Two Lutron RA2 Switches - both switched on, and RCD trips, either on and no problems

[Paul F]

Only a DIY'er here, usually safe and competent enough to fix straight forward problems, but this one has me stumped. I have two outside lighting circuits running through Lutron RA2 dimmers. Both go back to a Hager MTN106 RCD. All been working fine for over a year, but now the breaker keeps tripping. All LED lamps and well within 150w capacity of each dimmer controller. Common feed from the RCD split to the two circuits, and I can leave either circuit connected independently without problems. As soon as I connect both circuits, the RCD trips. Changed the Wago connector blocks hooking it all together in the junction box and tried a differnet RCD but the same problem. All installed by a qualified electrician, but assumed it would be an easy fix without calling him back. Any ideas?

 

[Avo Mk8]

I'm not clear what the outside circuits comprise, but it is possible there is a small amount of earth leakage in each circuit, where each is not enough to trip an RCD, but together they do. Such leakage can be inherent in the design of acessories or PSU filters, or occur through the ingress of moisture etc.
You could check this out by using an earth leakage clip-on milliammeter on the supply to each circuit.

 

[Paul F]

I'm not clear what the outside circuits comprise, but it is possible there is a small amount of earth leakage in each circuit, where each is not enough to trip an RCD, but together they do. Such leakage can be inherent in the design of acessories or PSU filters, or occur through the ingress of moisture etc.
You could check this out by using an earth leakage clip-on milliammeter on the supply to each circuit.

One circuit has 8 bollard lights and the other has 4 bollards and 8 recessed spots in the side of a planting bed. All fittings are IP65 rated but water ingress is a distinct possibility. I hadn't thought about the combined effect of earth leakage. Will investigate further. Many thanks