Outside light fed from 2 circuits

[HappyHippyDad]

I went to a small job today to change a sensor for an outside light. I expected it to be straight forward.

I started by isolating the supply, which ended up taking longer than expected as it needed 2 circuit breakers to be off in order to isolate it.

I explained that i would need to remedy this first before changing the sensor but the customer didn't want to pay for the extra work so that was the end of the job.

My question is, how does an outside light or indeed anything get fed from 2 circuits in the first place? It must be working from one circuit so why does someone feel the need to add it to another circuit as well? How could this fault occur?

 

[westward10]

Could be part of the emergency lighting, it is not uncommon to see maintained fittings with separate switch and charge supplies. This charge supply can also be linked through the general non emergency fittings. They should ideally be on the same circuit but sometimes simple lighting circuits blow people's minds.

 

[Octopus]

I would be recommending that the lighting circuits be investigated properly ....................

Of is it a case of the SL and PL coming from different points?

Some customers can be stupid ..............

 

[HappyHippyDad]

Could be part of the emergency lighting, it is not uncommon to see maintained fittings with separate switch and charge supplies. This charge supply can also be linked through the general non emergency fittings. They should ideally be on the same circuit but sometimes simple lighting circuits blow people's minds.

This was fed from 2 different socket circuits, domestic house.
I just can't see in what scenario this happens!

 

[Octopus]

Hum ......... what about the socket circuits - were they "dual fed" too?

I found a 2G socket on a lighting circuit yesterday ..............in an outhouse!

 

[HappyHippyDad]

Just had an unexpected email from the chap saying he'd like an electrical report done on the house! I guess he had a think about it.

The last report was 2000, so I suggested it was time for another.

I shall update according in a month or 2 on the dodgy socket circuits!

 

[Octopus]

Just had an unexpected email from the chap saying he'd like an electrical report done on the house! I guess he had a think about it.

I normally sew the seed of investigation with customers then leave them to ponder .................. the hard sell isn't my tactic, nor does you any favours with your clients....

 

[KEV 1 N]

There’s two circuits interconnected somewhere, if it’s sockets it could be the upstairs and downstairs legs of the ring mixed up at DB, unless the two ring circuits are on separate RCDs.
If there’s just one RCD, then the interconnection won’t cause it to trip, the problem only comes to light(pun intended!) when you want to isolate an individual circuit, and end up having to have two MCBs switched off.
Lighting circuits could be interconnected at the switch at the bottom of stairs where one controls the up light and the other for down.

 

[Pete999]

Now where is that bottle of Scotch Someone gave me at ELEX today? thanks mate a good pain killer.

 

[westward10]

This was fed from 2 different socket circuits, domestic house.
I just can't see in what scenario this happens!

Ah I assumed commercial, sounds like a wiring mess as there is no reason for it.

 

[Dave OCD]

HHD - This will almost certainly be the two RFCs wrongly connected at the DB, one leg from each ring in both MCBs, it's dodgy but seems to happen quite often.

 

[Wilko]

This was fed from 2 different socket circuits, domestic house. I just can't see in what scenario this happens!

Glad to hear you didn't get a belt off it HHD !
Being a competent and diligent person it's understandable you are trying to make sense of this circuit, but I think it's a waste of valuable drinking time . Edit - sorry didn't mean to sound offhand - fix first, then drink.

 

[Baddegg]

Glad to hear you didn't get a belt off it HHD !
Being a competent and diligent person it's understandable you are trying to make sense of this circuit, but I think it's a waste of valuable drinking time .

Smoking time.....he’s a hippy

 

[SJD]

I recently came across an outside PIR light fed from 2 different circuits. The previous owner had helpfully put a note in the fuse box to isolate the two circuits before working on one specific light.

The reason - the light with PIR was to come on either when the PIR operated (from socket circuit via FCU) or when the other outside lights were turned on (switched live from lighting circuit).

What the previous owner had failed to appreciate was the case when the PIR operated and the outside lights were turned on, when the two circuits were cross connected. I.e. beware of working on the socket circuit on a dark evening!

 

[HappyHippyDad]

HHD - This will almost certainly be the two RFCs wrongly connected at the DB, one leg from each ring in both MCBs, it's dodgy but seems to happen quite often.

Cheers Dave that makes perfect sense. A simple fix too!