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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, again
Randy wrote:
Hello, I have been running a small shop for several years and would now like to get my first CNC machine. To do this I will need to upgrade my phase convertor or get 3 phase from the power co. The power co has agreed to hook me to an exsisting 120/240 open delta supply ,there are two transfromers on the pole and the third leg is wild, not sure of the exact voltage. Will a CNC machine run off this? I know I have to make sure none of the controls are hooked to the wild leg, but other than that will it be OK? I'm looking at a Cincinnati Arrow 750. 17 HP spindle which is more than I need but the price and travels look good. However the 17 HP will exceed my current phase convertor, which is not CNC rated anyway. Randy Thank You, Randy Remove 333 from email address to reply. Hi Randy Your message deals with two separate issues sort of rolled into one. 'Open delta' is just a transformer connection scheme to deliver a 3 ph delta service with only two transformers. The 'wild leg' you refer to is the product of a center tapped delta service, which allows the more standard 120/240 V system to coexist with 240 3ph, all in the same service. Open delta can have stability problems compared to the same service done with three transformers. This could be an issue with CNC machines and their associated electronics. The wild leg will probably not be a consideration as most likely the machine you're looking at is 3ph and has no neutral connection back to the panel. Any low voltage control the machine requires is most likely done at the machine with control power transformers. It's my experience that machine connections tend to be 3ph or 1ph, not both. I'd be suspicious of a machine that required a 3ph connection and a separate 120 V 1ph connection. A work light on a mill might be an example, but certainly not the machine controls themselves. The only problem with center tapped delta services, other than using the wild leg with a neutral which is just carelessness, is the fact that if your service panel contains many 120v 1ph branch circuits you'll tend to have unused slots in the panel. Careful placement of 3 ph and 2 pole 1ph (anything with no neutral) branch circuits can minimize this trait. Regards Paul -- ----------------------------------------- It's a Linux world....well, it oughta be. ----------------------------------------- |
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three phase question, again
On Mon, 22 Sep 2003 14:04:48 GMT, someone who calls themselves Randy
wrote: Hello, I have been running a small shop for several years and would now like to get my first CNC machine. To do this I will need to upgrade my phase convertor or get 3 phase from the power co. Unless you want to go with a rotary converter, it's a lot easier in the long run to let the Power Company provide the 3-phase to you directly, and unless the other power users sharing that transformer with you are real power-pigs it's usually cleaner power. And it's consistent, there's no phase converter to break or wear out, and no need to play around with balancing capacitors or pony motors to get a rotary converter started. The only time I suggest using a phase converter is when the utility refuses to supply 3Ph (usually to a residence), a hobby shop where it is only going to be used very occasionally, or if the utility starts quoting 5-figure prices to extend the third leg line to your location... The power co has agreed to hook me to an exsisting 120/240 open delta supply ,there are two transfromers on the pole and the third leg is wild, not sure of the exact voltage. The wild leg is somewhere around 208V to ground. This is why it gets color-coded orange, and you have to be very careful to never connect any 120v breakers to that leg. And put BIG warning labels on the panel that it's a high-leg - I've seen 'handymen' accidentally plug the breaker for a string of condo-garage fluorescents onto the House Panel high-leg, and the results aren't pretty. ;-P I'm going to be extending an existing 240V open-Delta well service on Wednesday and Thursday to run a grape stemmer-crusher about 700' away, which is why we're running #4 CU power leg wires for a (for now) 7 amp 3Ph motor load. Voltage drop is a serious concern, and I want to have a big enough line there for when they need the next size larger crusher in a few years. They expect that with the heat in the Malibu hills they'll need to start picking & crushing grapes by Friday or Saturday. Nothing like leaving little things like the power line till the last minute... ;-) (The other choices were a 700' run to a 480V Delta service, or a 1,500' run to a 240V 1PH service and a converter, both not good. The ranch hands can break a phase converter too easily by plugging the crusher motor with it jammed, and barbecue themselves "extra-crispy" by messing around with a hot 480V line.) -- Bruce -- -- Bruce L. Bergman, POB 394, Woodland Hills CA 91365, USA Electrician, Westend Electric (#726700) Agoura, CA WARNING: UCE Spam E-mail is not welcome here. I report violators. SpamBlock In Use - Remove the "Python" with a "net" to E-Mail. |
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