RCBO tripping on outside lights

[An Buachaillín Bán]

Hi all,

Wondering if you could offer some advice please.
I carried out a small outdoor lighting project today at a commercial property. 4 lights controlled by a photocell.

As a background, the cables were installed by the resident electricians. 1.5 SWA at all 4 lights. The supply is ran back to a 10amp C type mcb near the main building.

Site management requested that the lights have a timer and photocell on them, which gives them a couple of options going forward. So in a large JB, I brought the supply cable to a 6A rcbo, onto the timer, from timer on to photocell, from photocell to a contactor, which brings on lights when pulled in by photocell.

However, when I powered up, the 6A rcbo tripped. After checking wiring was OK, I chanced replacing the rcbo for an mcb just to see. And it didn't trip. So I'm assuming it's a neutral issue, as all neutrals were common.

Can anyone shed some light on what might have caused this?

Thanks all

 

[westward10]

If you have interconnected the neutral conductors between the lighting and control circuits an RCBO it is bound to trip. Aside from these circuits needing separation as you have created a dangerous situation does it actually need an RCBO.

 

[An Buachaillín Bán]

If you have interconnected the neutral conductors between the lighting and control circuits an RCBO it is bound to trip. Aside from these circuits needing separation as you have created a dangerous situation does it actually need an RCBO.

Thanks for the response.

I'd be more of a domestic sparks but I'm now picking up more work in commercial sector. So from that I did understand, to an extent, that this separation was needed. In my own head I wanted to offer more protection to the circuit by using an rcbo, ie O/Load and S/Circuit protection. And isn't always a good idea to have some form of rcd protection on certain external installs?

Just to add, the mcb feeding our control box was a 20A. So that had RCD protection of its own. Is it correct for me to assume I crossed the neutrals given that the 20A was coming off an rcd neutral bar?

 

[westward10]

I'll avoid RCD protection unless it is absolutely required for additional or fault protection.
Not really understanding your last sentence.

 

[kevincoolnomix]

Hi all,

Wondering if you could offer some advice please.
I carried out a small outdoor lighting project today at a commercial property. 4 lights controlled by a photocell.

As a background, the cables were installed by the resident electricians. 1.5 SWA at all 4 lights. The supply is ran back to a 10amp C type mcb near the main building.

Site management requested that the lights have a timer and photocell on them, which gives them a couple of options going forward. So in a large JB, I brought the supply cable to a 6A rcbo, onto the timer, from timer on to photocell, from photocell to a contactor, which brings on lights when pulled in by photocell.

However, when I powered up, the 6A rcbo tripped. After checking wiring was OK, I chanced replacing the rcbo for an mcb just to see. And it didn't trip. So I'm assuming it's a neutral issue, as all neutrals were common.

Can anyone shed some light on what might have caused this?

Thanks all

Did you test all lights individually before installing them? One of them might be the problem. Kind regards, Kevin

 

[An Buachaillín Bán]

Did you test all lights individually before installing them? One of them might be the problem. Kind regards, Kevin

Hi Kevin,

Thanks for the reply. No I didn't test them individually, as when it tripped a couple of times, I changed the rcbo out for an mcb and all lights worked fine. I had cross connected neutrals I think.

Thanks