RCD tripping times, 0.4 or <200 etc.....

[Engineer54]

quick question as well re RCDs, testing a village hall with 30ma up front of everthing rcd trips on 1/2 test With message TRP on the tester fine at x1 28 ms, same as 1/2 on x5 trips with TRP message, checked the booklet with the tester says that message is leekage on the curcuit, but its the same for all 16 curcuits, TT system 194 oms RA sound like a faultly trip ? All insulation test are >500 .

You should be testing at the load terminals of the RCD with the circuit/load cables disconnected. You won't see any natural leakage then... What do you expect with 16 circuits being monitored??

 

[spark 68]

I would do a ramp test and see what value it is actually tripping at with everything disconnected, it could be that on a single up front RCD that you have too much (normal) leakage, which is pushing it over the edge at 1/2Idn, and of course as you know, it should not trip at 1/2Idn.

 

[huntos33]

I would do a ramp test and see what value it is actually tripping at with everything disconnected, it could be that on a single up front RCD that you have too much (normal) leakage, which is pushing it over the edge at 1/2Idn, and of course as you know, it should not trip at 1/2Idn.

The ramp test came in at 18ms with all curcuits/loads which can effect readings off.

 

[spark 68]

The ramp test came in at 18ms with all curcuits/loads which can effect readings off

But what was the mA reading it tripped at ?

 

[huntos33]

But what was the mA reading it tripped at ?

18 ma on ramp sorry not ms, not come across this before hence my ignorance.

 

[spark 68]

So your RCD is likely OK then, as it is over 15mA , which is @ 1/2 Idn, I usually get circa 20-24 mA or there abouts.

It looks like you may have to split the circuits up across more than one RCD due to (legitimate ?) accumulated leakage currents.

 

[Engineer54]

This is the major problem with up-front RCD devices that are in effect monitoring the whole installation, and will be seeing all the normal/natural leakages from those circuits. The same goes for these dual RCD 17th CU's especially on the larger 12 and up way CU's... Nothing but trouble, when trying to fault find nuisance tripping as well!!

 

[spark 68]

It may be worth trying another less sensitive RCD first, as 18mA is a little on the sensitive side.

But I don't think this will cure your underlying problem of too many (16 ?) circuits with accumulated leakage on one RCD, and this I think will be a problem of unwanted nuisance tripping further down the line. This is not good practice to have that many circuits on one RCD either, if not a direct contravention of the regs (reg 314).

Edit: Cross posted with E54

 

[huntos33]

Thanks for the input guys, i have a load of square d rcbo's left over from a job i did when i was on the books ( which i can offer at a knock down price ), so think i will put this down as a code 3 with a veiw of installing 1 board with seperate rccbos, given the situation and the fact the current boards are full with some curcuits doubled up i think is a fair assessment.

 

[spark 68]

Seperate RCBO's is by far the best (but most expensive!) solution, and should sort out your issues.:sifone:

 

[huntos33]

Seperate RCBO's is by far the best (but most expensive!) solution, and should sort out your issues.:sifone:

I'l be sure to do a good price as they are all ready in stock waiting for such a day !

 

[timo1]

RCBO's are a dream when it comes to fault finding, i've only fit one dual board in the last 2 years and that was by way of an apology to compensate for my mate thumping a dirty great hole in the living room plaster while working on the other side in kitchen lol.

 

[Engineer54]

All RCBO CU's are and will always be the preferred set-up and should be considered essential on TT installations!! Dual RCD CU's are basically a compromise, based purely on cost!!