120/240 volt 3 phase

[Greg1707]

I have drawings for a coffee shop. The electrical riser diagram shows 120/240 volt 3 phase. I have little experience with 3 phase but I am more familiar with 120/208. Any information would be helpful.

 

[Hv&Lv]

It’s either an open or closed 240 delta bank. Usually for a mixture of single phase 120/240 loads and three phase 240V loads.

Remember, in the breaker the high leg in the middle. On the meterbase the high leg on the right.
You screw up and put the high leg on the left or right of the breaker panel your lights and single phase stuff won’t last long.

 

[__dan]

120/240 V 3 phase is a red leg delta system. The 120 volt loads can only be served from one phase of the three phase primary., and if all the load was single phase you could not use more than x % of the tranny rated kVA.

For a coffee shop a red leg delta would be the wrong transformer. You would have to confirm, either the drawing is wrong and the system is 120/208 Y, will be Y. If they have or think they want a red leg delta for a coffee shop, their idea of what they want should change.

 

[Hv&Lv]

120/240 V 3 phase is a red leg delta system. The 120 volt loads can only be served from one phase of the three phase primary., and if all the load was single phase you could not use more than x % of the tranny rated kVA.

For a coffee shop a red leg delta would be the wrong transformer. You would have to confirm, either the drawing is wrong and the system is 120/208 Y, will be Y. If they have or think they want a red leg delta for a coffee shop, their idea of what they want should change.

Two legs for single phase applications. They are 180 out. The wild leg is for the three phase.
on a phasor the voltages look (0, 180, and either 90 or 270) depending on the phase of the wild leg.
currents on single phase also will line up 180 out.
With three phase the currents will shift to (0,120,240) depending on single phase loading.

 

[Strombea]

To simplify just simply use phase A and C for single phase. DO NOT use B leg as it is 208v to ground.try to put barista machine and other 2 pole breakers on phase B to even it out with the 120v loads. There has been a lot of discussion on here about the meter jaws and hooking up the high leg but now days the panel manufactures are pretty dang good at labeling the lugs

 

[__dan]

Many times it is a matter of guessing the right answer. It is easy to order the wrong transformer as 120/240 three phase is available but rare, as a reg leg delta. But the red leg delta only offers 120 V on one primary winding out of three so it is the wrong transformer choice if single phase 120 Volt loads predominate. If it was a machine shop with all motor loads, 120/240 delta could be good.

Knowing or guessing the right result is necessary. Knowing the 120/240 3 phase (delta) is wrong for the cofee shop when they may have intended 120/208 Y,.All the equipment coming in is 120/208 Y, I would guess it is either a misprint on the drawing and 120/208 Y is intended or present. If they intend to have a red leg delta for a cofree shop they have reached a defective conclusion and it is time to check their premises for defects.

 

[Hv&Lv]

Many times it is a matter of guessing the right answer. It is easy to order the wrong transformer as 120/240 three phase is available but rare, as a reg leg delta. But the red leg delta only offers 120 V on one primary winding out of three so it is the wrong transformer choice if single phase 120 Volt loads predominate. If it was a machine shop with all motor loads, 120/240 delta could be good.

Knowing or guessing the right result is necessary. Knowing the 120/240 3 phase (delta) is wrong for the cofee shop when they may have intended 120/208 Y,.All the equipment coming in is 120/208 Y, I would guess it is either a misprint on the drawing and 120/208 Y is intended or present. If they intend to have a red leg delta for a cofree shop they have reached a defective conclusion and it is time to check their premises for defects.

Maybe in missing something here...
Are you referring to a dry pack or a transformer bank built by the utility?

 

[Greg1707]

Many times it is a matter of guessing the right answer. It is easy to order the wrong transformer as 120/240 three phase is available but rare, as a reg leg delta. But the red leg delta only offers 120 V on one primary winding out of three so it is the wrong transformer choice if single phase 120 Volt loads predominate. If it was a machine shop with all motor loads, 120/240 delta could be good.

