Does this strange coil really consume 1700Amps?

[leviterande]

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 can't 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

 

[Jony130]

Can you post the link to this video?

 

[leviterande]

Can you post the link to this video?

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!

 

[sday]

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.

 

[leviterande]

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.

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?

 

[sday]

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.

 

[leviterande]

I Check this out http://en.m.wikipedia.org/wiki/Maximum_prospective_short_circuit_current. Sounds like 1700 might be possible for a "moment"

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?

 

[sday]

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 I am 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. :).

 

[leviterande]

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 that's 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 let's 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)

 

[nsaspook]

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

 

[leviterande]

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

The word consume is not fitting as you said. I am sorry but I think I am however getting more confused so let's 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?

 

[sday]

@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

 

[nsaspook]

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

 

[leviterande]

nsaspook, considering all the losses, let's just assume that the coils you said consumed less than 1000A, let's assume the coil consumed 300A. Is the amount of amps coming out from the breaker still 1000A in this case?

 

[sday]

But if that coil draws 1000amps, isn't it accurate to say 1000amps were consumed as heat since its being shorted out?

 

[leviterande]

But if that coil draws 1000amps, isn't it accurate to say 1000amps were consumed as heat since its being shorted out?

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??

 

[sday]

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?

 

[nsaspook]

@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

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.

 

[nsaspook]

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?

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

 

[leviterande]

My original wondering is simple yet I couldn't find an answer: How do I know if my fuse/circuit-breaker won't break upon connecting a coil?, because that's 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), that's 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?

 

[nsaspook]

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

Don't.

 

[leviterande]

Don't.

I know but I wanted to know what will happen, will it break the fuse, yes very likely but how wasnt the circuit broken when he connected the coils of his?

 

[jim hardy]

for your original question, one has to appreciate that the impedances of:
the wires coming from the transformer into the house,
the kwh meter outside
the circuit breakers in the house panel,
the wires running from the panel through the walls to the outlet itself
and the cord that connects the fellow's coil to the outlet

all help limit the current.
Probably they all add to around an ohm, so he had more like a hundred amps through his coil.
The energy is not all dissipated in the coil it gets distributed amongst the things mentioned above.

Perhaps the transformer on your power pole is itself capable of delivering 1700 amps into a short right at its output terminals (probably that's about all it could do) , but you get less as you move farther away from it.

Most household circuit breakers are thermal devices which take a finite amount of time to trip.

Typical thermal breaker time at 5X rating is a second or two.

Here's a chart
http://www.geindustrial.com/publibrary/checkout/GES-6201?TNR=Time Current Curves|GES-6201|generic

from this link
http://www.geindustrial.com/publist/Dispatcher?REQUEST=TIMECURRENTCURVE


old jim

 

[leviterande]

for your original question, one has to appreciate that the impedances of:
the wires coming from the transformer into the house,
the kwh meter outside
the circuit breakers in the house panel,
the wires running from the panel through the walls to the outlet itself
and the cord that connects the fellow's coil to the outlet

all help limit the current.
Probably they all add to around an ohm, so he had more like a hundred amps through his coil.
The energy is not all dissipated in the coil it gets distributed amongst the things mentioned above.

Perhaps the transformer on your power pole is itself capable of delivering 1700 amps into a short right at its output terminals (probably that's about all it could do) , but you get less as you move farther away from it.

Most household circuit breakers are thermal devices which take a finite amount of time to trip.

Typical thermal breaker time at 5X rating is a second or two.

Here's a chart
http://www.geindustrial.com/publibrary/checkout/GES-6201?TNR=Time Current Curves|GES-6201|generic

from this link
http://www.geindustrial.com/publist/Dispatcher?REQUEST=TIMECURRENTCURVE


old jim

Thanx for the reply, so what you are saying is:

1- that his circuit breaker won't trip immediately but in 1-2 seconds.. in any case the circuit breaker will eventually trip in the end after a second or so, is this correct?

2-However if his circuit breaker had a 120A rating, the coil with the above dimensions would never trip his breaker, am I correct?

 

[jim hardy]

1- that his circuit breaker won't trip immediately but in 1-2 seconds..

correct. did you see the GE breaker trip curve? current horizontal, time vertical.

2-However if his circuit breaker had a 120A rating, the coil with the above dimensions would never trip his breaker, am I correct?

let's think for a second...
if there were a 120 amp breaker in the panel, the electricians would have put in much larger wires to the outlet
and it would be a very different looking outlet
and a 120 amp breaker has less internal resistance than a 15 amp breaker
so the interconnecting wires would not be very much help limiting current

so there would have been a lot more current into the little coil
and it would have certainly exploded in a substantial fireball,
showering him with molten wire and setting his clothes afire,
probably disfiguring him permanently.
Maybe all that before the breaker eventually tripped .

That's why house wiring is the way it is - to keep fools from hurting themselves.
Copper vapor expands according to the same gas law as dynamite vapor.

It is difficult to get enough energy out of a household outlet to make a big explosion
thank goodness.
and that's on purpose

electricity has no remorse
dont play with the stuff.


EDIT NSAspook's video shows the size of conductors necessary to get 1000 amps. And the fireball from the let-through energy of whatever protective device they used...

 

[leviterande]

AHa I think I see, so his circuit-breaker never let even 100A to get out, i.e. " as the current climbed beyond 15A and towards 100A, temperature increased and took around 1-2 seconds to trip the breaker"?

 

[jim hardy]

AHa I think I see, so his circuit-breaker never let even 100A to get out, i.e. " as the current climbed beyond 15A and towards 100A, temperature increased and took around 1-2 seconds to trip the breaker"?

i would say that's probably right.

he'd have a race between the breaker tripping and his wire melting
if you saw no flash and smoke the breaker won the race.

it's really bad judgement to "play chicken" against a circuit breaker.

old jim

 

[Averagesupernova]

it's really bad judgement to "play chicken" against a circuit breaker.

old jim

Oh that is just golden. You should make that your signature. It's just so damn funny that someone actually needs to post it. But, apparently it needed to be posted.

 

[mdjensen22]

OP - Something to think about:
circuit breakers are specifically designed to have a 'time lag' so that they open on fault conditions but yet don't trip every time the washing machine, refrigerator, lights, etc. turn on.

Anything with an inductive load (incandescent bulbs, motors, etc) will have an inrush current that can be several times the nominal current. If it weren't for this latency in the breaker, the breakers would constantly be tripping.

 

[leviterande]

OP - Something to think about:
circuit breakers are specifically designed to have a 'time lag' so that they open on fault conditions but yet don't trip every time the washing machine, refrigerator, lights, etc. turn on.

Anything with an inductive load (incandescent bulbs, motors, etc) will have an inrush current that can be several times the nominal current. If it weren't for this latency in the breaker, the breakers would constantly be tripping.

Aha that really makes sense, its like the breaker is "controlling the incoming load" first.

 

[jim hardy]

Thanks Nova

if i ever figure out how to add a signature i'll do that...