| | A "Delta breaker" is a breaker that was used to feed a single three phase | load on..."/>

NEC 408.36(E)

NEC 408.36(E): Delta Breakers. A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than
3-phase buses. Delta breakers shall not be installed in panelboards.
Are all 3-pole breakers interpreted as a 3-phase overcurrent device?
What is a "Delta breaker"? The code didn't define this.
Suppose you have one of those duplex receptacles that has a NEMA 6-15 on one half and a NEMA 5-15 on the other half. You need to supply dedicated loads, one 120 volt and the other 240 volt. Considering NEC 210.7(B) how would you wire this? It would seem to me that a 3-pole breaker would work to comply with NEC 210.7(B). But there's NEC 408.36(E) that seems to say no. Would 3 separate 1-pole breakers interconnected with a listed handle tie meet NEC 210.7(B) without violating NEC 408.36(E)?
http://phil.ipal.org/usenet/aee/2006-10-04/dual.html
NEC 210.7(B): Multiple Branch Circuits. Where two or more branch circuits supply devices on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point the branch circuits originate.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 4 Oct 2006 14:31:00 GMT, snipped-for-privacy@ipal.net wrote:

Not if they are connected to a single phase system.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Wed, 04 Oct 2006 13:09:04 -0400 snipped-for-privacy@aol.com wrote: | On 4 Oct 2006 14:31:00 GMT, snipped-for-privacy@ipal.net wrote: | |>Are all 3-pole breakers interpreted as a 3-phase overcurrent device? | | Not if they are connected to a single phase system.
So I can put a 3-pole breaker in a 2-bus (not counting the nuetral and ground bars) single phase panel, NOT call it a 3-phase breaker, and this will be OK? Sounds like a plan to me.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

I would think so. Up to the AHJ
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

This would usually come down to a listing/labelling issue. If the panel manufacturer says it is OK it is OK.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Why would you want to do that? You would be opening three single-phase circuits if one overloads.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
| |> So I can put a 3-pole breaker in a 2-bus (not counting the nuetral and |> ground bars) single phase panel, NOT call it a 3-phase breaker, and this |> will be OK? Sounds like a plan to me. | | Why would you want to do that? You would be opening three single-phase | circuits if one overloads.
Actually, I would be opening one 2-wire 120 volt circuit and one 2-wire 240 volt circuit, per NEC 210.7(B), on a device like the following:
http://phil.ipal.org/usenet/aee/2006-10-07/leviton-5031-w.png
http://phil.ipal.org/usenet/aee/2006-10-07/leviton-5844.png
Tell me how you would comply with 210.7(B) with this device split to support full loads up to 12 or 16 amps on both halves at the same time.
NEC 210.7(B):
Multiple Branch Circuits. Where two or more branch circuits supply devices on the same yoke, a means to simultaneously disconnect the ungrounded conductors supplying those devices shall be provided at the point the branch circuits originate.
The wiring might actually look like a 3-phase circuit. 14/4 or 12/4 would be wired to it, with white and black serving the 120 volt half, and red and blue serving the 240 volt half, and green/bare grounding the box and device. That it would be coming from a 3-pole breaker in the single phase panel could then also be confusing.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Technically, what you propose will work. However, you are stuffing a lot of wires into the box, especially if you daisy chain to other receptacles. SInce you will need an oversize box anyhow, why not use two individual devices (a 120 & a 240) in a larger box, then there is no requirement for simultaneous disconnect. This provides a higher reliability system since each circuit can be energized or deenergized independant of the other. You still would want ot deenergize both if you open the box, but at least if an overload occurs only one circuit goes out.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|> Actually, I would be opening one 2-wire 120 volt circuit and one 2-wire |> 240 volt circuit, per NEC 210.7(B), on a device like the following: |> |>
http://phil.ipal.org/usenet/aee/2006-10-07/leviton-5031-w.png
|>
http://phil.ipal.org/usenet/aee/2006-10-07/leviton-5844.png
|> |> Tell me how you would comply with 210.7(B) with this device split to |> support full loads up to 12 or 16 amps on both halves at the same time. | | Technically, what you propose will work. However, you are stuffing a lot of | wires into the box, especially if you daisy chain to other receptacles.
