View the thread, titled "Question regarding 400V three phase lighting connected in Delta, without Neutral." which is posted in Commercial Electrical Advice on Electricians Forums.

I regularly used to demonstrate this by having three 60w lamps connected across three phases
This works in star with a floating star point using filament lamps, because the loads, despite their large temperature coefficient, are approximately resistive for a small change in temperature, and at least are always electrically continuous. Electronic drivers are switched-mode power supplies that work at approximately constant power input so they can have negative dynamic resistance, i.e. the current falls as the voltage rises. A unit that, through minor differences in load or construction tolerance, is using slightly less current, will receive slightly higher voltage just as though they were in series on a single pahse supply. This will further reduce the current and the system will experience positive feedback, almost inevitably swinging to extreme unbalance until one unit receives too low a voltage and shuts down. At that time almost the full 400V will be across the unit that is still operating, until it decides not to operate any more! The same will occur if one unit starts up slightly quicker than another.

In summary - identical single-phase loads in star with floating star point, OK with constant resistance loads like heating elements, no good with electronic loads even if apparently perfectly balanced.
 
Agree and it would be foolhardy to install any lighting circuits across a three phase supply with no neutral.
 
Single Phase would indeed do the job well, if it wasn't for the length of the cable run, which would be about 50m from the Consumer Unit to the last light fitting, which may entail unacceptable voltage drop, and in turn require the use of 2.5 or 4mm conductors, which could be rather difficult to terminate in lighting accessories.

So make the main run in 4mm², or whatever, then into a junction box and drop down to 1mm² or 1.5mm² for the final link to the fittings.
 
Single Phase would indeed do the job well, if it wasn't for the length of the cable run, which would be about 50m from the Consumer Unit to the last light fitting, which may entail unacceptable voltage drop, and in turn require the use of 2.5 or 4mm conductors, which could be rather difficult to terminate in lighting accessories.

So make the main run in 4mm², or whatever, then into a junction box and drop down to 1mm² or 1.5mm² for the final link to the fittings.
 
Of course perfectly balanced single phase loads will function perfectly well without a neutral until something fails and then things don't function so well.

In star yes, but he's talking about delta, balancing of the loads won't be necessary.
 
You know @westward10 that sorcery you do with the lights you ought to set up a rig and demonstrate that here on the forum. It would be great to demonstrate graphically to all the theory of circuits and 3 phase etc. Of course you would have to warn us not to do it at home.
 
Anyway, I realise that 400V, 3 Phase LED lighting is probably overkill in this case. Single Phase would indeed do the job well, if it wasn't for the length of the cable run, which would be about 50m from the Consumer Unit to the last light fitting, which may entail unacceptable voltage drop, and in turn require the use of 2.5 or 4mm conductors, which could be rather difficult to terminate in lighting accessories.

It would be an unconventional, and in my opinion design which will lead to maintanence issues in the future as the drivers will be non-standard and hard to replace. You will also be putting 400V where nobody normally expects to find it.
You'll also need the neutral anyway as you almost certainly won't get emergency lighting that'll work on 400V.


2.5mm is pretty common as a minimum size of conductor for lighting circuits in commercial jobs. It's not too bad to terminate into the usual fittings (rock rose etc) if you're careful.

Have you actually calculated the voltage drop or are you just guessing?
Even if you were daft enough to put the whole lot on to one single phase circuit a quick calculation suggests that 1.5mm would be fine if you connected the whole load at the very end of a 60m cable run. So in a real world scenario where the load would be distributed along the length of the circuit, and you'd almost certainly spread them across at least two circuits for a bit of redundancy should one circuit trip, I can't see any issue.
 

Reply to the thread, titled "Question regarding 400V three phase lighting connected in Delta, without Neutral." which is posted in Commercial Electrical Advice on Electricians Forums.

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