# Some 3 phase questions



## Magnettica (Jan 23, 2007)

Yes, it's single phase because it's only a 2-pole circuit. 

It would be three phase if it were a 3-pole circuit.


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## pawirenut (May 28, 2008)

Magnettica said:


> Yes, it's single phase because it's only a 2-pole circuit.
> 
> It would be three phase if it were a 3-pole circuit.


That's what i thought. So if you use a 3 pole breaker it's 3phase 208v? The panel is a 208v/120v.


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## 480sparky (Sep 20, 2007)

pawirenut said:


> That's what i thought. So if you use a 3 pole breaker it's 3phase 208v? The panel is a 208v/120v.


 
It would be 208v 3ph is there are only ungrounded conductors in the branch circuit. If there's a neutral, it would be 120/208v.


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## B4T (Feb 10, 2009)

*ALWAYS *check voltage from each leg to neutral... most will be 120V per leg.

A "Delta" 3/phase service will have (1) leg that is 240V from neutral to hot.


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## pawirenut (May 28, 2008)

480sparky said:


> It would be 208v 3ph is there are only ungrounded conductors in the branch circuit. If there's a neutral, it would be 120/208v.


Ok the panel is 4 wire 3 hot and a neutral. I still don't understand what voltage you get from a 3 pole breaker though? In the same panel there are many 100 amp 3 pole breakers. A 2 pole gives you 208v so what does a 3 pole give you?


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## kbsparky (Sep 20, 2007)

> ...A 2 pole gives you 208v so what does a 3 pole give you?...


208 Volts. You can only measure the potential difference between 2 points at any given time. You'll get the same result no matter which 2 lines you test on. :blink:


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## kbsparky (Sep 20, 2007)

Black4Truck said:


> *ALWAYS *check voltage from each leg to neutral... most will be 120V per leg.
> 
> A "Delta" 3/phase service will have (1) leg that is 240V from neutral to hot.


I've never seen a delta service that had any more than 208 Volts on the high leg. You get 240 Volts when measuring between any 2 hot legs. :whistling2:


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## brian john (Mar 11, 2007)

Black4Truck said:


> *ALWAYS *check voltage from each leg to neutral... most will be 120V per leg.
> 
> A "Delta" 3/phase service will have (1) leg that is 240V from neutral to hot.


Actually in a high leg delta the voltages are A-B 240 VAC, B-C 240 VAC, C-A 240 VAC, A to Neutral 120 VAC, C to Neutral 120 VAC and B to neutral 208. Assuming the B phase is the high leg.

In the OP's post his voltage on a 208/120 VAC 3-phase 4-wire distribution system the voltages are A-B 208 VAC, B-C 208 VAC, C-A 208 VAc and A-B-C phase to ground or the neutral (grounded conductor) 120 VAC assuming the measurements are taken at the point of the neutral to ground bond.

There will be a slight difference in Phase to neutral and phase to ground as you measure away from the main bond, based on load and distance from the neutral/ground bond..


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## B4T (Feb 10, 2009)

brian john said:


> Actually in a high leg delta the voltages are A-B 240 VAC, B-C 240 VAC, C-A 240 VAC, A to Neutral 120 VAC, C to Neutral 120 VAC and B to neutral 208. Assuming the B phase is the high leg.


"C" is always the high leg (red) here and I thought it was higher than 208 :blink:


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## B4T (Feb 10, 2009)

kbsparky said:


> I've never seen a delta service that had any more than 208 Volts on the high leg. You get 240 Volts when measuring between any 2 hot legs. :whistling2:


I never put a digital meter on the high leg.. always used a wiggy


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## JayH (Nov 13, 2009)

B is always the high leg in California and it is marked orange per 230.56 & 408.3(E).


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## Magnettica (Jan 23, 2007)

pawirenut said:


> Ok the panel is 4 wire 3 hot and a neutral. I still don't understand what voltage you get from a 3 pole breaker though? In the same panel there are many 100 amp 3 pole breakers. A 2 pole gives you 208v so what does a 3 pole give you?



The 3-poles are 120º (electrical degrees) out of phase with one another. This is great for getting motors to do work. 

