Testing 240V Circuit

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  #1  
Old 03-14-05, 10:49 PM
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Testing 240V Circuit

I had a sub panel installed in my house. I plugged in my 220V table saw to my new 220V receptacle and my saw doesn't start. I tested the outlet and have 120V between each hot and the ground. I, however, have no voltage between the two hots. I am testing this by placing the voltmeter electrodes against the hot wires. I get nothing.

In the panel there is a double pole 20A breaker with 12-2 wire. The neutral is to the neutral bus and the white and black wires are to the hot poles on the breaker. The outlet has only room for two hots and a ground. The two hots are hooked up right and the ground is hooked up. I can't get the tool to start.

Any advice is welcome. I'm at a total loss as to why I don't have 240 between the two hots. Am I testing it wrong? The previously working tool is not working now so I suspect that the circuit has something wrong.

Thanks.
 
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  #2  
Old 03-15-05, 01:15 AM
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Originally Posted by htimst
I tested the outlet and have 120V between each hot and the ground. I, however, have no voltage between the two hots.
Who installed your two pole breaker and when ?

If you have 120 volts from one hot wire to ground and 120 volts from the second hot wire to ground.
and zero volts hot to hot.
You don't have a two pole breaker.
You may have two breakers on the same 120 volt line.

Did you measure 240 volts feeding into your sub-panel ?
 
  #3  
Old 03-15-05, 06:06 AM
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I didn't even check the feed to the sub panel. There is an actual two pole breaker for the circuit I'm checking. The sub panel is fed with a 40A two pole breaker from the main.
 
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Old 03-15-05, 06:43 AM
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Are these 240 volt breakers real 240 volt breakers, or are they twin 120 volt (tandem) breakers? In other words, what is the width of this 240 volt breaker? One inc? Two inches?
 
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Old 03-15-05, 06:58 AM
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You apparently have a two-pole breaker, but it's the wrong kind and/or installed in the wrong slot. It is a tandem (aka twin, skinny) breaker. It doesn't hit both power legs. In some panels (e.g., GE), you can make a tandem breaker hit both legs if you position it correctly. But in most panels, a 1" thick breaker cannot provide 240 volts. You need a 2" thick breaker.
 
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Old 03-15-05, 08:55 AM
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Thanks guys, that was the problem. It was a 1" thick two pole breaker that wasn't spanning both power legs. I moved the breaker and all is good. The breaker is delivering 220V now. It is rated at 220V so it's not a twin pole 120V breaker. It all works now and I appreciate the replies.
 
  #7  
Old 03-15-05, 10:53 AM
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John, if this is a tandem breaker, wouldn't he now have supply from the two phases but not mechanically linked? Or is there such a thing as a 1" double pole (as opposed to tandem) breaker?
 
  #8  
Old 03-15-05, 11:24 AM
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Some panels have half size spaces. In these panels it is possible to install a tandem breaker such that it picks up both legs, or just one leg.
 
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