How big of a circuit for a 7.5 hp motor?
 

I've got a new (to me) lathe coming in. It has a 7.5 hp motor, 3 phase.
I've got a 10hp phase converter for it, and in the process of having a
circuit added. What I dont know, though, is what size circuit should I have
installed for this? 50 amps? more? Less?

I'm sure this is a basic question, but i'm not an electrician. Thanks for
any info.

Greg Deputy wrote:

I've got a new (to me) lathe coming in. It has a 7.5 hp motor, 3 phase.
I've got a 10hp phase converter for it, and in the process of having a
circuit added. What I dont know, though, is what size circuit should I have
installed for this? 50 amps? more? Less?

I'm sure this is a basic question, but i'm not an electrician. Thanks for
any info.





It doesn't answer your amp question but you may be a little light
running a 7.5 off a 10 HP rotary converter. I'm running a 5hp 2 speed
from a 7.5hp converter and for 95% it works fine, but there are a couple
of gear changes it doesn't like. This is especially true when running
at the lowest speeds (low speed range on the motor). High speeds take a
bit of time for the motor to wing up to speed and that taxes the
converter also. One of these days I'll bypass the rotary and use a VFD
but I'm too cheap and lazy right now.

Koz

Thanks for the info

Yes, I'm certainly interested in the cord, what are you asking for it?
Please reply to my email address, I post here with a valid address.

"Ignoramus24456" wrote in message
...
On Wed, 2 Mar 2005 13:06:47 -0800, Greg Deputy wrote:
I've got a new (to me) lathe coming in. It has a 7.5 hp motor, 3 phase.
I've got a 10hp phase converter for it, and in the process of having a
circuit added. What I dont know, though, is what size circuit should I
have
installed for this? 50 amps? more? Less?

50 amps at 220 volts supplies 11 kilowatts, or 14.6 horsepower. It
should be adequate. If I was doing this, I would run a full blown
subpanel ($19.99) and used 6 gauge wires and 60 amps service. You have
to run 6 gauge wire anyway, why not run a bit more electricity and
have a nice subpanel instead of just one circuit. One of the breakers
on a subpanel can be 50 amps for your phase converter.

By the way, I have a 50 amp four prong plug with 8 foot flexible #8 cord
for
sale. (note that even though the plug is 4 prong, the cord has 3 wires
inside, white, black and green). It would work for your 220V phase
converter input.

i

Full load amperage of a 3-phase 7.5 HP motor on 240 v is around 20 - 21
amps. The motor and phase converter should be connected to a 30 amp
breaker, at least. Best to check local "code" and install recommended
breaker.

Bob Swinney

"Greg Deputy" wrote in message
...
I've got a new (to me) lathe coming in. It has a 7.5 hp motor, 3 phase.
I've got a 10hp phase converter for it, and in the process of having a
circuit added. What I dont know, though, is what size circuit should I
have
installed for this? 50 amps? more? Less?

I'm sure this is a basic question, but i'm not an electrician. Thanks for
any info.

Sounds great, email me at and i'll work out the details
with you.


"Ignoramus24456" wrote in message
...
On 2 Mar 2005 22:47:40 GMT, Ignoramus24456
wrote:
On Wed, 2 Mar 2005 13:32:11 -0800, Greg Deputy
wrote:
Thanks for the info

Yes, I'm certainly interested in the cord, what are you asking for it?
Please reply to my email address, I post here with a valid address.

I will make pictures tonight or tomorrow and will post/email them. I
usually make many super detailed pictures.

Turns out that I already have pictures. The cord/plug is from this
UPS. The UPS itself is RIP, taken apart, disassembled, and
demolished. I sold a lot of parts from it (IGBT, rectifiers,
contactors, outlet panel), but the cord is what you see on the
pictures.

http://igor.chudov.com/tmp/Clary-3-Phase-UPS/

$20 plus shipping (free local pickup in chicagoland) will take it. It
is 8 feet long, very flexible, very thick outside jacket, 3 conductors
(white, black and green), terminal lug at the green end and no lugs
on the black/white ends.

I also have a regular 3 prong range plug with 8 foot cord (from a 1
phase UPS), but this one I would prefer to keep for my future
projects.

i

A 7.5 motor 220/3p will run all day on a 30 amp circuit, which only requires
10 gauge wiring. Matter of fact I recently wired a 7.5hp 3450 ventilator fan
for a truck garage.

Tony


"Greg Deputy" wrote in message
...
I've got a new (to me) lathe coming in. It has a 7.5 hp motor, 3 phase.
I've got a 10hp phase converter for it, and in the process of having a
circuit added. What I dont know, though, is what size circuit should I
have
installed for this? 50 amps? more? Less?

I'm sure this is a basic question, but i'm not an electrician. Thanks for
any info.