240V Electric Service Type

[steve66]

I've got a 3 phase service, and on the utility pole there are only 2 transformers. So I was thinking it might be an open delta.

The customer verified that the service is indeed a 3 phase, 120/240V service.

However, one of the main panels is a 3 phase panel, and it has all single pole breakers in the 1st 20 slots.

It also has a few 2 pole and one 3 pole breakers toward the bottom in the same panel.

How can that be? I was thinking you can't have 120V to ground on all three phases unless it's a 208V service?

Or am I thinking about this completely wrong?

 

[kwired]

I've got a 3 phase service, and on the utility pole there are only 2 transformers. So I was thinking it might be an open delta.

The customer verified that the service is indeed a 3 phase, 120/240V service.

However, one of the main panels is a 3 phase panel, and it has all single pole breakers in the 1st 20 slots.

It also has a few 2 pole and one 3 pole breakers toward the bottom in the same panel.

How can that be? I was thinking you can't have 120V to ground on all three phases unless it's a 208V service?

Or am I thinking about this completely wrong?

Did you take a look at the bus behind the breakers?

Many older panels had bolt on "fingers" that the breakers plug onto attached to the main bus(es) that maybe someone reconfigured to omit the high leg in the upper portion of the panel?

 

[steve66]

Its a Square D QOC 40MG225 panel.

I can't find much on that part number doing a search, but it appears the main breaker is a 2 pole breaker, and therefore its a single phase panel.

Now that I think about it, its definitely a 40 space panel, and that also seems to also indicate a single phase panel.

However, it does have a 3 pole breaker installed in it, and its labeled "3 Phase Air Compressor". Go figure??

 

[steve66]

but there is another 30 space QO panel that has single pole breakers in every phase, and 2 more 3 pole breakers.

 

[MAC702]

Is it possible someone is using 3-pole breakers, but only using two of the poles to power single-phase equipment? I've seen that before.

how many wires are on those breakers?

Have you inspected those compressors?

 

[Jraef]

It's also possible that they are using that 3 pole breaker for 2 poles as stated, but they are then using a Phase Converter to run the 3 phase compressor, because they only had the single phase panel to feed it. Seems dumb if they have 3 phase available at the site, but sometimes people do with what they have; the alternative may have been to change out the entire panel to a 3 phase version and that was not going to be possible for some other reason that was important at the time.

But if you have a 2 pole main, you CANNOT be feeding all three phases even if you have 3 phase available at the site unless someone did some sort of major hack job, in which case you should fix it now.

 

[steve66]

Made a trip back to the site.

The panel is definitely a 40 space, 3 phase panel, fed with a 120/240V high leg delta.

But the branch breakers don't match the standard panel phasing. The 1st 10 breakers on the left side are all on the same phase. And the 1st 10 on the right are on the second phase.

Toward the bottom of the panel, where the 2 and 3 pole breakers are, the phasing seems to be standard.

I guess its possible this is some type of special panel. More likely, an electrician did some re-arranging and replacement of the fingers that the branch breakers mount to.

 

[Jraef]

If I'm not mistaken, some mfrs, Sq. D included, used to make special panels for High Leg systems that didn't allow you to plug into the B phase with single pole breakers, and the top part of the panel buses were configured to allow side-x-side deployment of 1 pole breakers on A and C phases so as to not "waste" pole spaces.

 

[jim dungar]

Made a trip back to the site.

The panel is definitely a 40 space, 3 phase panel, fed with a 120/240V high leg delta.

But the branch breakers don't match the standard panel phasing. The 1st 10 breakers on the left side are all on the same phase. And the 1st 10 on the right are on the second phase.

Toward the bottom of the panel, where the 2 and 3 pole breakers are, the phasing seems to be standard.

I guess its possible this is some type of special panel. More likely, an electrician did some re-arranging and replacement of the fingers that the branch breakers mount to.


View attachment 18746

The part number, in the OP, is for the loadcenter cover.

Back in the old days, the panel bussing employed connector fingers which allowed for some pretty strange breaker connections when it came to 240/120V 3ph 4wire systems. The main bus bars were flat across the back and there was one type of bus extension for breakers to plug on and a different one for bolt-on breakers. The normal bus extension would have been with the phasing across the panel rather than on one side only.

 

[kwired]

Made a trip back to the site.

The panel is definitely a 40 space, 3 phase panel, fed with a 120/240V high leg delta.

But the branch breakers don't match the standard panel phasing. The 1st 10 breakers on the left side are all on the same phase. And the 1st 10 on the right are on the second phase.

