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Does this strange coil really consume 1700Amps?

  1. Aug 11, 2012 #1
    Hi,

    I have seen a couple of videos on youtube where people simply hook a homemade simple coil of copper wire directly to the House 120v AC. One of them for example hooked a close wound aircore coil with 14 gage wire(01.6mm), 6"(152mm)diameter, about 1" length and 30 turns only.. and viola the coil starts and vibrates from the 60hz for a couple of seconds before the insulation is melted!! That is eating my mind. How is that even possible without trigging the circuit-breaker instantly upon power-connection! circuit-breaker tripping limit is around 30A max right?

    I wanted therefore to find out the amp draw and found out that the total AC resistance, impedance is 0.068 ohms!!!!!! that would mean a very high amp draw around 1700A from the coil, but that cant be real since the circuit-breaker should trip IMMIDEATLEY upon powering the coil .. or am I wrong? please enlighten me.


    To calculate impedance i.e. total resistance of the AC coil we need to find inductance which from this online calculator http://www.66pacific.com/calculators/coil_calc.aspx is: 178 uH.

    The AC Impedance of the coil is:|Z|=2πfL= 2*3.14*60*0.000178H=0.068ohms


    With 0.07Ohms the current is 120v/0.07= 1700amps!!!!

    So , is my calculation for the total AC resistance way wrong here?
    Or is something limiting the current flow to the coil? but how?

    Thanks for your time and help
     
  2. jcsd
  3. Aug 11, 2012 #2
    Can you post the link to this video?
     
  4. Aug 11, 2012 #3
    there are many such videos... with coils connected directly to the outlet..

    http://www.youtube.com/watch?v=muJqtz-ECfg&feature=plcp




    There are many videos of his and like this, this is not the point. The point is how the coils with low impedance connected directly to the 120v Ac outlet DO not trip the circuit-breaker immediately!
     
    Last edited by a moderator: Sep 25, 2014
  5. Aug 11, 2012 #4
    Most outlets are 15 amps with utility outlets or garage outlets sometimes 20amp breakers. But I don't think we can make the generalization because I've seen people replace breakers with whatever size they find, not really understanding their purpose.

    As for them popping right away, again that depends on the condition of the breaker and the type of breaker. Most breakers can handle a momentary over amperage, even significant over amperages.
     
  6. Aug 11, 2012 #5

    So you mean that his circuit breaker could handle 1700A momentary? I get that.
    I never ahd circuit-breakers, only have fuses in my house so as fast as I get over 16A they break. However could it be that the "circuit-breaker" "limits the current" to some value like 30A without breaking the circuit?? You understand what I mean?.. i.e. the circuit breaker maintains an output of 30A maximum regardless of your appliance that may want to pull 100A???
     
  7. Aug 11, 2012 #6
    I don't know how much they can handle for how long, but they don't limit as you asked. That would be nice. Check this out http://en.m.wikipedia.org/wiki/Maximum_prospective_short_circuit_current. Sounds like 1700 might be possible for a "moment"

    Current code requires arc fault breakers in garage and I think bedrooms. Those break much quicker if the equipment sparks. So it depends on breaker. Even fuses depend. Slow burn fuses for say HVAC that allows momentary high current draws to start the heat pump.
     
  8. Aug 11, 2012 #7
    I read that too, but got a little confused: considering the "..order of a few thousand amperes for a standard domestic mains.." are they talking about the point at which the breaker trips, right? So if by "several thousand amperes" they mean that the breaker trips at 4000A, pulling 1700A should work for a couple of seconds.. am I understanding this correctly?
     
  9. Aug 11, 2012 #8
    I'm not sure. They did say "main" so they could be talking about the 200amp main breaker typical in a small size residential home. How much the 15 or 20 amp breaker can take when working properly is a good question, but im guessing it is a load vs. time function. Someone who can confirm your formula may know. I did get a kick out of listening to those "scientists" in the video. :).
     
  10. Aug 11, 2012 #9
    if the house´s circuit. breaker can take a couple of thousand of amps , than that can explain how his coil could be fed 1700 amps for a couple of seconds instead of instantly tripping the breaking. IF thats not the case... well..., I will be very confused.... anyone that can confirm or have another take on this? like my amp calculations are wrong? but lets assume the total impedance is actually higher because of other factors like the length of the connecting wire etc... still the amp draw would be 400A minimum?? mainly because of the low turn number(30) and low frequency (60hz)
     
  11. Aug 11, 2012 #10

    nsaspook

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    http://ecmweb.com/content/beware-simplistic-fault-current-calculations
    http://ecmweb.com/content/short-circuit-calculation-methods

    Some standard fault-current calculations. That air coil is still almost a bolt short at 60hz so there might be 1000 plus amps of current flow. The word "consume" means little here as most of energy across the coil will be in the magnetic field and very little energy will be in the electric field (assuming normal household wiring) so only a small amount of power will be actually "consumed" by the coil compared to a normal load at those current levels.

