rcd, rcbo query

Rockomuir · Jun 27, 2013

Been working on my local campsite and the client has mentioned that he is having a problem with his caravan hook ups. Basically there are 5 hook ups protected by a type c16amp rcd. Each of these hook ups are supplied from buried armoured cable from a type b20 rcbo. the client is complaning that the rcbo trips before the rcd. A few of the rcds seems to not work properly and need replacing but i think this problem has exsisted for a while. I was just after some advice on likely solutions and whether it has anything to do the type b and type c rcbo and rcd.

Many Thanks

Brightspark2 · Jun 29, 2013

Rockomuir said:
sorry about the late replys , the joys of bt home hub being out of action for 2 days. Thank you for the replys. Yes they are two rcbos was not thinking when typing. I not sure yet if the tripping is overcurrent or earth leakage as i am not due back on site till monday. I have got a feeling it will be overcurrent though. To clear a few things up there are 5 type b20 amp rcbos. Each one individually supplys a caravan hook up where there are 2 type c 16 amp rcbo, both rcbo are 30ma Should i change the 20 amp Rcbo to time delay?

The first RCBO would need to be time delayed otherwise if they are both 30mA it just depends which device is quicker as to which one will trip first.

Richard Burns · Jun 29, 2013

So you have this arrangement repeated five times?

[ElectriciansForums.net] rcd, rcbo query

Earth fault: e.g. if both 16A have 20mA fault current then they will likely not trip but the 20A will see 40mA and will trip.

If the current is rising on a fault and reaches 30mA if the 20A RCBO take 150ms to trip and the 16A 100ms then the 16A would trip, but if one 16A has normal 8mA leakage and the other goes into fault then the 20A would see 30mA possibly 50ms before the 16A and so would go first.
Almost random which would go but erring toward the 20A as it sees more fault current.

Over current: e.g. if both are taking 16 A then the 20A will go in about 15mins but the 16A s will not go.

You need to get discrimination between the two points, for over current this would be a two step gap e.g. 10A to 20A or 16A to 32A (in very rough terms, should really be checking the manufacturers tripping characteristics). For earth leakage it would be 100mA time delay upstream and 30mA non time delay down stream.

Knobhead · Jun 30, 2013

Rockomuir said:
sorry about the late replys , the joys of bt home hub being out of action for 2 days. Thank you for the replys. Yes they are two rcbos was not thinking when typing. I not sure yet if the tripping is overcurrent or earth leakage as i am not due back on site till monday. I have got a feeling it will be overcurrent though. To clear a few things up there are 5 type b20 amp rcbos. Each one individually supplys a caravan hook up where there are 2 type c 16 amp rcbo, both rcbo are 30ma Should i change the 20 amp Rcbo to time delay?

In the time between now and Monday, the unhappy caravaners have hitched up and cleared off to South West Kent.

You have a feeling? So do I, my feeling is you haven't a clue that you are doing or talking about!

bartkusal · Jun 30, 2013

Tony said:
In the time between now and Monday, the unhappy caravaners have hitched up and cleared off to South West Kent.

You have a feeling? So do I, my feeling is you haven't a clue that you are doing or talking about!

And with a weather like this weekend, I bet the park is full like never:90: