Convert 240 1 phase to 208 3 phase

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olc

Senior Member
We are converting a fairly small building from one phase to 208V three phase to accommodate an elevator. There are two existing single phase 120/240 panelboards.
Can we connect the panelboards to the three phases (say one to A-B and the other to B-C) and maybe shuffle some 1 pole circuit breakers to balance (move some breakers in both from B to A/C)?
Or should/must we replace the panelboards with 3 phase panelboards?
 
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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
olc said:
We are converting a fairly small building from one phase to 208V three phase to accommodate an elevator. There are two existing single phase 120/240 panelboards.
Can we connect the panelboards to the three phases (say one to A-B and the other to B-C) and maybe shuffle some 1 pole circuit breakers to balance (move some breakers in both from B to A/C)?
Or should/must we replace the panelboards with 3 phase panelboards?
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Since you are doing this just to accomodate one 3 phase load, have you considered just changing to a delta high leg service? In many cases the POCO will be happy as it is usually cheaper for them to do this than a full 208/120Y. Also, you could save a little by using a fusible switch as the service and just make the high leg big enough for the elevator.
 
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templdl

Senior Member
Location
Wisconsin
Getting 3ph from a 1ph source isn't going to happen by using a transformer. I static of rotory phase convertor must but used.
 
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olc

Senior Member
It will be a new service to the building.
240V 3 phase is an option (if the utility says it is an option).
 
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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
olc said:
It will be a new service to the building.
240V 3 phase is an option (if the utility says it is an option).
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I note you say this is a pretty small building. If you don't meet certain demand threshholds set by the POCO, I'd be very surprised if they would give you a 208/120Y service.
 
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olc

Senior Member
It's not that small.
Let's assume I can get 3 phase and I can't get a 1 phase elevator.
 
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hillbilly1

Senior Member
Location
North Georgia mountains
Occupation
Owner/electrical contractor
olc said:
It's not that small.
Let's assume I can get 3 phase and I can't get a 1 phase elevator.
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They do make single phase elevators, I wired a church were I put in three phase, but the church got a deal on a single phase elevator, so I had to upgrade my wire size. Turned out the elevator was three phase, but used a freq drive to convert it back to single phase :rant: but back to your situation, an open delta would be perfect for your application.
 
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templdl

Senior Member
Location
Wisconsin
texie said:
Huh? Who said anything about getting 3 phase from single phase?
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"We are converting a fairly small building from one phase to 208V three phase to accommodate an elevator."
Changing the service to 3ph because of a single elevator? Whatever floats your boat I guess.
You have to consider the options. One other guy's suggestion was a 1ph -3ph drive which is sort of like a static convertor.
 
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olc

Senior Member
I'll check out converters (never seen them).
No one has an opinion on the original question about the panelboards?
 
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templdl

Senior Member
Location
Wisconsin
olc said:
I'll check out converters (never seen them).
No one has an opinion on the original question about the panelboards?
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I appologize for not addressing that issue.
This is what I would consider:
I may be assuming that you have an existing 120/240v 1ph3w service and you are considering replacing it with a 208y/120 3ph4w service which of course would require a 208Y120 service entrance panel.
As such the existing 120/240 1ph3w panel would be rated for it because it could be feed with 2p breaker from the MDP for 120/208 1ph3w which would be OK should you only have 120v loads. If there were existing 240v L-L loads then there may definitely be an issue if the ended up being fed with 208v.
If you need 240v then a 208-120/240v 1ph3w transformer would have to be considered or a buck/boost transformer which would bump the 208v to 240v.
I may also suggest 240/120v 3ph/4w which would include a 240v delta with a 120/240v 1ph3w lighting tap but the lighting tap load would be limited if this were to be a single 3ph transformer. As such you have to use caution when using this configuration. But, if you had the POCO provide a 3 transformer bank service configured in a delta where one of the transformers is sized larger than the other two that had a 120v center tap to provide for the 120/240v 1ph3w loads. That yyou have the benefit of 240 3ph3w and 120/240v 1ph3w. Even though there will be 208v from the "wild leg" (the orange conductor) and the grounded center tap of the 120/240v it is not usable.
I don't believe that I overlooked anything but would welcome any ideas/comments from others.
 
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olc

Senior Member
Actually that brings up a good point.
The two existing panelboards each have a main circuit breaker which is a main service disconnect (currently).
I was going to make the elevator enclosed circuit breaker a third main disconnect. But then two of my 3 main disconnects would be 2 pole. Does this sound OK?
 
T

templdl

Senior Member
Location
Wisconsin
olc said:
Actually that brings up a good point.
The two existing panelboards each have a main circuit breaker which is a main service disconnect (currently).
I was going to make the elevator enclosed circuit breaker a third main disconnect. But then two of my 3 main disconnects would be 2 pole. Does this sound OK?
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Let's back the truck a second. Do you propose to have a 208Y/120 3ph4w or a 240/120 3ph4w service provided from the POCO? We should start there first. Then we can proceed with applying your 120/240v 1ph3w existing panels.
 
T

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
templdl said:
Let's back the truck a second. Do you propose to have a 208Y/120 3ph4w or a 240/120 3ph4w service provided from the POCO? We should start there first. Then we can proceed with applying your 120/240v 1ph3w existing panels.
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I agree. That's what I was getting at in my earlier post. The POCO holds the cards here. For example, one POCO I work with, the "standard" 3 phase service for small commercial customers is 4 wire delta. If you insist on 208Y/120, they require a minimum of 150 KW of demand (not calculated load) or you get your check book out. But it seems to me from the OP's description that a 4 wire delta might be the best choice here anyway.
 
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templdl

Senior Member
Location
Wisconsin
texie said:
I agree. That's what I was getting at in my earlier post. The POCO holds the cards here. For example, one POCO I work with, the "standard" 3 phase service for small commercial customers is 4 wire delta. If you insist on 208Y/120, they require a minimum of 150 KW of demand (not calculated load) or you get your check book out. But it seems to me from the OP's description that a 4 wire delta might be the best choice here anyway.
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I agree that a 240/120 3ph4w delta would be the least grief. The install a service entrance with his main disconnect there and feed his existing 1ph3w panels from that with a 3ph branch for the elevator. Then call it a day.
Otherwise this thing is getting way more complicated that it needs to be.
 
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