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    Chandra1977's Avatar
    Chandra1977 Posts: 7, Reputation: 1
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    #1

    Aug 7, 2012, 08:34 PM
    Minimum ohm
    What is the minimum load resistance for AC 230v.
    ma0641's Avatar
    ma0641 Posts: 15,675, Reputation: 1012
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    #2

    Aug 7, 2012, 08:46 PM
    Not sure what you are asking. You need 2 factors to utilize Ohms law. 240VAC is meaningless. Ohms are dependent on wire gauge, distance, wire type. In short lengths, copper wire, 14 or 12 AWG, has almost no resistance .
    Chandra1977's Avatar
    Chandra1977 Posts: 7, Reputation: 1
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    #3

    Aug 7, 2012, 10:50 PM
    Minimum ohm
    Hi ma0641,  If phase and neutral cable touch each other will short circuit and trip the mcb... The Question, for exp. Motor winding is pure copper wire and give them 230v ac why don't trip.? What is the minimum resistance value, to don't short circuit when giving load..
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #4

    Aug 8, 2012, 02:48 AM
    The issue is not what is the minimum resistance, it is what is the amp trip rating of the protective device, either fuse or circuit breaker.

    While a motor may be just a coil of wire, it is a coil, and the great distance of wire in the coil offers the resistance to be a load.

    Why are you asking this question?
    Chandra1977's Avatar
    Chandra1977 Posts: 7, Reputation: 1
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    #5

    Aug 8, 2012, 03:44 AM
    Quote Originally Posted by tkrussell View Post
    The issue is not what is the minimum resistance, it is what is the amp trip rating of the protective device, either fuse or circuit breaker.

    While a motor may be just a coil of wire, it is a coil, and the great distance of wire in the coil offers the resistance to be a load.

    Why are you asking this question?
    Because my friend was confused when I connecte live and neutral wire to the cooker heating element.. He asked me, live and neutral touched together it's short... And you connect at peace of metal plate don't short? I answered him... Because the heating element have a resistant... Then he asked me... The above question. Please help me... Thks.
    tkrussell's Avatar
    tkrussell Posts: 9,659, Reputation: 725
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    #6

    Aug 8, 2012, 04:46 AM
    With a phase to phase or phase to neutral short, the resistance is very low, and will allow the currnet flow to be very high.

    This high current will cause a circuit breaker to trip, as the current will exceed its rating.

    Theroectically, if the short circuit current is 10,000 amps, I could have a 10,000 amp rated circuit breaker, and not trip it.

    Shorting live and neutral is virtually zero ohms, the only resistance is the of the wire. Assuming #12 copper wire solid (3.31 MM squared) has 1.93 ohms resistance per 1000 feet, or .00193 ohms per foot, or 6.34 ohms per kilometer, 00634 ohms per meter.

    Assuming the circuit is only a total of 1000 feet of #12 wire, and 100 volts, using Ohms Law,

    I=E/R
    I= 100 volts divide by 1.93 ohms
    I = 51.8 amps

    #12 wire should not have a fuse or circuit breaker larger than 20 amp rated. If only 1000 feet of # 12 on that breaker, shorted, the 20 amp CB would trip.

    Does this illustration help?
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