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[jimmy101]

There is a correct way and many incorrect ways to connect to a plug.

You should have three wires connected to the pump.

The green wire is the ground. If you have a volt-ohm meter you should measure zero resistance between the green wire and the body of the compressor (find a place on the body where there isn't any paint to measure the resistance). If there is infinite resistance between the green wire's end and the case then it isn't connected. Find someplace on the body of the compressor to connect it with a screw. Perhaps to a hole in the foot of the compressor where they may have been a rubber shock mounting, or pehaps to a screw to the electrical box on the compressor. The other end of the green wire should be connected to the gound (roundish) blade of a three prong gounded 120VAC plug, which you can get at the hardware store for a couple bucks.

You now have two wires left. In the US, the standard color coding is that black is "HOT" and white is "COMMON". (In other countries brown is often HOT.)

The HOT wire is connected to the smaller of the two flat blades on the plug.

The COMMON wire is connected to the larger of the two flat blades on the plug.

If you are installing a switch it should be wired in series with HOT (black wire, small plug blade).

Your wire colors don't match the standard HOT=black, COMMON=white pattern but for an AC device it doesn't matter too much which is which. What does matter is that the connection to the wall plug puts the HOT on the narrow plug spade.

What's the difference between HOT, COMMON and GROUND? Lots. Current flows between HOT and COMMON. 60 times a second (in the US) the polarity switches between HOT and COMMON, HOT is + and COMMON is -, then it switches to HOT is - and COMMON is +. The key difference is that the electromotive force (EMF) is always on the HOT wire, which is the small spade on the plug. (This assumes everything in your house was wired correctly). The EMF is what makes current actually move through the wire. That means if you connect a voltmeter between COMMON and GROUND of a wall outlet you should measure zero voltage since the COMMON has no EMF. Only the HOT will read a voltage relative to GROUND.

In a standard three prong household outlet only the narrow spade (HOT, black wire) in the outlet is capable of giving a person a shock. (Assuming the house was wired correctly.)

There is never supposed to be any current on the GROUND (green) wire. It is there for two reasons; it provides a safety path to ground in case HOT ever gets shorted to the metal case of an appliance and it provides shielding to devices senstive to RF radiation (like TV, stereos etc.).

In the home's breaker box all the COMMON (white) and GROUND (green) wires are connected together, then to a stake in the ground and to the COMMON coming into the house from the electric company. So, at the breaker panel COMMON and GROUND are identical. In the walls or your house they are not, COMMON may have current flowing through it (but it can't supply the EMF), GROUND should neve have significant current flowing through it.

So, back to the problem at hand. Which wire on the compressor should be HOT and which should be COMMON given the colors of the compressors wire aren't black and white? The key is that the HOT wire from the wall outlet should take the shortest possible path before it is controlled by something. That means you want HOT from the wall to go directly to your switch. If you are installing a fuse, then the fuse goes before the switch. The other side of the switch can be connected to either of your compressor wires since the compressor's AC motor doesn't care which is HOT and which is COMMON. The remaining wire from the compressor is connected to the COMMON (large) spade on your plug.

When wired this way the EMF has the shortest possible path before it is controlled by something. The shorter the path the less chance there is of getting a dangerous short.

Electrical code in the US states that wire connections can be made with "wire nuts" but any and all connections must be enclosed in a suitable container. Usually, the container is a metal electrical work box (you can also used suitable plastic electrical work box). The metal of the box is connected to GROUND. Your compressor may already have a suitable electrical work box on it.

I would suggest getting a "single gang" metal work box, a 120 VAC wall switch, a standard plastic switch cover plate, a couple suitably sized "wire nuts" and the proper cable clamps for the metal box's knockouts. Cable clamps are threaded fittings with a screw operated clamp to hold the wire. If you pull on the exposed cable/cord the force is tranfered to the box instead of pulling on the connections inside the box.

You'll need a clamp to hold the AC power cord and the wires that'll go from the box to your compressor. Mount the box firmly to the compressor. Run your compressor wires through a clamp into the box. Run your three wire power cord with grounded plug into the box through another clamp. Connect the wires inside the box with wire nuts and run the HOT through the switch then to the compressor. All the gournd wires should be connected together and to the metal box. Screw the switch into the box then cover the switch with the switch plate.

