|
1 members (Scott35),
180
guests, and
20
robots. |
Key:
Admin,
Global Mod,
Mod
|
|
|
Joined: Jul 2004
Posts: 9,931 Likes: 34
Member
|
They can size the 120/240 center tapped transformer to what your expected load is. Typically it is a 37 or 50 in the installations I see and they put in something smaller for the 3p loads. Where we got in trouble was some of the DP equipment had 3P line cords but contained a significant amount of single phase load. Tape controllers were the worst because the satellite drives could be plugged into any one of 8 receptacles in the controller. As long as you plugged them in in sequence or had a "full boat" they were fairly well balanced but if someone only had a couple drives and they weren't careful to balance them you could corrupt the red leg balance.
Greg Fretwell
|
|
|
|
Joined: Jan 2005
Posts: 354
OP
Member
|
I still want to avoid three phase power at home. So I guess the thing to do is make sure I don't build a mega mansion. OTOH, if I were that rich, I could afford to bring in 480/277 and waste power transforming it to whatever I wanted Actually, If I had that kind of money, I'd more likely be doing something off-grid, anyway.
|
|
|
|
Joined: Jul 2004
Posts: 9,931 Likes: 34
Member
|
That is why delta is the best choice. You can run your big loads 240/3p and your 120/240 panel stays the same.
Greg Fretwell
|
|
|
|
Joined: Jul 2001
Posts: 599
Member
|
That is why delta is the best choice. You can run your big loads 240/3p and your 120/240 panel stays the same. Be careful with your words, not all deltas are centered tapped. I was at a facility, in October, that had both a 240V delta grounded B-phase 3PH 3W and a 120/240 1Ph 3W services.
|
|
|
|
Joined: Jul 2004
Posts: 9,931 Likes: 34
Member
|
I assumed we were talking center tapped delta. There are also times I could make a case for corner delta. If your equipment is good for 208, then wye makes sense but you can have harmonic problems on the L/N loads. All of these have good points and bad points depending on your customer. That's why the PoCo still sells them all.
Greg Fretwell
|
|
|
|
Joined: Jul 2001
Posts: 599
Member
|
My understanding is that 240 delta with one side center tapped for 120/240 had a limitation that the single phase loads could be no more than 5% to 10% of the total transformer capacity. It's certainly not a choice for buildings that have all or nearly all single phase loads, but so much load that the PoCo puts them in the "must use 3 phase" category. The 5% loading restriction only exists on center-tapped delta transformers that share a common core. In recent years several manufacturers have starting building some center-tapped single phase units that do not have this 5% restriction. Transformer banks created by using multiple single phase units may be sized to handle any mix of 3-phase and 1-phase loads.
|
|
|
Posts: 8,443
Joined: July 2002
|
|
|
|
|