I'm getting a workshop built, and can make a choice to have 3 phase
I'd like to buy some ex-factory machinery.
Q: Is it worth the expense? Or, with electronic solutions to running 3
ph. machines from single phase power, is it not worthwhile?
You definately want 3 phase. Probably 220v. I wouldn't go with the
440v even though a lot of industrial equipment uses this. 220 is fine
for most uses such as for welders and compressors. Plus you can run
seperate 120v off each leg and get a larger load off the main line.
220v welders provide a much longer duty cycle and you can get a bigger
air compressor also.
The cost will be more because of the extra wiring and use of bigger
wire but you will be glad as time goes by and you need more
outlets.....and you will.
480/277V service is great for really big shops, but is to be avoided if
you don't really have the need for it since the distribution panels and
switchgear are significantly more expensive than the 120/240V single
phase or 120/208V three phase versions.
Only if you get "Y" service which is 120/208V, not 220V. "Wild leg"
Delta service will give you 240V on your three phase and 120V from only
two of the three phase legs with the third leg being well above 120V
relative to the neutral.
Yes, but 220V is available from single phase service as well. Three
phase service will let you move up to the "next level" of welders and
compressors like 500A+ welders and 10 HP+ compressors.
Three phase installations will use *smaller* wire than the equivalent
single phase installation since a given load is distributed across 3 hot
leads vs. 2 hot leads. Total wire used is of course more due to that
That depends on what the utility offers, how big your shop is and
whether it's a business or personal shop. Three phase power will
generally put you on commercial peak metered rates vs. kWh based
residential rates. If your machines are all fairly small, there aren't
too many and you aren't on commercial rates anyway, using VFDs or a
rotary phase converter may be more cost effective. If you have anything
over about 3HP VFDs used as phase converters become less cost effective.
You basically have to make a spreadsheet listing everything you intent
to put in the shop and then work up the initial and operating costs for
the different options.
You don't give much detail about what you are doing. If for instance
this is to be a private workshop on a residential property, the
utility company may well be happy to provide a three phase (440???)
service, which gets you power at industrial rates, and you can run
your shop AND your house from it. You will have to buy a transformer
for it to get the 110/220 household requirement, but in so doing you
will then have a service suitable for all needs, eg single phase 110 &
220, and 3 phase 220 & 440. Good deal I think.
Ask to speak with a technical representative at your utility. They
can be very helpful.
The equipment is more expensive, but not solid gold expensive - 600V
Class gear (277Y/480V) is roughly double the same stuff for 300V
service. If you scrounge a little you can find it used, there are
brokers who resell used gear, and they might have a 200A 277Y/480V
service section for cheap because most of their sales would be of the
bigger 400A and 600A sections.
Do ask the power company about the rates you'll pay for your various
options, because they can have a profound effect on your decision that
lasts for years - you only pay once for the gear and the install.
Commercial power rates are normally higher than residential, and it
often has a "Time Of Use" factor - the KWH rate is cheap at night,
roughly the same as residential rates in the mornings and evenings,
but 10 AM or Noon to 5 PM "Peak Time" can be double or triple the
residential rates - and that'll kill you...
They're trying to get heavy industries to start work earlier and
shift their peak loads to the off-peak hours. Run the kiln and the
heat-treat oven overnight, do the welding and machining from 4 AM to
Noon. Leave the afternoon capacity available for air conditioners.
If you think you'll ever end up with any 480V equipment, get a
277V/480V Wye 4-wire system. You can easily run a transformer to drop
the 480V down to whatever you want, but boosting from 208V or 240V up
to 480V is a problem - you need double the amps and you run out of
240V panel feed real fast.
Having the neutral (4-wire Wye system) is important, because that
gives you both the 480V and 277V options, and a lot of industrial
high-bay lighting gear is 277V - one 20A circuit can light up a whole
lot of space for cheap.
(But you want the fixtures to have individual fuses in them so they
self-isolate, because with one lighting circuit having one bad ballast
trip the breaker knocks out all the lights.)
3 phase is a slam dunk. There might be a minimun monthly cost from the
power country but with your house and sho on 3 phase it will not
affect your bill.
Tuesday I am going to an auction where there will be lots of 3 phase
equipment that will go for 20? on the dollar.
If you need a 3 phase panels there are lots of them available on
For a home and/or home shop try to get 120/208 or 120/240 voltages.
The remark about meeting with the technical rep from the power company
is good. He can be valuable.