Two phases in one light switch... regulated against?

[Toneyz]

To have different phases in a light switch in a 3 phase installation is common and although the regs state a warning notice if voltages exceed 230v to earth (514.10.1) it is good practice to install label inside switch in fact MK provide one with grid yokes. My issue is with the two point of isolation eg fed from two distribution boards. Therefore I refer to Reg 514.11.1 .

 

[itsonly3wires]

Thanks chaps...

I will need to get the switch labelled up due to the isolation issue.

The problem is particularly apparent due to the switch being located right next to a consumer unit where one of the phases can be isolated.

Obviously there are many instances of 3 phases being switched in one light switch but I've rarely seen an instance where two consumer units in two separate areas of a building supply one light switch.

Thanks again for the words of advice!

 

[westward10]

Doesn't need a notice anyone working on it should undertake safe isolation procedures.

 

[itsonly3wires]

I've always treated 7671 as a minimum requirement.

No harm in safeguarding a fellow electrician... after all that install could test as isolated and no end of locking and tagging would prevent the other consumer unit from being switched on.

I could see myself incorrectly thinking I had isolated the supply.

I think in this instance it would really be necessary to see first hand why there could be confusion.

 

[Pete999]

Doesn't need a notice anyone working on it should undertake safe isolation procedures.

Providing they are proper Electricians Westy.

 

[westward10]

Whilst there is nothing wrong with fitting a notice you need to realise this is not something you need to note on an EICR.

 

[Toneyz]

To have different phases in a light switch in a 3 phase installation is common and although the regs state a warning notice if voltages exceed 230v to earth (514.10.1) it is good practice to install label inside switch in fact MK provide one with grid yokes. My issue is with the two point of isolation eg fed from two distribution boards. Therefore I refer to Reg 514.11.1 .

Whilst there is nothing wrong with fitting a notice you need to realise this is not something you need to note on an EICR.

May be not but it should be something to consider in reducing a risk for others that may assume. I referred in my post to Reg 514.11.1 which in turn refers to Reg 337.2.1.3.

 

[Lucien Nunes]

I have no issues with two phases, but I always fix a notice about the sources of supply being in two different 'main' DB's when they meet in a fitting. It's the same as orange wiring being used in a control panel to indicate an externally-fed circuit that the local main switch won't isolate. This situation does exist in large banks of switches in industrial locations but not normally a humble 2-way at the bottom of a stairwell - it's a different situation to two circuits from the same DB which is quite normal.

First, as the OP says, someone working on the switch might thinkg a lockout on the DB main switch would solve any possibility of either circuit being energised, and then be foiled when someone turns the other DB on. But more insidious is what happens if the two sides became interconnected, when neither section of the installation could be isolated by its main switch. You would only test insulation with respect to circuits in the local board, so if the other board were off the test would not reveal the problem. Then it would be backfed and everything live, but non-operational due to the neutral being isolated.

We would all prefer that only competent sparks changed accessories but we also know that most handy folks feel competent to do a like-for-like swap of a broken switch. A warning sign would help alert them to the consequences of getting things muddled up in this particular switch.

 

[ruston]

@Stspark . I agree , I do that with multiple boards and lighting supplies . It makes life easier for the next spark/tester following you .

 

[Mark42]

I have multiple phases in one switch enclosure in several places in my own house. No big deal, and no one really wants scary notices all over a domestic installation.
What I do though is to use grid switches, and write a warning on the internal grid.
I also leave a little note to posterity on a piece of folded paper inside the box, warning about the inter-phase voltage present, and often a sketch of the circuit if it's not straightforward.
But then I'm a romantic who often stuffs structural voids with old magazines, newspapers, and redundant children's toys ...

 

[David M]

I have multiple phases in one switch enclosure in several places in my own house. No big deal, and no one really wants scary notices all over a domestic installation.
What I do though is to use grid switches, and write a warning on the internal grid.
I also leave a little note to posterity on a piece of folded paper inside the box, warning about the inter-phase voltage present, and often a sketch of the circuit if it's not straightforward.
But then I'm a romantic who often stuffs structural voids with old magazines, newspapers, and redundant children's toys ...

Unusual to have multiple phases in a domestic property, at least for basic lighting purposes? (my bold) Or do you mean multiple separate circuits fed from a single phase supply?

 

[Mark42]

Unusual to have multiple phases in a domestic property, at least for basic lighting purposes? (my bold) Or do you mean multiple separate circuits fed from a single phase supply?

Hi David - No, I meant what I said. Three phase supply to my old farmhouse. I balance the loads across the phases: in this case three IR wall heaters in my workshop, and three metal halide hi-bays in a garage. Both installations switched from single-enclosure 3 gang gridswitches.
I believe it's better practice to share loads across phases, and so use thinner, easily-terminated cables, rather than jamming heavy loads onto one phase for no good reason. The presence of the interphase voltage in any one switch enclosure does not worry me at all.
Cheers, Mark

ps. Of course supplied from a TP breaker in both cases. NOT multiple supply.

 

[David M]

Hi David - No, I meant what I said. Three phase supply to my old farmhouse. I balance the loads across the phases: in this case three IR wall heaters in my workshop, and three metal halide hi-bays in a garage. Both installations switched from single-enclosure 3 gang gridswitches.
I believe it's better practice to share loads across phases, and so use thinner, easily-terminated cables, rather than jamming heavy loads onto one phase for no good reason. The presence of the interphase voltage in any one switch enclosure does not worry me at all.
Cheers, Mark

ps. Of course supplied from a TP breaker in both cases. NOT multiple supply.

Ha, right sorry for the confusion, that makes perfect sense now, thanks.

 

[Adam W]

I have no issues with two phases, but I always fix a notice about the sources of supply being in two different 'main' DB's when they meet in a fitting. It's the same as orange wiring being used in a control panel to indicate an externally-fed circuit that the local main switch won't isolate. This situation does exist in large banks of switches in industrial locations but not normally a humble 2-way at the bottom of a stairwell - it's a different situation to two circuits from the same DB which is quite normal.

First, as the OP says, someone working on the switch might thinkg a lockout on the DB main switch would solve any possibility of either circuit being energised, and then be foiled when someone turns the other DB on. But more insidious is what happens if the two sides became interconnected, when neither section of the installation could be isolated by its main switch. You would only test insulation with respect to circuits in the local board, so if the other board were off the test would not reveal the problem. Then it would be backfed and everything live, but non-operational due to the neutral being isolated.

We would all prefer that only competent sparks changed accessories but we also know that most handy folks feel competent to do a like-for-like swap of a broken switch. A warning sign would help alert them to the consequences of getting things muddled up in this particular switch.

This thread is getting on a bit but I agree - while it may be common to have more than one phase feeding a bank of switches, in this scenario where each property is fed from a separate single phase consumer unit and the switch in question is for a staircase to a residential property it may give rise to confusion, especially if it's a one piece moulded switch as opposed to a grid switch.