Oil furnace tripping breaker.

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  #1  
Old 03-18-14, 04:14 PM
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Oil furnace tripping breaker.

I just moved into a new place with an old Century oil furnace.
This is all the stats I can find on the furnace.

CENTURY ENGR. CORP
MODEL: D0100C
S/N:1167

The furnace appears to fire up well and runs for approximately >1 minute at which point the breaker trips. I checked the blower motor and it appears to be fine. CAD cell appears to be in working order. Any ideas where to start?

Thanks in advance for taking the time to look through this post.
 
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Old 03-18-14, 04:30 PM
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How did you "check" the blower motor and other items?
 
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Old 03-18-14, 04:52 PM
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On the blower motor I disconnected it, checked dead shorts, and wired to a pigtail to see if it would run on its own. The CAD sensor I checked the resistance on it both disconnected and running and appeared to be in working order.
 
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Old 03-18-14, 05:26 PM
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Did you check the oil burner motor? Do you have the ability to check amperage?

What is the manufacturer and complete model number of the primary control? The primary control is the unit that the cadmium sulphide cell is connected and is the safety control for the oil burner.

It IS the circuit breaker in your house CB panel that is tripping, correct?
 
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Old 03-18-14, 06:02 PM
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Yes it is the CB in the house that is tripping.
I do have a meter that can check amperage.
I did not check the oil burner with a meter.
I'm having trouble finding a serial # on the primary control. It is made by Honeywell. I will upload a picture of it.
 
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Old 03-18-14, 06:05 PM
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Old 03-18-14, 08:51 PM
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P,
Check the amperage on the line to the fuse box. If you have a 15 amp breaker it may not be enough to take the surge when the blower comes on. They used to want 15 amp breakers but now they recommend 20 amp.
As blower motors get old it takes a liitle more to start them. Between the burner motor and the blower motor starting sometimes for that second that it surges it's too much.

Good Luck,
 
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Old 03-18-14, 09:44 PM
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I got a read of 40A coming from the breaker.
 
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Old 03-19-14, 01:39 AM
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Look inside the cover to that primary control for a model number. Sometimes they are stamped on the control chassis as well.

Is the furnace the ONLY load on that circuit breaker? When in the cycle did you measure this 40 amperes? Does the ignition transformer stay energized during the entire burn cycle or does it stop after igniting the main flame? Does the room air blower start before tripping the circuit breaker or simultaneously with the tripping? Can you test the amperage draw of the individual components; the oil burner motor only, the ignition transformer only and the room air blower only?
 
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Old 03-19-14, 09:04 AM
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P,
The furnace is suppose to be the only thing on that breaker. With the furnace running if your drawing 40 amps I would say there's something deffinetly wrong.
Take the reading without the blower when the furnace comes on and then when the blower comes on.
If the furnace starts and runs for a short time before the breaker trips you must be drawing lower amps than your breaker or it would trip. It sounds like it's tripping when the the blower comes on. Possibly the surge.
Take both readings and that will narrow it down. Individual readings as Furd suggested is also useful to know although if it were the burner motor or transformer it would trip before the blower ever came on.

One more thought on that 40 amps. That's more than double the amps. that 14g wire is rated for.
Fortunately the breaker is tripping but be careful of overheated wires and a possible fire.
 
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Old 03-19-14, 06:15 PM
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Sorry, I don't believe the 40 amp reading. If the furnace were indeed drawing 40 amps, that breaker would trip in only a second or two. If the blower motor is what's tripping the breaker & the fan is belt driven, the belt could be too tight.
 
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