Emergency Light in Electric Cupboard - advice

[ban-all-sheds]

You were only criticised because you were wrong.

Untrue.

 

[SimonH2]

You were only criticised because you were wrong.

Don't expect BAS to accept that, even though it is correct.
I had missed that TTC had also suggested it by the time I saw BAS suggesting it - and replied to BAS's later post. So it wasn't a case of having a go at BAS and ignoring TTC - it was simply a case of replying to the last person to suggest it.

IMO there is only one* possible reason to have a "cut the power to turn the light ON" switch, and that's if you are somehow required to provide that function and cannot avoid having only a 2C+E cable between switch and light.
Otherwise you simply loop at the light (only needs 2C+E supply, and 2C+E to switch), or loop at the switch (which requires a 2C+E from switch to light), and have the switch provide switched power to the switched line input on the light. Done that way, there are no "surprises", nothing for the user to learn from when they forget to switch it off and it damages the battery, it just works as intended - switch on, light on; switch off light off; power fail, light on till power restored or battery runs down.

So given that the requirement above is going to be "quite rare" (and certainly not applicable in this case as the switch is going to be near the light), a general suggestion to use that setup would fall foul of "good design" and "good workmanship" general requirements in the wiring regs. As such, it would not meet wiring regs, hence is wrong- unless you can argue that deliberately designing a circuit in a very suboptimal way is good design

* I don't count a test switch in this as that's there for testing, not for functional switching. And if you also argue that "the light doesn't have a maintained function" is a reason then I'd counter that it's against the "good selection of materials" general requirement in the wiring regs.

 

[ban-all-sheds]

Don't expect BAS to accept that, even though it is correct.

No, it is not correct.

The issue there is not whether I was right or wrong, the issue is Risteard's assertion that I was only criticised because I was wrong.

Patently untrue, for the reason you go on to mention - the idea had already been put forward two weeks earlier by someone else.

So given that the requirement above is going to be "quite rare" (and certainly not applicable in this case as the switch is going to be near the light), a general suggestion to use that setup would fall foul of "good design" and "good workmanship" general requirements in the wiring regs. As such, it would not meet wiring regs, hence is wrong- unless you can argue that deliberately designing a circuit in a very suboptimal way is good design

Be careful - I regularly get criticised for suggesting that something not explicitly forbidden by the regulations could count as not being good workmanship.

 

[SimonH2]

So what you're saying is the "but others did it as well" defence ? Because someone else also suggested it, then to criticise you for suggesting it is wrong ?
Now, if there was a suggestion that the other person was right (which there isn't), I could see your point. As it is, you seem to be employing the defence so often used that it must be OK if others are doing it.

Yes occifer, I have had a bit to drink before driving home, but it's all right - others do it and don't get caught so it must be OK

 

[ban-all-sheds]

Whatever.

 

[Taylortwocities]

Zzzzzzz

 

[EFLImpudence]

IMO there is only one* possible reason to have a "cut the power to turn the light ON" switch,

Unless I have missed something -

Surely the lamp that comes on when the power is cut is not 230V.

 

[SimonH2]

And neither (normally) is the maintained lamp. In older units it would be something like an 8" flouro tube running from an inverter that takes power from a transformer/rectifier when the SL terminal is being fed, or from the battery when neither SL nor L are fed. These days more likely to be a bunch of LEDs, but other than that the principle is the same.