RCD trips for Zs

[Podooser]

The flat is on the ground floor and therefore the main MCB on the CU is an RCD. When doing the Zs for all the circuits I use the RCD setting on the EFLI setting on my Alphatek. This works fine for the ring and the cooker final circuits ie no RCD tripping. However it does trip on the lighting circuit test. Should I use the calculated Zs for the Schedule Of Test Result form and state this somewhere on the form? (measured Ze plus R1+R2).

 

[ricicle]

I think you mean the main SWITCH on the CU is an RCD.Do you mean the lighting circuit MCB trips when you do the loop test?

Loop testers do have a tendancy to trip 6A MCBs

You will therefore, as you say, have to note it down as the calculated Zs

 

[RF Lighting]

Does it trip the MCB even when your tester is on the soft test (Non RCD trip) setting?

 

[Podooser]

The main switch is a 100A / 30mA RCD and it trips when I do the soft test on the lighting circuit only.(The lighting circuit 6A MCB does not trip)
All OK on the other circuits.

 

[securespark]

The Alphatek No. 10 test is the soft test. They do not trip the breakers, because they only circulate mA.

To me, this suggests a fault on the lighting circuit. Do a No. 1 test on a ceiling rose and see if it trips on the first two tests (the half times tests). If it does, I would say there is a wiring fault somewhere on that circuit. Although having said that, I would have thought it would be picked up on a test elsewhere in the system...

 

[Podooser]

... I would say there is a wiring fault somewhere on that circuit. Although having said that, I would have thought it would be picked up on a test elsewhere in the system...

Securespark, the R1+R2 at the furthest point on the lighting circuit is 2.01 ohms, the measured Ze is 0.51 ohms (TN-S). So Zs = 2.52 ohms still bellow 6.4 ohms for type B 6A breaker. As there is no fault on the circuit why would it trip the RCD on this circuit and not on the ring etc.