Hi I have been asked to check voltage drop on some sports ground flood lights. Supply is a TNCS single phase supply, there are 4 sets of flood lights, four on each post. The four posts are on individual circuits, wired in 4mm swa protected by c32a 61009. Voltage on the furthest lights is 217v & 218v so too low. The client is talking about having a 3 phase supply installed. Will this make any difference to the voltage drop. I have not redesigned the circuits yet not sure on cable length & design current yet. Any thoughts cheers
Will single phase altered to 3 phase improve voltage drop
- Thread starter jus306
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its not wether single phase or 3 phase is installed thats the problem is length if the cable run, you need to see what the voltage drop works out to see if its within tolerance
depending on layout, it may be possible to use 2x phases instead of L&N, and use 400V control gear
Cheers thanks for replies, don't think they want to go down the route of changing the control gear, as said I need to calculate cable length & design current. They seem to think changing to 3 phase supply will help so needed an answer for them. Good thing if they change supply though I might get some work out of it.
I did some work on a local sport centre stadium lighting last year. They were indeed 400V Ballasts - 1500W MH I believe.
well its either change control gear, or change cables. probably cheaper to replace control gear
simply changing supply to TP will do nothing
[quote name='Andy
[quote name='Andy
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If you change to 3 phase, and COMPLETELY rewire with 4 core + earth cable, then wire it so that an equal number of 240V lamps are on each phase, then you WILL reduce your volt drop, because each phase will supply 1 third of the current. (assuming you keep the same CSA cable)
But the only reason you have less volt drop, is you now have more copper to share the load.
Sticking with single phase, and changing cable for one with 3 times the CSA will achieve the same reduction in volt drop.
But the only reason you have less volt drop, is you now have more copper to share the load.
Sticking with single phase, and changing cable for one with 3 times the CSA will achieve the same reduction in volt drop.
We could move the load centre and make the same diff by relocating the 1ph board if the supply has sufficient capacity.
Am I missing something - why wouldn't having a 3-phase supply improve the volt drop - without changing the cable or the switchgear?
One phase feeds towers 1 & 2. (the nearest towers)
The other two phases feed a tower each. (the further away towers.)
One phase feeds towers 1 & 2. (the nearest towers)
The other two phases feed a tower each. (the further away towers.)
ADS,
I think that your suggestion relies on the incoming supply being inadequate?
IF the lights are wired with a single cable to each tower as it stands say, I'm not sure of the exact layout as the OP has not said, then the cable runs will be identical even if you swap two of them over to another phase.
If the "problem" is within the install then the volt drop down the cable will be the same regardless of which phase it is on.
If the volt drop is due to an inadequate supply, i.e. supplier volt drop due to an overloaded supply, then yes it will improve by load shedding and balancing across multiple phases.
The OP will have to explain a little more about the actual physical layout and any other loads really to suggest an exact fix I believe.
If the voltage at the head stays up when all loads are on then there would be nothing gained by moving loads to other phases as the volt drop issue would remain within the install.
I think that your suggestion relies on the incoming supply being inadequate?
IF the lights are wired with a single cable to each tower as it stands say, I'm not sure of the exact layout as the OP has not said, then the cable runs will be identical even if you swap two of them over to another phase.
If the "problem" is within the install then the volt drop down the cable will be the same regardless of which phase it is on.
If the volt drop is due to an inadequate supply, i.e. supplier volt drop due to an overloaded supply, then yes it will improve by load shedding and balancing across multiple phases.
The OP will have to explain a little more about the actual physical layout and any other loads really to suggest an exact fix I believe.
If the voltage at the head stays up when all loads are on then there would be nothing gained by moving loads to other phases as the volt drop issue would remain within the install.
The OP has said the voltage at the supply is 231 volts - then he gives the volt drops at each tower.
Volt drop is dependant on load - so a four tower load will give the volt drop he has described - they are parallel loads - so that's four towers on one phase.
Volt drop from cut-out to each tower is about 14 volts.
If you split the towers off on to seperate phases, then obviosly you only have one tower(load) per phase - so the volt drop will definitely be lower - about 5 volts per phase.
All good comments thanks, when it stops raining I'll go and check the loading on each tower as some of the fittings are newer than others and measure the cable length. With regards to what the problem is they are complaining that the lights are dimmer than others, I'll also check the operating voltage
Jus306,
How did you measure the voltages at the towers to give the figures that you quoted - was it per individual tower with just that towers lighting on - or did you switch all towers on and measure the voltage at each tower?
If it's the second method, you may find that, per cable/tower, you may well be within the tolerance......it will be the volt drop across the whole installation that is too high - because as you switch each load in, then the voltage is going to drop........hence the formula, millivolts per amp per metre.
This does make me wonder why determining voltdrop is such an issue, because I don't think you can....accurately........because, surely you'ld need to have all loads of an installation switched on??
I don't know....I'm confusing myself now - I'll have to go off with a piece of paper and a pen and think about this
here's as i see it, simply keeping the cabling as is and changing the supply to a 3phase supply and splitting the circuits over the 3phases instead of the exisitng 1 wont change anything. yes the load affects the VD but so too does the length of run. the circuits will still be the same length and load. your still going to get the same 231'ish volts at the other phases independently.
you either need to reduce the load, reduce the length of run or upsize the cable
if you're going to try and encorporate the exisitng cabling but reduce the load so instead at each post you have 1 cable for 2 lights so each post will have two cables. or if you're starting from scratch use a bigger cable.
to me the 32A mcb suggests a big load on each cable which isn't allowing anything for VD. or you'd have the 4mm (30 odd amps rated) with a 10A mcb
to me ADS you're suggesting more about balancing the load????
hope i haven't waffled too much
james
---------- Post Auto-Merged at 13:52 ---------- Previous post was made at 13:50 ----------
i think i'm waffeling, the VD isn't so much to do with the supply voltage dropping it's there after, at the other end of the SWA there's only 217v, not the supply voltage dropping
you either need to reduce the load, reduce the length of run or upsize the cable
if you're going to try and encorporate the exisitng cabling but reduce the load so instead at each post you have 1 cable for 2 lights so each post will have two cables. or if you're starting from scratch use a bigger cable.
to me the 32A mcb suggests a big load on each cable which isn't allowing anything for VD. or you'd have the 4mm (30 odd amps rated) with a 10A mcb
to me ADS you're suggesting more about balancing the load????
hope i haven't waffled too much
james
---------- Post Auto-Merged at 13:52 ---------- Previous post was made at 13:50 ----------
i think i'm waffeling, the VD isn't so much to do with the supply voltage dropping it's there after, at the other end of the SWA there's only 217v, not the supply voltage dropping
Its stopped raining so bit more info, Took the voltage at supply with no load apart from a fridge in a nearby tennis hut got 240v. Took it again with all the floods on got 232v. The four towers are as follows, tower 1 about 15m from db with 4 x 400w lamps only one working, tower 2 approx 44m away from db with 4 x 1000w lamps all working, no probs with voltage drop on these, by the way ADS all voltage readings were taken at the isolator at the base of each tower with all four towers on, no other real load to speak of on this install. Towers 1 & 2 are the nearest to the db. Tower 3 far side is 4 x 400w only 3 working cable run bit difficult cant see if its run around the edge or under the pitch all in the ground, if under about 70 m,around about 125, finally tower 4, 4 times 400w one not working distant either 100m or 160m. So 4 radial circuits feeding ind. isolators which in turn feed an adjacent 32a commando.
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