Knowing or guessing the right result is necessary. Knowing the 120/240 3 phase (delta) is wrong for the cofee shop when they may have intended 120/208 Y,.All the equipment coming in is 120/208 Y, I would guess it is either a misprint on the drawing and 120/208 Y is intended or present. If they intend to have a red leg delta for a cofree shop they have reached a defective conclusion and it is time to check their premises for defects.

I agree this is just a misprint on the drawings. I will check this out. This is an existing small commercial building that has been used for retail and food for many years.

 

[electrofelon]

Many times it is a matter of guessing the right answer. It is easy to order the wrong transformer as 120/240 three phase is available but rare, as a reg leg delta. But the red leg delta only offers 120 V on one primary winding out of three so it is the wrong transformer choice if single phase 120 Volt loads predominate. If it was a machine shop with all motor loads, 120/240 delta could be good.

Knowing or guessing the right result is necessary. Knowing the 120/240 3 phase (delta) is wrong for the cofee shop when they may have intended 120/208 Y,.All the equipment coming in is 120/208 Y, I would guess it is either a misprint on the drawing and 120/208 Y is intended or present. If they intend to have a red leg delta for a cofree shop they have reached a defective conclusion and it is time to check their premises for defects.

Sounds to me like the customer doesn't have to worry about a transformer - utility will take care of that.

I see what you are saying about getting 120 out of only "one winding" but that is an odd way to put it. 2 out of three ungrounded conductors can be used for 120v loads.

I don't see anything wrong with using 120/240 three phase for this application - very common around here. I actually prefer having the "full" 240 voltage. Only concern is during planning make sure you have enough breaker spaces for your 120 loads. No need to overthink this.

 

[__dan]

I see what you are saying about getting 120 out of only "one winding" but that is an odd way to put it. 2 out of three ungrounded conductors can be used for 120v loads.

Yes I did not know how much miscommunication there would be. I could have said 120 Volt is only available on 1/3 of the kVA rating, but that's only for standard single can units. The bank can be built heavier on one side but I do not see that around here. 240 V corner grounded delta I have seen more of for old machine and industrial shops. I rarely run into red leg delta except on stuff that is coming out. The point was to first deterime is the nominal system voltage is correct or not and what needs to be done to correct.

I have seen 120/240 red leg delta specc on the drawing and that's what they would have received. Caught that early because (I guessed) the office loads would be mostly 120.

 

[electrofelon]

Yes I did not know how much miscommunication there would be. I could have said 120 Volt is only available on 1/3 of the kVA rating, but that's only for standard single can units. The bank can be built heavier on one side.....

And all that is nothing the customer or electrician has to worry about for utility provided 120/240 three phase. Let the utility worry about their transformers. I do agree confirm Poco has been briefed and approves all this.

 

[kwired]

I agree this is just a misprint on the drawings. I will check this out. This is an existing small commercial building that has been used for retail and food for many years.

Chances are 120/240 delta is what has been supplying that building for years and the plan is to continue using it. If someone designed this they probably already figured out it has necessary capacity for the new use.

If this is in an old "downtown district" chances are several businesses in the immediate vicinity are all supplied from the same source and getting a different voltage system from POCO in this situation may not be so simple, unless you make room on your own property to place a padmount transformer, otherwise often there is limited space in alleys in such areas and only place to put transfomers is on poles and every pole is already full of equipment and they don't have room to add more transformers for a separate system.

If starting from scratch on an undeveloped lot or one that was totally demolished then start over most likely 208/120 wye would have been preferred system voltage.

 

[Greg1707]

This is a proposed cafe in a small 4 space commercial building There will be minimal load in other tenant spaces. .

We have existing:

400 amp 3 phase 120/240 Volt Delta Service.
200 amp 3 PHASE HVAC fused disconnect fed through trough
200 amp single phase MDP

The engineer has proposed replacing the MDP 200 amp single phase panel with a 400 AMP 3 PHASE MDP panel without changing the service.

The total load for this building is not an issue. Can a 200 amp HVAC and a 400 amp MDP be fed by only a 400 amp service?

