Motors and starters are one of my weak areas, so please forgive the basic nature of these questions.

My dad has just purchased a new metal lathe for his home workshop. Since it has a 208 volt 3-phase motor and starter, it is not very useful right now.

Anyway, we have decided to change the motor to 1 HP, 230 volt, single phase. I looked into a phase converter and buck boost transformers but changing the motor seems like the more practical way to go.

I checked the NEMA chart and it looks like I need a 00 starter (reversing, by the way.)
How do I size the heaters?

What code article should I consult to size the circuit for the lathe?

Does a twist-lock cord and plug connection serve as an adequate disconnect? I don't intend to hard wire the lathe.


Peter

Dare I say it, you may want to re-thing the phase convertor. If you have a shop with a lathe, whats to say the next time you go out tool shopping you don't come home with another 3-phase item. For the cost of a decent size rotory convertor will negate the cost of trying to re-work this machine, and the next one. And use the convertor for both, not at the same time of course. But you may find that rebirthing this machine as single phase may not be all its cracked up to be mechanically. The relays in the unit now may work, just find the manufatures chart for the voltage and horse power, and get the new heaters for it, you might not have to change them at all. The reversing of a single phase motor may be a little tricky. Still a convertor around the shop is a good thing......


http://www.phaseconverter.com/


http://www.americanrotary.com/html/rotary_converters.html

[This message has been edited by e57 (edited 10-06-2004).]

Hey CT,
Are you close to wisconsin? I have a rotary converter that will be available if my customer decides he doesn't want it. It's rated 11/2 hp max and 5 total. Retail is $650.00. I'm would like to get $200.00. May be listing on ebay soon. It is used.
ron

Circuit sizing, etc., are covered in the "motors" section of the NEC (430). Heaters are sized based upon the motor nameplate (as are fuses), but the NEC tables are used for conductor sizing. Motor and fuse sizes are later adjusted for the application; typically, the fuse is increased (nuisanse tripping) while the heaters are down-sized (more precise protection).

A cord & plug are typically not listed for disconnection under load. You will need a disconnect on the wall; there are disconnects with receptacles built in, so connection by plug & cord is possible.

Starting at 1hp, and certainly by 3hp., the advantages of three-phase are evident. They cost much less to run, draw fewer amps, and the motors cost much less.
One alternative to phase converters is to use a variable frequency drive. These drives essentially create three phase from single phase.

another link to 1-3 phase convertors for our Australian & NZ members is http://www.phasechanger.com/

[This message has been edited by 32VAC (edited 10-08-2004).]

Motor Circuit Rules


Fuses are considered as: "branch-circuit short-circuit and ground-fault protection"

"Separate motor overload protection shall be based on the motor nameplate current rating."