A large lathe and mill on one circuit?

[Noltz]

I'm bringing home a large 240v 5HP Willson lathe from a friend next week. My shop has a 6/3 run from the panel to a 6-50 outlet that's about 10' away, and I plan for a knee mill in the future that'll be 5' on the other side of this current outlet.

What's the best way to install these two to share the 6/3 run? I'm thinking a small sub panel but if there's a better option I'd like to hear it.

 

[theoldwizard1]

I'm bringing home a large 240v 5HP Willson lathe from a friend next week. My shop has a 6/3 run from the panel to a 6-50 outlet that's about 10' away, and I plan for a knee mill in the future that'll be 5' on the other side of this current outlet.

I am pretty sure that a 6-50 is not rated for a 5 HP motor.

Yes, a sub panel with flexible conduit to each tool is the best solution.

 

[cvairwerks]

6-50 is only rated for 3 hp.

 

[Noltz]

Yeah the runs were terminated with 6-50's because he was welding in there. There's multiple drops as illustrated including a dedicated one for electric heat in that future cave room (which is very heavily insulated, was used for mixing and curing epoxies where temperatures were critical). Seems they went overkill on the wiring.

Quick Edit; 6-50s are on the walls but the walls have 6-3 wires in them. I just need to connect the neutrals in the LC.

 

[rsanter]

I run my mill, lathe, MIG, TIG, and spot welder all on one circuit.
I'm a one man shop so only one of those is running at a time

 

[nadogail]

My tools and my wife’s clothes dryer time shared the same 220 circuit for a few years.

 

[PelicanPines]

The key take away is... the existing wiring would NOT POWER the lathe.

 

[lund]

6-50 is only rated for 3 hp.

Sorry dumb question: Why is a 6-50 plug rated to only 3 hp? Is that the max hp that code allows to be plugged? 6-50 can source 50 A @ 240 V which delivers 12,000 Watts. Using online conversion calculators, 3hp = 2237.1 Watts, which is only about 19% of the plug's power rating.

 

[ez-duzit]

I am pretty sure that a 6-50 is not rated for a 5 HP motor.

Yes, a sub panel with flexible conduit to each tool is the best solution.

Wrong. That outlet is plenty for 5 hp.

 

[Noltz]

The key take away is... the existing wiring would NOT POWER the lathe.

The wiring is fine. It's 6-3 in my walls to 6-50s. It's much larger than the wire that fed the lathe in it's old home. I have to check but I believe the lathe was on a 30A breaker. Unless you meant the existing plug would not (safely) power the lathe. I'd agree and I'm hoping Wylie will chime in on if a 5HP must be hardwired.

I run my mill, lathe, MIG, TIG, and spot welder all on one circuit.
I'm a one man shop so only one of those is running at a time

Did you use a sub panel to split the circuit or are they on plugs?

 

[Norcal]

Wrong. That outlet is plenty for 5 hp.

Might be in your mind, but if one is going to do it in a code compliant manner it's not.

 

[sparky 1971]

Sorry dumb question: Why is a 6-50 plug rated to only 3 hp? Is that the max hp that code allows to be plugged? 6-50 can source 50 A @ 240 V which delivers 12,000 Watts. Using online conversion calculators, 3hp = 2237.1 Watts, which is only about 19% of the plug's power rating.

Because some people are a special kind of stupid and can't be trusted to not unplug to cord while the machine is running, which could potentially make a heck of an arc flash.

To plug in a 5HP, A pin and sleeve connector should be used. It's a whole bunch cheaper to hardwire.

 

[ez-duzit]

Might be in your mind, but if one is going to do it in a code compliant manner it's not.

5 horsepower at 230-volts is less than 30 amps. The receptacle is rated at 50-amps.

 

[sparky 1971]

5 horsepower at 230-volts is less than 30 amps. The receptacle is rated at 50-amps.

It's different when it comes to HP. 5HP is pin and sleeve territory if it's going to be done right.

 

[mm08822]

Devices used in a motor circuit must be HP rated per NEC - 430.109(F). This is ensure sufficient connection capacity during a locked rotor condition and start-up.

 

[mm08822]

The key take away is... the existing wiring would NOT POWER the lathe.

Why? 5HP @230VAC single phase requires 32A, add 25% (8A) = 40A. Even NM-B #6 is good for 50A. THHN or XHHW is higher.

 

[ez-duzit]

My apology to old wizard.

 

[mm08822]

Sorry dumb question: Why is a 6-50 plug rated to only 3 hp? Is that the max hp that code allows to be plugged? 6-50 can source 50 A @ 240 V which delivers 12,000 Watts. Using online conversion calculators, 3hp = 2237.1 Watts, which is only about 19% of the plug's power rating.

Type of load matters. A resistive load (heater) is not an issue for the contacts. An inductive load (motor) has high in-rush current until up to speed, if it doesn't get up to speed or turn at all (locked rotor) it could be drawing several times motor nameplate current. Also, if disconnected under load or a locked rotor, the arc flash would be tremenous, possibly damaging plug/recept and the person pulling them apart.

 

[Noltz]

Why? 5HP @230VAC single phase requires 32A, add 25% (8A) = 40A. Even NM-B #6 is good for 50A. THHN or XHHW is higher.

This is the actual condition I'm asking about right now. I have NM-b #6 in the wall there currently on a 40A breaker. I don't use the 6-50 and want to change it to a sub panel unless someone else has a better idea. Although I'm happy we're discussing the proper useages of a receptacle I'm still curious if anyone else would do something other than replacing this 6-50 with a sub panel and hard-wiring the two tools. One man shop. If the motors are 3HP or smaller (on the lathe and the future mill) I could use the existing receptacle but I don't think swapping plugs between machines is a good solution.

 

[mm08822]

I would add the panel so I wouldn't have to plug in each equipment each time when needed.

 

[rsanter]

The wiring is fine. It's 6-3 in my walls to 6-50s. It's much larger than the wire that fed the lathe in it's old home. I have to check but I believe the lathe was on a 30A breaker. Unless you meant the existing plug would not (safely) power the lathe. I'd agree and I'm hoping Wylie will chime in on if a 5HP must be hardwired.

Did you use a sub panel to split the circuit or are they on plugs?

They are on plugs

 

[lund]

Because some people are a special kind of stupid and can't be trusted to not unplug to cord while the machine is running, which could potentially make a heck of an arc flash.

To plug in a 5HP, A pin and sleeve connector should be used. It's a whole bunch cheaper to hardwire.

Thanks. Make some sense at least in a Murphy's Law context.

The arc concern really applies to anything with a significant amount of inductance though. A welder with a transformer is probably in a similar category. So it is odd that the code rules things out by Hp for motors but not something with a plug in transformer. Granted, people are not generally lugging around 3 hp + electric motors so hard wire is probably fine for most large motors. But high power welders and other stuff need to be moved.

 

[dave*99]

Thanks. Make some sense at least in a Murphy's Law context.

The arc concern really applies to anything with a significant amount of inductance though. A welder with a transformer is probably in a similar category. So it is odd that the code rules things out by Hp for motors but not something with a plug in transformer. Granted, people are not generally lugging around 3 hp + electric motors so hard wire is probably fine for most large motors. But high power welders and other stuff need to be moved.

A spinning motor creates back EMF too. So pull the plug on a running motor and you have the mass and inertia of the spinning rotor and load equipment driving energy into the collapsing magnetic field. It's the combination of inductance and back EMF that makes the BIG SPARK.

A welder...... not so much.