Which 3 phase Voltage to get?

If it's just a home shop do not get 440v. You're out of the realm of do-it-yourself electrical work and accidents involving 440 are *not* fun.

First of all, I'm no expert and I'll certainly defer to the pro electricians in the group.

That said, 440/480 is uniquely dangerous in it's ability to sustain a plasma fire without tripping upstream breakers. A screwdriver dropped onto busbars can evolve into something that will burn your arm off or worse.

I think the electrocution risk is substantially greater than 240V as well.

Part of the problem is that standards enforcement is primarily a local issue. I agree that stuff like using a clothes dryer ground lead to pull current for the motor or lamp is pretty much nonsense.

I wired my garage subpanel myself as well. When I call the city inspector to sign it off, he said "You must have done it yourself, it's too neat for an electrician.

If you are in USA or Canada wire 120/208 three phase. If you need 440 , 480.

277 , 575 , 347 ?600 use step transformers. All your lighting and most of your motors will work off of this system. Your utility company will have you install a seven jaw 3 1/2 element meter to measure your single phase and three phase loads. Try to keep away from demand metering, the penalties can really sour a fun day in the shop if your instantaneous demands are high and prolonged.Power factor is not something you want to have to monitor and correct. My two cents worth!

Pete

Brrrrrrrrr...no...440 is into the "fiery plasma ball exploding flaming bits of molten metal in a grenade like sphere of hell" sort of thing.

220 would be cool.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

I have three phase, and have had it as long as I've had a shop (since '67). First shop was an open delta system, which is fine for light duty----no large motors, say, under 7-1/2 hp.. I now have a 400 amp service, again, delta. I had the option of 480, but didn't want to deal with the higher voltage, even though one of my machines (a cylindrical universal grinder) requires 480 volts. I have a transformer for that one machine.

The one negative is that with a delta service, you have a wild leg (208 volts, the B phase) that can't be used for 120V service. That's no big deal, but it costs you one space out of three on your panel. You can use the space for 240 volts single phase, however, so something like a welder or water heater can occupy the otherwise unused space. If you select a delta service (240 volts), be sure to keep that in mind so you size your panel properly. The advantage of delta over wye (star) is the 240 volts instead of 208. Motors will run cooler--although you're not supposed to be sacrificing any power with the wye system. Dunno, I'm not an EE, nor an electrician. I do know that a close friend had problems with some CNC grinders when he moved to his new shop, equipped with 208 volts instead of

240.

Hope this helps more than it confuses.

Harold

My shop is wired 415V 3 phase. Did it all myself with an inspection by the electrical contractor before the sub board was 'hot'. Can't see it'll kill you any deader than lower voltages. I did it all to code because *I* was the one going to be using it.

Then again my single phase supply here in Aus is 240V, so I think our general wiring standards are waaay tighter than yours. When I lived in the USA a few years ago, at least, the general wiring standard, frankly, sucked.

Get the supply you think is going to be most useful for the size motors etc you're going to be running and do it to or above code requirements.

PDW

I'm going to agree with the folks recommending against the 480v. That's the evil power, everyone I've ever discussed it with agrees. Another angle is that you need top quality stuff for 480, you just don't want to use used wire and plugs on it, where with 240 you can use stuff that's less than absolutely perfect. A little carbon tracking in a plug, it'll arc with 480v where it just doesn't seem to with 240.

If you're willing to buy all new stuff, there's the natural gain of lower amperage draw with 480.. but it'll find any problems in your wiring, etc. far quicker than 240v. Motor insulation is no problem, the windings only see 240v either way, it's the plugs and wiring that's the issue.

John

Update:

Thanks for all the help so far. OK, the 440v is out. Any future 400+v requirements will be avoided or met with my own transformer and new top notch gear downstream.

Delta vs Wye?, 208 vs 240 ? It seems like there are some definite compromises there. In particular - whether or not you have 110v single and 240v single available, and whether you have three well balanced legs? (if I understand correctly).

Any other additions to the delta / wye 208 /240 debate would be greatly appreciated.

Thanks again for all the help. Jess

I suspect the 440 you're referring to is a different animal, then. Our

415 3 phase is pretty common, used a lot for domestic air conditioners and the like. Country places off 3 phase are the only sites I've ever come across with 480V and it's single phase, not 3.

Heh. That's exactly what the inspector said to me when he checked my last place. It doesn't take *that* much longer to do it neatly than sloppily.

