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Old 03-19-2019, 03:39 PM   #1
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Default Wild leg

Can you, by NEC, install a 20a 120v receptacle fed from a panel board with "B" phase being the wild leg? If you use A or C phase you should be okay.
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Old 03-19-2019, 05:31 PM   #2
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Of course you can


Well....I can anyway. I don't know your skill level
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Old 03-19-2019, 05:34 PM   #3
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Quote:
Originally Posted by pencil View Post
Can you, by NEC, install a 20a 120v receptacle fed from a panel board with "B" phase being the wild leg? If you use A or C phase you should be okay.
There's no reference point available in the system that's 120V to B -

AB = 240
BC = 240
BN = 208 = BG

So if you were to install a 120V 20a receptacle with B to hot and N to neutral it would be at 208V, violating the listing, the rating, and probably a lot of other things.

As you mention AN or CN is 120V as intended, that's how it's supposed to work with the high leg delta.
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Old 03-19-2019, 06:51 PM   #4
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Quote:
Originally Posted by pencil View Post
Can you, by NEC, install a 20a 120v receptacle fed from a panel board with "B" phase being the wild leg? If you use A or C phase you should be okay.
That is the whole reason for Delta-Hi-Leg distribution
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Old 03-19-2019, 11:26 PM   #5
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Think of a 120/240 3 4 wire system as a single phase system with a high leg added.

The two 120 volt legs are exactly the same as a basic 120/240 single phase system, the high leg is the only oddball.
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Old 03-20-2019, 10:08 AM   #6
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what he said.
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Old 03-20-2019, 12:33 PM   #7
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Welcome aboard @pencil!

Enjoy your ride here.

A receptacle wired in the manner you mention might just take the lead out of your pencil!
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Old 03-22-2019, 08:45 AM   #8
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Quote:
Originally Posted by splatz View Post
BN = 208 = BG

So if you were to install a 120V 20a receptacle with B to hot and N to neutral it would be at 208V, violating the listing, the rating, and probably a lot of other things.
Do they make sp breakers rated for 240V?

I suppose if they did, you could fee 208V equipment from it, couldn't you?
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Old 03-22-2019, 11:37 AM   #9
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Quote:
Originally Posted by Helmut View Post
Do they make sp breakers rated for 240V?

I suppose if they did, you could fee 208V equipment from it, couldn't you?
I can't think of a reason why it wouldn't work,
but that doesn't mean there isn't a reason
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Old 03-22-2019, 12:30 PM   #10
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Quote:
Originally Posted by Helmut View Post
Do they make sp breakers rated for 240V?

I suppose if they did, you could fee 208V equipment from it, couldn't you?
It would "work" but you may be loading the neutral and the transformer in an unintended way
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Old 03-22-2019, 12:45 PM   #11
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Quote:
Originally Posted by splatz View Post
I can't think of a reason why it wouldn't work,
but that doesn't mean there isn't a reason

Back in the stone age when I was in school they said no it is unusable because vector wise it goes to 240 first then subtracts to 208. I have heard people on here say you could, if breaker was rated. But I don't think it would be good.


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Old 03-22-2019, 05:11 PM   #12
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Quote:
Originally Posted by just the cowboy View Post
Back in the stone age when I was in school they said no it is unusable because vector wise it goes to 240 first then subtracts to 208. I have heard people on here say you could, if breaker was rated. But I don't think it would be good.


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This doesn't make sense to me, can you elaborate?

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Old 03-22-2019, 05:18 PM   #13
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Quote:
Originally Posted by just the cowboy View Post
Back in the stone age when I was in school they said no it is unusable because vector wise it goes to 240 first then subtracts to 208. I have heard people on here say you could, if breaker was rated. But I don't think it would be good.
Quote:
Originally Posted by B-Nabs View Post
This doesn't make sense to me, can you elaborate?
I was trying to think ... which winding would supply the voltage?

Would it be
N-C-B = 208 - half the AC winding plus the BC winding
or
B-A-N = 208 - other half of the AC winding plus the AB winding
or
both
?
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Old 03-22-2019, 10:16 PM   #14
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The open delta 4-wire is where you will find the wonky imbalance if you use the high leg to neutral. Not sure of the exact reason, but a closed delta wouldn't have that problem if the transformer with the neutral were sized right.
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Old 03-22-2019, 10:17 PM   #15
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Quote:
Originally Posted by splatz View Post
I was trying to think ... which winding would supply the voltage?

Would it be
N-C-B = 208 - half the AC winding plus the BC winding
or
B-A-N = 208 - other half of the AC winding plus the AB winding
or
both
?
Yes.
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Old 03-22-2019, 11:42 PM   #16
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Quote:
Originally Posted by Helmut View Post
Do they make sp breakers rated for 240V?

I suppose if they did, you could fee 208V equipment from it, couldn't you?
Years ago, when I was a carpenter, I had a 240 volt worm-drive skilsaw and my compressor was also 240.

I made up some clip less (yes, they were fused) and whenever I worked anywhere there was a 240 ∆, I would use the high leg and the neutral.

Never had a lick of trouble but got some flak from electricians who didn't know better.
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Old 09-11-2019, 07:46 PM   #17
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Quote:
Originally Posted by Helmut View Post
Do they make sp breakers rated for 240V?

I suppose if they did, you could fee 208V equipment from it, couldn't you?
SD was making 240 the last time i checked
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Old 09-11-2019, 08:21 PM   #18
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What was the intended purpose or advantage of using this system back in the day . If you cannot use the b phase with a single pole braker To feed peices of equipment with
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Old 09-11-2019, 08:26 PM   #19
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Quote:
Originally Posted by Fist of lightning View Post
What was the intended purpose or advantage of using this system back in the day . If you cannot use the b phase with a single pole braker To feed peices of equipment with

1) You got 240 three phase for big motor loads
2) You got 120 V for general power
3) You got an easy place to ground the system
4) You got a nice closed delta to cancel harmonic currents


The 208 volt high leg was just a side effect. You want 240 volt three phase and 120 V single phase from a delta, well, you have to live with the 208. The physics won't have it any other way.


It really is a pretty good and stable system, especially if you have a bunch of motors.
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Old 09-12-2019, 02:58 PM   #20
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Quote:
Originally Posted by CoolWill View Post
1) You got 240 three phase for big motor loads
2) You got 120 V for general power
3) You got an easy place to ground the system
4) You got a nice closed delta to cancel harmonic currents


The 208 volt high leg was just a side effect. You want 240 volt three phase and 120 V single phase from a delta, well, you have to live with the 208. The physics won't have it any other way.


It really is a pretty good and stable system, especially if you have a bunch of motors.
The operative issue was however, that your loads were PREDOMINANTLY 240V 3 phase, with SOME 120V loads. So think of a machine shop with lots of 3 phase machine tools all around, then a small front office, snack room and bathrooms that need 120V outlets. In some areas the utility will limit the 120V to 5% of the total load because it results in an imbalance. if your loads are predominantly single phase, they will push you to 208Y120.
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