Strange thing

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tjacobs

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Moorestown, NJ
Got a call about a clothes dryer not making heat. Went to the house and this is what happened. I started the dryer and the drum was rotating but no heat. Pulled the 4" vent duct off and it was blowing strong. I figured a bad heat element. The customer had already bought a brand new dryer and had it sitting there. I hooked up the new dryer and same thing. I pulled the breaker panel cover and got my meter out. I put my meter leads on each pole of the breaker and read zero volts. Meanwhile the dryer is still running and blowing cold air. I thought I was seeing things. Took my meter leads and went from each pole of the breaker to the neutral bar and had 120 volts on each pole. I replaced the breaker and the dryer worked perfect ( making heat ). Has anyone ever had a breaker do this? 120 from each pole but zero between poles instead of 240 volts. Very strange.
 
The easy answer would be that the 2 pole breaker was a "twin", meaning both poles were connected to the same panel bus. The drum is 120V, so that's why it worked with only 120V to Neutral.

The hard part is that you said you removed it then put it back in and it worked correctly... which means it was NOT a twin, but in fact a true 2 pole breaker.

My guess is that you lost one pole connection to the bus, but it happened to be the one that was NOT feeding the drum motor, that's why the drum continued to work. But when you were reading 120V line to N, I'm betting you used a digital multi meter, right? You were reading the same single working pole through the heater element, but because you are not putting any burden on the circuit with that DMM, the heater element's resistance and no noticeable effect. had you used a Wiggy/Knopp inductive tester, you would have seen no or very low voltage on that other pole. When you reinstalled the breaker, it made better contact with the bus again.
 
tjacobs said:
Got a call about a clothes dryer not making heat. Went to the house and this is what happened. I started the dryer and the drum was rotating but no heat. Pulled the 4" vent duct off and it was blowing strong. I figured a bad heat element. The customer had already bought a brand new dryer and had it sitting there. I hooked up the new dryer and same thing. I pulled the breaker panel cover and got my meter out. I put my meter leads on each pole of the breaker and read zero volts. Meanwhile the dryer is still running and blowing cold air. I thought I was seeing things. Took my meter leads and went from each pole of the breaker to the neutral bar and had 120 volts on each pole. I replaced the breaker and the dryer worked perfect ( making heat ). Has anyone ever had a breaker do this? 120 from each pole but zero between poles instead of 240 volts. Very strange.
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Seen it once or a few several times. Last was a single pole that my meter showed 42V across. Slightly less maddening than a breaker that kicks back (trips) like there is a dead short, only to find there are no wiring errors on your part and the breaker has failed and does the same thing in your hand.

Did the HO have the new dryer returned? I would guess the "problem" with the old was actually the breaker. jmho, checking voltage at the outlet is one of the first steps. Sure, you came off the hero today but swapping in a new piece of eqpt could be disastrous with a lost service neutral or with a high-leg improperly connected to a receptacle; there was a thread here last week where that happened that fried a DC drive.

Glad it all worked out and ty for posting a troubleshooting topic with the problem and resolution. :)
 
What brand, GE THQP by chance?


thql-mini-circuit-breaker-1.jpg


Some "thin" 2 pole breakers can grab one stab despite all the modern ones having a rejection feature that I have seen preventing this.
 
Jraef said:
The easy answer would be that the 2 pole breaker was a "twin", meaning both poles were connected to the same panel bus. The drum is 120V, so that's why it worked with only 120V to Neutral.

The hard part is that you said you removed it then put it back in and it worked correctly... which means it was NOT a twin, but in fact a true 2 pole breaker.

My guess is that you lost one pole connection to the bus, but it happened to be the one that was NOT feeding the drum motor, that's why the drum continued to work. But when you were reading 120V line to N, I'm betting you used a digital multi meter, right? You were reading the same single working pole through the heater element, but because you are not putting any burden on the circuit with that DMM, the heater element's resistance and no noticeable effect. had you used a Wiggy/Knopp inductive tester, you would have seen no or very low voltage on that other pole. When you reinstalled the breaker, it made better contact with the bus again.
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Yup, outside the heater most parts tend to be 120 volts:
 
bottom line is you lost one leg. Seen the same thing happen many times with a blown fuse, tree branch rubbed through one lead of an overhead service drop, one line of underground service lateral failed.... Whatever you did when you had the breaker out - cleared the issue - at least temporarily, if there is a mechanical problem in the breaker it may do it again.

Had you lost the other leg the dryer wouldn't have ever started.
 
ptonsparky said:
One pole of the CB is open. See it often enough that it isn't to surprising. Sometimes bugs crawl in, the breaker internals fail, etc.
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mbrooke said:
Hopefully that is the end of it.
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As ptonsparky says it was just a bad breaker.

When the OP had the breaker out he could have checked between line and load of each leg of the breaker with a resistance check to see which leg was bad.

It's always a good idea to inspect the buss for damage when you replace a breaker to make sure it's not pitted or burned in any way. Sometimes you may need to change the location of a breaker to a better buss section.
 
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