Has anyone seen 3 phase lighting

[Adp]

Hi new to this, has anyone ever seen lighting on a 3 phase breaker ? A company wanted to use a 5core swa and and share the neutral for using on the other 3 phases, they were told they can’t do this but have now decided to try get round it by using a 3 phase breaker. This is in a 3 phase board and the lighting is going round a premises. Surely this can’t be right ???

 

[littlespark]

The lighting would have to run on 400v, not 230v

Probably can’t be done.

Why were they told they couldn’t have 1 neutral for all 3 phases?

 

[westward10]

It is not uncommon on large lighting installations to have groups of lighting across a three phase protective device using a single neutral conductor provided the protective device is linked so all lines simultaneously trip. See Reg 559.5.5

 

[Adp]

They were wanting to have say 1L1 5L1 and 8L1 with one neutral, if you isolate one of these to work and the one you work on may become live. Yeah it’s one linked protective device. I just think it’s silly as if there is a fault with one phase you lose all lighting.

 

[westward10]

They can't use a triple pole linked device across the same L1 line it needs to be 1L1, 1L2 and 1L3. It is perfectly acceptable to use this method.

 

[shaun1]

There would be no benefit to running the same phase down 3 cores with one neutral as the neutral conductor would need to be sized to carry the 3 combined phase currents so you might as well use one live. If they want 3 individually switchable circuits, I believe a 5core SWA could be used if all the switchable circuits were fed from the same MCB and so had 1 point of isolation.

Otherwise, as mentioned above you could run a 3ph circuit with 230v lights split across the 3 phases.

 

[Deleted member 26818]

There would be no benefit to running the same phase down 3 cores with one neutral as the neutral conductor would need to be sized to carry the 3 combined phase currents so you might as well use one live. If they want 3 individually switchable circuits, I believe a 5core SWA could be used if all the switchable circuits were fed from the same MCB and so had 1 point of isolation.

Otherwise, as mentioned above you could run a 3ph circuit with 230v lights split across the 3 phases.

No the neutral wouldn’t.

 

[The Ghost]

No.

 

[shaun1]

The Neutral wouldn't what?

 

[westward10]

No the neutral wouldn’t.

I believe it would, three circuits with a shared neutral where the three circuits are connected to the same line of the three phase supply, linked protective device or not. It is only feasible when they are across separate phases.

 

[Adp]

The idea at the start was 3 separate circuits from the same line sharing the neutral for each circuit. Now they are using a linked 3 phase breaker and neutral to supply the lights. I just don’t like the idea of it for fault finding, issue with a light on one phase and it trips you lose them all. Compared to just a third

 

[westward10]

No it is perfectly acceptable providing it uses all three phases.

 

[Adp]

Cheers guys

 

[Deleted member 26818]

The Neutral wouldn't what?

The Neutral wouldn’t need to be sized to carry the combined 3 phase currents.

 

[davesparks]

The Neutral wouldn’t need to be sized to carry the combined 3 phase currents.

The post you were replying to was a response to the Ops situation where someone has suggested running three different circuits, all connected to L1 down the 5 core, sharing the neutral. The neutral would need to be 3x the size for this, if it was permitted.

 

[dmxtothemax]

QUOTE = L1 down the 5 core, sharing the neutral. The neutral would need to be 3x the size for this, if it was permitted.

QUITE WRONG ME THINKS,
you are forgeting it is a three phase source,
so all theree phase neutral currents don't run simultaniously,
only two phases will interact at any one time,
So the figure will be around about 1.7 times the current
at any one time.

 

[Bobster]

Some days I'd like to bang my head against a wall reading threads like this.

Come on guys, it's basic theory.

 

[streamer]

The confusion here is that the op mentioned a three phase lighting system and then later mentioned three separate supplies from the same phase with a shared neutral. They are two very different things!

 

[dmxtothemax]

star or delta ?
The O / P was referring to star wasn't he ?
So where is the error ?

In a three phase star,
the current in the neutral could be,
as high as 1.7 times the individual phase currents.

it is NOT ever 3 times
(not at any one time).

 

[streamer]

He mentioned three supplies from the same phase.