New shed circuit tripping RCD at house consumer unit

[solgen]

Hi,

I've recently run 4mm 4 core SWA from a 20A MCB house consumer unit to a garage unit installed in a shed 50M away. The garage unit has 16A and 6A breakers protected by 40A 30mA RCD main switch. All wiring connections seem to be correct, however, as soon as anything is placed under load either from socket or light, the RCD back at the house consumer unit trips. I have visually inspected everthing so far and cannot see any problems.

I looked for neutral problems and cannot see anything amiss.

Can anyone suggest where the problem maybe?

Thanks

 

[jeremy]

Have you done your IR tests?

 

[monkeyelectric]

Have you tested anything?

 

[Hawk81]

Have you done any testing?? What sort of trip is in the house? 30mA? Are you sure you have the neutral in the correct bar in the house CU? If it is a 30mA RCD in the house then you don't need a 30mA in the shed

 

[Octopus]

Why did you put a 30mA RCD in the shed if there's one in the house??

If its worked for a while may be its got a bit wet

 

[ste mac]

From the title of your post and the content of your post it would seem you have 2 RCD's in series. Is that correct?

- - - Updated - - -

Too slow typing!!!

 

[Deleted member 26818]

I would imagine, that the RCD tripping indicates there is a fault.
It could conceivably be due to an accumulation of earth leakage from a number of circuits being protected by the RCD at the house.
Have you tried switching off the other circuits and then switching on a load in the shed?

 

[Robospark]

Your neutral for the shed circuit at the house CCU is in the wrong neutral bar.

50M on a 4mm pulling up to 20A - did you think about volt drop?

Nowt to do with your present problem just sayin.

 

[Hawk81]

Your neutral for the shed circuit at the house CCU is in the wrong neutral bar..

How can you say this with such certainty without all the facts or seeing the job????

 

[markc123]

Most common thing i find with shed installs is water getting into the fittings somewhere, we've had a lot of rain recently and if its just started happening - this is where, if i were you, id probably start looking first.

Spiderman onto the shed roof and see if the felt / tiles (whatever it is) are knocking on death's door.

As above, IR test.

 

[Robospark]

I've seen it numerous times. Everything seems fine - IR all circuits, all +100m, then only when you connect a load the supply RCD trips.
As the neutral current is not returned to the sub circuit RCD it throws it out of balance and trips.

 

[Hawk81]

I've seen it numerous times. Everything seems fine - IR all circuits, all +100m, then only when you connect a load the supply RCD trips.
As the neutral current is not returned to the sub circuit RCD it throws it out of balance and trips.

I know all this but we can say that is definitely the problem here

 

[Robospark]

As the RCD will constantly monitor P-E and N-E faults in no load conditions I would say it's highly likely to be a wrongly connected supply neutral but you are right, there maybe circumstances where it could be something else.

Solgen any chance of a picture of the CCU?

 

[dim_bulb]

I think the op just needs to get his tester out and give us some readings
trip times on both rcds?

 

[trev]

My money is on an IR issue.

 

[Robospark]

The other circumstances where this would occur would be that there is, by chance, faults on all loads connected - but why isn't the local RCD tripping! Is it less sensitive than the house CCU RCD - could be!

I'll stick with wrong neutral bar.

 

[Octopus]

Hi,

I've recently run 4mm 4 core SWA from a 20A MCB house consumer unit to a garage unit installed in a shed 50M away. The garage unit has 16A and 6A breakers protected by 40A 30mA RCD main switch. All wiring connections seem to be correct, however, as soon as anything is placed under load either from socket or light, the RCD back at the house consumer unit trips. I have visually inspected everthing so far and cannot see any problems.

I looked for neutral problems and cannot see anything amiss.

Can anyone suggest where the problem maybe?

Thanks

Yup. you need to post more info mate.

 

[Silly Sausage]

I'll stick with wrong neutral bar.

I'll stick with a complete test of the whole affair and bin one of those RCDs.

 

[markc123]

This is the electricians forum, how the hell are we supposed to know whats going on here?

if i were the OP id take it to the plumbers forum.

They know best.

 

[Pauldicker]

Ive got a similar issue with a customer. Although i have not done any tests yet as i popped in when passing. 40amp mcb in the cu not on rcd. 4mm Swa to summer house in garden. 40amp rcd as main switch in summer house.
The RCD trips on every circuit when load is required. But is fine when all mcb's are off, Now it was working fine up until a couple of months ago when it stopped.
So im going back when they return from their hols in 4 weeks or so im thinking the swa has failed ir or faulty rcd.