200A 120/208 3phase service feed from 120/240 Delta transformer

[GISdude]

Hi all,

I have a situation where an existing customer has an old 1-phase 120/240v panel that will be demo'd and they want to replace with a 120/208 3phase 400A panel. I'm trying to figure out how the existing branch circuits and loads would need to be wired. This is a restaurant that is expanding their floor/dining space and I'm trying to get a feel if the existing feed from the poco will work with the new main panel.

Thanks for any help,

 

[don_resqcapt19]

If the existing equipment is single phase, you only have two ungrounded conductors and a grounded conductor. A 208Y/120 system is a 3 phase system and requires 3 ungrounded conductors and a grounded conductor.

 

[LarryFine]

I'm trying to figure out how the existing branch circuits and loads would need to be wired.

1p 120v circuits will be fine, 2p MWBs will be fine for the L-N loads, but any 2p 120.240v or 240v L-L loads must be able to tolerate 208v.

I'm trying to get a feel if the existing feed from the poco will work with the new main panel.

No, because you will be lacking a third line conductor.

 

[hillbilly1]

1p 120v circuits will be fine, 2p MWBs will be fine for the L-N loads, but any 2p 120.240v or 240v L-L loads must be able to tolerate 208v.

No, because you will be lacking a third line conductor.

Exactly, years ago one of our salesmen sold that exact same job, and I had to make it work. Lots of 240 volt refrigeration. It was a high end beer and wine store. Lots of legwork to find all of the compressor ratings. Store was on the historic register just to give you an idea of how old it was! LOL!

 

[winnie]

Question: the title says 120/240 Delta but the first post says 120/240 single phase.

Is the existing system single or three phase? Does it have many 3 phase 240V motors?

-Jon

 

[GISdude]

Question: the title says 120/240 Delta but the first post says 120/240 single phase.

Is the existing system single or three phase? Does it have many 3 phase 240V motors?

-Jon

The feed is 3 phase from the POCO. The existing system is 1 phase. No motor loads. Lighting, refrigerator.

 

[winnie]

The feed is 3 phase from the POCO. The existing system is 1 phase. No motor loads. Lighting, refrigerator.

Refrigeration can be 3 phase, and can be line-line or line-neutral.

Lighting is often L-N but can be L-L

In the existing system is the 3rd phase simply 'capped off'?

If you have a single phase 120/240V panel, it is likely also rated for use at 'single phase' 120/208V, tapped off of a three phase 208/120V system.

If you only have L-N (120V) loads, then these will work just fine with either 120/240V or 120/208V brought to this panel.

If you have an L-L (240V) loads, these may work at 208V, but you would need to examine the individual loads.

Any multi-wire branch circuits will change their neutral loading, which may cause derating problems for any situation where multiple MWBCs are run in a single conduit.

So depending upon the exact panel rating and the loads connected, you _may_ be able to install the new 3 phase 120/208V service, then simply supply this panel from two of the legs, putting new loads on the new service.

-Jon

 

[petersonra]

If you have only single phase loads, or loads that can tolerate 208 V L-L rather than 240 V, there is no reason you would have to replace the panel at all. Just bring in 2 of the 3 phases to the old panel. Maybe add a 3 phase panel that the service comes into and feed two of the phases through to the old panel. That way you do not have to redo so much stuff.