Getting 120v Single Phase from 3 Phase

Actually, in this instance, I paid for the transformers as a part of the cost of having the service installed. It had nothing to do with my decision to use a delta service, however.

Strangely, in Utah, my second service, which was three phase delta to our house, the power company started off playing hardball with me. They said the cost would be prohibitive, if they would supply it, but they wouldn't. Having already been through something similar with them once before, I very calmly explained to the clerk that if I didn't get satisfaction, my next stop would be the public services commission, where I'd file a complaint against the company. At that time (and perhaps still) they were a monopoly, and were bound to provide that which the customer needed. Interestingly, it suddenly went from "you can't have it, but it would be expensive if you could" to "no problem, and we can probably provide it free of charge, providing you sign a contract that guarantees a specific amount of use". It ended up costing us nothing to have it installed. It was also 3 phase delta, 240 volts. They had to install two poles, and, naturally, three transformers. It was not an open delta.

Harold

A pure delta service does not have a neutral at all. There is no 120v on it, only 240v phase to phase. The corner ground is strictly for safety purposes to limit the relative voltage from any phase to ground. This can make that phase look superficially like a neutral, but it is not.

How are you going to wire the mill? Separate conduit from each panel to separate boxes overhead and separate drops to the mill head and the light / power feed? Is the neutral present in your three phase panel so you can do a single feed from there? You can't or at least shouldn't (I'd have to look in the code book) combine circuits fed from separate breakers in separate panels in a single conduit run to the mill.

For the mill I would likely feed it strictly three phase and locally derive the 120v with a small transformer. Of course I got about a dozen

Pete C.

A pure delta service does not have a neutral at all. There is no 120v on it, only 240v phase to phase. The corner ground is strictly for safety purposes to limit the relative voltage from any phase to ground. This can make that phase look superficially like a neutral, but it is not.

How are you going to wire the mill? Separate conduit from each panel to separate boxes overhead and separate drops to the mill head and the light / power feed? Is the neutral present in your three phase panel so you can do a single feed from there? You can't or at least shouldn't (I'd have to look in the code book) combine circuits fed from separate breakers in separate panels in a single conduit run to the mill.

For the mill I would likely feed it strictly three phase and locally derive the 120v with a small transformer. Of course I got about a dozen

Pete C.

A pure delta service does not have a neutral at all. There is no 120v on it, only 240v phase to phase. The corner ground is strictly for safety purposes to limit the relative voltage from any phase to ground. This can make that phase look superficially like a neutral, but it is not.

How are you going to wire the mill? Separate conduit from each panel to separate boxes overhead and separate drops to the mill head and the light / power feed? Is the neutral present in your three phase panel so you can do a single feed from there? You can't or at least shouldn't (I'd have to look in the code book) combine circuits fed from separate breakers in separate panels in a single conduit run to the mill.

For the mill I would likely feed it strictly three phase and locally derive the 120v with a small transformer. Of course I got about a dozen

Pete C.

A pure delta service does not have a neutral at all. There is no 120v on it, only 240v phase to phase. The corner ground is strictly for safety purposes to limit the relative voltage from any phase to ground. This can make that phase look superficially like a neutral, but it is not.

How are you going to wire the mill? Separate conduit from each panel to separate boxes overhead and separate drops to the mill head and the light / power feed? Is the neutral present in your three phase panel so you can do a single feed from there? You can't or at least shouldn't (I'd have to look in the code book) combine circuits fed from separate breakers in separate panels in a single conduit run to the mill.

For the mill I would likely feed it strictly three phase and locally derive the 120v with a small transformer. Of course I got about a dozen

Pete C.

So you're telling me they don't have a "hog wagon" or two parked at the local utility yard, all ready to grab and go? Around here they have several of them available in each area yard for most KVA sizes and voltages.

(A trailer-mounted multi-tap transformer and a bunch of HV stranded motor-lead cable set up to come out of a hole on the top, or a big piece of liquidtight for armor to run into a pad-mount manhole. They just park it next to the dead transformer, set the taps to the supply and load voltages they need, run the cables down into the manhole or up to the top of the pole, and jumper around the dead transformer. Then you surround it with a jillion cones around the pole, or a portable fence to keep kiddies out of the manhole.)

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OK, that makes sense. From what you're saying, then, is that you don't object to delta so long as you don't derive any 120V from it aside from transforming. For all practical purposes, that's what I'm doing this time, using my delta service only for 3 phase, with all (except one place) of the 120V stuff coming from my single phase panel, which I would have done anyway, due to the demand meter. However, using the delta service for 120V is done routinely, as you likely know. The only real disadvantage I am aware of is the lost space in the panel---the B phase, the wild leg. Byond that, I don't see any issues. As far as I'm concerned, changing to

As I said, my 3 phase service is 5 wire, meaning it is capable of delivering

Chuckle! Put one of them in the mail to me and I'll wire it that way, so you won't worry about me and my safety! :-)

Harold

Sorry 'bout all the dupes, had a little news server issue.

Pete C.

Actually now that I think about it I believe they were marked at $10 and I got them for about $8 'cause I took the whole lot. I'm pretty sure the cost to ship one of those heavy little buggers across the country would far exceed what I paid for them although it would be much less than the $150 they seem to list for.

Pete C.

I've seen plenty of those trailer setups as well, some rather large and "polished" looking with cooling fans and everything.

The scariest temp setup I ever saw was in Philly. I'm walking down a nice tree lined street and see a few cones and a plywood box wall around a spot along side the sidewalk. Getting closer I see that there is a short run of the Yellow-jacket cable guard running between the plywood wall and the nearest tree. When I got up to it and looked over the 4' high plywood wall I saw a half excavated manhole with three HV "elbow" connectors feeding three HV lines that went through the Yellow-jacket and then exposed up the side of the tree. The lines continued along from tree to tree, perhaps 8' up, tied in place with pieces of yellow poly rope for what had to be at least 400' down the street before they crossed over the street and continued down and alley as far as I could see, tied off to fire escapes and whatever else was handy. I don't recall a single high voltage warning sign anywhere. I wish I had a camera with me.

Pete C.

Wrong. If it is a grounded (not grounding) circuit conductor, it IS a neutral, by definition. jk