 

[LarryFine]

The engineer has proposed replacing the MDP 200 amp single phase panel with a 400 AMP 3 PHASE MDP panel without changing the service.

The total load for this building is not an issue. Can a 200 amp HVAC and a 400 amp MDP be fed by only a 400 amp service?

Unless you absolutely need the capacity or circuit count, If the 200a 1ph panel is sufficient, I would try to keep what's there now.

Adding a 3ph panel to a 4-wire delta service is not as cost-effective as it is adding one to a wye service with 1ph loads.

The big question: excluding the HVAC, what are your 1ph and 3ph loads? What do your or the engineer's load calcs show?

 

[Greg1707]

Unless you absolutely need the capacity or circuit count, If the 200a 1ph panel is sufficient, I would try to keep what's there now.

Adding a 3ph panel to a 4-wire delta service is not as cost-effective as it is adding one to a wye service with 1ph loads.

The big question: excluding the HVAC, what are your 1ph and 3ph loads? What do your or the engineer's load calcs show?

Larry,
The total load for the proposed 400 amp 3 phase MDP panel would be: 180 amps. We will need 3 phase for water heater and convection oven.

 

[LarryFine]

Larry,
The total load for the proposed 400 amp 3 phase MDP panel would be: 180 amps. We will need 3 phase for water heater and convection oven.

Are they the onlyl load on that panel, or does the 180a include other loads, too? What is the total 1ph load and total 3ph load?

I'm asking about the entire load numbers, not just to the proposed panel swap.

I might add a small 3ph panel for just those loads. If you have a couple of 240v-only 1ph loads, they can be supplied here, too.

 

[Greg1707]

Here is the drawing.

 

[__dan]

He is marking the red leg as 1 pole 208. That would be a no no. It should say 'Do Not Use' for single phase line to neutral load. I believe the nominal voltage at that point, red leg to N, is like 183 V irrc.

I like Larry's idea of not taking any 120 Volt loads out the 400 A delta MDP. You can try to balance the loads by taking the lighting out at 240 V single phase with two pole breakers, but I do not see that on the drawing. The equipment schedule does not look like a lot. It looks like they don't make much more than coffee and toast.

One thing comes to mind. I seem to recall some weird piece of cafe equipment that had 208 V single phase with a neutral as the feed. H, H, N, 208 V. It might have been an ice cream maker with a separate countertop machine and a rooftop unit. I wired it and changed the breaker from 3 pole to 2 pole without any thought but the plumber was making jokes about seeing the last one go up in smoke.

If you get something like that it could be trouble if it takes a 2 pole breaker and a neutral. You would have to be sure the 2 pole breaker is not on the red leg if the load takes the neutral.

Anything with a drive in it would have to be checked also. The drive is usually specced for grounded Y, the drive front end is usually grounded Y. You would have to check with the drive manufacturer for their instructions about having a delta supply. It can be done but you have to be careful. Some of the loads may be expecting a Y source.

 

[electrofelon]

This is a proposed cafe in a small 4 space commercial building There will be minimal load in other tenant spaces. .

We have existing:

400 amp 3 phase 120/240 Volt Delta Service.
200 amp 3 PHASE HVAC fused disconnect fed through trough
200 amp single phase MDP

The engineer has proposed replacing the MDP 200 amp single phase panel with a 400 AMP 3 PHASE MDP panel without changing the service.

The total load for this building is not an issue. Can a 200 amp HVAC and a 400 amp MDP be fed by only a 400 amp service?

No problem with the sum of breakers or equipment ratings served by a service adding up to more than the service. Most times it works out that way.

 

[LarryFine]

I'm still recommending a 1ph 120/240v panel for all 120v and 120/240v loads, and a 3ph panel for the two 3ph loads and any 240v 1ph loads you have.

I did that years ago when I rewired an old restaurant with two new panels, using the existing 225a 1ph and 100a 3ph fused disconnects on the building.

I installed two 3p and three 2p breakers in the small 3ph panel, and everything else in the larger 1ph panel. Worked out perfectly and saved me money.