Tripping RCBO

[gman76]

Circuit is as follows:
16A RCBO feeding small CU with 30mA RCD + 15A MCB for one double socket + 5A MCB for lights.

The lights are two 2ft fluorescents with 2 way switching, for some reason the lights intermittently trip the RCBO when they are switched off. But only from one of the switches.

Any ideas?

TIA

 

[securespark]

Why have you got RCBO & RCD?

 

[gman76]

I'm not sure - I didn't design the circuit. But the RCD never trips.

 

[securespark]

Check the switch for loose connections?

 

[gman76]

Yes, I've checked - all nice & tight.

To elaborate - the small CU feeds a lean-to greenhouse attached to house. GH was replaced, so I stripped out the electrics (some non IP rated fittings & mini trunking) beforehand & refitted it using IP rated accessories & 20mm conduit in the new GH.

I retained the two light fittings as they are IP rated. All the cables enter the rear of one of the lights & then in singles through the conduit, through the second light to socket & light switch.

The second switch is in the kitchen, this is the problematic one.

My folks say that it has historically tripped occasionally. Now it seems much more apparent.

I'm quite puzzled!

 

[securespark]

Best to check the insulation resistance then. And the operation of the RCD's. You may need a spark.

 

[gman76]

Thanks for your input secure.

I think I might change the RCBO to an MCB and see what happens.

If the RCD continues to trip - like you say, it may be sparky time. I don't have a Megger.

Thanks again.

 

[Iggifer]

I think I might change the RCBO to an MCB and see what happens.

That's ok as a very temporary measure. But it's likely there's an RCBO there as the submain cable is installed in such a way that it requires RCD protection.

If it's an SWA cable from the dis board to the sub board, then an MCB is what should have been installed in the first place and is fine as a permanent change.

 

[gman76]

The feed is 2.5 t &e and exits the CU which is at ceiling level into the loft (bungalow), then is surface clipped down the wall into the secondary CU, so I guess it will be ok long term?

 

[Iggifer]

The feed is 2.5 t &e and exits the CU which is at ceiling level into the loft (bungalow), then is surface clipped down the wall into the secondary CU, so I guess it will be ok long term?

So long as it's completely visible throughout it's run then that will be fine. That's how it should have been done originally.

Make sure you get the correct manufacturer of MCB, mix and matching is a no-no

 

[gman76]

Starbreaker so should be easy enough.

Thanks for the advice.

 

[Iggifer]

Yea even Screwfix stock Crabtree (if it's the current range)

 

[Risteard]

That's ok as a very temporary measure. But it's likely there's an RCBO there as the submain cable is installed in such a way that it requires RCD protection.

If that is the case then it absolutely wouldn't be acceptable, even as "a very temporary measure."

 

[flameport]

Temporary usually ends up as being permanent..
Do it properly the first time.