Toward the bottom of the panel, where the 2 and 3 pole breakers are, the phasing seems to be standard.

I guess its possible this is some type of special panel. More likely, an electrician did some re-arranging and replacement of the fingers that the branch breakers mount to.


View attachment 18746

That panel is old enough the bus design is like I tried to mention earlier and the fingers that the breakers plug onto are easily moved - may not have been intended to do that but is easy to do. I think some Cutler Hammer panels from about the same time were similar. GE, Siemens, and others of that style I don't think you could do that kind of thing with though.

 

[meternerd]

You're right...you can't get 120 on all three phases to neutral unless it's 208/120. Open delta is sometimes used when a three phase load is small and not worth a third transformer. Total bank KVA rating is, of course, less than a three transformer bank, but it's cheaper. Since the main is three wire, it must be a custom bussed panel. I don't remember ever seeing anything like that, though. Kinda weird. You should still have a 208 L-N high leg and 240 L-L.

 

[kwired]

here is a picture I found that shows bus that is likely similar design to what OP has. It is really easy to reconfigure the phase arrangement and omit the high leg in any portion of the panel -you may have needed to purchase extra panels for spare parts to get what you wanted, unless they happened to sell those parts separately at the time that style was in production. All you do is take the bolt out that holds the "fingers" in place and arrange them in any order you want to. They came from the factory configured in the conventional way we are used to seeing.



(click on image to see larger)

No critiquing that install - it is not mine it is just something I found with a google search, looking for one with that particular bus style.

 

[steve66]

That panel is old enough the bus design is like I tried to mention earlier and the fingers that the breakers plug onto are easily moved - may not have been intended to do that but is easy to do. I think some Cutler Hammer panels from about the same time were similar. GE, Siemens, and others of that style I don't think you could do that kind of thing with though.

Looking back, that's exactly what you mentioned. Your nailed it.

The part number, in the OP, is for the loadcenter cover.

Back in the old days, the panel bussing employed connector fingers which allowed for some pretty strange breaker connections when it came to 240/120V 3ph 4wire systems. The main bus bars were flat across the back and there was one type of bus extension for breakers to plug on and a different one for bolt-on breakers. The normal bus extension would have been with the phasing across the panel rather than on one side only.

I always seem to get the wrong part number off SQ D loadcenters. I either get the box number, or the cover number, or the some other strange part number, but I never seem to find the actual loadcenter part number. I'm pretty sure those are classified top secret, or maybe there is a code requirement that requires to load schedule to be pasted over the part number with super glue.

 

[kwired]

Looking back, that's exactly what you mentioned. Your nailed it.



I always seem to get the wrong part number off SQ D loadcenters. I either get the box number, or the cover number, or the some other strange part number, but I never seem to find the actual loadcenter part number. I'm pretty sure those are classified top secret, or maybe there is a code requirement that requires to load schedule to be pasted over the part number with super glue.

Your load center in this case is old enough the label likely peeled off and is gone. Cover labels from that series seemed to last longer for some reason.

 

[steve66]

So does anyone see any code issues with the non-standard breaker phasing?

 

[kwired]

So does anyone see any code issues with the non-standard breaker phasing?

Maybe, maybe not.

If it were a single phase panel it would go ABABAB. I sort of see no reason why you can't have a single phase section to the panel and a three phase section elsewhere.

Take an I line panel - you have all three buses in every possible breaker position, you select which bus to connect to by the breaker you chose to install there. If you wanted to fill an I line with single pole breakers that all connected to phase A you certainly could do so. If you are using an I line panel for single phase three wire (like 120/240) you simply don't use one of the buses and only select breakers that attach to the other two buses. They don't make a single phase I line panel.

 

[jim dungar]

I always seem to get the wrong part number off SQ D loadcenters. I either get the box number, or the cover number, or the some other strange part number, but I never seem to find the actual loadcenter part number. I'm pretty sure those are classified top secret, or maybe there is a code requirement that requires to load schedule to be pasted over the part number with super glue.

The panel cabinet has a part number for its cover. The numbers begin with QOC typically followed by the number of 1 pole spaces. The cover is usually the easiest part number to find, but it is often not enough as it quite often can be used with several different loadcenters. The cabinet, or enclosure, part number is usually similar to its matching cover. The numbers begin with QOB. I think these can be found near the UL Listing label.

The interior of the panel has its own part number. This is the number you would like to see, but it is usually not visible when it is installed. The numbers begin with QON. Interiors are usually mounted in the loadcenter enclosure at the factory, so you almost never its number.