    Over-current protection devices. http://www.ieee.li/pdf/viewgraphs/overcurrent_protectors.pdf
     
    Last edited: Aug 11, 2012
  12. Aug 11, 2012 #11

    The word consume is not fitting as you said. Im sorry but I think Im however getting more confused so lets see if I interpreted what you said correctly: when you said only a small amount of power will be actually consumed, does this still mean that the breaker is STILL letting 1000+ amps of current flow out?
     
  13. Aug 11, 2012 #12
    @nsaspook - I would love to understand what you are saying here. This is a conceptual gap I have not yet bridged. Although not all electrical energy, isn't the sum of magnetic, electrical and heat energy what is being measured by the breaker. (not really measured but you know what I mean)

    So the breaker is allowing 1000 amps to pass and the coil then distributes that energy in various ways to total the 1000 amps?

    thanks
     
  14. Aug 11, 2012 #13

    nsaspook

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    Power is the product of current and voltage. For example if we measured 0.5 volts across that coil at 1000A that would be 500 watts of power vs 115,000 Watts at 115 volts. So the actual power is dependant on several things like the total circuit impedance from the line transformer, the voltage at the transformer during that load and what percentage of the total circuit impedance the coil is.

    Knowing the resistance of the coil and the current will give you the copper loss.
    http://upload.wikimedia.org/wikipedia/en/math/1/3/1/131cfd55bc0448d31576f79e7f0ae4b8.png
     
  15. Aug 11, 2012 #14
    nsaspook, considering all the losses, lets just assume that the coils you said consumed less than 1000A, lets assume the coil consumed 300A. Is the amount of amps coming out from the breaker still 1000A in this case?
     
    Last edited: Aug 11, 2012
  16. Aug 11, 2012 #15
    But if that coil draws 1000amps, isn't it accurate to say 1000amps were consumed as heat since its being shorted out?
     
  17. Aug 11, 2012 #16
    Yes, exactly what I think , whether it goes away as heat, vibration that is really another issue(?) For instance if a very inefficient engine draws 1000Amps i..e drains a battery very fast but yet turns at 3rpm with poor torque.. it still consumed/took 1000amps.. so is that what you are talking about, nsaspook ? or are you saying that the actual amps coming from the breaker output are also decreased??
     
  18. Aug 11, 2012 #17
    Or are we saying that on a short burst the coil is unable to translate all available power (that formulas dictate) in such a short period of time, which means the load at circuit breaker didn't ramp up to max calculated value? Is there a delay like that? I would think so as the coil heats up so does resistance right?
     
  19. Aug 11, 2012 #18

    nsaspook

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    The main "conceptual gap" is that people "incorrectly" think that current means electrical energy. In a household with nominal line voltage "current" can be a proxy for power as we normally think of loads with constant voltage. How much energy that 1000 amps factors to at the breaker depends on the voltage and that voltage is unlikely to at nominal line voltage for more that a microsecond at 1000 amps when feed from a normal residential utility feed.
     
  20. Aug 11, 2012 #19

    nsaspook

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    If the breaker is a normal Thermal Magnetic the reaction to a line short fault should be extremely fast because the electromagnet can interrupt the circuit in milliseconds while the thermal section using the heating of a bimetallic strip might take several seconds to trip with normal overload.

    This is what a 1000A short at real line voltage looks like. http://www.youtube.com/watch?v=sGeM7EHwmo0&playnext=1&list=PLBCD9678B59149A10&feature=results_video
     
  21. Aug 11, 2012 #20
    My original wondering is simple yet I couldnt find an answer: How do I know if my fuse/circuit-breaker wont break upon connecting a coil?, cuz thats what I want to do, I want to directly connect an aircore coil into the outlet, as countlessly many people have done w/o calculating and they didnt trip their circuit-breaker!!!.

    My circuit-fuse happens to be at 16A. So I obviously need to have enough resistance in the coil so it draws only 15A(high turn number, thin wire), thats it right? However if I connect a coil with very low impedance(similar to that guys coil) the fuse will break immediatley which brings me back to how did his coil manage to run at very low resistance which could alternatively be explained by the very short time maximum amp draw that assosiated with the circuit-breaker.

    So final question:

    What will happen when I plug a coil of the same dimensions into my outlet?
     
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