This is topic 3 phase 220 volt wiring in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.


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Posted by Richard May (Member # 2627) on 12-15-2009, 02:57 PM:
 
I was at a theater the other day and came across something new to me. While measuring the 3 phases at the panel, two of them measured 120 volts to ground. The third phase measured 220 volts to ground. I didn't know that you could hook this up to a 3 phase rectifier. How doesn't it damage anything?
 

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Posted by Robert Minichino (Member # 3495) on 12-15-2009, 03:11 PM:
 
That's a high-leg delta service. The phase-phase voltage for all 3 phases is 240V, but one of the sides of the delta is center-tapped and grounded (that's the neutral). This gives you two phases of 120V for lighting and small loads, and 240V 3 phase for your larger loads. The 3rd leg should be about 208V to ground, and shouldn't be used phase-ground.
 

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Posted by Richard May (Member # 2627) on 12-15-2009, 03:14 PM:
 
So then the 3 phase rectifiers should be set to the setting closest to 240volts incoming voltage I assume.
 

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Posted by Gordon Bachlund (Member # 124) on 12-15-2009, 04:18 PM:
 
Robert is quite correct. This used to be a fairly common service for commercial buildings with single-phase "light" meters and three-phase "power" meters. This was driven by (1) a higher kw-h rate for lighting service than for power service, and (2) the use of a larger tapped transformer connected in delta with two smaller transformers.

You would be correct in setting the rectifier transformer taps for 240-volts.
 

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Posted by Richard May (Member # 2627) on 12-15-2009, 04:22 PM:
 
Thanks guys.
 

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Posted by Mark Gulbrandsen (Member # 72) on 12-15-2009, 08:52 PM:
 
Measure between the phases and set the taps accordingly. Don't measure between each phase and neutral to determine this. You'll still get 208...210 or what ever the building is set up for when you measure between any two phases.

Mark
 

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Posted by Tim Reed (Member # 137) on 12-15-2009, 09:13 PM:
 
This would be the famed "wild leg"...


 

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Posted by Monte L Fullmer (Member # 2797) on 12-16-2009, 12:48 AM:
 
(thought it was called, "crazy leg" .. )
 

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Posted by Phil Hill (Member # 371) on 12-16-2009, 12:59 AM:
 
Hot Legs - Rod Stewart
 

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Posted by Randy Bowden (Member # 587) on 12-16-2009, 02:03 AM:
 
We have the same wiring set up at our shop. we call it the "Hot Leg"
 

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Posted by Tim Reed (Member # 137) on 12-16-2009, 08:33 AM:
 
All of the legs are hot in a 3-phase system. High leg delta (aka, "wild leg")
 

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Posted by Richard May (Member # 2627) on 12-16-2009, 10:24 AM:
 
Thanks Tim. That was very helpful.
 

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Posted by Louis Bornwasser (Member # 3063) on 12-16-2009, 04:10 PM:
 
Usually you see 2 breakers in the panel, a spacer, then a repeat. Dead givaway that "wild leg" is a possibility.

Sometimes you can use the wild leg as one side of a 220/240 single phase load, opening up more 120v breaker positions. Louis
 

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Posted by Richard May (Member # 2627) on 12-16-2009, 04:28 PM:
 
Like a single phase 220 Orc power supply?
 

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Posted by Randy Bowden (Member # 587) on 12-16-2009, 04:34 PM:
 
All of the legs are hot in a 3-phase system

I think that goes without saying.
 

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Posted by Robert Minichino (Member # 3495) on 12-16-2009, 04:42 PM:
 
Not in a corner-grounded delta
 

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Posted by Tim Reed (Member # 137) on 12-16-2009, 05:55 PM:
 

quote: Randy Bowden

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I think that goes without saying.

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Then, why would anyone call a wild leg a hot leg? They're all hot.
 

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Posted by Steve Guttag (Member # 268) on 12-16-2009, 06:37 PM:
 
Around here, they are all called "high-leg" and yes, the abundance of every 3rd breaker not being filled is the give away. If the panel is open, you should have a Black, a Red and then either an Orange, Yellow or Brown on the "high-leg". If you work in an "old town" you are going to come across the high-leg situation.

I have also come across the grounded Delta...just plain freaky if you ask me, and I'm an EE. There is something un-nerving about seeing one of the phases tied to ground and that the remaining two hot legs having a 220 potential to ground. The reason I was given was that it reduced cost as only three conductors needed to be pulled of the heavy copper instead of four...and only double pole breakers instead of triple.

Since most don't get Delta power and also most will have 120V circuits in their system, a grounded Delta does not come up much...in fact, only once in my time in the booth (about 30-years).

High-leg has come up multiple times though...its more annoying than anything since you have to get a breaker panel that is 33% larger to get the breakers you need. In a couple of these situations, the building had high-leg for 3-phase only and had a separate service to the building for single phase power (120/240). I would prefer that if offered since there are generally 10-20 single phase circuits versus 3-phase. I suspect that ratio is going to go higher as we move to switch mode power supplies for the newer projectors since most DCinema projectors only need single phase up to 4KW.

Steve
 

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Posted by John Hawkinson (Member # 1135) on 12-16-2009, 08:12 PM:
 
Remember, specific color codes aren't mandated NEC or most jurisdictions -- so don't count on any particular color meaning anything anywhere -- ever.