There won't be any daisy chaining.
| SInce you will need an oversize box anyhow, why not use two individual | devices (a 120 & a 240) in a larger box, then there is no requirement for | simultaneous disconnect. This provides a higher reliability system since | each circuit can be energized or deenergized independant of the other. You | still would want ot deenergize both if you open the box, but at least if an | overload occurs only one circuit goes out.
This is trying to squeeze in around other boxes. There's not enough room to go to a 2-gang. Doing this in a 1-gang on a duplex is really what I want to do. The only thing that was holding this back was what I thought to be a rule against a three phase breaker in a single phase panel. Then I would have had to decide which rule to break (though I probably would have gone with breaking the 3 phase breaker rule, had it applied).
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A "Delta breaker" is a breaker that was used to feed a single three phase load on a single phase panelboard. They were used on "Red Leg" Delta systems (center tapped delta). Often this was used to a power three phase air conditioner on residential or light commercial systems. The two legs with 120V to ground are connected to the top of the single phase panelboard. A delta breaker has a connection to the bussbars for two of the phases. The third line connection is a lug on the breaker body where the incoming feed for the high leg can land. It has three lugs for the three phase load connection. They were meant to be used in split bus panels where the delta breaker would be one of the main breakers.
It couldn't be used below a main becuase if the main was open and the delta breaker was closed, it would back feed the panel.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|
| |> NEC 408.36(E): | |> What is a "Delta breaker"? The code didn't define this. |> | | A "Delta breaker" is a breaker that was used to feed a single three phase | load on a single phase panelboard. They were used on "Red Leg" Delta | systems (center tapped delta). Often this was used to a power three phase | air conditioner on residential or light commercial systems. The two legs | with 120V to ground are connected to the top of the single phase panelboard. | A delta breaker has a connection to the bussbars for two of the phases. The | third line connection is a lug on the breaker body where the incoming feed | for the high leg | can land. It has three lugs for the three phase load connection. They were | meant to be used in split bus panels where the delta breaker would be one of | the main breakers. | | It couldn't be used below a main becuase if the main was open and the delta | breaker was closed, it would back feed the panel.
You could have used a 3 phase main, if it would fit (that appears to be the case on some panels, but probably not on other) with the wild leg not attached to a bus, but to a jumper going down to the breaker you just described.
There is a breaker type called SWN for switched neutral. It seems like one could make a 2-pole SWN into a 3-phase delta breaker by recoloring the white pigtail and connecting that to the wild leg source. But of course, this risks escaping steam from the AHJ.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

I guess what you could do is use a three phase breaker main breaker, grab the high leg like you discribe, and sub feed lugs to pick up the other two phases. Then feed all three to a breaker with line lugs in a adjactent box.
Normally high leg services would use a full three phase panel, and just not install breakers on the high leg except for three phase loads. Most utilities don't offer new service installations for center tapped delta so this would be only for replacements.

I don't think the SWN breakers sense current on the neutral. That would leave the high leg unprotected from ground faults.
BTW, the reason for eliminating the delta breaker is the elimination of split bus panels for light and appliance panelboards. Since the delta breaker was only used for mostly single phase loads with one three phase loads, they would be used in light and appliance panelboards, there was no longer a place to apply them.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|> You could have used a 3 phase main, if it would fit (that appears to be |> the case on some panels, but probably not on other) with the wild leg |> not attached to a bus, but to a jumper going down to the breaker you |> just described. | | I guess what you could do is use a three phase breaker main breaker, grab | the high leg like you discribe, and sub feed lugs to pick up the other two | phases. Then feed all three to a breaker with line lugs in a adjactent box.
