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  • neophyte
    started a topic Shop Electrical

    Shop Electrical

    Hey guys,
    I was wondering if anyone out there had a copy of the NEC. I have an inspector telling me I can't run a 20 amp 240 air compressor circuit on 12-2 and reidentify the white as black. He stated that I needed to run 12-3. If my internet search on the Pass & Seymour web was correct, NEC Sec 200-7 covers this but they do not go into enough detail on the website regarding this issue.

    I know the inspector is always right!!........ but in this case I am pretty sure that he is wrong and him being wrong means more money out the door on a roll of 12-3.

    Wiring in the new shop and garage is complete. I ran 6-3 for the welder and 8-3 for the RV hookup. Have a total of 58 electrical openings for 960 sqr ft. Should be able to find an outlet or a light at most every turn. I plan on throwing in a mess of insulation tomorrow.

    Your help is appreciated...

  • drewworm
    replied
    I don't see any reason to second guess it if you are looking at the book, but for the minimal extra cost to do it with correct color wire and #10 it's worth it.

    Leave a comment:


  • neophyte
    replied
    Originally posted by drewworm View Post
    I'd double check an electrical calculator because I'm thinking a 240v compressor would require more power than can be carried safely on #12 or even #10.
    My motor is rated at 15 amps 208-230V. My run is about 60 feet of 12-3 coming off a 20 amp breaker.

    My book states that I can run a 3hp-230-V motor at 17 amps up to 65 feet on #12 so long as I don't use 60C rated wire. Am I missing something here?

    Leave a comment:


  • Sberry
    replied
    Originally posted by drewworm View Post
    I'd double check an electrical calculator because I'm thinking a 240v compressor would require more power than can be carried safely on #12 or even #10.
    This certainly would depend on the motor size, but the rule is you need a wire with 125% of the ampacity of the run current of the motor and in most cases it could be breakered up to a point to prevent tripps. Some equipment has listed breaker sizes, owners manuals have the electrical requirements. Its one of the reasons to use 240, you can reduce the wire size. 10 will run modern 5 hp, 30A, when you get to 7 1/2 it will need 8 wire and a larger breaker. That is all assuming we have singlle circuit to a motor which would be normal in most residental or small shops. Some of these comps can run from a 12 wire, ones that have a run current of 15A and can be breakered at 30. Personally I would likely put a 10 wire in if I could but it could certainly be a legal install with less depending on the connected equipment. In my mind, say if a customer asked for a common compressor circuit in a small garage it would be a 10/30

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  • drewworm
    replied
    #12 wire is cheap. I mean cheap! Don't start whining until you have to run #4. Even then, #4 with any color insulator besides black is even more money. That's when you break out the colored electrical tape. Here's the deal: Any color besides green or white can be used for power. If you have a big shop and lots of conduits running around this helps you identify wires when you are all the way across the shop from the electrical panel. White is typically associated with common on a 110 circuit. Seriously, if you want to keep from electricuting yourself 5 years after you install this circuit and forget the white was not common, then use red and black wire (third wire is ground). Spend the extra 10 bucks, keep the inspector off your back, and keep yourself alive. While you are at it, step up to #10 - wires lose voltage over distance, with temperature, and startup requirements on electrical motors are different from running requirments. There is much more draw at startup. When you decide that compressor doesn't meet your needs you already have the power for a bigger one. I'd double check an electrical calculator because I'm thinking a 240v compressor would require more power than can be carried safely on #12 or even #10.

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  • harcosparky
    replied
    Originally posted by Sberry View Post
    No, there will be no local code variations on this aspect of grounding systems and bonding, none, nada, period.
    With 3 wire feeds the second panel must be bonded, with 4 its isolated.
    Actually my reference was directed more to the INSPECTOR and not so much the code. Inspector can be a real pain.

    And I did say with 3 wire you bond, with 4 you don't because the bonding was done at the main panel.

