RCD tripping since fitting new MCB for boiler

[ZETEC153]

hi

you might remember seeing my other post about fitting a new feed to the boiler (and yes, i notified building control first!!)

thing is, i have got a split CU, with what looks like a split neutral block. The neutral line of the RCD side is connected to one side only - with all the neutrals of the circuits on the same neutral block.

I fitted the MCB (Type B, 6A), and connected via a connecting box to the 2.5 T&E going to the 3 A fused spur in the airing cupboard where the boiler is. Connected neutral into same block as RCD and other circuits on that side.

All fine when turned power on initially, but when the boiler was turned on, it tripped straight out. Tried a steamer, then a hoover in and the same thing happened.

When i moved tghe neutral to the other neutral block, the RCD stopped tripping but then i had split the circuit and it would not function properly.

Rang and spoke to a sparky and he said to fit it on the non RCD protected side as RCD's can be a pain in the arse when it comes to things like boilers cos of the electronics and pump and fans etc.

Anyway, i moved the MCB to the other side and all is now fine. As the cable goes up into the floorboards and then straight up into the airing cupboard into FCU, then i should be ok with regard to the regs.

Does this sound ok??

cheers

george

 

[laughingjester]

sounds like your mcb size is too small buddy try a 10amp instead.!!!!..if you have just got your boiler on that one 6A mcb, and its wired as a radial in 2.5mm, why are you trying your hoover and steamer out on that circuit when they are 13A appliances ? its always going to trip.

.i always put boiler on rcd side of circuits because its expensive kit, and if there is a fault you dont want the electronics fried in it,

 

[ZETEC153]

true, but its not the MCB which trips, its the RCD. hoover is 1200watts.
I=P/V = 1200/230 = 5.2 amps.

why when i moved the neutral into the other bar without the RCD neutral in did it stop tripping??

the MCB is now on the incominbg side and its working fine now.

cheers

george

 

[laughingjester]

it stopped tripping because it is no longer being monitored by the rcd>>>>

 

[electronicsuk]

Sounds as if you have mixed your neutral bars up. Just to clear things up, what you're saying is this:

- Wired into RCD side, RCD trips every time boiler turned on
- Moved neutral to non-RCD side, RCD doesn't trip

That suggests to me that you have the two sides of the CU confused, and in the first instance you had actually taken L from RCD side and N from non-RCD side.

You go on to mention something about the circuit not operating when split. Apart from the RCD tripping, there is no other reason for the circuit not to operate with a live from one side and a neutral from the other.

I also doubt that building control were notified, as this would have been identified during inspection and testing. Comments such as "what looks like a split neutral busbar" do not fill me with confidence with regard to your electrical expertise.

Also, what is this "connector box"?

 

[ZETEC153]

so, with the MCB on the incoming side now, it doesnt matter which block the neutral goes into, as it is no longer on the RCD protected side??

i have heard of these things before with electronics and RCD's so not too worried.

As long as its safe, thats all i am worried about. All the other circuits, ring main, kitchen sockets are on the RCD side, lights and cooker and now boiler are on the incoming side.

george

 

[Spark123]

If the MCB is on the RCD side of the CU then the neutral MUST be in the RCD protected rail.
If the MCB is on the non-RCD protected side of the CU then the neutral MUST be in the NON-RCD protected Rail.
If there are unprotected concealed cables buried less than 50mm from a surface anywhere on the circuit then to comply with the 17th edn regs it needs to be protected by a 30mA RCD.

 

[ZETEC153]

Sounds as if you have mixed your neutral bars up. Just to clear things up, what you're saying is this:

- Wired into RCD side, RCD trips every time boiler turned on
- Moved neutral to non-RCD side, RCD doesn't trip

That suggests to me that you have the two sides of the CU confused, and in the first instance you had actually taken L from RCD side and N from non-RCD side.

You go on to mention something about the circuit not operating when split. Apart from the RCD tripping, there is no other reason for the circuit not to operate with a live from one side and a neutral from the other.

I also doubt that building control were notified, as this would have been identified during inspection and testing.

#

well i notified them, but they havnt been out to check it yet, as i wasnt aware they had to check it as i went along, just when the job was done??

yeah, i fitted MCB into live bar on RCD side, and neutral a connected into RCD neutral bar. Then i moved the neutral into other side, and it stopped but it meant the circuit was 'split' - is that right terminology??

george

 

[electronicsuk]

so, with the MCB on the incoming side now, it doesnt matter which block the neutral goes into, as it is no longer on the RCD protected side??

No, no and no. It matters very much. The RCD looks at current in both the live and neutral conductors of the circuits it protects. If there is an imbalance, it will trip. As such, only RCD potected circuits must be fed from the RCDs neutral busbar.

No offence, but an RCD offers no protection unless correctly installed, and I'm not convinced you know what you're doing. I would be worried.

I wouldn't mention to building control that you powered up the circuit before testing.

 

[laughingjester]

yeeeeeeeee haaaaa !

 

[ZETEC153]

ok, i will get it all checked.

thanks for all the, umm, help and advice!!!

 

[laughingjester]

When i moved tghe neutral to the other neutral block, george

yeeeeeeeeeeeeeeeeee haaaaaaaa !!!

 

[electronicsuk]

well i notified them, but they havnt been out to check it yet, as i wasnt aware they had to check it as i went along, just when the job was done??

Surely if you had contacted BC at all, they would have explained the procedures to you? You would be aware that cable runs need to be inspected at first fix, and then final inspection and testing carried out before the circuit is powered up. Why waste our time...?

yeah, i fitted MCB into live bar on RCD side, and neutral a connected into RCD neutral bar. Then i moved the neutral into other side, and it stopped but it meant the circuit was 'split' - is that right terminology??

george

Once again, it sounds as if what you think to be the RCD neutral busbar is actually for the non-RCD side. There is no other obvious explanation as to why the circuit would work when you moved the neutrals around. If you had truly 'split' the circuit, as you call it, then the RCD would trip as soon as load was applied.

thanks for all the, um , help and advice!!!

No need to be, um, patronising