That's viable too. Whether the code allows that is unclear, but it might be good enough to accomplish it. The wire going to the other box for at least the wild leg would have to be rated at the protection level of the main breaker.
| Normally high leg services would use a full three phase panel, and just not | install breakers on the high leg except for three phase loads. Most | utilities don't offer new service installations for center tapped delta so | this would be only for replacements.
However, back when they were installing a wild leg to support three phase air conditioners at homes, that was all the three phase needed, so it was seen as a waste to up the whole panel to three phase. And it was mostly fuses back in those days.
Having been in a situation where we had tens of thousands of dollars of damage and even more loss due to down time, all because of 240 volt motors being run at 208 volts, and burning up, I can definitely say there are some issues with the way they have done three phase. The different ratio between single phase and three phase sure throws a wrench into things. The center tapped delta was supposed to be a way to make that work. In more civilized countries, homes do regularly have three phase. But then, they also have more efficeint voltages, too.
|> There is a breaker type called SWN for switched neutral. It seems like |> one could make a 2-pole SWN into a 3-phase delta breaker by recoloring |> the white pigtail and connecting that to the wild leg source. But of |> course, this risks escaping steam from the AHJ. | | I don't think the SWN breakers sense current on the neutral. That would | leave the high leg unprotected from ground faults.
Ah, right.
| BTW, the reason for eliminating the delta breaker is the elimination of | split bus panels for light and appliance panelboards. Since the delta | breaker was only used for mostly single phase loads with one three phase | loads, they would be used in light and appliance panelboards, there was no | longer a place to apply them.
As long as they would allow a 3-pole breaker in a 2-bus single phase panel.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|> Having been in a situation where we had tens of thousands of dollars of |> damage and even more loss due to down time, all because of 240 volt motors |> being run at 208 volts, and burning up, I can definitely say there are |> some issues with the way they have done three phase. | | Motors rated at 208 (OK, namplated 200) are there for a reason. Draw much | power at all, and 480 becomes a option for motor loads.
The motor was in an air conditioner that was probably being overworked due to the added equipment. It was replaced per manufacturer spec, twice and still kept burning out. Finally someone had the idea to find a matching motor of another manufacture rated for 208, after he realized the motors that were being put in were for 240. That finally did the trick. But it was with 4 times total shutdown of equipment when the A/C was down, while they went up to the roof to repair it.
So basically, as I understand it, motors design for 240, especially if not well designed for heavy duty, will fail at 208 if worked hard enough. But with more 208 around these days, it would see that's what things should be designed directly for, instead of retrofitting.
|>The different ratio |> between single phase and three phase sure throws a wrench into things. |> The center tapped delta was supposed to be a way to make that work. In |> more civilized countries, homes do regularly have three phase. | | As far as I understand, only some of them do. I thought most of them had | 220/230/240 single phase.
At a given L-N voltage, you're going to get L-L at 2x with single phase and L-L at 1.732x for three phase. So single phase and three phase just do not mix well unless the common equipment connection method (be it L-N or L-L) is at a voltage that is fixed. And since L-L is favored for heavy duty stuff, and is effectively what three phase does, anyway (unless it needs the neutral for some reason like soft starting), that's where things need to be standardized at. As long as single phase is 120/240, then we need three phase to be 240 (240Y/139 would work) or we need a separate service or transformer to get that voltage ... as a standard way to hook things up (especially in the commercial office space environment). Perhaps the best is to always be sure to have 480Y/277 and put in three 120/240 single phase transformers. If things are big enough that single phase 240 is not enough then maybe they will have a 480 version. OTOH, I later found out, after all the air conditioner fiasco, that the voltage coming in to that building (which potentially we could have used directly, with a lot of cost to make use of it) and being transformed down to 208Y/120 was actually 600Y/346. So even if it had been an option to replace the whole A/C unit with higher voltage (might have involved replacing the whole unit), they likely would not have a 600 volt version at all.
