What in an installation can make RCD's trip at 17ms when, its not faulty?

[LlandrilloSpark]

Hi fellas

Can anybody think of a reason why a new RCD which ramps at 28mA in one installation trips at 17mA in another?, is it a supply problem?, on the X1 test on 0 degrees it trips in 31ms but on 180 degrees I get noS ?, tester is a megger RCDT 320

Cheers

 

[a1guvner]

what about at X5 does it trip on both sides

 

[LlandrilloSpark]

Yes m8 trips on that no prob

 

[Silly Sausage]

Were you testing at the RCD?
Were the load cables disconnected?

 

[a1guvner]

Yes m8 trips on that no prob

Have you got another RCD available to compare results/actions against

 

[CrazyScozzese]

There are lots of variables that affect RCD performance.

The main one is whatever is on the load side biasing the mechanism electronics, try a test with it disconnected. Minor differences can be caused by everything from the Voltage, Ze, Zs, noise or currents on the earthing/bonding, other parallel ccts, temperature of RCD, ditto your tester, the charge in the batteries, and even if the RCD case is under stress in some way.

Had a pdf on this somewhere, will try to look it out.

 

[Engineer54]

There are lots of variables that affect RCD performance.

The main one is whatever is on the load side biasing the mechanism electronics, try a test with it disconnected. Minor differences can be caused by everything from the Voltage, Ze, Zs, noise or currents on the earthing/bonding, other parallel ccts, temperature of RCD, ditto your tester, the charge in the batteries, and even if the RCD case is under stress in some way.

Had a pdf on this somewhere, will try to look it out.

Another reason to always do your RCD device testing at the load terminals of the device itself and not downstream at say a socket outlet. Your testing the ''Device'', NOT the circuit!! Your other specified BS7671 circuit testing had done that already, .....Well i hope anyway!! lol!!!

 

[Marvo]

Power factor and harmonics could make a difference or as already stated above maybe temperature.

 

[LlandrilloSpark]

Thanks for the replies fella's, interesting, I remember being taught to test an RCD on a circuit, this appears to be when i have most problems with them, so on new installs i often put a socket on a 16A breaker next to the ccu if i have a spare way, i use this for the rcd testing and have no trouble.

 

[aaelectric]

What tester has a ramp setting and how do you know how much earth leakage there is?

 

[Engineer54]

Thanks for the replies fella's, interesting, I remember being taught to test an RCD on a circuit, this appears to be when i have most problems with them, so on new installs i often put a socket on a 16A breaker next to the ccu if i have a spare way, i use this for the rcd testing and have no trouble.

It's fine to ''check'' an RCD at say a socket outlet on it's circuit, but when it comes to doing formal testing of the RCD device then that should always be at the device itself!! There's no reason to do what you do with a temporary socket....

I don't know who told you or taught you, to do your formal testing of RCD devices downstream, but if you check with any of the manufacturers, they will tell you differently.

 

[MarkieSparkie]

What tester has a ramp setting and how do you know how much earth leakage there is?

Most modern MFTs and RCD testers. The tester ramps up the leakage current in discrete steps, usually 1mA at a time, until the RCD trips, the tester displays the final current step value.

 

[LlandrilloSpark]

Megger RCDT320 has a ramp test and my Earth leakage clamp meter tells me how much if any current leaks to earth