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basic electricity question


Dave Horne

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In a three connector wall plug we have hot, neutral, and ground.

 

If the plug can be inserted in the wall in two different ways, what difference does it make if the hot and neutral wires are reversed?

 

I'm shortening cables in my rack case just to make it more neat and I have to use 'special' connectors to plug into my (Furman) power conditioner. I now know how to correctly wire up the plugs but was wondering what difference it makes to reverse the hot and neutral.

No guitarists were harmed during the making of this message.

 

In general, harmonic complexity is inversely proportional to the ratio between chording and non-chording instruments.

 

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Dave, I'm not sure how your plugs are done over there, but here in the states out standard 120V AC outlets look like this:

 

http://www.hometheaterhifi.com/volume_6_3/images/grounded-ac-plug-diagram.gif

 

you'll notice the heighth difference between the "Hot" and "Neutral" prongs. If the male plug that plugs in here has prongs that are both the heighth of the "Hot" slot then it doesn't matter. For instance a desk lamp will have two prongs that are the same height and it doesn't matter which way it plugs in.

 

The reason the plugs are made like this is that some AC stuff has circuitry inside that needs that neutral to be on a specific side for fusing to work right, etc.

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Originally posted by Dave Horne:

In a three connector wall plug we have hot, neutral, and ground.

 

If the plug can be inserted in the wall in two different ways, what difference does it make if the hot and neutral wires are reversed?

 

I'm shortening cables in my rack case just to make it more neat and I have to use 'special' connectors to plug into my (Furman) power conditioner. I now know how to correctly wire up the plugs but was wondering what difference it makes to reverse the hot and neutral.

In theory, it shouldn't make any difference if they are reversed. Since this is AC, the "hot" and "neutral" switch polarity 50 or 60 times per second. However, neutral is supposed to be connected to ground at the fuse (breaker) box, so neutral is supposed to be "safe" to touch at the outlet. All electric devices are supposed to be designed with both sides isolated from any part of the outer metal case of the device, so again it shouldn't matter which way the plug goes in. Unfortunately, this means that the case is "floating" electrically, so 1) it is *not* grounded, and 2) it is possible, if a wire frays or something, that the hot lead could contact the case, creating a "hot" case situation. The lack of polarity also is problematic for the situation where one device is to be connected to another device - in designing such gear, one cannot assume that the polarity of each device will be the same.

 

Notice all the "shoulds" in the description above. Things can and do go wrong, so the third wire was added to explicitly ground the metal case of devices, and one prong was made slightly wider than the other, to impose a polarity when something is plugged in. Manufacturers can still use plugs without the third wire, and without a polarized plug, if they can design their device to guarantee that neither wire can ever touch the case, as in "double-insulated" power tools, or things with plastic cases.

 

Hope this helps.

 

- Bob

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Bob, thanks for the clear explanation - I now understand it.

 

Overhere, most if not all plugs can be inserted both ways. The plugs in my Furman power conditioner seem to be the exception. The Furman uses the kind of plug you see as a power connection on the back of your computer tower (well, at least mine).

No guitarists were harmed during the making of this message.

 

In general, harmonic complexity is inversely proportional to the ratio between chording and non-chording instruments.

 

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