This setup would meet code requirements and be safe. To make it all even safer plug it into a Ground Fault Interupter GFI outlet. (Most modern kitchen, garage and outdoor plugs in the US are on GFI circuits.)

If the COMMON side of the circuit gets shorted to metal body of the device, and the device is turned off you, can't get a shock from the device body to ground. If the device is turned on and the COMMON and GROUND circuits are intact then you can only, hopefully, get a fairly minor shock if you do something like touch the now HOT body of the device and a good ground like a water faucet. The current would have three paths to ground; through the COMMON wire, through the GROUND wire and through you to the water pipes to ground.

If you don't ground the device and if the HOT and COMMON are reversed there is a much greater likelyhood of getting a lethal shock. If the device shorts, even when it is turned off, HOT is now applied to the body of the device. If you touch the devices body and a water faucet (for example) the only path for the EMF is through you. So you get a potentially lethal shock even though the device was turned off.

Usually, if HOT does short to the body of a grounded device then a fuse or breaker somewhere will shut off the circuit. Household breakers are not designed to protect devices plugged into the wall outlets. The breaker is designed to protect the wires in your wall. If a circuit draws too much current then there is a risk of melting/igniting the wires in your walls, the breaker is there to protect those wires. Well designed electrical devices should have their own breaker or fuse to protect themselves and should not rely on the house's breakers.

Crappy $0.99 extension cords are very dangerous things. They are typically 16 or higher gauge. The wires in your walls are typically 14G and the breaker is rated to protect those wires (typically 15 AMPS in the US for 14G wire). The larger Gauge number of the extension cord means the wire has smaller diameter. If something plugged into that cheap-ass extension cord shorts the cord is carry the full 15Amp capability of the wall wiring. The household breaker thinks that fine and won't trip since the wall wiring can handle the 15A. The extension cord can't handle that current and can melt/ignite without tripping the breaker.

damn I'm verbose

[POLAND_SPUD]

thanx jimmy that was very useful for me as I am not familiar with differences in color coding and generally with differences between the US and europe as far as plugs and sockets are concerned

just a question
I have don't have breakers in my house, just fuses... doesn't that make it safer ??


@FishBoy could you answer my questons on the second page as I am really curious what was your problem

I think I get it now... there are two cables sticking out of the compressor.. one of them has a plug and the other one was joined to the thermostat... and either:
1. there is green (grounding) wire in only one of them and that's why you disn't know what to do

2. you haven't checked if the second cable has grounding wire

I suppose that this suggest that there is already a sort of junction/connection box instaled in the compressor and that's why there are two cables... ?

well at least mine had a junction box mounted next to the compressor so in fact there was only one cable (but with 3 wires) leading directly to the compressor

[jimmy101]

thanx jimmy that was very useful for me as I am not familiar with differences in color coding and generally with differences between the US and europe as far as plugs and sockets are concerned

just a question
I have don't have breakers in my house, just fuses... doesn't that make it safer ??

Nope, not really. A fuse and a circuit breaker do the same thing.

A fuse is about as reliable (and as accurate) as a circuit breaker. The circuit breaker costs something like ten times as much as a fuse.

[POLAND_SPUD]

wel I've heard that fuses are more accurate and thus safer

[jimmy101]

wel I've heard that fuses are more accurate and thus safer

Yes and no. Fuses are much more stable over time. Breakers have a slight tendancy to fuse closed slightly if they are in use for many years and are never cycled.

On the other hand, when a breaker trips it is unlikely that the owner will just put in the next larger breaker to keep it from happening again. This happens often with fuses.

In the US, new homes are constructed with breakers, and not fuses, even though fuses would be cheaper. I assume that means that someone, somewhere, who's opinion matters, thinks breakers are better.

[POLAND_SPUD]

hmm that's interesting... maybee it's becasue breakers are inherently safer as there is no risk that the owner would electrocute himself while replacing a fuse or

put in the next larger breaker to keep it from happening again

EDIT
hmmm it seems you are right --> http://209.85.129.132/search?q=cache:hF ... =firefox-a

and

http://www.faqs.org/faqs/electrical-wir ... on-19.html