RCD trip on Zs

[highspark]

Was at a job today and did a Zs on sockets which tripped the RCD. Can't isolate circuit as computers needs to stay on. I've been asked to go back next month when everything can be isolated to find the fault. Guys in office say it happens from time to time when things are plugged in. I first presumed fault appliances being plugged in but it happend on a Zs test. Anyone any thoughts on the fault? Would appreciate some experiences from others on this type of fault. I'm going to ramp test the RCD first of all the follow on tests from there!

 

[topquark]

You may find that the accumulation of leakage (ostensibly valid) from the computers is accululating to a point that's almost tripping the RCD, the addition of the small current for Zs measurement (or other uses) is then sufficient to push the leakage over the threashold of the RCD.

Suggest checking the amount of "normal" in use leakage now (all computers on) and checking the threashold (ramp test) of the RCD on your return.

 

[ian.settle1]

1- Possible cause of RCD tripping is that it is near to 30mA and the extra equipment is taking it over.

2- What type of RCD tester are you using as when carrying out a Zs test it normally puts 25A down the circuit to get the Zs reading which is a hell off a lot more amps than 30mA. You need to use the low setting when carrying out a Zs test with RCDs fitted.

 

[highspark]

Thanks top!

Hi Ian I'm using a dilog. It's always fine with Zs tests. I feel there may be a leakage current problem as diagnosed. What solutions can we have? How about splitting the ring into 2 radials and putting on separate RCD's so leakage current is spread across 2 RCD's instead of the one?

 

[highspark]

Thanks top!

Hi Ian I'm using a dilog. It's always fine with Zs tests. I feel there may be a leakage current problem as diagnosed. What solutions can we have? How about splitting the ring into 2 radials and putting on separate RCD's so leakage current is spread across 2 RCD's instead of the one?

 

[topquark]

Splitting the circuits is probably the best option if it is accumulated leakaged.

 

[jimmy_one_ball]

Aren't you supposed to have seperate cpc terminals in the socket outlet plates? I'm just recently qualified so only got classroom experience to speak of, but thats what we were taught. Also separate the cpc terminals in the CU or DB so the cpc has seperated terminations all around the ring circuit. Also if you make two radials then you can link the cpc's together from the end socket outlet of each circuit to form a cpc ring. This is supposed to cure functional earth currents. I would be interested to hear if anyone has proved that this works!

Also just as an afterthought, stating the obvious, using three leads stops RCDs from tripping if your tester has this.

 

[Sintra]

Jimmy the method you have stated doesn't "cure functional earth currents". This method is used to minimise a cpc loss on a circuit.