High Leg

Status
Not open for further replies.

Ryan88

Member
Location
Philadelphia, PA
Hello all. I'm new to the forum so go easy on me.

In 17 yrs doing electrical I've only come accross high leg 3 phase a handfull of times. As I understand it you should have 120v on two phases and 190v-200v on other phase. I'm getting 136v on A phase, 109v on B phase and 210 on C phase from hot to neutral. 244v from phase to phase. I recently replaced a motor starter for a new customer and the 120v coil burnt up in a week. Replaced the coil and it started right up but seems to be running hot and starting to get that electrical burn smell. Its -120v coil. First time I tapped the coil on A phase. This time switched to B phase. Any thoughts on whats going on here. Also, is it normal to have such a big differential in voltage from two 120v phases?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
First off.... in regard to the coil: measure the voltage at the coil and also at the phase you are using. Arbitrarily switching is asking for trouble !
That variance in your phase voltages is, IMO, abnormal. I would check it at a point as close to the service point as you can. A poor neutral connection could contribute to the problem so its worth checking those connections.
If you show that imbalance at the service point I would ask you utility to check voltages.
 

Smart $

Esteemed Member
Location
Ohio
I'm inclined to agree with Gus (augie47)... a faulty neutral connection or conductor.

Also check line to ground. While it doesn't change the possibility of a faulty neutral, it could give an indication of which side of the main bonding jumper (service) or system bonding jumper (separately derive system) the faulty neutral is on.

Excessive load on one line while the other lightly loaded will cause an imbalance of line to neutral voltage... but it will not cause another line to elevate in voltage. This is why a faulty neutral is indicated.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
While I agree with the other comments, I'm wondering if this control circuit is powered from the line side of the starter or is from a separate source. I seem to get the impression that is from the starter and makes me wonder if that is the case why he has a 120 volt coil and where is the neutral coming from.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I'm still in shock that at 17 years old, he has already seen a high leg system "a handful of times"! I was probably around 30 before I ever came across one.
 

Smart $

Esteemed Member
Location
Ohio
I'm still in shock that at 17 years old, he has already seen a high leg system "a handful of times"! I was probably around 30 before I ever came across one.
He said 17 yrs doing electrical. I seriously doubt he started doing electrical at day 1... :D
 

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
I'm still in shock that at 17 years old, he has already seen a high leg system "a handful of times"! I was probably around 30 before I ever came across one.

I think you read his post a little too fast?

In 17 yrs doing electrical I've only come accross high leg 3 phase a handfull of times.

I think I came across my first 240v high leg system a year or two into my apprenticeship, around 23-24. You just might be a late bloomer.:D It might of been a few years after that when I discovered there was also a 480v high leg system too. I think the voltages were around 240-410-240 if I remember right. Now I'm curious so I'll have to google it.
 

Smart $

Esteemed Member
Location
Ohio
While I agree with the other comments, I'm wondering if this control circuit is powered from the line side of the starter or is from a separate source. I seem to get the impression that is from the starter and makes me wonder if that is the case why he has a 120 volt coil and where is the neutral coming from.
Good point.

A neutral is typically not run to a 3? starter and a 240-120V control transformer would be required to use a 120V coil.
 

Smart $

Esteemed Member
Location
Ohio
...It might of been a few years after that when I discovered there was also a 480v high leg system too. I think the voltages were around 240-410-240 if I remember right. Now I'm curious so I'll have to google it.
416V high leg on 480/240 3? 4W... it's exactly double a 240/120V 3? 4W.
 

Ryan88

Member
Location
Philadelphia, PA
While I agree with the other comments, I'm wondering if this control circuit is powered from the line side of the starter or is from a separate source. I seem to get the impression that is from the starter and makes me wonder if that is the case why he has a 120 volt coil and where is the neutral coming from.

Yes, 120v coil is powered from the line side of the starter. Neutral wire from the panel. So in my conduit I have 3 #8's, #12 white (neutral), and a ground.

Also, I'm getting these voltage readings at all equipment in this room and at the panel. Going to urge them to get Poco out to check out incoming service.
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
Going to urge them to get Poco out to check out incoming service.

