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Joined: Feb 2005
Posts: 693
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Larry, where did anyone say the (A for sake of conversation) high leg point did not have a purpose or was not a point of a system connection.

Here:

Quote
What is the 3 phase 208v wild leg usually used for in commercial panels?

But still not sure what that 208v wild leg is doing on the 3 phase motors?

I realize all that, but what is the 208v to ground (wild leg) used for usually?

Not sure I'm getting it... so the wild (208v) leg never gets used to neutral, what is it there for then? Doesn't seem like it would do anything on a 3 phase motor if your measuring 240v between each phase.

So there is no real purpose for the wild leg, since it does not affect a 3 phase motor, or is there another application it is used, right?

[This message has been edited by Larry Fine (edited 05-07-2006).]


Larry Fine
Fine Electric Co.
fineelectricco.com
Joined: Feb 2005
Posts: 693
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A very common design technique for Buildings with 4 Wire Deltas, was to use 1 Phase 3 Wire Panelboards - fed with Lines "A", "C" and the Center Tapped Neutral, where only 1 Phase loads were used (like in Office spaces and such), and using 3 Phase Panelboards - fed with Lines "A, B & C" only - no Grounded Conductor (Neutral), where only L-L and 3 Phase loads were used (like in the warehouse shop area or for HVAC equipment).

Scott, I just did this exact setup in a major restaurant remodel, where the service is open Delta. We have a 125a 3ph panel for the two RTU's (HVAC) and a 200a 1ph panel for everything else.

The original plans called for a new 208/120Y system with two 3ph panels, but I bumped heads with the engineer and we redesigned the service. Saved my customer $5-6K in new transformer costs.


Larry Fine
Fine Electric Co.
fineelectricco.com
Joined: Feb 2005
Posts: 693
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No use for high leg to neutral???? Some high-bay lighting and other HID ballasts can make good use of it.... There are also some single phase, dual rated equipment that can use it too. For instance, commercial kitchen equipment. Not off the shelf stuff often, but it is out there.

That's a bad idea. It's a relatively high-impedance source, not real stable, and I'm quite sure it's not an approved method of obtaining 208v.


Larry Fine
Fine Electric Co.
fineelectricco.com
Joined: Jun 2003
Posts: 681
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It is always fun to read and listen to guys discuss topic that I can easily learn from - very good!!!

On the topic of why NM cable is so inferior in commercial occupancies, I would like to hear from the guys who think it is so inferior as to why it is so. The NEC permits it whether you like it or not.
I am interested as to why you think it is so worthless. No personal opinions, give me some facts.


Pierre Belarge
Joined: Jun 2005
Posts: 91
G
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I thought two transformers indicated an ungrounded system? It actually means that the system is an "open delta"? It can still be a grounded system?

I agree with Pierre, good thread. I'm taking notes. [Linked Image]


-George
Joined: Oct 2005
Posts: 100
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Larry, you've done an EXCELLENT job explaining 3-phase and transformers. I've never heard a more concise and easy to understand explanation anywhere.

PCBelarge, the reason I believe Romex is inferior can be summed up in two words:

FIRE & ELECTROCUTION

Here's my list of best to worst wiring methods:

1. RMC
2. IMC
3. EMT
4. MC
5. AC/BX
6. PVC Conduit
7. Romex
8. K&T

The problem with Romex is it offers NO protection. You can easily drive a nail or screw through even CORRECTLY (according to code) installed Romex. Even staples can be a problem.

Metal ducting can pinch Romex and said ducting can become energized. Didn't we recently read about such an accident on this forum about a guy in FL who was electrocuted installing a dryer when the ducting became energized because of nicked Romex?

The flat, parallel nature conductor placement with most Romex cable is also an issue. In the event of overload, the parallel cooper in Romex will just keep getting hot until something ignites -- similar to heating elements. Not so with the twisted nature of MC and AC and to some degree, cable installed in conduit -- chances are when the wiring heats up, it will melt the insulation, immediately tripping the OCPD. And if fire should occur, there is the additional safety factor of it happening inside the flex or conduit. By the way, with MC and AC, the brown kraft paper will stop the fire from spreading up through the cable.

A residential rewire (where the walls are not ripped down) with Romex presents all sorts of problems. First is removal of old wiring. With conduit, obviously it's a breeze. With MC or AC, you can tug on cable and pop out the staples inside the wall. It's VERY difficult doing any of that with Romex.

Fishing unprotected Romex inside walls is even more problem prone. Code says fished Romex is considered "protected" but who knows where it will end up? Will it be snaked around a sharp nail or screw? MC or AC offers "instant" protection against this. What if snaked Romex ends up against a hot water pipe or heating duct? What may happen over time? Again, not as much of a problem with MC or AC.

Romex is also too easy to kink.

There IS a reason why Romex isn't used in commercial construction, and most local codes prohibit it. Heck, Chicago sparkys have to do residential in pipe. NYC recently allowed Romex, but almost no new construction I've seen takes advantage of it.

The only good thing about Romex is it can be made into a beautiful "looking" install, like we've seen on this forum, where it looks like it was done with an iron. But conduit looks even better. MC and AC is hard to get looking nice.

Romex is nothing more than glorified zip cord.


Joe

Joined: Jul 2004
Posts: 787
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quote:
--------------------------------------------------------------------------------
No use for high leg to neutral???? Some high-bay lighting and other HID ballasts can make good use of it.... There are also some single phase, dual rated equipment that can use it too. For instance, commercial kitchen equipment. Not off the shelf stuff often, but it is out there.
--------------------------------------------------------------------------------

That's a bad idea. It's a relatively high-impedance source, not real stable, and I'm quite sure it's not an approved method of obtaining 208v.

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

It's a relatively high-impedance source, not real stable ...

Can you expand on those two points? Are you concerned about a large single phase load shifting the neutral?

Thanks, LarryC

Joined: May 2003
Posts: 2,876
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e57 Offline
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Yeah, Larry, why not? Not trying to be a joker, but I have done it on rare occassion in the past. (when pinched) Not that it is my favorite way to go or anything. But don't know of any prohibition against it? Code or otherwise. The way I see it, it is simular to obtaining different voltages from the same autotransformer.

I do know that not all high-legs are 208 either, many, depending on where that neutral tap ends up are often off ~10 volts or more. If thats the case, those loads end up being single phase from high-leg to A or C at 240.....


Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: May 2003
Posts: 2,876
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As for 277/480 on romex. I too think that is just a bad idea. (Unless you provide anyone working in the building hot gloves and a course in CPR.) To me the difference there is a "little shock" or full arithmia, and a burn to go with the bite. Although not against the NEC, most of the places that I work in wont allow it in commercial, and I personally would be frightened by 277 in Romex. It is too fragile in terms of insulation integrety IMO for that hazardous a voltage. Little shock, and spark -vs.- death, and fire.


Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: Mar 2001
Posts: 2,056
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Regarding using the 208 high-leg for 208 volt loads...
I think it is generally accepted that single phase 208 volt equipment is designed for 2 hot legs of a wye system. Although "generally accepted" dosen't constitute a code rule, using a single pole "slash-rated" circuit breaker would be a violation of 240.85. Although I have used "straight rated" 2-pole CBs on delta systems, I'm not sure they are available as a single pole device.

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