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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Three phase question
I am building a new shop and have gotten the power company to commit
to bringing in three phase power(for no cost). They will be hanging three transformers(2 additional, but three new ones). What does this mean to me when I go about getting things wired up? Do I still have the infamous "wild" leg, or do I even care if I pull all of my single phase loads off the 2 other transformers? They will give me 400A three phase service if I want it. At first I said yes, but now am starting to wonder if it isn't massive overkill. I don't have anything now that requires a ton of power, other than the welder which at max current is 100A primary side. Opinions? Jeridiah |
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Three phase question
Jon Elson wrote in message ...
Peter H. wrote: They will be hanging three transformers (2 additional, but three new ones). Then, you'll have *true* three phase. What does this mean to me when I go about getting things wired up? Do I still have the infamous "wild" leg, or do I even care if I pull all of my single phase loads off the 2 other transformers? No "high leg" problem here. Do tell the utility if you want 120/240 volt Delta or 120/208 volt Wye, though. Wait a minute! If he has a 240 V Delta system, there will be NO 120 volt power available anywhere! There will be 3 wires, with 240 V between any combination of them. No neutral will be supplied on the delta system. The former is good for those cases where you have just lighting on 120 as only one of the three transformers can be used for 120/240 single-phase. Unless you have a lot of 240 V single phase loads, or motors that must have 240, and cannot be run on 208 V, you would do best, in most cases, with a 120/208 V Wye system. If the power company will only install 240 V delta power, you will then need a 240:120 V step-down transformer. (Since they are going to put in 3-phase FREE, you may do very well to get a used dry-type stepdown transformer to provide your 120 V supply for lighting, computers, hand tools, etc. Figure out your worst-case 120 V load, and size the transformer a little above that. If you can't find one big one, then get 2 or 3 smaller ones, and you can have several separate 120 V feeds. Smaller stepdown transformers in the 2-5 KVA range can often be had from scrapyards for the scrap metal value. Jon Perhaps I need to clarify.... They are putting in a 240V Delta xfrmr, with 2 piggy backed off from it to provide the single phase service. My understanding is this - all power will go through the 3 ph xfrmr. The single phase will be tapped off from the 2 piggy backed xfrmrs. Can't quite figure out why there are 2 "secondary" xfrmrs. Shouldn't it be a single 240 single phase and just center tap it to give me my 120 service? Or is it a balancing issue? As for the main panel... Talking to a electrical supplier, their recommendation for service cable for 400A was to use dual 3/0. Can I split this to 2 panels and be legal as far as code? Reason for doing this would be that I can get 200A 3 ph panels for free. Not sure about a 400A. I will have to check with my source on that. Thanks Jeridiah |
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Three phase question
Hi All: I have three phase open delta which consists of two transformers,
one of which is the normal single phast type 120/240 and one which is used for the third leg which is 208 ... This is a good one because you have 240 single phase where you need it instead of 208 and you also have three legs to power your three phase loads... Mike "Jeridiah" wrote in message m... I am building a new shop and have gotten the power company to commit to bringing in three phase power(for no cost). They will be hanging three transformers(2 additional, but three new ones). What does this mean to me when I go about getting things wired up? Do I still have the infamous "wild" leg, or do I even care if I pull all of my single phase loads off the 2 other transformers? They will give me 400A three phase service if I want it. At first I said yes, but now am starting to wonder if it isn't massive overkill. I don't have anything now that requires a ton of power, other than the welder which at max current is 100A primary side. Opinions? Jeridiah |
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Three phase question
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Three phase question
Perhaps I need to clarify.... They are putting in a 240V Delta xfrmr, with 2 piggy backed off from it to provide the single phase service. Jeridiah, I suspect what you will be getting is 3 single phase transformers wired into a 3-phase delta bank. All your single phase load will come off of one transformer and the other two will only be used for your 3-phase load. And you will have a high leg. Take a look at the transformer diagrams on my web page. If you scroll down the page the first one you come to is a 240V delta secondary like you will be getting. http://murrayranch.com/Electricity.htm An open delta bank like Mike says he has will have the same secondary voltages but an open delta is only good for 86.6% of the rating of the 2 units making up the 3-phase bank. They do make 3-phase transformers in both delta and wye secondaries with three and four bushing secondaries. If anyone would like to see wiring diagrams of them, I can post them on my web page. It doesn't make sense for a utility to hang a 3-phase transformer and 2 more to get single phase, kinda defeats the purpose of a 3-phase transformer; having it all in one can. Some questions you might want to ask the utility; what your rate structure will be, commercial or residential, is it going to be a demand meter, if you go 400A are you going to have to get a panel that will take current coils and a test block? Don |
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Three phase question
On Fri, 29 Aug 2003 05:55:17 GMT, Don Murray wrote:
It doesn't make sense for a utility to hang a 3-phase transformer and 2 more to get single phase, kinda defeats the purpose of a 3-phase transformer; having it all in one can. It makes sense if that's what they have lying in the yard at the time of the install. Utilities will often do odd things to use up what they have on hand rather than having to buy a transformer. Using two small 1 ph transformers to produce a derived neutral is one of those odd things. Gary |
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Three phase question
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Three phase question
The main disconnect must be external to the building, and plainly marked. As I said, it is so the fire department can make the building cold without waiting for the power company to show up and pull the pole fuses. Of course, and here in CA it is not uncommon to find six disconnects on the exterior of a multiple-use building, even though some of the units may not be "continuously occupied". We don't use pole fuses here, except on the line side of a large customer fed from the utility's subtransmisson system. |
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