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

[mondriver]

that's interesting ban-all-sheds.

The fuse in the pump is a 13amp, but I'm not sure the rating of the pump as it's quite old and the decal has worn off it.

It's not too big, so I can't imagine it's drawing too much power. 1000w max I would have thought.

 

[ban-all-sheds]

What other load is on that 40A breaker?

Anybody here got info on how a B40 and a 13A 1362 discriminate?

 

[mondriver]

The only other load is for the garage bits and pieces...strip lights...radio etc...
...all low load stuff.

In fact, I don't have anything else turned on sometimes in the garage, so the pump would be the only load being used.

Could you explain in simple easy language the difference then in what a spur socket RCD does and what the consumer board trip switch does please..?

Thanks very much

 

[ban-all-sheds]

An RCD detects an imbalance between the current flowing in the live conductor and the one flowing through the neutral.

If there is a difference it means that some current is flowing from live, or neutral, to somewhere else, probably to earth.

An MCB detects too much current flowing in the live conductor, again this could be because of a live - earth or neutral - earth fault, or also because of a live - neutral fault (often commonly called a short circuit).

As it's possible that the path is from live to earth through a person, which is a Bad Thing, we want to break the circuit long before the person comes to any harm. The problem with MCBs is that they are designed to allow large currents to flow - your 40A one will actually allow 45A to flow indefinitely, and 58A for up to an hour. It won't trip quickly until about 200A flows.

Since 100mA is enough to kill someone pretty quickly, and even 50mA if it lasts more than a few seconds, relying on an MCB to save people from electrocution is futile, hence RCDs, which react quickly to very small imbalances of current because they might be passing through someone's body.

Your RCD socket should have a sensitivity of 30mA - does it say that anywhere?

Your MCB is tripping because far too much current is flowing.

 

[mondriver]

ban-all-sheds

Thanks very much for that. Makes complete sense.

Yes - the RCD has a 30ma trip current rating.

Are you saying then, that the MCB could be tripping because there is a live/short maybe in the armoured cable running to the pump, or is it the pump could be faulty drawing too much current?

I've ordered a new pump, which should be arriving today - and I hope I don't have to rip up all the armoured cable as it's about 100ft long (installed by a previous owner). I know there is a join somewhere in it. Maybe the earth integrity is no good..?

Thanks for your continued help...really appreciated

Cheers

 

[ban-all-sheds]

Are you saying then, that the MCB could be tripping because there is a live/short maybe in the armoured cable running to the pump, or is it the pump could be faulty drawing too much current?

Either, although if I had to guess I'd say it wasn't the pump. The 13A fuse in the plug should blow in 0.1s at between 50 and 180A, approx, which is a lot faster than the B40 MCB.

In theory.

I know there is a join somewhere in it.

Do you know where and why?

Maybe the earth integrity is no good..?

You'd need an electrician to check the integrity of the cable.

 

[mondriver]

The cable was joined in about the last 5m apparently as the outlet was moved about a further 5m away from the original position.

Do you think it could be the join that's causing problems?

 

[ban-all-sheds]

It could be - depends how it was done.

It's not difficult to join buried cable in a way that works.

It's even easier to cock it up.

 

[mondriver]

Would an electrician be able to find out if the cable is good or bad then?
Is it a big/expensive job?

Cheers

 

[ban-all-sheds]

Would an electrician be able to find out if the cable is good or bad then?

Yes.

Is it a big/expensive job?

Not to test it, but there'll be a minimum charge.

Now you've ordered a new pump you might as well wait and see what happens.

 

[AndyPRK]

assuming there is a short length of cable and 13A plug on the pump, another option would be to unplug it and leave the burried cable powered up for a few days and see if you have a trip or not

 

[mondriver]

Well...update:

Installed the new pump - and no trips so far after an afternoon of it operating.

Not too sure why it was tripping the breaker on the consumer board, but a new pump seems to have solved it...(so far..!)

Hope it doesn't trip later on now that I've said that!!

Cheers