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Electrical questions on 240V circuit
Hello,
I'd like to add a 240V-only receptacle to my basement workshop to run two induction motor loads. I have experience running 120V household circuits, and I just have a couple questions on 240V circuits: 1) My understanding is that for NEMA 6-15 (240V 2-pole Grounded 15 amp) plugs and receptacles, the two hot prongs are undistinguished, i.e. there is no polarization as on 120V plugs and receptacles. Is that correct? Is there any convention? 2) I believe the NEC does not require GFCI protection on 240V circuits. Are economic 240V GFCI receptacles available? Thanks, Wayne |
"Wayne Whitney" wrote in message ... Hello, I'd like to add a 240V-only receptacle to my basement workshop to run two induction motor loads. I have experience running 120V household circuits, and I just have a couple questions on 240V circuits: 1) My understanding is that for NEMA 6-15 (240V 2-pole Grounded 15 amp) plugs and receptacles, the two hot prongs are undistinguished, i.e. there is no polarization as on 120V plugs and receptacles. Is that correct? Is there any convention? No reason to polorize a 240 volt plug/recepticle with two hot legs, where a 120 volt has one hot and a neutral conductor. Greg |
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In article , HA HA Budys
Here wrote: From: Wayne Whitney 1) My understanding is that for NEMA 6-15 (240V 2-pole Grounded 15 amp) plugs and receptacles, the two hot prongs are undistinguished, i.e. there is no polarization as on 120V plugs and receptacles. Is that correct? Is there any convention? Correct. Both prongs are "hot" and there is no neutral. No polorization. OK, just to be redundant, that means that in a 240V circuit, you don't have to keep track of black versus red and you can connect black to red, red to black willy-nilly? On a related note, if I rewire a 120/240V induction motor to 240V and change the 120V plug on its power cord, then I should mark the white conductor at the new plug and at the motor junction box? Thanks, Wayne |
In article , HA HA Budys
Here wrote: From: Wayne Whitney 2) I believe the NEC does not require GFCI protection on 240V circuits. Are economic 240V GFCI receptacles available? I don't think I've ever seen one. You can get a 240v GFCI circuit breaker though. Hmm, a SquareD QO220 breaker costs $15, while a QO220GFI breaker costs $90. I have two induction motor loads, a jointer and a dust collector. I wonder if the greater expense of GFCI protection would be a good reason not to rewire these motors to 220V. Thanks, Wayne |
Hmm, a SquareD QO220 breaker costs $15, while a QO220GFI breaker costs
$90. I have two induction motor loads, a jointer and a dust collector. I wonder if the greater expense of GFCI protection would be a good reason not to rewire these motors to 220V. You use your jointer right after stepping out of the shower? Why do you want a GFCI? Bear in mind that to get 240v you have to contact both hots. That is highly unlikely, and wouldn't trip a GFCI anyhow. Assuming your tools are grounded properly, any kind of shock (except from directly touching one of the wires) is unlikely, but would be exactly the same as a 120v shock anyhow. (I shouldn't admit this, but in the interest of full disclosure... while drywalling I forgot an outlet was hot and pulled on it, contacting the hot with one hand and the neutral with the other. Fortunately it was just a big surprise, but I might not have been so lucky with 240v! Stupid things like that are possible. A GFCI would not have helped because there was no current leakage.) To answer your other question, the hots are interchangable; there is no reason to distinquish between them. Accordingly, you have to mark the white wire with black tape on both ends so no one mistakenly thinks it is a neutral. You might want to think about using 4wire so your hots will be black and red. You will have the white available as a neutral if you ever need it. I didn't do that when I ran 240v to my shop and I regret it. 240v is no more difficult to wire than 120v, but you might want to read a wiring book first, because you don't seem to understand what 240v is. It is no more difficult when you know what it is; when you don't get it, I suppose a dumb mistake could easily happen. |
According to toller :
Hmm, a SquareD QO220 breaker costs $15, while a QO220GFI breaker costs $90. I have two induction motor loads, a jointer and a dust collector. I wonder if the greater expense of GFCI protection would be a good reason not to rewire these motors to 220V. You use your jointer right after stepping out of the shower? Why do you want a GFCI? Bear in mind that to get 240v you have to contact both hots. That is highly unlikely, and wouldn't trip a GFCI anyhow. Assuming your tools are grounded properly, any kind of shock (except from directly touching one of the wires) is unlikely, but would be exactly the same as a 120v shock anyhow. Most zaps from a 240V circuit will be 120V from hot-to-ground. Even if you hit hot-to-hot, you're likely to have _some_ additional leakage to ground too. As such, a GFCI _would_ work. However, the electrical code tends not to require GFCI's for large machinery that has solid grounds. Especially if they're single outlets. Think fridges or freezers for example, even in places that need GFCIs for normal outlets. I wouldn't put GFCIs on large 240V stationary power tools, but I'd take considerable care to ensure that their grounds are there, solid and work. If the ground is working properly, nothing short of taking the machine apart and sticking your fingers in the electricals will give you a shock. -- Chris Lewis, Una confibula non set est It's not just anyone who gets a Starship Cruiser class named after them. |
In article , Chris Lewis wrote:
According to Wayne Whitney : OK, just to be redundant, that means that in a 240V circuit, you don't have to keep track of black versus red and you can connect black to red, red to black willy-nilly? Yeah, but it's _sloppy_. Sure, I wouldn't do that. But I like to know why I'm doing something: neatness or safety. Cheers, Wayne |
In article ,
toller wrote: To answer your other question, the hots are interchangable; there is no reason to distinquish between them. In theory, true. But for my own house, I don't like it. On all the 240V circuits, I have checked that black and red are not mixed up. This is really easy to do when wiring the house, and makes everything look neater. Here's another thing that worked out good. When we built the house, the local electrical distributor had a sale on strange-colored wire. So I used quite a bit of blue, purple, red, and such. This makes a complicated box with multiple switches easier to understand. For example: Black is the hot feed going in; red is the output to the light, and blue and purple are the switch legs between three-way switches. You might want to think about using 4wire so your hots will be black and red. You will have the white available as a neutral if you ever need it. I didn't do that when I ran 240v to my shop and I regret it. Absolutely. All of my 240V outlet circuits are run with 4-wire cable (but not the dedicated 240V circuits for pump motors, where a neutral will never be needed). Sadly, all but two of the neutrals remain unused. The two used ones a The dryer (which uses the currently code-legal 4-pin connector), and the drill press (where rewiring the motor to 240V will require a neutral conductor so the work light on it can stay at 120V). -- The address in the header is invalid for obvious reasons. Please reconstruct the address from the information below (look for _). Ralph Becker-Szendy |
Most zaps from a 240V circuit will be 120V from hot-to-ground. Even if you hit hot-to-hot, you're likely to have _some_ additional leakage to ground too. As such, a GFCI _would_ work. Have you actually tried this, or are you just guessing? |
According to toller :
Most zaps from a 240V circuit will be 120V from hot-to-ground. Even if you hit hot-to-hot, you're likely to have _some_ additional leakage to ground too. As such, a GFCI _would_ work. Have you actually tried this, or are you just guessing? Think about it: for every time you touch the hot wire of a 120V circuit, how many times would you conduct enough current to, say, the floor you're standing on, to trip a GFCI? Most times. -- Chris Lewis, Una confibula non set est It's not just anyone who gets a Starship Cruiser class named after them. |
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