# 120/240 3 phase Delta Service



## RePhase277 (Feb 5, 2008)

Wow! A new 120/240 V delta? I figured most places were trying to phase those things out.

I think I would try to balance the loads as much as possible, and not neglect the B phase. If you have some single phase 240 V loads that could utilize the B phase, pull them from the 3-phase panel. Alot of the older delta systems I have seen were severely unbalanced because the installers or later electricians were avoiding the B phase, and heavily loading A and C with single phase 120 V loads.

I think you plan for splitting the two panels up is OK, just try to utilize A-B and B-C to keep everything balanced. And of course, LABEL THAT HIGH LEG!


----------



## abond82 (Feb 9, 2009)

Ya that is why I am not familiar with this system. We are adding a new builiding to a very old cabinet plant where they are moving existing equipment in so we basically had to go 120/240 3 phase. My only concern was going from AB / BC for my single phase loads, I guess this is fine? I just wasnt familiar with how this system works! The second panle was mainly for extra room for 120v circuits. Thanks for the info.


----------



## RePhase277 (Feb 5, 2008)

abond82 said:


> Ya that is why I am not familiar with this system. We are adding a new builiding to a very old cabinet plant where they are moving existing equipment in so we basically had to go 120/240 3 phase. My only concern was going from AB / BC for my single phase loads, I guess this is fine? I just wasnt familiar with how this system works! The second panle was mainly for extra room for 120v circuits. Thanks for the info.


Yeah, and A-B or B-C loads are fine as long as they are 240 V. Just don't use B-N for any 120 V stuff, because you will let the magic smoke out of the equipment, and once it is out you can't get it back in.


----------



## abond82 (Feb 9, 2009)

LOL ya i knew that. I was always under the impression that you should completely stay away from the B phase unless it was a three phase load. Guess I was misinformed. Thanks for your help


----------



## RePhase277 (Feb 5, 2008)

I was just thinking, are the 200 A panels going to have mains breakers in them? If not, then what size fuses do you plan on installing in the 400 A disco? I'm thinking that with 400 A fuses and 200 A mains in each panel, then an application of the taps rules (depending on the distance involved) would allow this. If these are MLO panels, then I think you might have a problem unless you fuse at 200 A.


----------



## abond82 (Feb 9, 2009)

they are both 200A MB load centers. Got ya covered.


----------



## 220/221 (Sep 25, 2007)

> For these loads should I take out of my single phase panel with the Aand C phase


To avoid confusion in the future, I would keep all single phase loads on the single phase panel or at least avoid the high leg.

There are still quite a few delta services in certain parts of town here and there are quite a few service people that have no clue about them. A water heater repair guy or HVAC guy might think something's wrong with the appliance circuit if he reads 200V to ground on one leg. It makes sense to me just to avoid the situation if possible..


----------



## Innovative (Jan 26, 2010)

InPhase277 said:


> Wow! A new 120/240 V delta? I figured most places were trying to phase those things out.
> 
> I think I would try to balance the loads as much as possible, and not neglect the B phase. If you have some single phase 240 V loads that could utilize the B phase, pull them from the 3-phase panel. Alot of the older delta systems I have seen were severely unbalanced because the installers or later electricians were avoiding the B phase, and heavily loading A and C with single phase 120 V loads.
> 
> I think you plan for splitting the two panels up is OK, just try to utilize A-B and B-C to keep everything balanced. And of course, LABEL THAT HIGH LEG!


Phasing out 120/240 delta?? not sure about that. We do tons of Delta services in new buildings. These are not old areas either, these are brand new commercial and industrial parks.


----------



## Jamuz (Aug 8, 2007)

Yup, that's all we use.:thumbup:


----------



## MDShunk (Jan 7, 2007)

The installation you propose is a fairly typical arrangement for a delta service. If you ever start running out of room in the single-phase panel, you can always start pulling some of your straight 240 loads out of the delta panel later. No biggie. Just mark the delta panel well. I've even taken a red sharpie and colored each high-leg bus finger in red to warn anyone in the future (maybe me!).


----------



## RePhase277 (Feb 5, 2008)

Innovative said:


> Phasing out 120/240 delta?? not sure about that. We do tons of Delta services in new buildings. These are not old areas either, these are brand new commercial and industrial parks.


