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Old 01-31-2017, 12:29 PM   #1
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Default 4 wire delta & open delta

I'm trying to find some information on 4 wire delta and open delta systems. I fully understand how they work, but I don't think I've ever come across one. All of the 3 phase systems that I have worked on were 3 wire delta, and 3 or 4 wire wye. I am wondering what some examples are of where they would be used. If anyone is familiar with either of these systems I'd like to hear about it.
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Old 01-31-2017, 02:13 PM   #2
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Around here the PoCo uses them all the time. Two transformers, two phases and the secondary is three phase. They save having to run a three phase distribution line.
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Old 01-31-2017, 04:14 PM   #3
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In Alex VA, the 4-wire Delta was utilized in industrial areas you had 3-phase for motor loads and 120 vac for lighting and receptacles.


In LA I saw 4-wire Delta quite a bit, the areas were office BUT may have been industrial at some point.
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Old 01-31-2017, 04:32 PM   #4
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The 4-wire delta can also come in the open delta variety. An open delta uses one less transformer but still gives you three phase, but it can only deliver 57.7% of the power a full closed delta can.
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Old 01-31-2017, 07:49 PM   #5
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There are a couple of residential subdivisions around here from the 70s that have a 3 ∆ service. It's a 3 meter, a single phase panel and a ∆ breaker (usually a 30) for the A/C. Some of those 3 A/C units from the 70s are still in use.

A ∆ breaker looks like a normal 3 pole breaker except it has only 2 bus stabs and the 3rd pole has 2 lugs. One for the incoming high leg, the other for the load. Sort of a 2 pole with the 3rd pole added on.

In the older parts of town there are lots of 240∆ services, most are closed, some are open. A lot of the older buildings have a big single phase service (200 or 400 amp) and a smaller 3 one. Often the 3 part is just a fused disconnect and it usually feeds the boiler fan and feed pump.

Basically, every 120/240 3 4 wire ∆ service is nothing more than a single phase service with the high leg added in. Open or closed makes no difference.
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Old 01-31-2017, 09:06 PM   #6
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I see you're from Vancouver. Just about the only places you're going to see delta services around here are old industrial buildings. These buildings either had two services, a three phase delta for motors and a single phase for lights and receptacles; or they had a high leg delta (not very common in my observation); or even may have had a delta service, with a single phase transformer on the premises for their lights and receptacles. All of these arrangements are legacy now. BC Hydro no longer supports delta services, so facilities with them may continue operating, but if they renovate beyond a certain extent, or if they need to replace some major piece of the system, BC Hydro will force them to change to a wye service (either 208Y120 or 600Y347).
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Old 02-01-2017, 10:26 AM   #7
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Thanks guys!! That's just the type of real world information I was looking for. Text books are good at explaining it, but don't give much info on where you would actually see them.
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