Two Circuits feeding 2G switch

[Super Dragpack]

Hi all,

I am struggling to get a definate answer on this one, and wondered if any of you know the truth of this please (with the relevant source data if possible):

Lets say we have two circuits as follow (both sharing a common RCD):

Circuit 1 - Downstairs lights - fed from a B6 MCB
Circuit 2 - Outside light - fed from another B6 MCB

The issue is that the outside light switch shares a 1G backbox with the hallway light switch (both seperately connected to a 2G switch). So you have two seperate circuits inside the same backbox. Nothing is inter-connected except the PE obviously.

Is this permitted? Or should it have a box seperator within the back box, or should there be mechanical connection between the MCB trips etc (so they both get turned off together)?

Any suggestions appreciated please.

Thank you.

Mick

 

[D Skelton]

Technically it is a no no unless a warning sign is present at that point informing of the need to isolate the accessory in two different places, but we all do it anyway. Think hallway and landing two way lighting circuits! No need for a separator either, remember your DB has lots of different circuits within it and they don't require physical barriers to keep them apart.

The right way do do it but also preserving aesthetics would be to slide a sticker into the backbox warning of the danger that there are two seperate circuits present, then again, anyone who hasn't safely isolated the circuit checking all conductors contained within shouldn't be opening up the accessory anyway!

However, where there are two different phases present at a single point of utilisation or at an accessory (a switch for example) and it isn't expected that you would find 400V there then the appropriate warning label must be placed there warning of the higher potential! Screw the aesthetics!

I take it you are a trainee?

 

[Super Dragpack]

I take it you are a trainee?

Certainly not, but I did get into a heated debate on this matter and wanted a definate answer. I may make some calls about this tomorrow perhaps.

 

[D Skelton]

Oh... Well, no need to make calls mate, the answer is in my previous post in black and white. Technically it's a no no without a warning label, but we occasionally do it anyway. Section 537

 

[Deleted member 9648]

I dont believe it is technically a 'no-no' to have more than one circuit at a switch.As long as they are from the same source of supply and are capable of being simultaneously isolated by means of the main switch on the CU I can see nothing in the regulations preventing this or even requiring labelling.

 

[Badged01]

Ive often pondered on this one as the regs state from "supply conductors" but there is no de-facto definition of "supply". Do the regs mean individual circuit supplies or just supplies (DNO) to the house in question?

Ive always read it as DNO supplies so no stickers required (I dont want to be putting any "stickers" on the likes of hallway/landing two way switching as its to niff naffy and trivial). But even if it refers to individual circuit supplies, all the 'live supplies' can be isolated by the CU main switch so that covers the regs angle on isolation of a group of circuits I believe (the lights!).

Bottom line, for me you can interpret the regs to say no "sticker" required!

 

[trigger]

Funnily enough my first electric shock as an apprentice was from a similar scenario.
Changing ground floor hallway 2g switch. Turned off 'ground floor lights MCB' however I failed to realise the two way switch for the second floor lights was supplied off a separate MCB and was the second gang on this light switch.
Alas, I've not made the same mistake. One bitten, twice shy and all that.
If in doubt, just put a sticker in the back box if possible? . Its not going to do anyone any harm.

 

[Darkwood]

I don't believe their is any issue at all here ...as multiple circuits are common even over different phases in commercial and industrial its normal practice. When at domestic level it is only often questioned as its not thought about as much. Anyone removing the switch should be competent to do so and safe isolation and testing would ensure no risk of such practices.

You only need to mark up if having multiple circuits within an enclosure wouldn't be expected and as its normal practice then no need for a ugly sticker in a domestic install.

 

[Badged01]

Absolutely correct Darkwood but the subtle difference is that in Commercial/Industrial you expect the work to be done by 'competent' tradesmen but in the domestic scenario the householder or DIY Joe could be getting his fingers in there to fit that shiny brass faceplate!

To label or not then becomes the dilemma .....

 

[SPARTYKUS]

Safe isolation. Double checking. Expecting the unexpected.

 

[Risteard]

Technically it is a no no unless a warning sign is present at that point informing of the need to isolate the accessory in two different places

The main switch is the isolation device for a domestic installation, so no warning label should be necessary. Of course, it is very common for the hall and landing lights to be on a 2-gang switch fed from two separate final circuits.

 

[Risteard]

However, where there are two different phases present at a single point of utilisation or at an accessory (a switch for example) and it isn't expected that you would find 400V there then the appropriate warning label must be placed there warning of the higher potential!

Don't forget that Uo does not exceed 230V.

 

[Octopus]

And many village halls etc have their lighting fed off different phases and use grid switches!

 

[Guest55]

Technically it's a no no

rubbish.
;-)

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I don't believe their is any issue at all here ...as multiple circuits are common even over different phases in commercial and industrial its normal practice. When at domestic level it is only often questioned as its not thought about as much. Anyone removing the switch should be competent to do so and safe isolation and testing would ensure no risk of such practices.

You only need to mark up if having multiple circuits within an enclosure wouldn't be expected and as its normal practice then no need for a ugly sticker in a domestic install.

correct.

 

[Guest55]

Absolutely correct Darkwood but the subtle difference is that in Commercial/Industrial you expect the work to be done by 'competent' tradesmen but in the domestic scenario the householder or DIY Joe could be getting his fingers in there to fit that shiny brass faceplate!

To label or not then becomes the dilemma .....

the regs make no distinction between domestic and commercial and there is no obligation to design out multi circuit points due to no proper isolation proceedure from mr diy.