Need help with how to circuit my panel schedule on a 120/240V, 3PH, 4W high leg

[Volt-Amps]

Hi,

I am designing power distribution for a restaurant. The incoming service is 120/240V, 3PH, 4W with high leg.
I was told I can not use phase B for 120V loads.

(1) What if some of my equipment is rated for 208V? Do I need a transformer for each load to boost voltage to 240V?
(2) how about 208V or 240V, single phase loads? Do I use A-B, B-C, C-A with no problem?
(3) How about 208V or 240V, 3 phase loads? Can I use A-B-C, B-C-A, C-A-B with no problem?
(4) Do I use only A or C when circuiting 120V loads?

I read some posts, but got a little complicated for me since I don't have much experience. At this point, I want to learn how to populate my panel schedule.

Can anyone help please?

 

[ron]

Wkkipedia has a good description
https://en.wikipedia.org/wiki/High-leg_delta

The 208V equipment needs to be able to handle 240V or you need a buck/boost transformer to drop the 240V to 208.

 

[Volt-Amps]

Need help with how to circuit my panel schedule on a 120/240V, 3PH, 4W high leg

Thanks Ron, any help on the other questions in the post? I feel this is a dumb question but I like to go by the saying "the only stupid question, is the one you don't ask".

 

[ActionDave]

Hi,

I am designing power distribution for a restaurant. The incoming service is 120/240V, 3PH, 4W with high leg.
I was told I can not use phase B for 120V loads.

(1) What if some of my equipment is rated for 208V? Do I need a transformer for each load to boost voltage to 240V?

Don't use the high leg for any line to neutral loads. There are reasons for it but no time to explain now.

(2) how about 208V or 240V, single phase loads? Do I use A-B, B-C, C-A with no problem?

For 240V loads yes. Not likely you will have any 208V loads. Most will be 240/208 or 240V

(3) How about 208V or 240V, 3 phase loads? Can I use A-B-C, B-C-A, C-A-B with no problem?

Yes

(4) Do I use only A or C when circuiting 120V loads?

A to neutral or C to neutral for 120V loads, A-C+ neutral for any 120/240V loads. It is common to set up a panel with all three phases for three phase loads and a sub panel fed from A-C for single phase loads, makes things easier and you don't end up with so many empty breaker spaces.

 

[chris kennedy]

May want to edit your last answer Dave.

 

[ActionDave]

May want to edit your last answer Dave.

Thank you. Got it.

Sunny and 34 degrees here today. How 'bout you

 

[Smart $]

... It is common to set up a panel with all three phases for three phase loads and a sub panel fed from A-C for single phase loads, makes things easier and you don't end up with so many empty breaker spaces.

When set up this way, you can put line-to-line (240V) loads in either panel... which aids in balancing the overall load.

All breakers connected to B-phase cannot be slash rated (i.e. 120/240). Must be straight 240V-rated breakers.

 

[Volt-Amps]

Thank you so much, you helped me a lot. Just to clarify:

I can setup a 3-phase panel for the 3 phase loads then maybe use the last 2 breakers to feed a 120/240, single phase panel to feed my 120V and 240V single phase loads, is this correct?
The breaker in the 3-phase panel that feeds the single phase sub panel should be C-A right? not A-B, not B-C.?

I always get confused with phase to ground and phase to neutral. When you have lighting loads, receptacle loads and other 120V loads, is that phase to ground or phase to neutral.

I know I suck, I need to learn more and I am working on it.

 

[GoldDigger]

Thank you so much, you helped me a lot. Just to clarify:

I can setup a 3-phase panel for the 3 phase loads then maybe use the last 2 breakers to feed a 120/240, single phase panel to feed my 120V and 240V single phase loads, is this correct?
The breaker in the 3-phase panel that feeds the single phase sub panel should be C-A right? not A-B, not B-C.?

I always get confused with phase to ground and phase to neutral. When you have lighting loads, receptacle loads and other 120V loads, is that phase to ground or phase to neutral.

I know I suck, I need to learn more and I am working on it.

You can measure voltages from hot to ground or from hot to neutral (if there is one). In general, and in all residential, there will be one grounded conductor and it will be the neutral if there is a neutral.
Since the neutral conductor is grounded (bonded to ground) the line-neutral voltage will be very close to the line-ground voltage.

