Rccd Tripping

[pjelec]

Can anyone help I am really confused.
I am working on a camp site where Scattered around the small site is 5 fuseboards each supplying 10 caravans each. Each box is not connected to an RCCD. In each fuseboard there is a 20a Circuit Breaker and 30ma 40a RCCD feeding each caravan. Most of these RCCDs trip out at least once a day. Never once has the RCCD tripped in the fuseboard in the Caravans

I have done an Insulation Resistance tests on the caravans and the cable to the vans and all was clear. One caravan had a low reading in the caravan and on the main cable feeding it. I found the fault inside and replaced the cable to the van. It is still tripping.
As a test I disconnected all RCCDs in one fuseboard controlling 10 vans and in that week nothing tripped.

I can not understand why this happens. An Rccd will only trip if there is a fault after it. If the fault is in the van it should trip out the caravan rccd.
Could it be overload and it is missing out the 20a circuit breaker.

Any help would be appreciated Thanks

 

[pushrod]

At the fuseboard outside the rcd feeding thevan is fed from a 20a mcb, which does not trip out. This means that the rcd is not even at its full capacity.

the rcd trips on a 30 mA imbalance between phase and neutral.

 

[pjelec]

Not that this makes any diffence but I live in Tenerife and have an Electrical business for the last 7 years. The Voltage is the same and rcds and Mcbs are the same. The only differece is would be regulations. We do get very low voltages at times even down to 200v. This means the amps go up and could cause tripping if a fault is close to 30ma. You would think the one in the van would trip first as the voltage would be lower than the one outside due to voltage drop.

 

[pjelec]

I know how an rcd works with the imbalance. But i can not find any leakage to earth. This is what is throwing me. Remember this is not just one caravan doing this but several of them.

the rcd trips on a 30 mA imbalance between phase and neutral.

 

[Guest123]

Have you tried an earth leakage clamp meter on the earthing conductor to see if there is any fault at all present???

 

[davelerave]

i assume there''s no SPD between the 2 series rcd's

you need to do the tests anyhow and sort the discrimination issue