Emergency lighting problem

[BathSparks]

I was asked recently to add a couple of sockets into a ring in a local village hall. When I turned off the small fuse board (Fitted with plug-in MCBs). The emergency lights came on.

I was still getting current running through the neutral at a socket on the ring circuit?. The main incoming supply is TT protected by an RCD. When this is turned off, (the whole installation made dead) the ring is dead. Not having much experience of emergency lighting systems I am wondering what is going on here. Will be going back to investigate further. Any ideas as to what is going on here?

 

[Schneker]

Hi mate,

No offence intended and I'm sure you mean well by helping the village hall out but, please leave the job to an electrician.

 

[dazza1981]

Well emergency lights will illuminate if there is a power failure...... its just what they do !!!!

 

[davesparks]

How did you establish that there was current running through the neutral?

 

[BathSparks]

Hi mate,

No offence intended and I'm sure you mean well by helping the village hall out but, please leave the job to an electrician.

Of course, I am an electrician and I fully expect the emergency lights to come on.

However, the only experience I have had with emergency lights involved self contained units with batteries that energise a lamp when the mains goes. These usually have isolation transformers in them to isolate them from the mains supply.

 

[BathSparks]

How did you establish that there was current running through the neutral?

First confirmed CU was off
After receiving a small shock, tested with Metrel MI 3112 multifunction tester at socket.
The only experience I have had with emergency lights involved self contained units with batteries that energise a lamp when the mains goes. These usually have isolation transformers in them to isolate them from the mains supply.

 

[dazza1981]

You confirmed consumer unit was off.......... then got a shock pmsl

 

[davesparks]

First confirmed CU was off
After receiving a small shock, tested with Metrel MI 3112 multifunction tester at socket.
The only experience I have had with emergency lights involved self contained units with batteries that energise a lamp when the mains goes. These usually have isolation transformers in them to isolate them from the mains supply.

Ok, doesn't answer how you confirmed current was flowing though.

The shock implies that there was voltage present, where did the current flow come from?

And what has this got to do with emergency lights? It's a socket cct isn't it!

 

[BathSparks]

Ok, doesn't answer how you confirmed current was flowing though.

The shock implies that there was voltage present, where did the current flow come from?

And what has this got to do with emergency lights? It's a socket cct isn't it!

Tested between Live and neutral, Live and Earth, Neutral and Earth.
That is the reason I am asking these questions. There should be no current flowing if the circuit is turned off. With the CU off, there should not be any current at the sockets.
By turning of the Main RCD, there is no current at the sockets as you would expect. The emergency light are lit, as you would expect. Turning the local board off, however, still leaves current flowing between N and E. at a socket fed from the same board.

 

[dazza1981]

What reading did you get when doing the above tests

 

[BathSparks]

What reading did you get when doing the above tests

LN = 0
LE = 0
NE =120v
On the circuit I was to add sockets the following readings were added to the MEIWC
IR
LN = 200MΩ
LE = 200MΩ
NE = 200MΩ
Loop imp = 0.37Ω
The Main RCD
Rated current 30 mA
time = 18 ms
Probably too much info here as most of this seems normal enough.
If there is a central inverter, then could be this.
A neon tester at the local board also lit up when on the Neutral busbar.
even with the main switch for this board OFF
Seems to be some kind of 'backfeeding' going on.

 

[Plonker 3]

Are there any other DBs in the building?

Oh and throw away your neon screwdriver.

 

[BathSparks]

Are there any other DBs in the building?

Oh and throw away your neon screwdriver.

I expect that is what I will have to find out when I go back.
I know about those neons and I do not trust them generally.

 

[Chrisuk]

I was asked recently to add a couple of sockets into a ring in a local village hall. When I turned off the small fuse board (Fitted with plug-in MCBs). The emergency lights came on.

I was still getting current running through the neutral at a socket on the ring circuit?. The main incoming supply is TT protected by an RCD. When this is turned off, (the whole installation made dead) the ring is dead. Not having much experience of emergency lighting systems I am wondering what is going on here. Will be going back to investigate further. Any ideas as to what is going on here?

Not read all but like will of been said, emergency lights are exactly that....when there's an emergency and the lights go out..they kick in running off a battery pack
More investigation is needed me thinks

 

[BathSparks]

You confirmed consumer unit was off.......... then got a shock pmsl

Correct. The main switch on the sub-board (2 6A, 1 32A and 1 16A) was turned OFF. All the light went off, the emergency light came on (as expected). The sockets were presumed dead. I initially tested this with one of three light testers (again limited in fault finding but ok for this) after unscrewing the front plate, I got the shock and proceeded to further testing.

