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Old 05-24-2012, 12:37 AM   #1
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Default Outlet sparks - electrical question

Why does my outlet spark when I plug my laptop charger or tv plug in?

Does it cause damage to whatever hardware is being plugged in?


Thanks.

edit - *not sure why I asked this question here instead of google search*

Last edited by kenzo42; 05-24-2012 at 03:32 AM.
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Old 05-24-2012, 03:30 AM   #2
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My laptop power supply does this fairly often. Apparently there is quite an inrush currrent.

Others have already said why this happens and how to avoid it, but what hasn't been mentioned is the why of it.

Every time you see sparks when you plug something in, an arc of electricity is pitting the contact surfaces of the plug and the outlet. Over time, these pits accumulate and reduce the contact area that current has to flow through between the outlet and the appliance. By reducing the contact area, the resistance of the junction is increased and can lead to problems including fires in your electrical system. Not a good thing.

For this reason, you should NEVER plug anything into the wall while it is turned on. This is especially true of high current appliances like vacuum cleaners, irons, toasters, hair dryers, etc. Not only do they draw a lot of amperage, they are also likely to be plugged in the same place every tim
e, which makes the situation that much worse.
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Old 05-24-2012, 04:56 AM   #3
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Doesn't help that you don't have a 3 pin plug over there.

The UK has 3 pin plugs, with the Earth being the first and last to make contact, no sparks.
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Old 05-24-2012, 04:48 PM   #4
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Originally Posted by richyvrlimited View Post
Doesn't help that you don't have a 3 pin plug over there.
?

The power plug standards in the US are electrically quite similar to those in mainland Europe. We have two primary standards; the NEMA 5 (three wire, earthing) and NEMA 1 (two wire, non-earthing.) One primary difference is that both the two-wire and three-wire receptacles here are polarized (as are the majority of the plugs) so that the correct orientation of the hot wire and the neutral wire can be preserved.




Sparking from inrush current, however, has nothing at all to do with whether the appliance is equipped with a two pin or three pin plug. Inrush current flows only between the hot and neutral conductors, and never flows through the earth pin except in the case of a fault.

I would suspect that part of the reason why you don't see this in the UK is that the pins on your power plugs don't actually make electrical contact with the contacts in the receptacle until they have been inserted a considerable distance, whereas most receptacles in the states make contract with the pin on the plug during the first few mm of insertion. This, of course, leads to the potentially unsafe state of having a plug partially inserted and the energized pins still exposed, which is something the UK's BS 1363 standard avoids by sheathing the pins in plastic for all but the last few mm at the tip.
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Old 05-24-2012, 07:27 PM   #5
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Stand corrected, cheers Joe.

Had no idea the US had 3 pin plugs too tho!
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Old 05-24-2012, 08:13 PM   #6
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Originally Posted by richyvrlimited View Post
Had no idea the US had 3 pin plugs too tho!
It's a fairly recent standard- prior to the early 1970s, most homes only had two-pin receptacles, and only large appliances were earthed.

These days, all receptacles are required to be of the 3-pin type, although 2-pin cords are still widely used on a lot of devices. Only one type of outlet is required, and will accommodate either a 2-pin or a 3-pin plug (like the round Europlug socket). TV sets, lamps, laptop chargers, most small devices like that only use a two-pin plug, and rely on electrical insulation for safety.

Pretty much anything with a metal chassis over here uses a 3-wire plug. Computers, refrigerators, clothes-washers, automotive battery chargers, drill presses, table saws, etc.

Ironically, while a lot of small power tools in the 70s and 80s used 3-wire plugs (because they had metal chassis), most newer power tools with plastic bodies have gone back to the 2-wire standard as well.


We don't typically have switches on our outlets, nor are the plugs commonly fused. The fusing in particular is one thing I've always liked about the UK standard. (Of course, you guys also have ring main circuits, which is one of the most perplexing wiring standards I have ever seen.)
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Old 05-25-2012, 04:59 AM   #7
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What don't you like about ring mains? I thought it was a safety thing?

An awful lot of low powered stuff here are technically 2 pin now I think about it. the Earth is just a plastic pin to open the flaps for netural and live.
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Old 05-25-2012, 08:53 AM   #8
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I have never understood why the US standard allows power to flow through exposed contacts. The UK thing seems like a much better idea.
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Old 05-25-2012, 02:40 PM   #9
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What don't you like about ring mains? I thought it was a safety thing?
Well, I'm no expert in UK mains wiring. My understanding is that it was originally implemented as a way to save copper after the war, as it theoretically reduces the diameter of wire required to service a given circuit, by spreading the load across the ring in both directions. The downside is that the rings tend to be fused for the total current-carrying capacity of the combined ring, rather than for the current capacity of any one individual conductor.

They obviously work, they're just much more complex to design and test properly, and lend themselves towards a number of potentially interesting fault conditions (eg, a single break in the ring will allow all outlets to continue operating, but leaves the ring unbalanced and potentially overloaded on one side.)

We lazy Americans prefer radial circuits simply because they're easier to deal with.



Quote:
Originally Posted by richyvrlimited View Post
An awful lot of low powered stuff here are technically 2 pin now I think about it. the Earth is just a plastic pin to open the flaps for netural and live.
Yeah, that's another think that the UK (as well as the Germans / French / Danish / etc) really got right. The US electrical code only started requiring shuttered receptacles a few years ago, and only in new construction. So the vast majority of the receptacles in the states, both in existing homes and for sale at the hardware stores, are still completely open and unprotected.



Quote:
Originally Posted by skidude View Post
I have never understood why the US standard allows power to flow through exposed contacts. The UK thing seems like a much better idea.
Yeah, sometimes I'm amazed at how poor our domestic wiring standards are as compared to most of the rest of the world. Even the trivial little stuff, like how conductors are tied together inside J-boxes and connected to receptacles. Compared to most European countries, our household wiring is just... ugly.

A lot of it is just inertia. In the US, there has always been a strong emphasis placed on interchangeability and backwards-compatibility. We've been using essentially the same standard for electrical plugs and receptacles since at least the late 1920s, and every new style of receptacle has been compatible with every previous style of plug. You could literally take a lamp or a vacuum cleaner made in 1935 and plug it into an electrical outlet in a house built in 2012, and it would work just fine.

By contrast, the UK (as well as many other European nations) have gone through many different and incompatible plug standards over the years. In Britian, they've had round-pin plugs in two different sizes in both earthed and unearthed versions which were incompatible with one another (a total of four different standards there), square-pin plugs, square-pin plugs with all the pins rotated 90, plugs with flat pins except for a round earth pin, two-pin plugs for electric shavers, and even a plug which was specific to electric wall-clocks and incompatible with everything else.

As a result of all of this turmoil, these countries have had the opportunity to make significant improvements to the connector standards as time has progressed. In the US, we've never really had a radical overhaul of the system. On the plus side, we have nearly universal standardization of plugs and receptacles across the country, and also across time. On the minus side, we're still using the same basic technology from a hundred years ago.
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