Has anyone seen 3 phase lighting

[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.

 

[davesparks]

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).

The OP was referring to 3 circuits, all connected to the same phase, sharing a neutral.

 

[shaun1]

Also, where does the 1.7 come from? If the load is resistive (or phase angles are all the same) then the Neutral current should never be more than the highest phase current. I know harmonics etc can increase neutral current but didn't know 1.7 was a rule for this?

 

[Adp]

See for the lights to work with a 3 phase breaker and one neutral could you have 3 switches or just one switch to a contactor ? My thinking 3 separate switches potentially the neutral carrying a return voltage if you work on other lights

 

[shaun1]

See for the lights to work with a 3 phase breaker and one neutral could you have 3 switches or just one switch to a contactor ? My thinking 3 separate switches potentially the neutral carrying a return voltage if you work on other lights

I was thinking that but with a single pole switch the neutral would not be broken so would remain at neutral potential. And you should really be fully isolating the circuit to work on it which would be done either via a linked 3ph MCB or maybe a 3/4 pole isolator next to the switches. Not sure if regs permit this though.

 

[Pete999]

If you intend to wire a large area with lighting split over a 3 phase supply, then you would surely, wire the lighting utilizing 3 SP supplies L and N, trying to avoid the Stroboscopic effect especially if you are using fluorescent lighting, something a competent Electrician should be aware of, just saying. Where does the confusion lye?

 

[Adp]

It’s not me that’s wiring this someone is wanting to wire like this. 3 phase breaker 1 neutral and have the different phases to switch 3 sections of lights. That’s what they want to do, doesn’t sound ok to me

 

[Deleted member 26818]

It’s not me that’s wiring this someone is wanting to wire like this. 3 phase breaker 1 neutral and have the different phases to switch 3 sections of lights. That’s what they want to do, doesn’t sound ok to me

What you describe there is fine.
Just to be clear though, it has to be 3 different phases.

 

[DefyG]

3 Phase lights - Yes
and Lighting over 3 phases - Yes

 

[Deleted member 26818]

3 Phase lights - Yes
and Lighting over 3 phases - Yes

As far as I am aware, there are no 3 phase light fittings.
3 phase lighting is either wired as 3 separate single phase circuits with a line and neutral conductor for each phase, or as as 3 phase circuit with the phases supplying alternate fittings and a single neutral conductor supplying all the fittings.
With the second option the neutral conductor is usually the same size as the phase conductors.
Some situations (such as street lighting) use a 5 core cable which is daisy chained to each fitting.
Other situations use a track system with clip on fittings, each fitting designed to only connect between a single phase and the neutral.

 

[davesparks]

See for the lights to work with a 3 phase breaker and one neutral could you have 3 switches or just one switch to a contactor ? My thinking 3 separate switches potentially the neutral carrying a return voltage if you work on other lights

If the lighting is fed from a three phase mcb then a switch and contactor to control the lights would be the better option in my opinion. If you want each phase on a separate switch then three seperate circuits would be the way to go in my opinion.