3phase to single phase
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URL: https://forum.speakerplans.com/forum_posts.asp?TID=86982
Printed Date: 26 March 2026 at 7:10pm
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Topic: 3phase to single phase
Posted By: soundguymatt
Subject: 3phase to single phase
Date Posted: 27 May 2014 at 8:36pm
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So my mate has a cable to go from a 32/3 to a 32/1, where he uses one of the three phases. The other two are not connected. (system is 3p star). council bod seems to think this is illegal. Am i right in thinking that as long as there's a distro with appropriate breakers there's nothing wrong with doing this? I think it's fine and i cannot find anything anywhere saying i can't do this. Does anyone know if i can't do it, and can point me to a document saying this. ------------- -- Matt |
Replies:
Posted By: ceharden
Date Posted: 27 May 2014 at 8:42pm
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It's fairly normal (and I don't think there is anything wrong with it) to own a cable with a 32/3 plug and a 32/1 socket which just takes one phase from the supply. Never heard anyone say you can't do it. |
Posted By: shagnasty
Date Posted: 27 May 2014 at 8:44pm
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Might want to ask the council what his qualifications in this arena are, as long as the cable has the right rating (3g6) and the ends are properly made off, I can see no issues there. What the hell does he think happens in a 3PNE DB when you connect a ring main to it??? I think the guy needs to wind his limited knowledge back in a bit. Conversely if the thing looks like a death trap... |
Posted By: soundguymatt
Date Posted: 27 May 2014 at 8:44pm
That's what i was thinking :) ------------- -- Matt |
ceharden wrote:Posted By: soundguymatt
Date Posted: 27 May 2014 at 9:18pm
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Thanks :) i'll tell him that as i thought there isn't anything wrong with his cable (it is 3g6 lineax), and to ask the council people to write down exactly why they think that is isn't legal and to show the relevant rules. The DB point is the one i would have made. You just take a live, the neutral and the earth for each circuit. ------------- -- Matt |
Posted By: djeddie
Date Posted: 27 May 2014 at 9:39pm
Give him a break Shag. It probably took him all day to do the PAT course. Anyway, I had a similar problem once but it turned out the bloke thought ALL phases had been connected to the single phase! So took the plug apart and showed him... even though he had no idea what he was looking at. ------------- Chas n Dave : it's like Drum and Bass but with beards. E=mc² ±3dB |
Posted By: shagnasty
Date Posted: 27 May 2014 at 10:31pm
There Kinda sits my point, you connect all 3phases and you need a new breaker as a 415V delta short tends to burst the MCB!!! Patience with people who are responsible for safety but do not have the knowledge to discharge their remit, from me, is Zero.  |
Posted By: SamV
Date Posted: 15 July 2014 at 12:34am
| O.oh that mean that someone can make me a 32/3 to 3x 32/1 cable? Cos I have 3x 32/1 to 6x16a distros. |
Posted By: James Tengo
Date Posted: 15 July 2014 at 6:45am
| Yes. We have them in our hire stock, I am using one on the Rudimental festival floor package as we speak, 32a3ph outlet on my dimmer rack, then a 32a3ph plug to a rubber box with 3x 32a1ph sockets with no breakers on it, to our u type distros which are 32a1ph plug to a rubber box with 4x 16a1ph outlets each with a 16a d curve mcb. |
Posted By: SamV
Date Posted: 15 July 2014 at 7:20am
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3 phase makes my head hurt. On a 1ph supply the Earth is a bigger pin than the others but then on a 3ph it's the same and shared with the others, along with the neutral. So why isn't it noticeably bigger as a ratio? And why no 1to1 ratio between live and neutral? |
Posted By: audiomik
Date Posted: 15 July 2014 at 7:38am
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Sam not very easy to explain, but a 3 phase balanced system ends up with a zero neutral current.... More info on Wikipedia here: https://en.wikipedia.org/wiki/Three-phase_electric_power A 3 phase 3 terminal connection with only a 1 phase load is a real no-no unless you really want 415 Volts instead of 240  Mik ------------- Warning! May contain Nuts plus springs, washers, screws, etc, etc. |
Posted By: James Tengo
Date Posted: 16 July 2014 at 8:15am
In certain cases there is an argument for an over sized neutral, especially where loads that create harmonics are concerned. I've been shouted down on here on this point before, the "fact" that the current in the neutral "can never rise above that of any of the one phase due to cancellation" Well here is a real world example for my case. The photos attached are from the MDU at Brixton Academy, the rig was a good mix of discharge, LED, moles and strobes    For most of the gig the neutral current was lower than any of the individual phases, but with dimmer harmonics adding up the neutral current can be higher than you might expect. |
Posted By: oldskool
Date Posted: 16 July 2014 at 8:57am
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You are quite right James. With three balanced phases then the theoretical neutral current is zero as the neutral currents arrive at the star point 120 degrees out of phase and cancel each other out. Once you add harmonic currents to the mix things get very different. Standard dimmers, normally being single phase devices connected between a phase and neutral cause lots of third harmonic distortion at 150 Hz. There are also higher multiples, the greatest in magnitude being typically 9th, 15th etc. These multiples of three are known as triplens. They are unique in the harmonics scenario in that they add arithmetically in the neutral. It is not uncommon to see neutral currents higher than phase currents on networks with a lot of harmonic distortion produced by single phase devices. Just to illustrate the point i had to resolve these issues at the Royal Opera House with their 3MW of dimmers a while back and tackle these things every day.
------------- Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies |
Posted By: James Tengo
Date Posted: 16 July 2014 at 2:51pm
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http://forum.speakerplans.com/why-cant-i-find-a-32-amp-version-of-this_topic77828_page3.html?KW=neutral" rel="nofollow - Last time I mentioned it on a very similar topic |
Posted By: oldskool
Date Posted: 16 July 2014 at 3:05pm
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Have sorted similar problems for the last 25 years at Shepperton Studios, Marks & Spencer etc etc etc. These phenomena are nothing new. The crap spewed out by all those switch mode power supplies found in everything these days is just making the problem worse nationally. Funny, in some parts of the grid you can clearly see the harmonic nasties due to everybody switching their televisons on about 5.00 to 6.00 PM and then disappear again about 11.00 PM. The last time I measured that was on an 11kV feed to a big hospital surrounded by housing estates. ------------- Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly and applying the wrong remedies |