red leg service
- Thread starter sleepy
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Re: red leg service
search for "high leg" "stinger" "120/240 3phase 4 wire" "centertapped delta"
http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=3;t=001181#000000
is a good link to start with
Jim
search for "high leg" "stinger" "120/240 3phase 4 wire" "centertapped delta"
http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=3;t=001181#000000
is a good link to start with
Jim
Re: red leg service
What do you need to know? If you are talking about 120/240 3 phase service, the neutral for the 120's is made by tapping the center of one transformer secondary in a delta connected bank of 2 or 3 power co. transformers. This results in the "red" leg which is around 208 volts measured to the neutral. Voltage is 240 between any two legs and it is true 3 phase if you use all 3.
Jim
What do you need to know? If you are talking about 120/240 3 phase service, the neutral for the 120's is made by tapping the center of one transformer secondary in a delta connected bank of 2 or 3 power co. transformers. This results in the "red" leg which is around 208 volts measured to the neutral. Voltage is 240 between any two legs and it is true 3 phase if you use all 3.
Jim
edavis2293
Member
- Location
- Houston, Texas
Re: red leg service
One of the better books around about transformers is by Tom Henry; Transformer calculations. It is a part of my library.
The "high leg" is 208v to neutral or ground on a 120/240v 3 Phase, 4 wire delta connected transformer. The high leg is calculated by the formula 120 volts x square root of 3 = 208 volts.
These are widely used in commercial and industrial applications.
I haven't really looked at this edition of the NEC to see if a change in the code was made concerning the high leg located in a panel that did not supply 3 phase loads. If it wasn't changed, it needs to be.
The NEC requires the high leg be B phase and colored orange. 110.15, 408.3(E),
One of the better books around about transformers is by Tom Henry; Transformer calculations. It is a part of my library.
The "high leg" is 208v to neutral or ground on a 120/240v 3 Phase, 4 wire delta connected transformer. The high leg is calculated by the formula 120 volts x square root of 3 = 208 volts.
These are widely used in commercial and industrial applications.
I haven't really looked at this edition of the NEC to see if a change in the code was made concerning the high leg located in a panel that did not supply 3 phase loads. If it wasn't changed, it needs to be.
The NEC requires the high leg be B phase and colored orange. 110.15, 408.3(E),
Ed MacLaren
Senior Member
Re: red leg service
Although it results in the same answer, the high leg to neutral voltage is actually calculated as shown below.
Ed
Although it results in the same answer, the high leg to neutral voltage is actually calculated as shown below.
We are now required to install a separate panel for the single phase loads.
Ed
edavis2293
Member
- Location
- Houston, Texas
Re: red leg service
Ed MacLaren: Where in the NEC is the requirement for a separate panel if we have line-to-neutral loads. I have been looking for it.
Thanks
Ed MacLaren: Where in the NEC is the requirement for a separate panel if we have line-to-neutral loads. I have been looking for it.
Thanks
- Location
- Massachusetts
Re: red leg service
What would be the need for the rule, 110.4 already covers it.
I don't believe there is such a rule.
What would be the need for the rule, 110.4 already covers it.
- Location
- Illinois
- Occupation
- retired electrician
Re: red leg service
Ed,
The square root of three works because the tangent of 60 degrees is equal to the square root of 3. The tangent of an angle in a right triangle is equal to opposite/adjacnet.
tan60=x/120
tan60=square root of 3
(square root of 3)(120)= x
x=high leg voltage
Ed,
The square root of three works because the tangent of 60 degrees is equal to the square root of 3. The tangent of an angle in a right triangle is equal to opposite/adjacnet.
tan60=x/120
tan60=square root of 3
(square root of 3)(120)= x
x=high leg voltage
Ed MacLaren
Senior Member
Re: red leg service
Sorry, edavis2293, I should have been more specific. I was referring to one of our local requirements.
Ed
Sorry, edavis2293, I should have been more specific. I was referring to one of our local requirements.
Ed
- Location
- Massachusetts
Re: red leg service
Shouldn't a qualified person know how to feed a line to neutral load from a high leg panel?
Ed what do you think of this rule?
Shouldn't a qualified person know how to feed a line to neutral load from a high leg panel?
Ed MacLaren
Senior Member
Re: red leg service
But, we both know that there are unqualified people doing electrical work, right?
I remember an incident that happened to a couple of my co-workers. They were installing a three phase motor at a local dairy, and when connecting to the panel, they discovered that, although there was no three-pole spaces available, there were a number of single-pole spaces.
So, they moved some single pole breakers up into those empty spaces to make room for their new three-pole breaker.
You can guess the result.
Ed
Yes, I agree.
But, we both know that there are unqualified people doing electrical work, right?
I remember an incident that happened to a couple of my co-workers. They were installing a three phase motor at a local dairy, and when connecting to the panel, they discovered that, although there was no three-pole spaces available, there were a number of single-pole spaces.
So, they moved some single pole breakers up into those empty spaces to make room for their new three-pole breaker.
You can guess the result.
Ed
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: red leg service
Yes.
To my knowledge there is no three phase unit available that can be loaded more than 5% @ 120V. This is because of a single (common) core.
Most 240/120 high-leg systems are made up of two or three single phase units.
Yes.
To my knowledge there is no three phase unit available that can be loaded more than 5% @ 120V. This is because of a single (common) core.
Most 240/120 high-leg systems are made up of two or three single phase units.
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: red leg service
A closed delta can be 57% out of balance?
I'm not sure if I got this right.
Wouldn't that only apply to an open delta?
A closed delta can be 57% out of balance?
I'm not sure if I got this right.
- Location
- Illinois
- Occupation
- retired electrician
Re: red leg service
Wayne,
Jim is talking about a 3 phase transformer on a single core. You are are talking about a 3 phase bank made up of two or three single phase transformers.
Don
Wayne,
Jim is talking about a 3 phase transformer on a single core. You are are talking about a 3 phase bank made up of two or three single phase transformers.
Don
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: red leg service
Thank's Don I didn't think about it
I guess I still have much to learn
Thank's Don I didn't think about it
I guess I still have much to learn
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