240/120V, 3PH, 4W Panel???

[anbm]

In one of site report, It indicates 240/120V, 3-Phase, 4 Wire panel.

I assume this is delta wiring system, Do they really make 240/120V, 3PH, 4W panel? How does neutral wire work? We can only share neutral between phase A and C and not phase B (high leg)? That means you can't feed any 120V load from phase B?


I thought they either make 240V, 3Phase, 3W or or 240/120V, 1Phase, 3W panels. Correct me if I am wrong. Thanks!

 

[augie47]

In one of site report, It indicates 240/120V, 3-Phase, 4 Wire panel.

I assume this is delta wiring system, Do they really make 240/120V, 3PH, 4W panel? !

Yes

How does neutral wire work? We can only share neutral between phase A and C and not phase B (high leg)? That means you can't feed any 120V load from phase B?

Correct

I thought they either make 240V, 3Phase, 3W or or 240/120V, 1Phase, 3W panels. Correct me if I am wrong. Thanks!

You are

 

[augie47]

from Square D catalog

View attachment 3775

 

[markdc26]

A three phase panel can be either delta or wye. It has a neutral bus and three hot busses. Voltage from the B phase to neutral will be about 208 which means that you can't use it for 120 volt loads. That is kind of a nuisance, because, typically, most of your breakers are for single phase loads and so nearly a third of your breaker spaces are not uasble. Another problem is the possibility that an electrician will not know about the high leg, or just not be paying attention and may connect a 120 volt load to that leg and damage the equipment.

 

[anbm]

Why did they use this kind of panel anyway?

 

[augie47]

The panel, of course, matches the service voltages. As to why the 240/120 3ph 4 wire systems exist, I believe they are in use due to it being an advantage to the power companies where there is limited 3 phase loads compared to the single phase loads such as small groceries/shops etc.
POCO can use a smaller transformer for the limited 3 phase load.
The system is not very common in this area any more.

 

[LarryFine]

Why did they use this kind of panel anyway?

The 240/120v 4-wire Delta started out as a 3-ph "upgrade" modification to existing 120/240v 1ph services. The designation is a service configuration, not a panel type, and is one type of service 3ph panels may be used on.

 

[Johnmcca]

POCO can do this with an open delta transformer set up, saving them a can, and still providing the 3 phase power. I'm not a fan of this set up, but I am a victim of it.

 

[Leestarkweather]

This service is the only 3-phase service you can get from Los Angeles DWP fed from a pole mounted transformer, maxes out at 800A. Any wye service (208Y/120V or 480Y/277V) of any size must be fed by a pad mount xfmr. or a station on customer property. Old 240V 3-phase 3-wire services (and some 480V 3-phase 3-wire) are still around, fed off of poles or from street vaults.

This is a very common service in industrial parks in the LA Area. Many small machine or woodworking shops have about 3KW in lighting/C.O. loads and 50-60HP in machine 3-phase loads. The POCO can install a large center-tapped xfmr. and only 1 additional xfmr. (Open Delta), then add the 3rd can later if the park fills up with heavy users.

Older installs had a single phase service for lights/CO and a 3-phase service for heavy machine loads---2 meters, 2 Mains, 2 risers, and less flexibility.

I have done retail stores where we change the delta to a wye with a floor or wall mounted xfmr (dry type) owned by the customer. We keep the A/C's (and elevator) on 240V Delta and put in small (75-150 KVA) transformers for the other loads--it balances out great, and is tens of thousands cheaper than a slab-box or pad. Also, many stores (older parts of town) are sidewalk to alley with no place for pads.

If any electrician sees a panel with about 1/3 of the spaces blank, and doesn't think "check for delta", then he should be installing sewer pipe instead. In fact, that goes for any electrician that doesn't check the buss to neutral voltage on any panel before adding new cb's.

 

[gravy]

This service is the only 3-phase service you can get from Los Angeles DWP fed from a pole mounted transformer, maxes out at 800A. Any wye service (208Y/120V or 480Y/277V) of any size must be fed by a pad mount xfmr. or a station on customer property. Old 240V 3-phase 3-wire services (and some 480V 3-phase 3-wire) are still around, fed off of poles or from street vaults.

This is a very common service in industrial parks in the LA Area. Many small machine or woodworking shops have about 3KW in lighting/C.O. loads and 50-60HP in machine 3-phase loads. The POCO can install a large center-tapped xfmr. and only 1 additional xfmr. (Open Delta), then add the 3rd can later if the park fills up with heavy users.

Older installs had a single phase service for lights/CO and a 3-phase service for heavy machine loads---2 meters, 2 Mains, 2 risers, and less flexibility.

I have done retail stores where we change the delta to a wye with a floor or wall mounted xfmr (dry type) owned by the customer. We keep the A/C's (and elevator) on 240V Delta and put in small (75-150 KVA) transformers for the other loads--it balances out great, and is tens of thousands cheaper than a slab-box or pad. Also, many stores (older parts of town) are sidewalk to alley with no place for pads.

If any electrician sees a panel with about 1/3 of the spaces blank, and doesn't think "check for delta", then he should be installing sewer pipe instead. In fact, that goes for any electrician that doesn't check the buss to neutral voltage on any panel before adding new cb's.

I was very interested in this post, and have been searching these threads for exactly this to help with a current design project for a retail store in PA. Site survey states "240V, 2-phase, 5-wire service". I was thrown by the 2-phase, as I've never experienced this. I suspect I am getting a red-leg delta (120/240V, 3-phase, 4-wire) and that the site surveyor got it wrong (I will check of course). My questions: Can a service be 2-phase and what is the 5th conductor for? Regardless, from this service it sounds like I can serve all three phase HVAC loads direct from the main panel....but I like the idea of providing a delta-wye transformer to serve lighting and receptacle branch panelboards. Any pitfalls here? Thanks in advance for any help!

 

[benaround]

gravy,

See 240.20 (B)(3) OCPD for 5wire-2phase systems.

 

[Volta]

I was very interested in this post, and have been searching these threads for exactly this to help with a current design project for a retail store in PA. Site survey states "240V, 2-phase, 5-wire service". I was thrown by the 2-phase, as I've never experienced this. I suspect I am getting a red-leg delta (120/240V, 3-phase, 4-wire) and that the site surveyor got it wrong (I will check of course). My questions: Can a service be 2-phase and what is the 5th conductor for? Regardless, from this service it sounds like I can serve all three phase HVAC loads direct from the main panel....but I like the idea of providing a delta-wye transformer to serve lighting and receptacle branch panelboards. Any pitfalls here? Thanks in advance for any help!

While it would be extremely rare, a true 2-phase system would have two phases 90-degrees apart. If the mid-points are tapped and grounded, that would be the connection for the fifth wire.

It would not be three-phase power. Not for three-phase loads.

I've personally never seen it. Someone should double check that one.

 

[infinity]

In one of site report, It indicates 240/120V, 3-Phase, 4 Wire panel.

This service is common around here too for small stores and machine shops. Just about any place that can have a larger three phase load presence and not that many 120 volt loads.