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Author Topic: What do you call three hot legs?  (Read 2597 times)

John Fruits

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What do you call three hot legs?
« on: February 02, 2014, 05:50:07 pm »

I was somewhat curious that different names exist for the three hot legs in three phase power. The ones I have seen are
X,Y and Z
A,B and C
H1,H2 and H3
L1,L2 and L3
I was wondering if there was any reasoning behind this or is it perhaps a regional thing.

Incorrect answers:
Half a hot time for ZZ Top
Curly, Larry and Moe.
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Ray Aberle

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Re: What do you call three hot legs?
« Reply #1 on: February 02, 2014, 06:58:52 pm »

I was somewhat curious that different names exist for the three hot legs in three phase power. The ones I have seen are
X,Y and Z
A,B and C
H1,H2 and H3
L1,L2 and L3
I was wondering if there was any reasoning behind this or is it perhaps a regional thing.

Incorrect answers:
Half a hot time for ZZ Top
Curly, Larry and Moe.
I use X, Y and Z, but just cos that is what is labeled on the cable ends...

Ray
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Regional - Serving Pacific Northwest (OR, WA, ID, BC)

Mike Sokol

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Re: What do you call three hot legs?
« Reply #2 on: February 02, 2014, 07:02:24 pm »

I use X, Y and Z, but just cos that is what is labeled on the cable ends...

Ray

We used L1, L2 and L3 for industrial wiring ladder diagrams. Also marked 3-phase power with a 3P or 3/P

Stephen Swaffer

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Re: What do you call three hot legs?
« Reply #3 on: February 03, 2014, 12:00:57 am »

I think it is more industry/equipment related.  When working with power panels we usually refer to A phase-B phase-C phase.  On some CNC equipment and VFDs  you might see U,V,W and R,S,T depending in input/output.  Three phase transformers are usually marked H1, H2, H3 and X1, X2, X3 for primary and secondary respectively (if there is an X0 it would be the neutral.)  As Mike noted, L1,L2,L3 is common on industrial diagrams and line side of contactors-T1,T2,T3 on the motor side.

I am sure there is probably a NEMA or industry standard somewhere-seems to be too consistent to just be the random preference of the design engineer-though there are a few that seem determined to be creative!
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Steve Swaffer

Steve M Smith

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Re: What do you call three hot legs?
« Reply #4 on: February 03, 2014, 01:50:18 am »

L1, L2 and L3 over here.


Steve.
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RYAN LOUDMUSIC JENKINS

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Re: What do you call three hot legs?
« Reply #5 on: February 03, 2014, 10:17:25 am »

Since we are generally dealing with Cams we call them Red, Black and Blue.
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John Fruits

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Re: What do you call three hot legs?
« Reply #6 on: February 03, 2014, 10:54:00 am »

Since we are generally dealing with Cams we call them Red, Black and Blue.
Just be careful if you go to Australia or New Zealand.
http://en.wikipedia.org/wiki/Electrical_wiring
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Mike Sokol

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Re: What do you call three hot legs?
« Reply #7 on: February 03, 2014, 12:11:55 pm »

Just be careful if you go to Australia or New Zealand.
http://en.wikipedia.org/wiki/Electrical_wiring

Also in America be careful if you see anything in a 3-phase panel with orange tape on a wire. That's likely a High-Leg Delta service (also called Wild-Leg Delta or Red-Leg Delta). This was found in older industrial buildings that needed mostly 3-phase 240-volt power for motors, and limited amounts of split-phase 120/240-volt power for offices. Note that the Orange High-Leg have 208-volts to neutral, instead of the 120-volts to neutral of the other two legs. Of course, connecting 208 volts to anything expecting 120 volts will make for a very bad day.

See http://en.wikipedia.org/wiki/High-leg_delta for a good tutorial on how this all works.   

Jonathan Johnson

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Re: What do you call three hot legs?
« Reply #8 on: February 03, 2014, 02:05:12 pm »

Also in America be careful if you see anything in a 3-phase panel with orange tape on a wire. That's likely a High-Leg Delta service (also called Wild-Leg Delta or Red-Leg Delta). This was found in older industrial buildings that needed mostly 3-phase 240-volt power for motors, and limited amounts of split-phase 120/240-volt power for offices. Note that the Orange High-Leg have 208-volts to neutral, instead of the 120-volts to neutral of the other two legs. Of course, connecting 208 volts to anything expecting 120 volts will make for a very bad day.

My understanding is that 208V (pole to neutral) is used mostly for fluorescent lighting loads and occasionally for heating loads. This allows for a single-pole 20A circuit providing 3328VA versus 1920VA of lighting on a 120V circuit. Therefore, you can have more lights on a single switch. The advantage of 208V over 240V is that 240V is double-pole, requiring double-pole breakers and switches.

(Note on the math: while a 208V 20A circuit has a capacity of 4160VA, code requires limiting a continuous load to 80% of the circuit capacity. That's how I get 3328VA.)
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Stop confusing the issue with facts and logic!

Patrick Tracy

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Re: What do you call three hot legs?
« Reply #9 on: February 03, 2014, 02:09:58 pm »

Disregard.......
« Last Edit: February 03, 2014, 03:32:50 pm by Patrick Tracy »
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