If we could just standardize on 480Y/277 for everything three phase and do lower voltage only in single phase 120/240, and say bye-bye to 208, that would seem to make life easier. As long as the USA is a country where it is standard to supply single phase to homes (exceptions exist, but this is the standard), this is what I think the need is. While I do occaisionally see some heavier duty single phase appliances that are designed to work fine on 208 volts (like a stove with special elements), most only have 240 volt versions. And some that do have 208 specify a 60 amp circuit instead of a 50 amp circuit for 240.
|> But then, |> they also have more efficeint voltages, too. | | Their big loads are 240, our big loads are 240. How's that different? We | use the lower voltage for only a small fraction of our used power.
Their big loads are 400 volts. Three phase in Europe is 400Y/230 and it is more commonly available to homes in continental Europe.
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
|
| wrote: |> |> |> Having been in a situation where we had tens of thousands of dollars of |> |> damage and even more loss due to down time, all because of 240 volt |> motors |> |> being run at 208 volts, and burning up, I can definitely say there are |> |> some issues with the way they have done three phase. |> | |> | Motors rated at 208 (OK, namplated 200) are there for a reason. Draw |> much |> | power at all, and 480 becomes a option for motor loads. |> |> The motor was in an air conditioner that was probably being overworked due |> to the added equipment. It was replaced per manufacturer spec, twice and |> still kept burning out. Finally someone had the idea to find a matching |> motor of another manufacture rated for 208, after he realized the motors |> that were being put in were for 240. That finally did the trick. But it |> was with 4 times total shutdown of equipment when the A/C was down, while |> they went up to the roof to repair it. |> |> So basically, as I understand it, motors design for 240, especially if not |> well designed for heavy duty, will fail at 208 if worked hard enough. But |> with more 208 around these days, it would see that's what things should be |> designed directly for, instead of retrofitting. | | Many motors specify a service factor for 240V and no service factor for | 208V. Refrigeration systems are a common problem since the designer of the | system knows exactly what the load will be and they don't put a service | factor on their motor load. That's why AC's and fridge's are so dang | sensitive to low voltage. Because of this problem, 208V AC units are widely | available. If it was done 20 years ago I understand the mistake, but if it | was recent, the AC contractor was negligent.
The very same AC system worked for every other tenant in the building. Each tenant had the same system per unit (though a couple tenants used 2 systems because they rented 2 units together). The AC system was there before the owners rented the place, which was before I came to work there. It was failing at a point we had about 50 computers in one room. This had been an issue brought up with the landlord who didn't want anything added on by us. He said if the AC would not do the job then he'd upgrade the AC at no cost to us. They did have a rather substantial about of BTUs and rough calculations suggested they would work fine as there was plenty of capacity. I think the problem was that the voltage got changed after the AC was put in. Each unit has its own 208Y/120 transformer fed by 600 volts. And that was a change from something they had before that. But the tenant in the middle building (of 3) who had the whole building, needed 600 volts for some reason. So they changed things around to give them 600. So I suspect things were 240 prior to that, and the AC system had originally been selected for that. It all did have the look that the electrical had been majorly redone at one point. The mater bank was all new. The 600 volt main in each unit was new. The transformer was new. But the build was older as was the AC. So I suspect the power company foisted a change from 240 to 208 on the landlord as part of the agreement to get 600 volts in (unusual in the USA). Or it could have been the electrical contractor. But I do know as soon as they had a different model of motor (it was the blower motor) put in, the AC system worked and worked well (it definitely had the capacity but it would run constantly in the peak of Texas summer). The building looked to be 30 to 50 years old (all 3 of them).
| Was this in Canada? The standard industrial voltage is 600Y/346. That | votlage is also common in many mills since their EEs figured out that they | could get more power through the same breaker.
