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  • 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.

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  • 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?

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  • 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.

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  • 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.

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  • 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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  • harcosparky
    replied
    Originally posted by burninbriar View Post
    Once the equipment ground is as close to the transformer as it can get, it is bonded to the neutral so it also has a path to the transformer center tap, this is because the center tap of the transformer is the only suitable ground to trip a breaker. To understand this you must accept the fact that neutral and ground are totally different. One is non currant carrying and the other carries current. I know some here don't believe that, but if it were not true, these rules would make no sense at all.
    What if the transformer has not " center tap "? Which transformer are you referring to?

    I don't recommend doing this because one could be severly injured.

    If you install a breaker and bring out a lead from that breaker and also a lead from each the GROUND and the NEUTRAL and short the GROUND to the hot from the breaker, the breaker will trip. Do the test again with the NEUTRAL and the breaker will trip. That breaker will trip when either the Neutral or Ground come into contact with the hot.

    Neutral wires MAY and CAN carry a current under normal operation in one circumstance, a load imbalance between the two hots. If the current load on Hot A is the same as on Hot B, Neutral will have no current. If there is a difference, that the current delta would be felt on the neutral. That is why the neural is insulated and the equipment grounding conductor is not.

    I still wonder what transformer and center tap you refer to? If there is a center tap, it would be on the transformer secondary and in looking at the schematic for say the MM210 there are no center taps on the transformer. It has one primary and two secondaries, one secondary is tapped for 24V and 29V. The second primary is TAPPED for use in selecting weld power level. This output feeds the rectifiers that provide weld current.

    Spectrum 375 has 2 primaries ( to allow for 120/240 VAC ) operation and 4 secondaries. Again no 'center taps'.

    Perhaps you are speaking to the power company transformer? If that is the case even at the power company transformer, earth ground ( equipment ground ) and neutral are bonded together.

    Let's look at it another way. If they are " different " why bond them together electrically inside the house?

    Once you bond Wire A to Wire B, what do they become electrically?

    All my comments are based on the assumption we are discussing SINGLE PHASE service for 120/124 VAC. In a multi-phase service it all changes.

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