220 wire basics

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Old 03-18-13, 06:38 PM
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220 wire basics

I am comfortable with basic 120 home wireing and usually check for the hot leg or power in a 120 circut by simply touching one lead of my tester to the wire and the other to ground(metal bx sheath or box)
Is checking 220 basically the same idea with the exception that both legs are hot.
Also in our home i see the 220 dryer circut is two wire 10ga bx, is this common practise for metal bx wire or is three wire preffered.
 
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Old 03-18-13, 07:05 PM
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I am comfortable with basic 120 home wireing and usually check for the hot leg or power in a 120 circut by simply touching one lead of my tester to the wire and the other to ground(metal bx sheath or box)
Is checking 220 basically the same idea with the exception that both legs are hot.
That's one important part of it. Your house has a 120/240V service. What that means is that you have 240V coming in that is split onto two legs carrying 120V, to neutral or other ground, each. You don't have 220V power.

in our home i see the 220 dryer circut is two wire 10ga bx, is this common practise for metal bx wire or is three wire preffered.
Your dryer should be connected to three sets of potential - two hots, one neutral and one ground. If the dryer circuit is protected by a 240V 30A breaker, then #10 AWG copper is the correct conductor size. Inside the flexible metal cable jacket, there should be three insulated current-carrying conductors - one black and one red for the two hot wires and one white for the neutral. The flexible metal conduit jacket can provide the path to groung if the cable also contains a small silver (actually aluminum) bond wire and that bond wire has been turned back over the anti-short bushing and laid into the spiral grooves in the jacket before the cable jacket was secured to the cable clamp.

Why do you ask?
 
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Old 03-18-13, 07:06 PM
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To check for 240V (not 220) you check between the two legs of the 240.

 
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Old 03-18-13, 10:32 PM
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thanks for the reply's

yes ..
it is 10ga wire and the breaker is 30a, and the small silver wire is wound around the grooves in the bx jacket. however it is only 2 conductor wire, black and white with the metal bx jacket acting as ground (and or neutral?)

is this an acceptable practice?
 
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Old 03-18-13, 10:50 PM
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is this an acceptable practice?
Not today, but it probably was when it was installed.
It's a 240V circuit, so it "doesn't need a neutral," the thinking went. That's still true for some 240V circuits, but not as many as there once were.

If you check the installation instructions for your dryer, it probably shows alternate cords and cord connections for 3-wire and 4-wire supplies.

Do you have a dryer plugged into this circuit now? Is it working as you would like it to?

Why are you asking?
 
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Old 03-18-13, 10:50 PM
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and the small silver wire is wound around the grooves in the bx jacket. however it is only 2 conductor wire, black and white with the metal bx jacket acting as ground (and or neutral
Not unless the dryer ia straight 240 volts and most aren't. Most dryers are 120/240. That is the dryer itself, motor, and controls are 120v with a 240v heat source. (Actually gas and electric dryers are often identical except one has 240v electric heat and one has gas heat.) The cable needs to be changed if it is 120/240 volts.
 
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Old 03-19-13, 01:20 PM
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its an old dryer 25 years old and still going strong, no problems. so i am interpreting that if its a straight 240 the wiring is acceptable but i guess that when its time to replace the dryer the cable should be replaced with 10-3
also?
 
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Old 03-19-13, 03:38 PM
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i guess that when its time to replace the dryer the cable should be replaced with 10-3 also?
If you're replacing it with a 30A 240V electric dryer, then yes.
 
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