Author Topic: Why Rapid Spark Occurs After Plugging Out Iron With EU Plug From Wall Outlet?  (Read 6288 times)

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Offline Boris_yo

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I have this 15 years old iron bought from country with EU power standards and have been using it occassionally in a current country with same power standards but today I have noticed that plugging it out from wall outlet produces silent rapid spark that I possibly failed to notice earlier. You can see it in the following video but due to variable slow frame rate it is noticeable in my 4th attempt in unplugging:



What I don't understand is that I have tried doing same with coffee maker that I have bought in EU country recently, but haven't seen any sparks at all. Let me add that EU plugs cannot be grounded in my country.
 

Offline mariush

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Perhaps something to do with the magnetic field in the transformer breaking down when you pull the plug?

Either way, that iron has a socket with GROUNDING for a good reason, use a proper socket with ground when you use that iron!
 

Online tom66

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Because you're suddenly interrupting the current. Doing that will create an arc. If you were able to move it a small distance from making contact (say, a few mm) you could potentially get a continuous arc.

It's the same reason switches crackle, and create radio interference, when they are switched on or off.

It's also why it's potentially risky to operate switches while there is a gas leak or flammable vapour present.
 

Offline Jeff1946

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When the last little bit of the plug is in contact there is enought current (iron uses about 5A I guess) to heat the metal to where it vaporizes, the ionized vapor gives color to the spark.  The first bit of sparking also heats the air which causes it to ionize and become a conductor.  This is why higher current fuses need to be designed not to keep conducting via an arc.
 

Offline vk6zgo

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Because you're suddenly interrupting the current. Doing that will create an arc. If you were able to move it a small distance from making contact (say, a few mm) you could potentially get a continuous arc.

It's the same reason switches crackle, and create radio interference, when they are switched on or off.

It's also why it's potentially risky to operate switches while there is a gas leak or flammable vapour present.
The arc would extinguish at the first zero crossing of the AC waveform.
With DC,--yes you could get a continuous arc.
 

Offline Boris_yo

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Because you're suddenly interrupting the current.

Interesting but let me remind once again that coffee maker was turned on as well when I unplugged it and though I was interrupting current, there were no sparks.
 

Online Psi

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Irons require a lot of power, maybe the full 2.4kW. I doubt your coffee maker uses that.
You'll get a small spark when you make/brake any high energy circuit.

In the case of an inductive load you have the back emf as well.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Kremmen

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The mere presence of voltage does not create an arc, current must flow as well. A coffee maker uses some tens of watts making the current too small for anything really to happen. An iron is another story as others have pointed out. The heater element in there could be slightly inductive as well, causing an additional kick but even so, the current should easily be enough to create a spark (not an arc really, that is something different). Whether you get a spark or not depends on if the thermostat is closed at the moment you pull the plug and, what exactly happens to be the phase angle of the line voltage at the instant of disconnection. At zero crossing (of either voltage or current if the load is inductive) you get nothing. And anyway whatever spark there is, will be extinguished at the next zero crossing.
So don't worry about it, it is not a problem. Just an interesting electrical phenomenon.
Nothing sings like a kilovolt.
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Online Simon

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the power packs for my modem and router make interesting sparks when plugged in and sometimes unpluged. it is to do with the point in the phase that the plug goes in and the inrush current to charge the capacitor in the SMPS adapter
 

Offline amyk

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You're essentially switching an inductive load (the transformer in the iron), and occasionally do it at the current peaks of the cycle where there's enough energy to make an arc form. The coffee maker's element is probably not very inductive at all, which is why it doesn't spark.
 

Offline Zero999

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Mains plugs aren't really designed to be connected/disconnected under load. Ideally, the power should be turned off before plugging/unplugging the device.
 

Offline Kremmen

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A vanilla iron won't have a transformer so that can't be the reason, although you are right as far as inductive load causing arcing is concerned.
Nothing sings like a kilovolt.
Dr W. Bishop
 

Offline nixxon

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Does it spark when you unplug the iron while it is really hot and has reached the selected temperature? (this is while the thermostat has switched the heater element off)
 

Offline G7PSK

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If the arc is hot enough it will reignite after the zero crossing, that,s why you can weld with AC. Is there a small capacitor in the iron that has failed as that will cause arcing if there was none previously. You can make just about anything arc though if you pull the plug live slowly enough.
 

Offline Jere

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If the heating element in the iron is wire wound resistor. Wire wound resistors have also some inductance and that's why you get spark. Coffee maker may have some other type of resistor that does not have parasitic inductance.
 

Offline T4P

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I thought most consumer heating elements were made from NiCr?
 

Offline IanB

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If the heating element in the iron is wire wound resistor. Wire wound resistors have also some inductance and that's why you get spark.

It's nothing to do with inductive components in the device under test. Simply interrupting a circuit, any circuit, produces a spark. When I was a child I discovered that connecting and disconnecting a small torch bulb and a battery produced a spark. Try it yourself and see.
I'm not an EE--what am I doing here?
 

Offline krish2487

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The type of load is immaterial as far as arcing during plugging and unplugging is concerned.

It is pretty much the same reason as that of high voltage insulation slots given on pcbs.

While the phenomenon itself does not have anything to do with the load current, it is more noticeable under large loads.
i.e the load current is not a cause, it only makes it stronger for observation. case in point ( say a geyser vs a coffee maker)

Both are inductive loads but the phenomenon is more easily noticeable with a geyser.
(You can even observe the arcing for the geyser while switching it on-off not just plugging it in or unplugging)

when un plugging, you are at a point where the distance between the plug and socket is small enough that the potential difference between both is large enough and the distance between the conductors is small enough to ionize the air between the conductors and hence not requiring a physical metal conductor to carry current.

Notice that this phenomenon is 'more' easily noticeable while unplugging and not so frequently while plugging in. This is because while unplugging the device the mains is already applied to the device during the process of unplugging the sparking phenomenon is noticeable.

while plugging in the device, since the device is not powered on, there is no,hmm lets say initiative, for the conductors to arc. however if even of the prongs (mains / neutral) makes a contact then the other shall arc at a small enough distance.
« Last Edit: October 24, 2012, 09:14:07 am by krish2487 »
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and we are this stupid
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