As the others have said, always check your voltages to be certain you know what you're working with. 120/ 208 V.A.C. (volts of alternating current) is a Wye voltage.


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## ONTHEGO (Jan 9, 2010)

pawirenut said:


> ok the panel is 4 wire 3 hot and a neutral. I still don't understand what voltage you get from a 3 pole breaker though? In the same panel there are many 100 amp 3 pole breakers. A 2 pole gives you 208v so what does a 3 pole give you?


you check voltage two wires at a time, whether it be phase to phase or phase to neutral or phase to ground. Now you can check three phase but it is for rotation only.


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## brian john (Mar 11, 2007)

Black4Truck said:


> "C" is always the high leg (red) here and I thought it was higher than 208 :blink:


And that's assuming, I have seen the high leg on A, B and C depending on the utility, and vintage of the service.


Mathematically it works out to 208, it will be higher if the phase to phase voltage is higher.


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## brian john (Mar 11, 2007)

Black4Truck said:


> I never put a digital meter on the high leg.. always used a wiggy


I prefer a wiggy for a go no go tester, but if my digital is out I use it.


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## brian john (Mar 11, 2007)

ONTHEGO said:


> you check voltage two wires at a time, whether it be phase to phase or phase to neutral or phase to ground. Now you can check three phase but it is for rotation only.


I own plenty of voltage meters that measure phase to phase, phase to ground, phase to neutral simultaneously and current A-B-C-N-Gnd.

This is just one of the different power analyzers we utilize.

http://us.fluke.com/usen/Products/F...ukeUnitedStates&category=PHASE3(FlukeProducts)


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## tsccgy19 (Jan 18, 2010)

*Tape on the screwdriver*

Yes you can tape the screwdriver shaft and bolt on the breakers... lots of heroes do that.

However if you have ever seen someone burned from and arc flash, you wont do that. You will follow your instincts and de-energize the panel before working on it. You get paid no extra to take those chances. I have been doing this for 30 years and have a healthy respect for electricity. My policy is that if I can shut it off, I will, if I can't I will use proper insulated screwdrivers (Klein makes them) and use a face shield and goggles. 

There are not many mission criticial applications that cannot be shut down.

Don't be a hero, your family is counting on you to come home tonight.


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## ampman (Apr 2, 2009)

Black4Truck said:


> I never put a digital meter on the high leg.. always used a wiggy


 why ?


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## Jeff000 (Jun 18, 2008)

tsccgy19 said:


> My policy is that if I can shut it off, I will, if I can't I will use proper insulated screwdrivers (Klein makes them) and use a face shield and goggles.
> 
> There are not many mission criticial applications that cannot be shut down.



Same here. I've never trusted taping up my tools for insulation. 
I do lots of hospitals and airports. So lots of live.


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## Old Spark (Nov 18, 2008)

Regarding the delta 3 phase 120/240. The utility in California brings the high leg in on phase "C". N.E. C. requires that we move the wire from the bottom of the meter between B and C to change the high leg to the B phase. I only see about half of the systems here done correctly. I guess a lot of electricians and inspectors don't know this requirement. The orange phasing of the high leg was changed from Red about 25 years ago. It insures that a trained electrician will recognize immediatly that it is not 120/208. N.E.C. also requires that we label a panel with a warning that the panel has a high leg. This also is usually skipped. The high leg can cause lots of problems for electricians or anyone working in a panel if they assume every leg is 120 to ground.
P.S. The high leg should be about 208 to ground anywhere in the US.


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## jwjrw (Jan 14, 2010)

pawirenut said:


> Ok the panel is 4 wire 3 hot and a neutral. I still don't understand what voltage you get from a 3 pole breaker though? In the same panel there are many 100 amp 3 pole breakers. A 2 pole gives you 208v so what does a 3 pole give you?


 Picture this you have a 100a 3pole breaker with 3 100 amp circuits. You have 12k watts per phase available or a total of 36k watts for the 3 phase 100 amp breaker


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## IBEW501Ed (Oct 4, 2009)

The high leg of a grounded delta is alway 1.73 x the voltage to ground on either of the other 2 phases.


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