No. It was in Texas. I don't know what necessitated the 600 volts, but I know the tenant in the middle building had 800 amps of it going in, whereas the small tenants in the other 2 buildings had only 80 amps per unit based on the transformer's disconnect. I don't specifically recall the transformer rating, but thinking back on it I'd have to say it must have been 75 kVA. The padmount transformer that was feeding the 3 buildings looked like a well oversized unit, so I might guess it was 1500 to 2500 kVA.
|> If we could just standardize on 480Y/277 for everything three phase and do |> lower voltage only in single phase 120/240, and say bye-bye to 208, that |> would seem to make life easier. | | Somewhat. They would have to worry about phase ballance more. Plus they | can share a neutral with a three wire multi-wire branch circuit on 208Y/120 | instead of two wire ones with 120/240. Doing as you propose would eliminate | the problem with neutral current.
Or you could have 3 single phases, which would be a "6" phase if you put them all together. That would be my preference. Instead of a 150 kVA 208Y/120 you'd have 3 separate 50 kVAs for 120/240.
|> As long as the USA is a country where it |> is standard to supply single phase to homes (exceptions exist, but this is |> the standard), this is what I think the need is. While I do occaisionally |> see some heavier duty single phase appliances that are designed to work |> fine on 208 volts (like a stove with special elements), most only have |> 240 volt versions. And some that do have 208 specify a 60 amp circuit |> instead of a 50 amp circuit for 240. | | The place where I absolutly agree is with network service to homes & | apartments. That would just suck to have only 208 available as the higher | power level, other than the fact that with a transformer you could make the | third phase and have three phase to use in a shop.
Those situations tend to be big apartment buildings, so a shop is unlikely. But I do know how to wire up a transformer to re-derive the third phase from just the 2 provided.
What I would do if designing a big building intended for multi-residential is have a vertical stack of electrical closets and run 480Y/277 vertically. Then on each floor put in a single phase 480 -> 120/240 transformer. The phases would be diversified by floor. If it was larger than one transformer could handle, then maybe 2 or 3 per floor. But I would definitely want to provide genuine 120/240 for residential and even for office tenants. Then if there was any specific need for three phase somewhere (e.g. elevator in the commons, central A/C), run that from the 480. Exterior security lights could be run from 480 or 277.
|> Their big loads are 400 volts. Three phase in Europe is 400Y/230 and it |> is |> more commonly available to homes in continental Europe. | | In homes? Just how often are residential loads 400V? I don't see much | difference in saftey between 120V or 240V. But I see a big one with 400V. | 400V is cabable of systaining arcing faults.
Three phase to home is common in places like Germany. And you know they have 230 volts L-N. You can do the math.
BTW, I have been looking for some information on the physics of arcs and how and when arcs can or cannot be sustained. What little I have found suggests that what type of metal (e.g. copper, aluminum) is involved is part of the determination of what voltage would sustain an arc. That gives me the idea that it has a specific voltage drop at the arc interface and once exceeded by 2 times (once for each wire) the arc can sustain. Most of that is guessing, and I can't find much about it, otherwise. What I'd like to know is if what I've been guessing is true, and if so, what the particulars of different metals are with regard to sustaining an arc. That and how many amps would I need to sustain one.
I've seen where people can get a nice arc from a Tesla coil or a pole pig in reverse, but I'm sure that's way more voltage than they need just to sustain the arc.
| I could argue that their industrial systems are inefficient since theirs are | only 400V and ours are 480V.
They do have a next step up at 690Y/400. But either way it's 50 Hz.
I do find it interesting that the ratio between their voltage in the same class, and ours, is also the same as the ratio between their frequency and ours. A transformer could be designed for 400Y/230 50 Hz or 480Y/277 60 Hz and have the same saturation point. The same thing also exists between North American (120 60 Hz) and the eastern half of Japan (100 50 Hz).
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here. All logos and trade names are the property of their respective owners.