Let us know the result, please.
(In this area there would be a good chance POCO will check it "find nothing wrong"
yet the problem is mysteriously resolved :))
 

kwired

Electron manager
Location
NE Nebraska
Yep, I see a number of these out in the oil patch where they only have 2 primary phases available.
We have a lot of high leg systems around here as well both 480 and 240 volts. In fact I just got off the phone with a customer where we will be having a brand new service - 120/240 with high leg for a grain bin. Why go with a 208 volt system when the 120 volt load is limited to just a couple convenience receptacles and minimal lighting? The main load is three phase motors.

Yes, 120v coil is powered from the line side of the starter. Neutral wire from the panel. So in my conduit I have 3 #8's, #12 white (neutral), and a ground.

Also, I'm getting these voltage readings at all equipment in this room and at the panel. Going to urge them to get Poco out to check out incoming service.
You do need to make sure you do not connect that control circuit to the high leg. But as others said - you have other issues - likely a bad neutral somewhere contributing to the unbalanced voltages you saw.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Yes, 120v coil is powered from the line side of the starter. Neutral wire from the panel. So in my conduit I have 3 #8's, #12 white (neutral), and a ground.

Also, I'm getting these voltage readings at all equipment in this room and at the panel. Going to urge them to get Poco out to check out incoming service.

While I am unsure of the OCPD size on your circuit, it seems unlikely that the #12 neutral would be large enough to comply with 250.122. I know this is not directly addressed in the code for branch circuits as it is for service conductors and feeders, but I think it is implied.
 

growler

Senior Member
Location
Atlanta,GA
In 17 yrs doing electrical I've only come accross high leg 3 phase a handfull of times.

I was probably around 30 before I ever came across one.


I know of electricians that have been working for years and never seen a delta system.

Depends on the type of work you normally do and the areas where you work.

Around my local area a high leg is rare but I can drive a few miles to some areas that used to be very industrial and high leg sytems are all over the place.
 

Smart $

Esteemed Member
Location
Ohio
While I am unsure of the OCPD size on your circuit, it seems unlikely that the #12 neutral would be large enough to comply with 250.122. I know this is not directly addressed in the code for branch circuits as it is for service conductors and feeders, but I think it is implied.
Neutral size cannot be reduced at the branch circuit level like it can be for service and feeder conductors [except for household cooking appliances under 210.19(A)(3) Exception No. 2 (AFAIK)]
 

kwired

Electron manager
Location
NE Nebraska
While I am unsure of the OCPD size on your circuit, it seems unlikely that the #12 neutral would be large enough to comply with 250.122. I know this is not directly addressed in the code for branch circuits as it is for service conductors and feeders, but I think it is implied.
You are correct that it is not addressed.

Neutral size cannot be reduced at the branch circuit level like it can be for service and feeder conductors [except for household cooking appliances under 210.19(A)(3) Exception No. 2 (AFAIK)]
Not addressed but I don't see that a reduced grounded conductor is prohibited either for branch circuits.

For a grounded conductor that only carries a few volt amps @ 120 volts because all that is connected to it is a coil of a magnetic contactor-

210.19(A)(1) only tells us conductors shall have an ampacity not less then the max load to be served, plus additional 25% for continuous duty, and any necessary adjustment factors.

Overcurrent protection doesn't matter - it is a grounded conductor so we have no overcurrent device to go by. If you imply that rules for feeders also apply then you must at least size this conductor to 250.122 and the overcurrent device on the ungrounded conductors of that circuit. Otherwise if you take it for what is actually written - I don't think there is a minimum grounded conductor size for branch circuits other then it needs to be able to carry max load it will ever see.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Neutral size cannot be reduced at the branch circuit level like it can be for service and feeder conductors [except for household cooking appliances under 210.19(A)(3) Exception No. 2 (AFAIK)]

I never understood why we don't have language in Art. 210 similar to 215.2(A)(2) for the cases where a piece of equipment needs a limited neutral for whatever reason. It would seem obvious that if this is done, as in the OPs case, that it needs to be a least as large as an EGC. But maybe you are right, it needs to be full sized except for the exceptions. But that seems crazy to me.
 
Status
Not open for further replies.
Top