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Thread: multiple outlets on one 240-volt circuit?

  1. #1

    multiple outlets on one 240-volt circuit?

    A 240-volt line runs between the floor joists directly above my basement shop on the way to an outlet upstairs behind the stove. I have a gas stove, so I could re-route the line entirely and put the outlet down in the shop. But it got me curious. What about two or three outlets on the same 240-volt line? I'm fairly familiar with 120-volt wiring conventions (I recently finished 1300 sq. ft. of basement and ran multiple circuits without a hitch and passed inspection) but I don't know what's kosher with 240.

  2. #2
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    Quote Originally Posted by Bill Bryant View Post
    ... What about two or three outlets on the same 240-volt line? ...
    There seems to be some sentiment that there can only be one outlet on a 240 circuit. That is not the case. A 240 circuit can feed multiple outlets just as a 120 circuit can feed multiple outlets. The only differences are that there is a 240 volt potential between the two conductors instead of a 120 volts and that both conductors instead of just one have a 120 volt potential relative to ground.

    My shop, wired by a licensed electrician and inspected by the local code enforcement inspectors, has 4 separate general purpose circuits, all of which are 240 volt and each of which feeds multiple outlets. The wiring is 3-wire plus ground and the outlets are dual-voltage duplex receptacles - one 120 and one 240 outlet in each receptacle. If I hadn't wanted the 120 available, it could have been wired with 2 + ground and with multiple 240 volt outlets.
    Tom Veatch
    Wichita, KS
    USA

  3. #3
    Rob Will Guest
    Quote Originally Posted by Bill Bryant View Post
    A 240-volt line runs between the floor joists directly above my basement shop on the way to an outlet upstairs behind the stove. I have a gas stove, so I could re-route the line entirely and put the outlet down in the shop. But it got me curious. What about two or three outlets on the same 240-volt line? I'm fairly familiar with 120-volt wiring conventions (I recently finished 1300 sq. ft. of basement and ran multiple circuits without a hitch and passed inspection) but I don't know what's kosher with 240.
    Bill, if the stove wire is 4-wire you could use it to feed a sub panel in the basement. That would be an easy way to terminate the existing wire and provide a good take off point for extra circuits.

    If the stove wire happens to be 6/4 romex, I would install a sub panel with a 50 amp breaker as a main disconnect. The main problem with using your existing wire alone is that the breaker in the panel upstairs is also probably 50 amp. For anything short of a welder plug or a range plug, that is too big. You will want to step down to smaller wire for most of your tool outlets. These wires must be individually protected with the proper size breaker, hence the sub-panel.

    Rob

  4. #4
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    Bill There is nothing in the NEC that precludes multiple outlets off a 220 branch circuit.
    I believe that the reason that you read "there can only be one" is that typically 220 supplies motors in the shop. Placing multiple motors on a single 220 circuit requires that the branch, and breaker be sized accordingly to run multiple 220 loads simultaneously.
    The motors section of the NEC has covers this. There is a little flowchart at the beginning of the motors sections that guides you through it.
    In a small shop though, it may be easier, and more cost effective to run seperate circuits depending on the layout, machinery involved and the local inspectors interpertation and application of the code requirements.

    In the scenario you described you may be better off running a complete seperate circuit from the breaker,and "spare" the existing circuit to the electric range for future reuse. If the breaker panel is not in your shop area, consider placing a subpanel off the main panel breaker to assist you in having more flexibility meeting the line of sight disconnect requirements should that become an issue.
    If you passed one inspection already. You have a relationship established with the local inspector. Ask the inspector what the "best way" to do it would be, and what would they be looking for on the inspection.

  5. #5
    I just checked on this. You can absolutely run more than one 240 receptacle on one breaker. The issue is the wire might need to be big enough to accommodate both receptacles being used simulataneously, something we home hobbyists don't tend to do, and our argument we use when we push code. I just finished my rough in, 3 240 circuits, one dedicated to air conditioner/heat pump (code requires dedicated), and two 240 receptacle circuits, one with two receptacle and one with three. Used the bigger wire, so I could use them simulaneously, but keeping breakers at 20A for now, to discourage that (since my feed is only 50A)Ray Knight

  6. #6
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    I have two 240v circuits in my shop, each with multiple outlets. My logic being that I am only one person and can only run one machine at a time. Having said that, I had a friend over a couple of weeks ago and we were running my Griz 8" jointer and Unisaw at the same time off the same circuit and I didn't even think about it until later. No problem whatsoever.

  7. #7
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    I'm running two outlets off each 220 off each 220 breaker in my shop.
    Where did I put that tape measure...

  8. I think Rob addressed this situation the best. Because this circuit is probably a 50-amp circuit, you will need to step it down to more reasonable size. You cannot install any other size outlet on a 50-amp circuit besides 40-amp or 50-amp, and these can be very expensive.

    Install the 50-amp subpanel and then you can run your circuits how ever you choose down in the shop.

  9. #9
    I just looked the situation over.

    The circuit going to my stove is on a 40-amp breaker and uses 8/3 with ground.

    Does this change anybody's thinking?

  10. I have no idea what your local electrical code may require but where I live, a plug is required for an electric stove, even if you have a gas stove. This means that you should check local rules before reusing the wire for the stove plug.


