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Old 11-17-2009, 01:13 PM   #1
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20 amp 240 volt


Hello all,

I'm running a 20amp 240 volt circuit to power a new table saw as per the saws requirement. I purchased a length of 12-3 wire and ran it through the wall and everything but hesitate to hook it up. Few concerns first:
1. 240 volt will kill me so I want to make sure #'s 2, 3, and 4 are cleared up;
2. should a 240 volt wire be run through a conduit? it is in the basement in the ceiling
3. the receptacle has only 2 terminals and a ground. That said, if I'm running a 240 volt I now have 2 hot wires. Do i pigtail these into one terminal and connect the neutral (white) on the other? or,
4. is it best to just use a 12-2 wire and treat the white wire as the second hot wire?

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Old 11-17-2009, 01:20 PM   #2
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20 amp 240 volt


12-3 is a cable, so not required to be in conduit
Only individual wires need to be run in conduit
Some areas Do require everything in Conduit (Chicago for one ?)
Check with your building Inspector for local codes

What kind of receptacle are you using ? Twist lock plug ?
2 hots are connected to the 240v circuit breaker
2 hots get connected on either side, usually you only use 12-2
Then the white is remarked black as a hot wire

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Old 11-17-2009, 01:48 PM   #3
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20 amp 240 volt


Connect red & black to the two ungrounded terminals. Connect the bare/green to the ground terminal. You do not need the white. You can cut it off. At the panel connect the red & black to a 20 amp 2 pole breaker and connect the bare/green to the ground terminal strip. Either cut the white or put a wire nut on it and tuck it in. This is for 220 volt, 3 wire connection.
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Old 11-17-2009, 01:51 PM   #4
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20 amp 240 volt


NEC requires min 6" of conductor in any box, if you cut it off leave atleast 6".

Last edited by Grimlock; 11-17-2009 at 01:51 PM. Reason: Typo
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Old 11-17-2009, 02:10 PM   #5
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20 amp 240 volt


Thanks for the quick reply everyone.

It is not a twist lock, just a standard 20 amp 240v outlet mounted on the wall. The extra wire was my big concern. I think I'll just run a new 12-2 line and save the 12-3 for something else. Paid good money for it to just cut one wire out of the mix.
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Old 11-17-2009, 03:53 PM   #6
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20 amp 240 volt


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Originally Posted by konabear View Post
240 volt will kill me
Not likely; 1 chance in 200,000, per year, in the US. In any case, wear sneakers so you won't be grounded.

I'd be more worried about shorting it and having globs of molten copper flying through the air.
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Old 11-17-2009, 04:26 PM   #7
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20 amp 240 volt


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Originally Posted by Yoyizit View Post
Not likely; 1 chance in 200,000, per year, in the US. In any case, wear sneakers so you won't be grounded.

I'd be more worried about shorting it and having globs of molten copper flying through the air.
50 volts + can kill you... Work safe and work with the power OFF!!! It takes 1/10 of one amp to stop your heart!
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Old 11-17-2009, 08:51 PM   #8
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20 amp 240 volt


I'd use 12/2, and save the 12/3 for something that needs a neutral.

If you use 12/2, you'll have a black that goes to one side of the breaker and one side of the receptacle. You'll have a white that goes to the other side of the breaker and the other side of the receptacle. The bare ground goes on the ground bus in the panel, and on the ground terminal of the receptacle.

Be careful that the bare ground doesn't touch anything hot. Like the line side of the main breaker. It's still hot even when the breaker is off.

Mark the white with either colored tape (usually red), or a felt-tipped pen. Just make it so it isn't confused with the other whites.

To get shocked by 240 from a typical residential service, you must already be touching one of the hots, then touch the other. You can't get a 240 volt shock from a hot to ground. The only voltage there is to ground is 120.

Unless you live in a really dry climate, and you're not sweating at all, 120 certainly can kill a person.

Just make sure the power is off when working on anything above 50 volts.

Rob
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Old 11-17-2009, 09:10 PM   #9
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20 amp 240 volt


Quote:
Originally Posted by Grimlock View Post
50 volts + can kill you... Work safe and work with the power OFF!!! It takes 1/10 of one amp to stop your heart!
There's lot of dependencies on this such as exposure time. If you have fast reflexes chances are you wont be exposed long enough.

But best to just play it safe, electric shocks are well, shocking, and that alone can pose a danger especially if on a ladder or something. It will "throw" you (mostly due to your own fast reaction).

I can also confirm that it takes about 13 daisy chained 9 volt batteries before you can feel a shock. Just in case anyone has ever wondered. 13 is the magic number. This is why they come in packs of 12, I guess.
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Old 11-18-2009, 03:10 PM   #10
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20 amp 240 volt


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Originally Posted by Red Squirrel View Post
I can also confirm that it takes about 13 daisy chained 9 volt batteries before you can feel a shock. Just in case anyone has ever wondered. 13 is the magic number. This is why they come in packs of 12, I guess.
117v/.001A = 117k skin+body resistance is high for this forum. But the people on this forum who complained about shocks mostly had wet hands.
Since the 50vdc phone line gives me a slight shock, my skin resistance must be 50/.001 = 50k.


Last edited by Yoyizit; 11-18-2009 at 05:06 PM.
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