Electric Boiler tripping MCB

[krissiboy]

Hi all.

Still a bit new to this so here goes.

Just been called out to an electric central heating boiler. Customer says its been tripping the 40A MCB for a couple of months.- Not often but customer is a landlord and he doesn't want to lose his tenant over this.

Its fed with 10mm t+e cable via a 45a DP sw and is protected by a 30mA RCD. The rating of the boiler is 9kw. I tested the voltage a few times at the heater which came out to be between 236 and 240volts. So doin a bit of maths the current should be at worst 38.14Amps.

Using a clamp meter I found the current to be 40.4Amps. I suppose the circuit board would use a little power too hence the higher current.

Would this very small overcurrent be enough to trip the MCB albeit over a bit of time? I thought about trying a 45a MCB type B but they dont seem to make them for Hager Boards and I'm loathed to stick in a 50A.

So could I put in a 45Amp MCB of another make. Are there any other makes that are compatible with Hager?

Thanks in advance.

 

[Guitarist]

A 40A MCB should be able to run all day at the current he is getting. I still think something is spiking it, either a switch or contactor. Have you tried setting the clamp on "Max" and see what you get as the unit clicks on and off?

 

[krissiboy]

Thanks for all that info.

I did check all connections when I initially looked at the boiler and all are tight including the c/u end. I also looked at the circuit board inside the boiler and found no signs of overheating. I did check the resistance of the elements and found that two of them were around 19 ohms and the third being around 20 ohms so didn't think there was anything wrong.

I will have a look for this adjustment screw though with a view to turning it down a tad. Will try another 40amp mcb to see if that makes a difference as well.

But now that we have all this sunny weather the tenant won't have it on any way so it'll be October time 'hopefully' when it will get the chance to trip again.

cheers to all for you input.

 

[sedgy34]

cant you upgrade mcb 45A on 10mm cable

 

[krissiboy]

cant you upgrade mcb 45A on 10mm cable

Hager don't seem to do 45 amp mcbs. Next up is a 50 amp which am not keen in using as cable is run between floors where there is a possibility of insulation.
Not keen on mixing mcb makes in c/u. Have heard the manufacturers don't warranty them in a different make of board.