RCB tripping..but the wrong one...!

[mondriver]

Hi guys

I have a 10a RCB on my consumer board feeding my garage.

In the garage (from the 10a feed) I have a socket spur RCB which feeds armoured cable to a submersible pump that should turn on to pump out water from the bottom of my garden.

Quite frequently now, the RCB on the consumer board (in the house) is tripping, due to the pump and not the RCB on the socket spur which the pump is connected to....!!

I've turned off the pump to test it is the pump that's tripping the RCB and it looks like that's the cause of the problem as the RCB doesn't trip when the pump is connected to the feed.

How can that be?

I would have thought the socket RCB would trip before the consumer board RCB "up current" of it...?

Any thoughts?

Cheers

 

[wingcoax]

Pound to a penny, they are different makes. this can happen even with same make, various tolerances on assembly can cause different trip rates but only by a small amount.

 

[Electrifying]

Hi guys

I have a 10a RCB on my consumer board feeding my garage.

In the garage (from the 10a feed) I have a socket spur RCB which feeds armoured cable to a submersible pump that should turn on to pump out water from the bottom of my garden.

Quite frequently now, the RCB on the consumer board (in the house) is tripping, due to the pump and not the RCB on the socket spur which the pump is connected to....!!

I've turned off the pump to test it is the pump that's tripping the RCB and it looks like that's the cause of the problem as the RCB doesn't trip when the pump is connected to the feed.

How can that be?

I would have thought the socket RCB would trip before the consumer board RCB "up current" of it...?

Any thoughts?

Cheers

What's an RCB?

Are you talking about an MCB, a RCCB or a RCBO?

Either way, sounds like you've got a discrimination problem between the two protective devices. but as you haven't been clear on the type of devices and their ratings, it's hard to say.

 

[mondriver]

Thanks guys.

Sorry - my mistake.
RCB - I think of reverse current breaker (as that's what it does)!

I mean RCD - Reverse current device.

The consumer board has a Multi 9 (Vigl C45) 40a 240/415v M6 device
and the spur socket is an "Eterna RCDFSMC" 40m/s trip speed.

Not too sure what's causing the RCD to trip.

Do you think it's most likely due to the armoured cable (which has been joined apparently, or the pump (which my be overheating etc)..?

Any advice gratefully received...!

Cheers

 

[wingcoax]

I think you mean that you have a miniature circuit breaker feeding your garage. An RCD(residual current device) is usually placed after the main switch on your consumer unit and before the MCB's.

 

[mondriver]

That's correct wingcoax...

WHy would that be tripping and not the RCD in the socket spur feeding the pump...any ideas?

 

[timtheenchanter]

because the rcd in the house has already got leakage going through it, not necessarily enough to trip it, but its there, PCs, washers etc are all culprits of this.
The pump is obviously leaking enough to push the main rcd over the limit, but not the full trip of the socket rcd.

 

[AndyPRK]

If they are both 30mA RCD's

then the house one will have more earth leakage already (from other equipment) before you even connect the pump. This maybe why it trips first.

Or your garage RCD is faulty

 

[Electrifying]

You said you have a 10A device in the CU

Hi guys

I have a 10a RCB on my consumer board feeding my garage.

Now you're saying it's 40A

The consumer board has a Multi 9 (Vigl C45) 40a 240/415v M6 device

Which is it?

If it's 10A and an MCB, then it could be tripping due to being overloaded by the pump - the RCD socket wouldn't detect overload.

 

[mondriver]

Sorry - read the wrong bit..it's a 40a trip switch on the consumer board.

Cheers

 

[ban-all-sheds]

And is it that that's tripping, not the 10A fuse in the shed FCU supplying the pump?

 

[1john]

Just for future reference, it's residual current device, not reverse.

 

[Grizzly]

Just for future reference, it's residual current device, not reverse.

Already been pointed out to the OP by wingcoax 3 days ago.

Do try and keep up (or at least read the whole thread before firing off a reply)!

 

[mondriver]

Hi ban-all-sheds

Yes - it's the 40a trip switch on the consumer board that's tripping, not the RCD in the garage which the pump is plugged in to.

Cheers

 

[ban-all-sheds]

Those two trip for different reasons - RCDs operate on a completely different kind of fault to an MCB.

What is the rating of the pump, and what fuse is in its plug?