Steve, I've recently seen electricians install a split-phase panel (well, it was rated for 208 hot-to-hot) on a 3-phase system and only pull two of the phases to it. Their thinking was they believed the customer had specified a very large number of loads all to be on the same phase (...) and so most of the panel positions would have ended up empty if they'd used a 3-phase panel. Of course, guarantee of unbalanced loads.

But in a 3-phase high-leg scenario, where the unbalanced load is a given, that seems a reasonable way to go.

--jhawk
 

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Posted by Steve Guttag (Member # 268) on 12-16-2009, 08:20 PM:
 
While it is true about the color code...the only protected color is WHITE for Neutral, I've generally found the color code pretty well respected...incuding in high-leg situations.

Now wires in a trough...no, I don't trust the jackets to mean anything...I presume all a lethal.

Steve
 

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Posted by John Hawkinson (Member # 1135) on 12-16-2009, 09:16 PM:
 
I dunno, I hear green is pretty reliable too

I have recently, canyoubelieveit, seen red for isolated ground (as distinct from the EGC which was green). Not real clear on how that could pass inspection.

--jhawk
 

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Posted by Steve Guttag (Member # 268) on 12-16-2009, 09:40 PM:
 
Oddly enough Green is not a protected color...though, in my opinion, it should be. Personally, I think all of the standard colors should be codified and enforced at least for 120V and higher circuits.

Again, White is the only color that I'm aware as being protected as being a Neutral.
 

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Posted by Jake Spell (Member # 5294) on 12-17-2009, 02:36 AM:
 
Yes White is the only color that is protected, however I have seen White used as a ground. Dont know how this passed inspection, I also have see plenty of people using the ground as a nuetral when they have a 240 volt appliance, with a small 120 load (like a 120 light in an attic that uses one hot from the A/C and the ground) when the installer is to lavy/cheep to run a netural back to the pannel
 

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Posted by Louis Bornwasser (Member # 3063) on 12-17-2009, 04:31 AM:
 
Jake: at one point all electric stoves were wired using the neutral as a ground. I wondered about this as a child. Now code requires 4 wires; seperate the ground from the neutral. Louis
 

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Posted by Steve Guttag (Member # 268) on 12-17-2009, 06:35 AM:
 
Yeah, using ground as a current carrying conductor (neutral) is dangerous. It is also true that electrical wiring/codes have evolved as the flaws in original designs showed themselves. Shoot, my house only had 2-prong outlets until I changed them. You can kinda tell when the 120/240 outlet come into being considering that a 240 outlet is a 6-series and the 120/240 is a 14-series. The outlet we all know as a standard 120V is a 5-series.

Steve
 

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Posted by Stephen Furley (Member # 1277) on 12-17-2009, 07:14 AM:
 
How common are those 240 V delta system sover there? I've only ever seen one, 120/208 and 277/480 Wye systems seem to be much more common, though I have to admit that I haven't seen many American installations. Whenever I'm in a building and see an electrician working I must admit that I have a look to see what sort of system it is.

We've got some horrible nonsense over here, caused by European harmonisation. Live wires used to be red, yellow and blue, with neutral black and earth green. Lives have now become brown, black and grey, yes seriously, with neutral blue and earth green with yellow stripe. So, blue, which used to be a phase conductor, is now neutral, and black, which used to be neutral, is now a phase conductor. Great opportunity for confusion when new wiring is added to an existing installation. The new neutral blue does seem to be a slightly lighter shade than the old blue. In mixed installations a special warning label has to be attached; I can't remember the exact wording.

'European harmonisation' was also the excuse, sorry reason, why all fire extinguishers now have to be red, rather than different colours for different types.
 

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Posted by Eric Robinson (Member # 2966) on 05-23-2010, 09:10 PM:
 
This is also known as a "bitch leg" or "stinger leg"

Be careful when using this setup with a Strong console. The strong console "Highlight IIa" for instance takes the 3 phases and passes them to the xenon power supply. (no problem here)
However:
The console also takes each phase and divides the load so that one phase powers the projector motor, the next powers the automation and fans, the next the convenience outlets... so if you have a stinger leg, you could pass 220V to one of these 120V devices.
 

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Posted by Steve Guttag (Member # 268) on 05-23-2010, 10:15 PM:
 
Eric,

Yes and no. There is a strap that is often installed so that the "C" phase powers the two 120V circuits. However, a competent installer will remove that strap and fire the the TWO 120V circuits from individual breakers. Or, failing that, use two legs of the 3-phase and rotate them about the complex to ensure the electrical panel load is balanced.

We service a former AMC house that used those stupid straps and they had the "C" phase severely overloaded as compared to the other two legs. It caused numerous 3-phase breaker failures since the C buss bar would get hot and transfer that heat to the three phase breakers.

That strap is a lazy person's way of installing...it is an incompetent way of installing a system.
 

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Posted by Stephen Furley (Member # 1277) on 05-24-2010, 11:53 AM:
 

quote: Steve Guttag

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I have also come across the grounded Delta...just plain freaky if you ask me, and I'm an EE. There is something un-nerving about seeing one of the phases tied to ground and that the remaining two hot legs having a 220 potential to ground. The reason I was given was that it reduced cost as only three conductors needed to be pulled of the heavy copper instead of four...and only double pole breakers instead of triple.

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