of this in normal domestic lighting situations i.e in what situations may it cause a problem of tripping?

Thanks in advance

fishdog

In what circumstances would you have to take account of this in normal domestic lighting situations

In normal domestic, none so dont worry about it. That is not the problem here. Large inductive loads can have a large transient currnet for an instant when first switched on that quickly reduces.

in what situations may it cause a problem of tripping?

For example if you were to plug a 2kVA 230/100V transformer (site type traffo) into a normal socket it will sometimes trip the MCB.

You may also suffer from this if you had say 10 twin fluorescents on one switch, the current may be less than 6A with all of the lights turned on, but at the instant of turning on the switch a 10A MCB may well trip. Solution: Simple, dont put all 10 on the same switch, but they can stay on ther same circuit.

DK47

its this simple, the mcb protects the circuit not the fitting. a 1.5 t+e requires a B10. this is why. the B20 would only trip when more than 20 amps flows. if lets say the fitting is drawing 18 amps over a period of time the insulation would degrade and fire would be a concern. if the fitting is tripping the B10, you have to change the fitting or upgrade the circuit no the mcb. it is cheaper and easer to replace the fitting. your electrician is a cowboy, if he dosent understand why is he uses what mcb where, he needs a new job.

Solair

dkhill47 wrote: »

its this simple, the mcb protects the circuit not the fitting. a 1.5 t+e requires a B10. this is why. the B20 would only trip when more than 20 amps flows. if lets say the fitting is drawing 18 amps over a period of time the insulation would degrade and fire would be a concern. if the fitting is tripping the B10, you have to change the fitting or upgrade the circuit no the mcb. it is cheaper and easer to replace the fitting. your electrician is a cowboy, if he dosent understand why is he uses what mcb where, he needs a new job.

100% agree with you there! The 'electrician' sounds clueless!. It's basic laws of physics i.e. ohms law. If you exceed the maximum load carrying capacity of the wire it will get hot, the insulation will melt off and your house will go on fire. Pretty much as simple as that!

Good luck claiming against your insurance too!

You cannot just change an MCB for a bigger one, they're designed to protect you being able to overload a circuit. If the MCB is tripping, it simply means you're drawing more power than the circuit can provide.

Your options are, re-wire the circuit with higher capacity cable, or, run a new circuit for some of the fittings on the circuit (a lot more easily done!)

joebre

Yes, I agree with you that the electrician sounds clueless!

I was not around the last time he called to do some snags.

I had it tested with a meter by a separate electrician recently.
I have 8 lighting MCBs in the house.
The lighting circuit drew 4.5A when I turned on a fancy light fitting with transformer and 20 G04 10W bulbs. It then settled at slightly over 3 amps.
Definitely no need to go from 10A to 20A !

Could it be that the original 10A was faulty and that I should get him back to put in a 10A again ?


Joe