Emergency lights fed by two supplies

[Sparkymark123]

Been doing some work in a school today and came across the following situation.

The school has had a recent a re-wire of part of the school in the last 6/7 years. In the 3 classrooms they have fluorescent light with some fittings have emergency battery back up inside. However the permanent charging feed is fed from a different circuit to the normal switched supply. In each classroom the two supplies are on the same phase but they share the same neutral. So they've basically taken a sheathed brown and cpc around all the fittings in a classroom but from a totally different circuit, pretty rough if you ask me. I was surprised to see such work on such a recent rewire job. I just cant get my head around what they were trying to achieve, am I missing something or is just incompetent wiring? Not least because the emergency lights in that room would not operate if the normal supply was interrupted on that circuit.

 

[odawire]

Been doing some work in a school today and came across the following situation.

The school has had a recent a re-wire of part of the school in the last 6/7 years. In the 3 classrooms they have fluorescent light with some fittings have emergency battery back up inside. However the permanent charging feed is fed from a different circuit to the normal switched supply. In each classroom the two supplies are on the same phase but they share the same neutral. So they've basically taken a sheathed brown and cpc around all the fittings in a classroom but from a totally different circuit, pretty rough if you ask me. I was surprised to see such work on such a recent rewire job. I just cant get my head around what they were trying to achieve, am I missing something or is just incompetent wiring? Not least because the emergency lights in that room would not operate if the normal supply was interrupted on that circuit.

So its the same phase but on a different breaker? can you not just switch it over to the same breaker?

 

[Darkwood]

If its wired as you say it should have been overseen by an electrical clark of works been recent and a school, to cover your back and clear any association it may be in your interest to call this in, if you are sure its wired as you say then yes sounds pretty poor as a failure of the lighting circuit wouldn't bring the light on and as you say a loss of permanent feed would initiate emergency light even though the light was still on.... if the electronics allowed this to occur? Also shared neutral, confusion for isolation .....where do i end....I suspect it was wired correctly but the idiot connecting the board up put it over different circuits, this shows the circuit hasn't been tested properly and the sparky connecting circuit isn't competent. Ask the school for the test sheets and have a browse and confirm the set-up is a connection error and doesn't go deeper.

 

[Sparkymark123]

It might be a solution in the classroom but would have to check the loads. The circuit charging the battery isn't just a dedicated circuit for that, it also feed some further lights in the same room. No easy solution in the corridors though, probably wouldn't get all 26 lights or so lights on one mcb and it's plasterboard ceiling with flat roof above! As darkwood mentions, I can't believe it wasn't picked up originally.

 

[odawire]

It might be a solution in the classroom but would have to check the loads. The circuit charging the battery isn't just a dedicated circuit for that, it also feed some further lights in the same room. No easy solution in the corridors though, probably wouldn't get all 26 lights or so lights on one mcb and it's plasterboard ceiling with flat roof above! As darkwood mentions, I can't believe it wasn't picked up originally.

are you sure the rooms lights aren't balanced across more than one phase? if it feeds some lights in the room then its not totally on a different circuit. was it a workshop?

 

[Darkwood]

What kind of fittings are these, are they standard emergency battens?

 

[Sparkymark123]

In the classroom there are 4 lighting circuits, 2 are general lighting and 2 are for effect in a dropped ceiling shaped like a cloud! All 4 are on different circuits but on the same phase.

The effect lighting are just standard fluorescent fittings with a coloured sheath. The general lights are circular fluorescent t5 lamps fittings that are dimmable. The effect lighting is just switched via an mk grid switch and they've fitted an em k/s in the same grid and taken the feed off the switch.

 

[Eggster71]

I come across similar in fire stations with their "call lighting" which is automatic when they get a shout... A lot of them have a "call lighting" db which is contactor supplied and they simply run out switchlines to the lights they need.

Most of the work I do is following EICRs so shower ltg needs rcd protection etc....sooooo borrowed neutral = RCD trips..

If I come across it irrespective of RCD requirements I have to rectify it and in most cases it means refeeding the lights. I think you have 2 crap choices, either partial rewire.....and check the rest of the school as well.....or as mentioned have a go at putting both ccts on the same breaker, not best practice but a damn site better than borrowed neutrals!

 

[Sparkymark123]

I think the doubling up of circuits is going to be making the best of a bad job to be honest. With a flat roof and nicely decorated plaster ceilings the options without causing mass destruction of the decor is limited I reckon.

 

[sxdave]

I have come across a similar situation to this and am looking for a suitable solution. The problem is with 2D fluorescent light fittings that are now failing due to age. Some of these 2D fittings are also emergency lights. They have two complete feeds (L, N & cpc for normal lighting and another L,N & cpc for charging the E/L battery).
I have not seen any replacements that cater for the two separate supply feeds. All LED replacement fittings I have seen cater only for single feed (L, Sw L, N & cpc).

Some background on the installation: A mid-late nineties installation I believe. Single phase supply to the building, RCDs on power ccts but not lighting.

 

[DPG]

I have come across a similar situation to this and am looking for a suitable solution. The problem is with 2D fluorescent light fittings that are now failing due to age. Some of these 2D fittings are also emergency lights. They have two complete feeds (L, N & cpc for normal lighting and another L,N & cpc for charging the E/L battery).
I have not seen any replacements that cater for the two separate supply feeds. All LED replacement fittings I have seen cater only for single feed (L, Sw L, N & cpc).

Some background on the installation: A mid-late nineties installation I believe. Single phase supply to the building, RCDs on power ccts but not lighting.

Are the earths and neutrals not just connected together within the fitting?

 

[sxdave]

Are the earths and neutrals not just connected together within the fitting?

Hello DPG, thanks for replying. The earths are commons you would expect. I am not sure about the neutrals. I am not at the site right now but I have a photo of the terminal block in one of the fittings. In this photo the neutrals are not obviously connected although they might be connected elsewhere in the fitting.