tomgilmartin
Member
- Location
- Vermont
Is there a case where NEC allows the neutral conductor in a 220V single phase service to be sized smaller than the phase conductors?
Reduced Neutral
- Thread starter tomgilmartin
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charlie
Senior Member
- Location
- Indianapolis
Re: Reduced Neutral
Sure, see section 220.22. Even 310.15(B)(6), the last sentence, states "The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met."
Sure, see section 220.22. Even 310.15(B)(6), the last sentence, states "The grounded conductor shall be permitted to be smaller than the ungrounded conductors, provided the requirements of 215.2, 220.22, and 230.42 are met."
bphgravity
Senior Member
- Location
- Florida
Re: Reduced Neutral
Reducing the neutral or grounded conductor is one of the worst things you can do to a service. With the increase of non-linear and harmonic loads, the neutral or grounded conductor is subject to high currents. For power quality and good workmanship, upsize the conductor if anything!
Reducing the neutral or grounded conductor is one of the worst things you can do to a service. With the increase of non-linear and harmonic loads, the neutral or grounded conductor is subject to high currents. For power quality and good workmanship, upsize the conductor if anything!
- Location
- Illinois
- Occupation
- retired electrician
Re: Reduced Neutral
Nonlinear loads do not cause problems in the grounded conductor of 120/240 volt single phase systems. These problems only exist in 3 phase 4 wire systems.
Don
Nonlinear loads do not cause problems in the grounded conductor of 120/240 volt single phase systems. These problems only exist in 3 phase 4 wire systems.
Don
lady sparks lover
Senior Member
Re: Reduced Neutral
That's true Don, but who uses 120/240 single phase for commerical buildings??
Also, if you do have 120V loads, wouldn't you stand the chance of running 120V loads on them like computers or lighting or something of that sort. Please explain.....
That's true Don, but who uses 120/240 single phase for commerical buildings??
Also, if you do have 120V loads, wouldn't you stand the chance of running 120V loads on them like computers or lighting or something of that sort. Please explain.....
- Location
- Illinois
- Occupation
- retired electrician
Re: Reduced Neutral
Patty,
First off, the original question asked about a reduced neutral in 220v single phase service.
Second, even with computers, HID lightning and other nonlinear loads, there is no problem with high neutral currents on 120/240 volt 3 wire single phase systems. That is a system that originates from a 120/240 volt single phase transformer. The harmonic currents do not add in the neutral on a single phase system like they do in 3 phase systems. If I was designing the electrical system for a facility where nonlinear loads were expected to be a major portion of the load, I would use 120/240 single phase for the panels that serve these types of loads. Of course, unless there are a number of 240 volt loads, the neutral serving a 120/240 volt single phase panel will have to be the same size as the hots, but there would be no reason to install an oversized neutral. Even if the service is 480/277 wye, you could use single phase 480 to 120/240 transformers to serve these loads. We don't hear much about using 120/240 single phase as a solution for the high neutral current problem. I wonder if that is because there is more profit in installing harmonic filters, harmonic blockers, K rated transformers and upsized neutrals.
Don
Patty,
First off, the original question asked about a reduced neutral in 220v single phase service.
Second, even with computers, HID lightning and other nonlinear loads, there is no problem with high neutral currents on 120/240 volt 3 wire single phase systems. That is a system that originates from a 120/240 volt single phase transformer. The harmonic currents do not add in the neutral on a single phase system like they do in 3 phase systems. If I was designing the electrical system for a facility where nonlinear loads were expected to be a major portion of the load, I would use 120/240 single phase for the panels that serve these types of loads. Of course, unless there are a number of 240 volt loads, the neutral serving a 120/240 volt single phase panel will have to be the same size as the hots, but there would be no reason to install an oversized neutral. Even if the service is 480/277 wye, you could use single phase 480 to 120/240 transformers to serve these loads. We don't hear much about using 120/240 single phase as a solution for the high neutral current problem. I wonder if that is because there is more profit in installing harmonic filters, harmonic blockers, K rated transformers and upsized neutrals.
Don
Re: Reduced Neutral
Patty, it is true there is no need for a full size neutral on a 240/120 system. For 3-phase it is really a design issue. If the system has significant non-linear loads then a full or oversize neutral is needed. On the other hand if all you have is lighting and a few non linear loads, probable not. That is why you get the big bucks to decide.
Patty, it is true there is no need for a full size neutral on a 240/120 system. For 3-phase it is really a design issue. If the system has significant non-linear loads then a full or oversize neutral is needed. On the other hand if all you have is lighting and a few non linear loads, probable not. That is why you get the big bucks to decide.
- Location
- Illinois
- Occupation
- retired electrician
Re: Reduced Neutral
gwz,
Look at 220.22. If there is any appreciable amount of 240 volt loads on the 120/240 volt panel the neutral can be reduced in size. If all of the loads are 120, then the neutral cannot be reduced. If there is an extremely large amount of 240 volt loads and only a small amount of 120 volt loads the service neutral will have to be sized based on 220.22 or 250.24(B)(1) which ever is larger.
Don
gwz,
Look at 220.22. If there is any appreciable amount of 240 volt loads on the 120/240 volt panel the neutral can be reduced in size. If all of the loads are 120, then the neutral cannot be reduced. If there is an extremely large amount of 240 volt loads and only a small amount of 120 volt loads the service neutral will have to be sized based on 220.22 or 250.24(B)(1) which ever is larger.
Don
Re: Reduced Neutral
The bottom line is, if we use all applicable code references, or connected load engineering, there is nothing wrong with reducing the neutral in any type system, and in reality more natural resource responsible.
To go one step further it is good design.
Before anyone throws the larger conductor is more cost effective in to play as fas as I^2 R loss, we would have to load any conductor continuously to a major percentage of it's ampacity to see any true savings.
