rcd not tripping

[matt12321]

looking for a fault on a caravan where the rcd trips when a main earth is added. with no main earth the rcd want trip. the caravan has only got an earth path via bonding from the earth rod to the db and no main earth from the earth rod to the db.

zs is 66.4 on sockets 67 on lights and 66 on the shower.

the board has been tested and no faults found. as soon as u add 4mm or a 10mm main earth the rcd trips when say the cooker or shower are turned on.

 

[sjm]

looking for a fault on a caravan where the rcd trips when a main earth is added. with no main earth the rcd want trip. the caravan has only got an earth path via bonding from the earth rod to the db and no main earth from the earth rod to the db.

Are you saying that there is a connection, earth cable, between the db and earth rod?
When you then say main earth what do you mean?

 

[topquark]

Sounds like a right bloody mess

What is the supply earth at the meter (assuming the van is individually metered) ... often TNS, then SWA to the CU.

I'd be tempted to sort out the earth first before looking for errant equipment.

 

[topquark]

Also what are the arrangements for RCD(s) is there just one or is each circuit protected individually?

 

[Des 56]

Sorry,but I got lost with the first paragraph

 

[SirKit Breaker]

Sorry,but I got lost with the first paragraph

So did I

 

[matt12321]

this is an old set up. swa in coming to rcd, rcd to card meter, then meter to db. there is currently no earth from the earth rod to the db. only from the caravan frame to the db. with this as it is the rcd doesnt trip. when u add an earth straight from the rod to the db the rcd will trip when ever the cooker or shower is turned on. all other caravans have the same set up and same earthing arrangement. its just this single caravan

 

[Des 56]

I would be tempted to fit the rod and earth to the caravan distribution board and re do the insulation resistance test and go from there

 

[matt12321]

ive tried that and IR is greater than 299 through out, but still when u turn appliances on it still trips witht he earth connected

 

[topquark]

From what you've described the RCD is before the meter? OR is/are there RCD(s) in the CU as well?

 

[matt12321]

rcd is before the meter and separate to the db

 

[topquark]

Then it sounds like you have a fault either in the wiring (or an appliance(s)), or possibly a faulty RCD. Do a ramp test and see at what current the RCD is actually tripping ... typically 20 odd milliamps (20-29) for one rated at 0.030 amps. If it's substantially less than that then replace it.

 

[matt12321]

all circuits have been tested, no faults found, rcd has been replaced twice with ones i know that work. appliances work fine when theres no main earth tho. rcd trips at 26.6 and 14.9 before appliances are turned on with main earth in place

 

[topquark]

all circuits have been tested, no faults found, rcd has been replaced twice with ones i know that work. appliances work fine when theres no main earth tho. rcd trips at 26.6 and 14.9 before appliances are turned on with main earth in place

How can there be two different trip currents for the RCD?

The only thing that leaves, if all tests are ok, is leaky appliances. The reason that it won't trip before the "main earth" is connected is that there is no where for the current imbalance to go (so line/neutral are in balance).

 

[matt12321]

1 x rated current of rcd
5 x rated current of rcd

so its gotta be the cooker then