LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

[ca_c10]

I am currently drawing plans for a 21 unit apartment complex for Senior's, and it will have a 120/240 Delta 3 phase service fed to the bldg. It will have a 20 HP, 3 PH. elevator and a 3 Phase 5 ton Gas Pack A/C unit. I am having serious Brain Fade trying to figure these load calcs. How do I show the VA's on the stinger leg? Do I assume the stinger leg will be 240 volts, 255, 270 etc. etc.? Anyone who has been through this and can help me would be greatly appreciated.

Thanks in advance.

Greg

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Greg, at the risk of being a bad guy, this is over your head if you are asking "how to" here.

How are you going to seal these documents with engineering from an electrical forum?


BTW, how far does a C-10 license go, are you allowed to act and design Multi-Dwelling buildings the same as a P.E.?

Roger

[ June 01, 2004, 08:11 PM: Message edited by: roger ]

 

[websparky]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

I wasn't aware that you can have 120V from a Delta?

 

[ca_c10]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Well, I guess this isn't the ask for help section. There are quite a few 120/240 Open Delta three phase services around here(Northern California). I guess it is kind of confusing because there are actually two transformers feeding one service. I have to assume that most electricians have seen this set up before. As far as what I was asking about the load calcs Roger, I guess I can just calc the elevator and A/C motors separately assuming 240 volts because as we all know that when voltage is checked across any of the two other legs with Stinger leg, the result is 240 volts, eh? Sorry if I confused anyone here. A C-10 can design any building up to 800 amps(3Phase) as long as you are the one doing the installation.

[ June 01, 2004, 08:54 PM: Message edited by: ca_c10 ]

 

[bphgravity]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

An open delta configuration provides the exact voltage and conductor orientation that a typical closed or three transformer bank delta setup would supply. The only difference is that the output is reduced to 57.7% (1.732/3).

Can't a center tapped delta configuration provide 120-volts? (3-phase, 120/240, 4-wire)

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Greg, the Delta is not a problem, (although the open with a lighter doesn't exist in my experience) the problem I have is when a person that has to ask "how to do this" on a forum is engineering a final product that will be housing people.

The bottom line is, the lighter / kicker (C winding) will have to be big enough to handle a service for 21 single phase 120/240v services and the delta configuration as a whole will have to carry what three phase loads are to serve the building.

Roger

 

[jim dungar]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

There really isn't anything special about designing a 124/240 3PH4W service. All of the special stuff involves the actual transformers, which is the utility's problem.

To design the service think of it as two individual services; one 240V 3PH3W and one 120/240 1PH 3W. In fact my preference is to always install the service in this way also, I find this reduces the problem of the "wild leg" being used. One 3 phase panel and a 2 pole breaker feeding a 1 phase panel (the 2 Pole can be fed from the three phase panel, or be seperately mounted or even be a main breaker in the single phase panel.

For calculating the conductor size just add the single phase amps to that of the common three phase conductors. For example, 20A three phase plus 40 amps single phase would give: 60A on phase A, 20A on phase B, 60A on phase C, and 40A on the "neutral". Again don't worry about the phase imbalance, that is the utility's problem (of course they will have the final say on your service sizing).

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Bryan, actually you can only have 120/240v three wire and 240v volt three wire serves (note I didn't say sevices) from a delta, there is no "4 wire" code compliant configuration from a delta.

Roger

[ June 01, 2004, 09:30 PM: Message edited by: roger ]

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

So Jim, you support anybody designing with out having the education? Please give more instruction to the novices, myself included.

Greg, there you have it from an engineer, send him your final figures and I'm sure he'll stamp them.


Roger

 

[don_resqcapt19]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Roger,

there is no "4 wire" code compliant configuration from a delta

See 250.20(B)(3). 120/240 3 phase 4 wire delta is a very common service for occupancies with a small 3 phase load and larger 120/240 volt single phase load. It is also common to have this as an open delta set up.
Don

 

[ca_c10]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Roger,

I can't relate to how things are done in N. Carolina, but with the rising costs out here in California, the "wave of the future" is having Electrical Contractors design and draw the electrical design for buildings, and then having an Engineer review them and then they are sent to plan check. Plans are seen by at least two Engineers before they hit the field. If there is a design problem/issue, it is rectified before installation. I can empathize with your concern over the design of buildings with residential occupancy, and trust me, if I felt I was swimming in uncharted water, I would turn this over to the proper people. BTW, I am no dummy, I have two Associated Degrees relating to the Electrical/Construction Field as well as full bore training in Auto Cad. I just asked for a little piece of advice but I guess I won't do that anymore-at least not here in this web site.

 

[bphgravity]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Originally posted by roger:
Bryan, actually you can only have 120/240v three wire and 240v volt three wire serves (note I didn't say sevices) from a delta, there is no "4 wire" code compliant configuration from a delta.

Roger

Huh?

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Don, please give me an example.

This is going back to some arguments of the past of where I consider this "center grounded conductor" a "neutral" and only referenced to one winding, yet the experts do not.

A wye can utilize a 4 wire multi-wire balance, a delta can not.(unless a true fluke)


Back to the original question, maybe I'm in a geographical area where I'm just used to the security of an engineer sealing designs.

Roger

[ June 01, 2004, 10:18 PM: Message edited by: roger ]

 

[explorer]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???



[ June 01, 2004, 11:54 PM: Message edited by: explorer ]

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Greg, I owe you and Jim an appology . I get stuck in the mind set that the way it's done here is the "Only Way" and that's not very productive.

Since this is the proceedure in Ca, I have no right to judge it wrong.

Good Luck with the project, and don't feel you can't ask questions here.

Roger

 

[bert47]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Here in my locality much of the initial design process centers around the anticipated "connected load" and the electric utility builds their service to serve the customer's system. Not the other way around. They may limit the options of delivery (delta vs. wye and primary voltage, etc)but will provide a service with adequate capacity to get it done. I would think that a 21 unit complex would be too much single phase load for a pole mounted "center tapped" open delta supply. (I'm assuming existing is currently pole mounted.)

 

[don_resqcapt19]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Roger,
It is called a 4 wire delta by both the code and most people in the trade. Nobody said that the 4 wire delta has the same voltage between each of the 3 hots and the grounded conductor.

Don

 

[roger]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Don, I never said there wasn't a "4 wire Delta" service, that was the reason I made it a point to say

(note I didn't say sevices)

I basically said (although not translated very well) there are no items served from a 4 wire delta branch cicuit and I can't think of a code compliant 4 wire delta branch circuit application.

After thinking about Bryans post, I know he wasn't talking about a branch circuit either.

Roger

 

[ca_c10]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Thanks for all the input. I never thought this post would get as much attention as it has. After looking back at all the replies, I guess my original question never really got completely answered. I was sent in right directions to look up calculations and such. I did get it figured out though. No sweat Roger, it's cool. I appreciate your apology, it shows your character-and I always tell the other trades, "Well, there really is no other trade. We are the most envied trade out there. We have all the "cool" tools, the best looking tool bags and bottom line: we just rock!" Thanks to all who helped me out on this post.

Greg

 

[don_resqcapt19]

Re: LOAD CALCULATIONS FOR 120/240, 3 PHASE DELTA SERVICE???

Roger,
Why can't we have some item that requires 3 phase power and 120 volt control circuit? Where would the code violation be? Not that I can remember something like this, I just don't see a code reason why you couldn't do it.
Don