 

[Farmelectrics]

suggest they get an eicr done

 

[BathSparks]

Not read all but like will of been said, emergency lights are exactly that....when there's an emergency and the lights go out..they kick in running off a battery pack
More investigation is needed me thinks

My fault, forgot to add "as expected" partly clocked this as a sign that the circuit was dead, and of course the main switch on this sub-main was switched to OFF.

 

[BathSparks]

Not read all but like will of been said, emergency lights are exactly that....when there's an emergency and the lights go out..they kick in running off a battery pack
More investigation is needed me thinks

My fault, forgot to add "as expected" partly clocked this as a sign that the circuit was dead, and of course the main switch on this sub-main was switched to OFF.

 

[davesparks]

Tested between Live and neutral, Live and Earth, Neutral and Earth.
That is the reason I am asking these questions. There should be no current flowing if the circuit is turned off. With the CU off, there should not be any current at the sockets.
By turning of the Main RCD, there is no current at the sockets as you would expect. The emergency light are lit, as you would expect. Turning the local board off, however, still leaves current flowing between N and E. at a socket fed from the same board.

I'm getting lost here.

You stated that current was flowing, but have described tests for voltage?

If current was flowing, how did you test it, how many amps and where was it flowing?

 

[Plonker 3]

Do you know how to check for safe isolation?

 

[Chrisuk]

Do you know how to check for safe isolation?

I know that to test if it's dead I use my tongue...that's right isn't it....that's what I was told haha

 

[BathSparks]

I'm getting lost here.

You stated that current was flowing, but have described tests for voltage?

If current was flowing, how did you test it, how many amps and where was it flowing?

Any significant current flowing would trip the RCD. My test instrument generates 10mA in stages, when doing an RCD test. I think I may be looking for 'borrowed neutral'. I cannot see how, with the main switch off on the sub-main board I still get a buzz from the neutral.

When I go back, I will take all the circuits out of the board and test them individually.
I only used my Kewtech probes at the board as I had not dismantled all the circuits.
so I only measured the voltage (120) at the board. and later used the Metrel mentioned earlier.

 

[Rockingit]

Sounds to me like there's some sort of polarity issue with the back-up circuits on the lights - when they come on they are back-feeding into the board (same principle here as for multiple energy sources). Isolate at the batteries as well, do the work, recommend a full inspection based on what you found.

 

[R G]

This Emergency lighting set up , is there a central battery bank by any chance that feeds a transformer ,,,,

 

[davesparks]

Sounds to me like a borrowed neutral across sub-boards.

If I have understood correctly the RCD is in the main switch position for the installation, so won't trip on any borrowed neutrals after it.

Despite what the regulations would have us believe RCDs aren't magical psychic devices.

 

[snowhead]

Simplified fault process;

Ignore the E.M lighting.

The "Dead" Sub board has a feed from elsewhere.
Isolate any other Sub boards 1 at a time.
Check whether "Current running though the Neutral at a socket" has gone.
If it has Isolate each circuit 1 at a time in the Other sub board.

If it hasn't, repeat above till you find it.

It took longer to come on here and post the problem than it would have done to try and isolate the problem.

 

[BathSparks]

This Emergency lighting set up , is there a central battery bank by any chance that feeds a transformer ,,,,

Hi. Just had discussion with a guy who was there when it was installed. Each light has it's own battery. Looks like I will have to check all of these. The polarity switch possibility looks like a plausible answer. Suppose some neutral from another circuit was connected to a light. This would stay live even if lighting circuit was off.
I did not intend to be doing EICR but looks like this may be necessary.

 

[BathSparks]

Simplified fault process;

Ignore the E.M lighting.

The "Dead" Sub board has a feed from elsewhere.
Isolate any other Sub boards 1 at a time.
Check whether "Current running though the Neutral at a socket" has gone.
If it has Isolate each circuit 1 at a time in the Other sub board.

If it hasn't, repeat above till you find it.

It took longer to come on here and post the problem than it would have done to try and isolate the problem.

Thanks for that. I am intending to disconnect all the circuits (there is only 4) from the board and check each one. Must be one of the lighting circuits got some feed from elswhere?

 

[BathSparks]

Sounds to me like there's some sort of polarity issue with the back-up circuits on the lights - when they come on they are back-feeding into the board (same principle here as for multiple energy sources). Isolate at the batteries as well, do the work, recommend a full inspection based on what you found.

Thankyou. I can only think that it must be this kind of problem. I will be disconnecting both ends of the lighting circuits and at each emergency light disconnecting the battery. Probably with the supply RCD (it is TT) tripped as this makes everthing in the building dead.

 

[davesparks]

I still don't get why the problem is being blamed on the emergency lighting?

Does the problem still exist on the ring when the lights are on mains power?

So far it sounds like you are flapping about blaming the emergency lights and disconnecting things randomly.