Don, I have always liked your idea of serving all non linear loads with single phase SDS's. The problem I see is, the ballancing of the service, (we would need some good design) the space needed to place these transformers, (you and I know we are strapped for space in any building) and if the true cost of one K rated transformer and wiring outweighs three single phase transformer and wiring (for ballancing).
Roger
The bottom line is, if we use all applicable code references, or connected load engineering, there is nothing wrong with reducing the neutral in any type system, and in reality more natural resource responsible.
To go one step further it is good design.
Before anyone throws the larger conductor is more cost effective in to play as fas as I^2 R loss, we would have to load any conductor continuously to a major percentage of it's ampacity to see any true savings.
Don, I have always liked your idea of serving all non linear loads with single phase SDS's. The problem I see is, the ballancing of the service, (we would need some good design) the space needed to place these transformers, (you and I know we are strapped for space in any building) and if the true cost of one K rated transformer and wiring outweighs three single phase transformer and wiring (for ballancing).
Roger
Re: Reduced Neutral
Don I think your idea has merit, but as Roger points out balancing the the 3 phase system and the use of three transformers outways a single k-rated transformer. But I will explore the idea some more and run some cost analysys as I am always looking for better ideas in this area.
DC
Don I think your idea has merit, but as Roger points out balancing the the 3 phase system and the use of three transformers outways a single k-rated transformer. But I will explore the idea some more and run some cost analysys as I am always looking for better ideas in this area.
DC
- Location
- Illinois
- Occupation
- retired electrician
Re: Reduced Neutral
It probably isn't cost effective on smaller buildings, but where you are already installing a number of 3 phase transformers, you would be adding 1/3 more single phase over the planned number of 3 phase transformers, or you would be replacing the planned 3 phase transformers with larger single phase transformers. Of course, it works out best for load balancing if you install the single phase transformers in multiples of 3.
Don
[ February 28, 2003, 08:23 AM: Message edited by: don_resqcapt19 ]
It probably isn't cost effective on smaller buildings, but where you are already installing a number of 3 phase transformers, you would be adding 1/3 more single phase over the planned number of 3 phase transformers, or you would be replacing the planned 3 phase transformers with larger single phase transformers. Of course, it works out best for load balancing if you install the single phase transformers in multiples of 3.
Don
[ February 28, 2003, 08:23 AM: Message edited by: don_resqcapt19 ]
lady sparks lover
Senior Member
Re: Reduced Neutral
I agree, but my only problem with doing the single phase transformers is, then you have single phase loads on a 120/240V panel, and come unexperienced person will put a 240V load on them. It's ok, but I've seen it happen. I like to keep them separate. You could always just ad a note to the panel.
I use do apply K-4 rated transformers to the 120V computer loads, anyway. Computers are such delicate instruments that produce such unstable loads, I had a client that lost close to 100 each year, and the only way to combact that was to apply surge suppression, and IG grounds to his system in order to prevent damages, for example for a lightning strike.
Oh, this is to the person who gave me 5 stars..
[ February 28, 2003, 09:53 AM: Message edited by: lady sparks lover ]
I agree, but my only problem with doing the single phase transformers is, then you have single phase loads on a 120/240V panel, and come unexperienced person will put a 240V load on them. It's ok, but I've seen it happen. I like to keep them separate. You could always just ad a note to the panel.
I use do apply K-4 rated transformers to the 120V computer loads, anyway. Computers are such delicate instruments that produce such unstable loads, I had a client that lost close to 100 each year, and the only way to combact that was to apply surge suppression, and IG grounds to his system in order to prevent damages, for example for a lightning strike.
Oh, this is to the person who gave me 5 stars..
[ February 28, 2003, 09:53 AM: Message edited by: lady sparks lover ]
- Location
- Illinois
- Occupation
- retired electrician
Re: Reduced Neutral
Patty,
Why is it a problem to put 240 volt single phase loads on a 120/240 volt single phase panel? And how would this be different from putting single or 3 phase 208 volt loads on the 120/208 volt wye panel?
As far as the computers being a sensitive load, why should the electrical industry have to make changes to protect poorly designed electronic equipment? This is just passing the cost on to another party. If the electronic equipment was properly designed, these problems would not exist, but it is cheaper for the electronic industry to supply poorly designed equipment and have others pay for the modifications to the electrical design and installation so that their equipment will function properly.
Don
Patty,
Why is it a problem to put 240 volt single phase loads on a 120/240 volt single phase panel? And how would this be different from putting single or 3 phase 208 volt loads on the 120/208 volt wye panel?
As far as the computers being a sensitive load, why should the electrical industry have to make changes to protect poorly designed electronic equipment? This is just passing the cost on to another party. If the electronic equipment was properly designed, these problems would not exist, but it is cheaper for the electronic industry to supply poorly designed equipment and have others pay for the modifications to the electrical design and installation so that their equipment will function properly.
Don
lady sparks lover
Senior Member
Re: Reduced Neutral
Well, you wouldn't believe what some people will do!!! Really, you're right there is no problem.
Also, I do agree about the cost effectiveness, plus Roger and Rereck's points.
Yes, they do build poor equipment, but there's nothing you can do if you install receptacles and equipment before the they buy the computers. You can't tell them what computers to buy or anything like that. I found it to be a safety issue for the equipment. It does happen....
Well, you wouldn't believe what some people will do!!! Really, you're right there is no problem.
Also, I do agree about the cost effectiveness, plus Roger and Rereck's points.
Yes, they do build poor equipment, but there's nothing you can do if you install receptacles and equipment before the they buy the computers. You can't tell them what computers to buy or anything like that. I found it to be a safety issue for the equipment. It does happen....
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