In my time, I have never seen a new 120/240 V delta. I have worked on alot of them, but they were all quite old when I found them.


----------



## brian john (Mar 11, 2007)

InPhase277 said:


> In my time, I have never seen a new 120/240 V delta. I have worked on alot of them, but they were all quite old when I found them.


I have never seen a new Center tapped Delta in my area, but in LA I worked on a few.


----------



## sparky723 (Jul 22, 2008)

Just stumbled across this thread and it got me to thinking about a commercial panel I installed for a Chinese food restaurant awhile back. The poco brought in 3 phase with phases like this:
A=120
B=120
C=208
Never seen one like that, but I went ahead and wired panel the same way.
The guy building the restaurant is was wondering if he could put his 240v appliances on the a/c and b/c legs to get his required voltage.
This works, but why?
I don't have a lot of exp. with this type panel, but all seems to be going good. 
Just don't really understand how I got 248v when I hit the breaker. Seems as though it should be higher.
Can someone explain to me like I am a 3rd grader?
Feeling' dumb.


----------



## RePhase277 (Feb 5, 2008)

Any two phases will have 240 V between them. So 248 V isn't too bad. The 208 V to ground is due to the fact that you are measuring through a coil and a half. And due to magical three phase math, it comes out to 208 V.


----------



## Southeast Power (Jan 18, 2009)

InPhase277 said:


> Wow!
> 
> If you have some single phase 240 V loads that could utilize the B phase, pull them from the 3-phase panel. Alot of the older delta systems I have seen were severely unbalanced because the installers or later electricians were avoiding the B phase, and heavily loading A and C with single phase 120 V loads.
> 
> I think you plan for splitting the two panels up is OK, just try to utilize A-B and B-C to keep everything balanced. And of course, LABEL THAT HIGH LEG!


Not really good advice. 
I would not consider using the center tap from the single phase transformer all of the way to the end of the second transformer to get single phase ANYTHING.
You will have plenty of circuits to use for the three phase and single phase loads.
It is very good practice to keep the 3 phase seperate and have the single phase as a sub-panel.
Half of what we see here is open delta and I can count on one hand how many times I have seen the 199 volts to neutral hack. I can usually tell who did it because the handyman 76B type wire nuts are taped.


----------



## RePhase277 (Feb 5, 2008)

jrannis said:


> Not really good advice.
> I would not consider using the center tap from the single phase transformer all of the way to the end of the second transformer to get single phase ANYTHING.
> You will have plenty of circuits to use for the three phase and single phase loads.
> It is very good practice to keep the 3 phase seperate and have the single phase as a sub-panel.
> Half of what we see here is open delta and I can count on one hand how many times I have seen the 199 volts to neutral hack. I can usually tell who did it because the handyman 76B type wire nuts are taped.


I wasn't talking about single phase high leg/neutral loads, but single phase 240 V loads. Any DOUBLE POLE breaker placed on A-B or B-C will be 240 V.


----------



## sparky723 (Jul 22, 2008)

InPhase277 said:


> I wasn't talking about single phase high leg/neutral loads, but single phase 240 V loads. Any DOUBLE POLE breaker placed on A-B or B-C will be 240 V.


Right..I gotcha earlier


----------



## Southeast Power (Jan 18, 2009)

InPhase277 said:


> I wasn't talking about single phase high leg/neutral loads, but single phase 240 V loads. Any DOUBLE POLE breaker placed on A-B or B-C will be 240 V.


Sorry about that, I see what you mean. Good advice. The load will not know the difference.


----------



## sparky723 (Jul 22, 2008)

jrannis said:


> Not really good advice.
> I would not consider using the center tap from the single phase transformer all of the way to the end of the second transformer to get single phase ANYTHING.
> You will have plenty of circuits to use for the three phase and single phase loads.
> It is very good practice to keep the 3 phase seperate and have the single phase as a sub-panel.
> Half of what we see here is open delta and I can count on one hand how many times I have seen the 199 volts to neutral hack. I can usually tell who did it because the handyman 76B type wire nuts are taped.


Not a fan of taped wire nuts?
What about tape around a receptacle before putting in box?
I think they are both good cheap insurance, not a sub. for proper work..just an addition.


----------

