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Wiring 240V for new Table Saw

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Forum topic by marsy00 posted 10-20-2013 03:43 AM 1181 views 0 times favorited 16 replies Add to Favorites Watch
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marsy00

15 posts in 721 days


10-20-2013 03:43 AM

Topic tags/keywords: table saw electrical circuit 240v electrician

Hello,

I currently have a 120V contractor saw and I’m upgrading to a 240V cabinet saw. I have a sub panel in my garage workshop, with an existing 120V circuit running through EMT along the ceiling to my existing saw. I want to keep the 120V circuit in place and pull new wires for a new 240V circuit.

The new saw has a 6-15P plug (3 wires). Obviously I need to pull two hots from the new breaker, and I assume a ground rather than a neutral… is this correct? The EMT is grounded to the subpanel ground bar, but I’ve also pulled dedicated ground wires for each existing circuit as well.

Second question: I’m going to put a L6-15R on the ceiling, and ideally I would run a L6-15P to 6-15R drop to the new saw’s existing plug. Is there a downside to using an extension cord like this? I want a lock receptacle in the ceiling for the drop, but I also want to be able to unplug the saw without getting on a ladder.

Thoughts?

Thanks in advance for the help!


16 replies so far

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marsy00

15 posts in 721 days


#1 posted 10-20-2013 03:54 AM

Sorry… one more question… NEC no longer permits 3 wire circuits for stoves/dryers… is it limited to household appliances? Is it allowable to run a 3 wire circuit for the tablesaw?

Thanks

View exelectrician's profile

exelectrician

1596 posts in 1093 days


#2 posted 10-20-2013 03:55 AM

Years ago working in my first year an an apprentice, my Journeyman asked what was the most important wire to connect out of the bunch of wires I had in front of me as I was connecting up an electric motor, I was confused and not sure, so I blurted “the red wires”...

NO ! he shouted “THE GROUND WIRE IS THE MOST IMPORTANT CONNECTION!!!! “

this is of course not to be confused with the white neutral which is also very important

-- Love thy neighbour as thyself

View UpstateNYdude's profile

UpstateNYdude

457 posts in 648 days


#3 posted 10-20-2013 04:00 AM

How many amps is it going to draw on startup? If it’s under 20 just get a double pole 20amp breaker run some 12/2 AWG and you should be fine, I wouldn’t use an extension cord but that is me.

-- Nick, “Discovering the truth about ourselves is a lifetime's work, but it's worth the effort.” ― Fred Rogers, Be My Neighbor

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TopamaxSurvivor

14793 posts in 2341 days


#4 posted 10-20-2013 04:06 AM

3 wires to the saw is fine; 2 hot and 1 ground. Appliances like dryers and ranges have been up graded to 4 wires because of neutral loads associated with modern control circuitry to keep those currents off the ground. Your plan sounds reasonable to me ;-)

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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marsy00

15 posts in 721 days


#5 posted 10-20-2013 04:29 AM

Thanks for the replies everyone… 13A is the startup draw.

View Charlie's profile

Charlie

38 posts in 377 days


#6 posted 10-20-2013 07:50 AM

The 13A must be the motor nameplate amps. Not inrush starting amps
Here is a nifty calculator for motor branch circuits.
http://www.electrician2.com/calculators/motor_ver_1.html

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darthford

532 posts in 589 days


#7 posted 10-20-2013 04:25 PM

My 1.5 HP Grizzly cyclone dust collector was drawing like 60 amps on start-up wired for 110.

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Shawn Masterson

1254 posts in 614 days


#8 posted 10-20-2013 05:02 PM

The only thing I see is the extra cost of the plugs involved in the cord. also a twist lock is not needed on the ceiling. unless you intend to yank on the cord.

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TopamaxSurvivor

14793 posts in 2341 days


#9 posted 10-20-2013 08:29 PM

Start up current is infinitesimal for the first cycle or 2. Don’t worry about it. FLA 13 amps at 240 volts should be a 2 hp motor by the old standard. A 20 or 25 map breaker should start it just fine.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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marsy00

15 posts in 721 days


#10 posted 10-20-2013 10:30 PM

Could you elaborate on the “old standard” vs “New standard?”

Thanks everyone for the replies.

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TopamaxSurvivor

14793 posts in 2341 days


#11 posted 10-20-2013 11:02 PM

The “old standard” was labeling power tools horsepower based on the full load current of the motor. Recent trend has been to use the locked rotor current to calculate tool hp. The effect has been to label a table saw with a 3/4 hp motor as a 2 or 3 hp machine.

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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jonah

453 posts in 1964 days


#12 posted 10-20-2013 11:54 PM

I have to respectfully disagree that three wires to the saw is fine. Chance are you’d be fine, but if you’re doing it right, why not just pull a normal 10/3 or 12/3 cable to the ceiling above the saw? You want to ground that receptacle (and the conduit, assuming you’re using EMT again) anyway, so there’s no reason not to do it with a 4 wire cable.

I’m not entirely clear why you’d even bother quibbling about a ground versus a neutral. Just pull the 10/3, install the L6-15R, add as short and sturdy a cable as you can get away with to go from the ceiling to the floor, and go to work.

View UpstateNYdude's profile

UpstateNYdude

457 posts in 648 days


#13 posted 10-21-2013 01:26 AM

Darthford – how the hell did it hit 60 amps on start up and not pop the breaker?

-- Nick, “Discovering the truth about ourselves is a lifetime's work, but it's worth the effort.” ― Fred Rogers, Be My Neighbor

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TopamaxSurvivor

14793 posts in 2341 days


#14 posted 10-21-2013 08:17 AM

Now I’m curious. Where would one terminate the 4th wire on a L6-15R? Certainly not by tying the neutral and ground together when they originate in a sub-panel!!

-- "some old things are lovely, warm still with life ... of the forgotten men who made them." - D.H. Lawrence

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jonah

453 posts in 1964 days


#15 posted 10-21-2013 01:17 PM

It’s been a while since I did anything 240V, but from memory, the receptacle has 4 terminals. You terminate the ground to the ground terminal.

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