PDW

Uh 220, and even 120 will do that as well. It's not the voltage. but the available current. jk

Not so at all

So can 25V if you work it right, but 440/480 is no worse that 240 for sustaining a phase to phase arc.

jk

I think the previous statement is likely correct. Given adequate current supply, voltage determines arcing ability. I don't know if 440 is the magic number, but certainly the higher the voltage, the more likely this ability becomes.

440 is worse for everything safety-wise. P=I^R=E^2/R, so the power capacity of higher voltage is quite significantly higher. But higher voltage also lowers power losses in wire, increasing motor efficiency. Which is why it's used in heavy duty applications. I've seen 208 in a shorted 3 ph plug sear the skin off a whole palm of a hand; imagine 440!

Proly 4x as great.

------------------ Mr. P.V.'d, formerly Droll Troll

Here's my opinion, for what it's worth, applied to a non-commercial shop in the U.S. The problem with 480V is not so much a safety issue (and the real danger is the available fault current more than the voltage) as one of economics. 480 volt wiring methods are the same as with lower voltages, but the power panels and breakers tend to be more costly and you'll need to provide for 120/240 single phase loads with a separate panel and transformer on a branch circuit. Unless you have several motors in the greater than 10 to 15 hp range rule 480V services out from the start.

120/208 wye service is not really appropriate for a shop either, this service is good for lighting but not so good for motor loads, save it for the next strip mall or office building you build. It's 208 because that's what your stuck with when you set out to get 120 volts phase to neutral in a wye connection.

For a hobby or small commercial shop go with a 240v center tapped delta service. You get 240 three phase and 240/120 single phase all out of one panel. Yes, you'll end up with a few unused slots in the panel due to the 'high leg', but who cares. If it's a mystery as to which phases supply which voltages to neutral don't even take the panel cover screws out and leave it to someone who knows, but it's really no big deal. The power company, at least around here, prefers this service as it generally has a lower installed cost, they can get by with just two transformers and wire it open delta. To you, the end user, it generally won't matter. You'll have extra work to due for single voltage 480V motors, but most machine tool motors are of the dual voltage variety anyway. I'm hard pressed for a valid reason to even consider another service for a small shop.

Regards Paul

My father was an electrician and I use to help him when I was a kid. At that time I thought 208 was the best because you could easily get 120 for lights and run real motors on three phase. Now I am not very fond of 208.

You should check your machines to see if the motors will actually run on 208. I suspect that many (or most) of than will not.

In my home shop I run all my 3 phase motors with VFDs. I hate 208 volt motors because they do not work well with a VFD and tend to over heat because they are getting 240V instead of 208V.

I have experimented with VFD parameters and managed to program a Teco drive to put out 208 instead of 240. My 1/2HP surface grinder works ok this way, but the 1HP motor on my rockwell lathe didn't like it much so I had to buy a new motor.

chuck

True..but how often have you seen 220 do that with a carbon track on a plug?

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

I have a 480 volt service to my shop and house. The main down side like mentioned above is the transformer to supply the lower voltage power. The problem with the transformer is it's cost of operation!! They suck lots of power just sitting there running! Having said that though, I would still run the same system for my shop if I was going to reinstall it today.

William...

I've given the idling transformer some thought, but I'm in the opposite position. I have only one machine that will run on 480 volts (can't be run lower), so my 3 phase delta 240 volt system is perfect for my application. The 480 volt transformer for the one machine will be kept turned off unless the machine is in service. That way I'm not heating the shop unnecessarily.

I avoided the lost spaces in my 3 phase panel by installing a single phase and a three phase panel. the shop is large, so it justified both panels. Only the 3 phase is on a demand meter, so I minimize my chances of paying high prices for power. On the other hand, I do have two power bills, but that was inevitable if I wanted three phase service. Policy at our Public Utility District is that 3 phase service is considered industrial------not residential-----so you have to have different metering. 3 phase is always on a demand meter here.

No way was I going to install a wye system.

Harold

The generally considered (such that there is one) "Magic number" is

100 V to sustain an arc in air.

400 some odd volts is in no way "uniquely dangerous". Yes it is more dangerous than 200 some odd, and less so than 600 some odd or 4160.

Only if you ASSUME that the available fault current is the same, which in general it is not.

That is based solely on arc currents, distance and exposure time, and the chances are better (if not good) that you have a current limiting device upstream at 440.

Probably and provably not. Far and away the greatest number of electrocutions occurs from 120 V circuits in the US. Yes the higher voltage can punch through the skin barrier easier, but far more people treat 120 in a very cavalier fashion. jk

Just as often as I have seen it happen on 480.

jk