    Keith

  11. #11
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    Quote Originally Posted by Keith Carscadden View Post
    I have no idea what your local electrical code may require but where I live, a plug is required for an electric stove, even if you have a gas stove. This means that you should check local rules before reusing the wire for the stove plug.


    Keith
    Not sure about that one Keith. 210.52 doesn't have anything addressing a "requirement" for the stove. Only the requirements for the dedicated appliances and service with reference to 410. Individual local reg's for a CO could require it. I don't know though.
    I have a gas stove and no electric wired for an electric stove. My house was built to code in '81 though.

    I would still leave it there though, as I recommended. It would only be more expensive to re-install it at a later date.

  12. #12
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    I have two 220 volt circuits in my shop with 2 tools on each circuit. Each circuit has a junction box with two DPST open power relays and a 3 position switch (closed/open/closed). I have a band saw and planer on one circuit and a jointer and tablesaw on the other circuit. I can only run one machine at a time on each circuit due to the 3 position switch. The switch allows only one machine to receive power at a time, therefore no way to overload the circuit. At the end of the day I turn both switches to the center/off position and the machines have no power at the machine switches for unsupervised hands or unauthorized users to turn on.

    Roy Hill

  13. #13
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    Quote Originally Posted by Ray Knight View Post
    ... The issue is the wire might need to be big enough to accommodate both receptacles being used simulataneously...
    Any particular idea as to why this might be a requirement and, more to the point, how would it be implemented. Seems like there are some inherent contradictions in that requirement as stated.

    Say you have 3 20 amp outlets on the circuit. Simultaneous use could draw current up to 60 amps. Therefore you would need wire with a 60 amp capacity. But without a 60 amp breaker, you couldn't use the 3 outlets simultaneously at their full capacity. So, adding a 60 amp breaker makes it a 60 amp circuit. But now you have 20 amp outlets on a 60 amp circuit....? So, increase the receptacles to 60 amp capacity. Now you're looking a a possible simultaneous draw of up to 180 amps ....?

    There's got to be more to it than just what you stated because it seems to me that way lies madness.
    Tom Veatch
    Wichita, KS
    USA

  14. #14
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    Quote Originally Posted by Tom Veatch View Post
    Any particular idea as to why this might be a requirement and, more to the point, how would it be implemented. Seems like there are some inherent contradictions in that requirement as stated.

    Say you have 3 20 amp outlets on the circuit. Simultaneous use could draw current up to 60 amps. Therefore you would need wire with a 60 amp capacity. But without a 60 amp breaker, you couldn't use the 3 outlets simultaneously at their full capacity. So, adding a 60 amp breaker makes it a 60 amp circuit. But now you have 20 amp outlets on a 60 amp circuit....? So, increase the receptacles to 60 amp capacity. Now you're looking a a possible simultaneous draw of up to 180 amps ....?

    There's got to be more to it than just what you stated because it seems to me that way lies madness.
    There are two things that need protection on a motor circuit. Whether there is a single motor, or multiple motors.
    The motor(s) needs to be protected. This is accomplished by determining the correct size wiring to carry the current.
    The wires, or conductors, or branch circuit need to be protected. These are protected by selecting the correct breaker size.
    The particular section of the NEC that deals with motors is Article 430. At the beginning of article 430 there is a flow diagram that breaks down the article into the parts and the sections of the code that apply to each part, and the reference to the correct article, not contained in 430, that apply.

    NEC 430.24 addresses multiple motors and branch circuit sizing requirements;
    125% of the FLC of the largest motor plus the sum of FLC of the other motors . to determine branch circuit sizing and breaker protection.
    My copy of the 2005 code is at work, so I'm kinda running off memory right now. Dangerous,I know.
    If someone has an NEC copy, perhaps they can work through Article 430 to answer the question more completely.
    Last edited by Mike Cutler; 11-24-2007 at 10:22 PM.

  15. #15
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    Quote Originally Posted by Mike Cutler View Post
    There are two things that need protection on a motor circuit. Whether there is a single motor, or multiple motors.
    The motor(s) needs to be protected. This is accomplished by determining the correct size wiring to carry the current.
    The wires, or conductors, or branch circuit need to be protected. These are protected by selecting the correct breaker size.
    The particular section of the NEC that deals with motors is Article 430. At the beginning of article 430 there is a flow diagram that breaks down the article into the parts and the sections of the code that apply to each part, and the reference to the correct article, not contained in 430, that apply.

    NEC 430.24 addresses multiple motors and branch circuit sizing requirements;
    125% of the FLC of the largest motor plus the sum of FLC of the other motors . to determine branch circuit sizing and breaker protection.
    My copy of the 2005 code is at work, so I'm kinda running off memory right now. Dangerous,I know.
    If someone has an NEC copy, perhaps they can work through Article 430 to answer the question more completely.
    Mike,

    I generally agree with what you posted, but there is another factor with motors - overload protection for the motors. To run multiple motors on the same circuit, one would need to ensure that the individual motors have appropriate overload protection. The circuit breaker protecting the wiring could well be too large to protect the motor. In that case, a separate overload is required to protect individual motors.

    Rob

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