Thread: Single Phase Motor and amps

No not off a normal SF outlet. You would need one supplying 22 amps at 240V.

The 480v supply would require a special transformer supply and it would be cheaper to get 22A@240V (if you have that much available).

These size/types of motors are usually hard wired in and have their own individual line and breaker.

What are you looking to drive with such a large motor?

Thanks Guys,

Bob, large bandsaws (32" - 36"). I have a few of these I am restoring. The smallest motor between them is a 3hp 3-phase and the largest being 7hp 3-phase (from memory). I liked the size of this motor but is probably not necessary as I would think a 3HP motor will be sufficient on these big bandsaws. I can get a cheap motor per below which will do the trick. The good thing is these will draw under 15amps so just need a 15amp outlet + plug, so no special considerations as normal households cater for this for the most part.

2.2kw 3HP 1400rpm shaft 28mm Electric motor single phase 240v

Originally Posted by Charlie_6ft

Thanks Guys,

Bob, large bandsaws (32" - 36"). I have a few of these I am restoring. The smallest motor between them is a 3hp 3-phase and the largest being 7hp 3-phase (from memory). I liked the size of this motor but is probably not necessary as I would think a 3HP motor will be sufficient on these big bandsaws. I can get a cheap motor per below which will do the trick. The good thing is these will draw under 15amps so just need a 15amp outlet + plug, so no special considerations as normal households cater for this for the most part.c

Thanks for that. Regarding power requirements, it depends what you plan to cut with them.

Old large bandsaws were made in the 30+" size range so they could have deep throats so large pieces could pass on the inboard side of the blade. The other interest was depth of cut or ripping depth capability which is limited by the distance between the wheels. Once this goes above a 12" then you may need more than 3HP. FWIW the horizontal milling bandsaw I use has a 36" diameter wheels and a 36" wide cutting capability and that has a 27HP Kohler motor. It uses a 50mm wide 1TPI blade.

Just a reminder that to be legal 15A sockets should be wired by a dedicated line to their own dedicated breaker.

Originally Posted by BobL

Thanks for that. Regarding power requirements, it depends what you plan to cut with them.

Just a reminder that to be legal 15A sockets should be wired by a dedicated line to their own dedicated breaker.

That reminder is not supported by AS/NZ 3000:2018, nor by the now obsolete AS/NZ 3018. You will note that the requirement under the Standard is 20A, not 15A as is so often stated in this forum.

The following extract from AS/NZ 3000:2018 is quite specific. The older AS/NZ 3018:2001 also had tables of allowed GPO/CB/cable combinations which included 2x 15A sockets on a 2.5mm 20A circuit. Both HPM and Clipsal have double 15A combination outlets in their product ranges, HPM also sell a 15A/10A combination.

"C5 NUMBER OF POINTS CONNECTED TO CIRCUITS
C5.1 Number of circuits
Each item of equipment that has a current rating in excess of 20 A per phase should be connected to a separate and distinct circuit.
Where more than one item of equipment is to be connected to a circuit, consideration needs to be given to—
(a) the number, distribution and type of equipment (lighting, socket-outlets or appliances, etc.), i.e. points, that are to be supplied in combination;
(b) the operating characteristics of the different items of equipment, including seasonal or daily variations;
(c) the circuit current under expected operating conditions and the coordination with cable and protective device ratings to minimize the risk of an overload fault; and
(d) the effects of an overload fault on the circuit, including loss of supply to equipment that performs a special function, e.g. security, emergency, medical or critical information and telecommunications purposes."

Chas.

Thanks for that. I was going off what a sparky that wired our men’s she’d told me. I guess he was trying to wrangle a few more $$ out of our shed. I’d be surprised if any sparky was to put a 15A GPO on a std household 10A cIrcuit. I do know about the double 15A GPOS as I have 5 in my shed.

Good info chaps. So in regards to the below motor drawing a max of ~14amps (at startup) I am guessing whilst in normal use a 10amp GPO will suffice, but it's best practise to have a 15amp GPO installed?

2.2kw 3HP 1400rpm shaft 28mm Electric motor single phase 240v

As far as the size of the motor goes the below motors where used on a couple of these saws. I am led to believe in going to a 3hp single phase motor equivalent will result in 35% less torque when compared to a 3-Phase motor.

Motor	HP	Phase	Volts	AMPS	RPM	Cycles (Hz)	RATING
Crompton	2.75	3	400/440	5	940	50	CONT
K. L. Electric Co.	3	3	415	4.3	1425	50	CONT

Originally Posted by Charlie_6ft

Good info chaps. So in regards to the below motor drawing a max of ~14amps (at startup) I am guessing whilst in normal use a 10amp GPO will suffice, but it's best practise to have a 15amp GPO installed?

2.2kw 3HP 1400rpm shaft 28mm Electric motor single phase 240v

No. 13.9 A is the current drawn by the motor when loaded to it's full rating. The actual current drawn in use depends upon lots of things, including feed rate, blade sharpness, material thickness and toughness, etc. The rated power is a recommended limit, not an ultimate limit. It's like the speed limit on a highway, exceed it at risk. If the operator exceeds the limit the motor will draw more than it's rated current (as well as exceed it rated temperature rise and possibly not meet it's rated lifetime, depending on ambient temperature).

Startup current, according to the spec you linked, will be about 70 A.


Startup current in the table is given by the LRA/RLA parameter. LRA is Locked Rotor Amps and RLA is Rated Load Amps. So, 5 x 14 = 70.

Originally Posted by Charlie_6ft

I am led to believe in going to a 3hp single phase motor equivalent will result in 35% less torque when compared to a 3-Phase motor.

You've been misled. Rated torque depends upon rated power and rated rpm. Pick any two and the third one is determined. 15 N-m and 1400 rpm is 2.2 kW regardless of the number of phases, the voltage, the current, etc.

Originally Posted by Charlie_6ft

Good info chaps. So in regards to the below motor drawing a max of ~14amps (at startup) I am guessing whilst in normal use a 10amp GPO will suffice, but it's best practise to have a 15amp GPO installed?

Yes

As far as the size of the motor goes the below motors where used on a couple of these saws. I am led to believe in going to a 3hp single phase motor equivalent will result in 35% less torque when compared to a 3-Phase motor.

Nope - as dmorse says the motors are normally rated on their outputs with rpm/HP/torque being closely related.