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3 Phase Basics?

1K views 9 replies 7 participants last post by  Gummi Bear 
#1 ·
I bought an industrial building with 3 phase 480V (according to the previous owner). Most of my tools are convertible with different voltages ranging from 208 to 440 and are easy to change voltage.

My overhead hoist appears to be wired strictly for 240V three phase only.

What are my options to use this hoist beside selling it and buying another one? Do I need a step down transformer to run the 240 & 208 voltages or are there other options? If I do use a step down transformer would it be advisable to run it to a separate subpanel and make lower voltage available more readily?

I have an inverter (transofrmer?) that changes the 3 phase to single phase 220V that feeds a separate panel running the welders, air compresser, lights, AC, etc. Is it possible this unit could be used to convert three phase 480 to three phase 240?

Thanks is advance.
 
#2 · (Edited)
You can step-down 480 to 240. If I were going to do that, I think I'd step-down and put in a subpanel of 240 three-phase to run other stuff too, but if you're only stepping-down enough amperage capacity to run the hoist, the step-down transformers will be cheaper.

As an alternate, what about just buying a 480 three-phase motor for the hoist, rather than a whole 'nother hoist?

On the conversion thing that you've already got, it's probably stepping-down two of the three phases, and just not using the third, but I'm not entirely sure how those work, as I've not used one before. Theoretically, 1-1/2 of that box, would transform-down all three phases to 240 three-phase, and picking two of the three phases, would be 220 single-phase, but those are both somewhat risky assumptions depending on phase timing and a bunch of other stuff. It won't have enough stuff in it, to step-down all three phases as-is, and buying a proper transformer would be far preferable over trying to add onto it.
 
#3 ·
Second Scott's idea of buying a new motor for the hoist. Used 3-phase motors usually go pretty cheap because few can use them. Usually people are pulling them off of things to put a single phase motor in.
 
#4 ·
Thanks for the feedback.

The hoist is just one issue I guess. I'm sure there will be other machines I purchase that will be wired for 208/240 and adding the flexibility now may make more sense than converting other items in the future.

I know absolutely zip about step down transformers. What should I look for to ensure I get a good quality one with capacity enough to handle several 5 hp machines simultaneously of a subpanel? What controls the capacity of a step down transformer?
 
#5 ·
I'm over my head to explain the intricacies of transforming three-phase, so rather than posting something dangerous, I'll leave that one to somebody else.

What I do know for sure is, the more horsepower you want to have, the more amps you'll need to run it.
More amps through a transformer = bigger copper windings.
More copper = more money.
Overbuying (in this case) will hurt your wallet, but probably little else--but because of the cost of a big transformer, I would advise running as little as possible on transformed 240 three-phase, and as much as possible, directly on 480, in order to keep the transformer cost minimal.

Here's where I start to get dangerous:

Poking around a little tiny bit, a single phase 240x480 transformer (you'd need one per phase), rated at 5KVA, runs $350. Poking around a little tiny bit more, 5hp 480/3phase motors pull around 8-10 amps, which would be in the 3.8-4.8 KVA range for one 5hp device.

FWIW, our rotary tumbler motor can be wired for either 240 or 480; our CNC mill (a Bridgeport clone), also 240 or 480, and our rotary phase converter idler motor, 240 or 480. I think the only multiphase item that we've got that won't deal with 480 is the static phase converter that starts the rotary idler motor, but I know of no application where you can get 480 single-phase anyway. So everything here is 220/240 (they're sorta-interchangeable) and lower.
 
#9 ·
Joey D said:
Check voltage before doing anything. Most buildings with 480 will have a trans and 120/208v panel in there as well for recpts and lights. May not be big enough, amps, but check 1st.
I ran into an electrician at a social event last night and he said the same thing. Ran over to the building and sure enough the subpanel I thought was single phase has a "wild leg" of 208 three phase every third bar.

Scott, the subpanel has a 250 amp breaker and room for 6 more three phase breakers. I think I'm good to go. Thanks!


pmurf1 said:
Check the motor on your hoist too, it may be a dual voltage motor. A lot of industrial ones are, you just change taps to different letter/number combinations. It'll usually say on the box or motor tag somewhere if it is.
All the other three phase machines are multi-voltage but the hoist is wired specifically for 240. I already switched the lathe, mill and one air compressor over to 440 and got them running.

Thanks everyone. I'm a happy man.
 
#10 ·
With a 240/120V system, you're looking at a high leg system.

Phase arrangement when you are looking at the panel is A B C N

B phase will be 240V, A and C phase should be 120V. Use your tester, at one point (in certain municipalities), it was not unusual to arrange the high leg on the "C" phase.

It is common for machine shops to operate with a 240V high leg system, a lot of the machines come wired from the factory with this voltage configuration.

It was mentioned earlier that you may be able to re-tap your motor. Pull the plate on it (also called the peckerhead) inside you will find either pins or pigtails, but it will be an array of 9. Get an electrician to help you with this, if you don't tap the motor correctly, it's a gonner.

Keep all of your lighting at 277/480. A watt, is a watt, is a watt, is a watt, however, your circuit load will be decreased significantly. This means that you can put more fixtures on a circuit than you can with a lower voltage system. Your electric rate can vary, and with many utility providers, you can negotiate your rate to a certain extent (they have programs you can join to conserve energy and such for a better rate) There is also average billing, where they average your consumption for a given amount of time, and spread it out over the year.

Congratulations on your new shop!
 
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