    Leave a comment:


  • Sberry
    replied
    Originally posted by harcosparky View Post
    Is the 3 wire feed from your house buried or is ot overhead? There seem to be several variables on this. Look at the URL I posted they show several scenarios. Even one taking into consideration if you have water running from the house to the garage/shop. Some have the Gnd/Neu tied together, others not.

    That seems to make a difference. Once again though, it goes back to what the Local Code/Inspector says.
    No, there will be no local code variations on this aspect of grounding systems and bonding, none, nada, period.
    With 3 wire feeds the second panel must be bonded, with 4 its isolated.

    Leave a comment:


  • Sberry
    replied
    "Basically IF you have an " equipment grounding " conductor run from the house to the garage/shop in the main feed 'marrying' the neutral and ground in the garage/shop panel is not necessary. It's already done in the main panel at the house."
    Not only is it not "necessary" but prohibited, and its not "already done" at the house, thats the ONLY place it should be done, already done implies that this bond can be done somewhere else.

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  • Sberry
    replied
    You could measure voltage drop in the wire, there will be some difference proportional to resistance of the wire? Correct or do I need to go to bed?

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  • burninbriar
    replied
    Originally posted by Sober_Pollock View Post
    O.K. Now.....

    Voltage is a measurement of potential between TWO points.....

    In your question you ask what the voltage would be on the neutral conductor.....

    In reference to what?.....

    The voltage between the neutral and one of the hots would be 120 volts.....

    The voltage between the neutral and the safety ground would be 0 volts.....

    What are you asking?.....The voltage between Neutral and what?.....

    And, you do not have to interupt a circuit to measure voltage.....you do not have to introduce a break in a conductor to measure voltage between it and something else.....

    Are you asking about current?.....
    I believe he might be referring to something I said in an older thread a while back ago. I said if you turn on an appliance with a break in the neutral and have a volt meter bridging the break you will read the voltage thus proving that the neutral is a currant carrying conductor. As to how you can tell if a neutral wire is carrying currant at the time without having a break in it is a good question.

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  • Sober_Pollock
    replied
    ..........

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  • burninbriar
    replied
    You need to remember that its alternating currant, that is it go's from the coil side of the transformer the the ground side and back again, back and forth. An appliance does not know the difference between hot and neutral, you can turn a plug any way you want and the appliance works the same. The reason for the polarized plugs is so the switches are on the hot side and believe it or not, for the sake of safety with the incondessent light bulb. The polarized plugs keep the hot contact in the socket where it is least accessible. The reason you don't feel the energy on the neutral side is that it shares the same value as the ground we stand on. If you were standing on the transformer coils you could touch the hot (black) wires all day and it would not have any effect, they would share the same value as the surface that you're standing on. Touch the white wire and you get zapped, it would now essentially be the hot wire. Every thing would reversed as we know it as far as neutral and ground.
    AC is similar to DC in this respect. If you go to you're car you have a + and - side of the battery. Both cables carry electricity. If you have you're headlights on and remove the - terminal it will spark because its carrying currant, but if you put a volt meter from that wire to the frame of the car it will show 0 volts as long as the cable is connected to the battery. This does not mean there is no energy in that cable, its just that it shares the same value as the car frame. Now disconnect the - terminal and put you're volt meter between the cable and the battery and it show the energy. I hope this makes since because I'm about burned out.

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  • harcosparky
    replied
    Originally posted by Sober_Pollock View Post
    Under normal operating conditions, the neutral carries current and the safety ground does not.
    What would the voltage potential be on the neutral conductor under normal conditions with no breaks or interruptions in the neutral conductor?

    How could you measure it without introducing an interruption ( break ) in the neutral conductor?

    Leave a comment:


  • burninbriar
    replied
    The other advantage of not bonding the equipment ground and the neutral at the garage is that if you loose you're path to the center tap (pole transformer)between the buildings , youre garage will loose all power. If theyb are bonded at the garage, you're garage would be able to operate but the ability to trip a breaker would be diminished.
    The reason the whole grounding system does not become energized is that like water, electricity takes the easyest path. Once you're at the main service, the easyest path is back to the transformer.

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  • Sober_Pollock
    replied
    Re Center Tap

    ..........

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