But the grounding (EGC) conductor is never intended to carry normal operating current, so a load may be connected to the neutral but never directly to the ground (EGC).

In your sub panel there will be terminal bars, one for the neutrals and one for the EGCs. The feeder from main to sub will have separate neutral and EGC connections, although the EGC may be in the form of metallic raceway rather than (or in addition to) a dedicated wire.

 

[Volt-Amps]

Thank you for your help, I appreciate it.

 

[Barbqranch]

You can also use your 3 phase panel for any 240 V single phase loads. If you run them between either A-B or B-C, it will help to balance the load from your 120/240 V panel.

 

[GoldDigger]

You can also use your 3 phase panel for any 240 V single phase loads. If you run them between either A-B or B-C, it will help to balance the load from your 120/240 V panel.

But the three phase four wire 120/240 service might not be designed for a balanced load on the A-B and B-C windings, but rather be a high current A-C winding with center tap and one or two smaller windings to provide the B phase voltage for a relatively small amount of true three phase load.

 

[Smart $]

But the three phase four wire 120/240 service might not be designed for a balanced load on the A-B and B-C windings, but rather be a high current A-C winding with center tap and one or two smaller windings to provide the B phase voltage for a relatively small amount of true three phase load.

It's still considered balancing the load, just as equal amperes on each leg, because we are balancing the loads on each leg to system capacity .

 

[Fulthrotl]

Hi,
I am designing power distribution for a restaurant. The incoming service is 120/240V, 3PH, 4W with high leg.
I was told I can not use phase B for 120V loads.

(1) What if some of my equipment is rated for 208V? Do I need a transformer for each load to boost voltage to 240V?
(2) how about 208V or 240V, single phase loads? Do I use A-B, B-C, C-A with no problem?
(3) How about 208V or 240V, 3 phase loads? Can I use A-B-C, B-C-A, C-A-B with no problem?
(4) Do I use only A or C when circuiting 120V loads?

I read some posts, but got a little complicated for me since I don't have much experience. At this point, I want to learn how to populate my panel schedule.

Can anyone help please?

correct. b phase on a center tapped delta service measures 208 volts to ground. hence the term, "high leg"

1) your 208 stuff should run fine on 240. i've never had an issue with any equipment i've hooked up.
2) don't use C-A for 240 single phase loads. those are your 120 volt to ground phases. you need them elsewhere.
3) yes.
4) yes.

put in all your three phase loads first. all is well.
put in all your single phase 240 loads between a-b, and b-c. all is well.
put in all your single phase 120 volt loads on a and c. all is well.

have too many single phase loads? put in a single phase subpanel,
with the two pole breaker feeding it across a-c. all is well.

 

[chris kennedy]

Sunny and 34 degrees here today. How 'bout you

Mid 70's, rainy and windy last few days.
I see Denver got snow yesterday.

 

[kwired]

But the three phase four wire 120/240 service might not be designed for a balanced load on the A-B and B-C windings, but rather be a high current A-C winding with center tap and one or two smaller windings to provide the B phase voltage for a relatively small amount of true three phase load.

It's still considered balancing the load, just as equal amperes on each leg, because we are balancing the loads on each leg to system capacity .

One needs to consider the design of the source, if it is a two winding source there will be limitations. That is sort of POCO's problem, but the customer is still going to experience an outage when it does fail if you overload it/a portion of it.

 

[Volt-Amps]

correct. b phase on a center tapped delta service measures 208 volts to ground. hence the term, "high leg"

1) your 208 stuff should run fine on 240. i've never had an issue with any equipment i've hooked up.
2) don't use C-A for 240 single phase loads. those are your 120 volt to ground phases. you need them elsewhere.
3) yes.
4) yes.

put in all your three phase loads first. all is well.
put in all your single phase 240 loads between a-b, and b-c. all is well.
put in all your single phase 120 volt loads on a and c. all is well.

have too many single phase loads? put in a single phase subpanel,
with the two pole breaker feeding it across a-c. all is well.

Thank you all, thank you "Fulthrotl", this is exactly what I was looking for.