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-   -   Breaker Consistantly tripping (http://www.houserepairtalk.com/f8/breaker-consistantly-tripping-6761/)

mjpogue 05-29-2009 08:49 PM

Breaker Consistantly tripping
 
OK......Here is my issue.

When my condenser attempts to kick on, the breaker automatically trips. I have already replaced the contractor, so I am figuring there is either a short to the compressor or maybe the capacitor is bad (I am going to check this tomorrow).

Does this process sound right, or should I be looking elsewhere????:confused:

Nestor_Kelebay 05-29-2009 11:38 PM

I would look at the temperature the circuit breaker is operating at. I know screw-in type fuses are temperature sensitive in that they will blow at lower amperages if the fuse is warmer. So, if you have your electrical panel in a warm place (such as a laundry room or above a source of heat, your fuses will blow at lower amperages than if they were cool.

Modern circuit breakers contain both a bi-metallic strip and a small electric solenoid. If you have a short circuit, then the current through the wiring can be several thousand amps, and this high current causes the solenoid to immediately energize and pull the contacts apart to break the circuit. Since all the current going to the circuit goes through the solenoid's wire coil, the magnetic field of the solenoid is exactly proportional to the current in the circuit. Consequently, a short circuit will cause the solenoid to trip the breaker in a fraction of a second.

By contrast, if the current is less than about 5 times the amperage rating of the circuit breaker, the magnetic field of the solenoid won't be strong enough to trip the breaker, and the breaker then operates on the bimetallic strip inside it. If the current is higher than the rating of the breaker, the breaker will trip, but the time it takes will depend on the time it takes for the bimetallic strip to heat up sufficiently, and higher overamperages will trip the breaker faster than lower ones. If the current is only a little above the rated amperage of the breaker, the bi-metallic strip may never bend enough to trip the breaker.

But, if your breaker trips more than a fraction of a second after the compressor starts, then your breaker is operating entirely on the bi-metallic strip, and that means that ANYTHING that causes that bi-metallic strip to be warmer than it otherwise would be will cause it to trip at a lower amperage. So, it would stand to reason that if the breaker is in a warm place it would take less current to trip the breaker. Similarily, if the breaker beside the one to the compressor is warm because of corroded contacts in it, it would also cause the breakers near it to trip at lower than rated amperages.

Maybe check to see if the electrical panel is mounted right on a chimney chase so that the hot flue gas from a gas fired water heater is heating the chimney and the electrical panel. Make sure the panel isn't sitting in direct sunlight as well since that would have a significant affect on the panel's temperature.

This graph shows the different tripping regimes of residential circuit breakers:

http://tonyelectric.com/images/stori...c/cb_curve.gif

and was ripped off from:
http://tonyelectric.com/residential-circuit-breakers

My understanding is that receptacle circuits in newer houses are wired with 20 amp breakers. I'd talk to your local electrical inspector to see if using a 20 amp breaker on that circuit with your existing wiring is gonna pi$$ him off. Or, I'd at least try that to see if you can get the compressor running so that your electrician can measure the amperage draw of the compressor to see if it's normal or not.

You don't need to know the rest.

The older screw-in type fuses are also sensitive to temperature since they trip when the solder holding two metal "springs" together melts. Since the melting temperature of solder is only about 200 deg. Celsius, a change in the ambient temperature requires a change in the amount of current necessary to melt the solder and blow the fuse.

This graph shows how the amperage at which a fuse blows varies with ambient temperature.

http://www.lnl.com/howto/images2/graph2.jpg

and was ripped off from:
http://www.lnl.com/howto/fuse.htm

Nestor_Kelebay 05-30-2009 01:53 AM

Here's a cutaway view of the inside of a typical residential circuit breaker:

http://upload.wikimedia.org/wikipedi...uitbreaker.jpg

You can see both the solenoid (#7) that trips the breaker at very high amperages and the bimetallic spring (#5) that opens the contacts (#3) at above-rated amperages.

mjpogue 05-30-2009 06:18 AM

That's interesting. so you do not think it is associated with the condenser at all?

Nestor_Kelebay 05-30-2009 03:09 PM

No, I didn't say that. My last post was primarily to make you aware that ambient temperature can have a significant effect on the amperage at which a circuit breaker trips so that if your breaker panel happened to be located in a hot area with the Sun shining on it all day, that might explain the problem if nothing else does.

But, don't look at ambient temperature before you've checked out the more likely causes.

I would definitely check the capacitor. That capacitor creates a time difference between the magnetic fields developed by the start and run windings in your compressor motor. It's that time difference in the magnetic fields of the two windings that creates the illusion of a ROTATING magnetic field for the rotor to follow, and that's what gives a capacitor start motor it's high starting torque. So, if that start capacitor is shot, that'd explain why the motor can't turn the compressor, and a motor that's not turning is essentially a short circuit, and would explain why it's tripping the breaker every time it tries to start. The electronics instructor at your local trade school should have the necessary equipment to accurately check a start capacitor.

If the capacitor checks out, then call either an electrician, HVAC contractor or appliance repairman to check the current draw with a clamp-on ammeter when the compressor motor is starting. It could be that the refrigerant pressure isn't equalizing across the compressor when the motor stops, so that the next time the motor starts it simply doesn't have the power to turn the compressor against the back pressure. It could also be bearings in the compressor or motor seizing up, and impeding the motor from turning. You need to check the current draw of the motor to see if it's drawing too much current starting, running or both.

If the capacitor checks out, and the compressor motor isn't drawing too much current, then I'd try replacing the breaker.

mjpogue 05-31-2009 07:00 AM

Good Morning-

The breaker that is tripping is in the main breaker panel. After reading your initial post checking the break makes perfect sense. Also, I did some additional recon to the unit, which is making me thing that it is the compressor. Here is what I did.

I have two wires that originate from the compressor (yellow and black). These wires connect to the contractor at the opposite poles. When I put my meter on them to check for resistance, I get a beep which indicates a short. This leaves me to believe that the compressor is bad.

Also, I checked the capacitor and it appears to be fine. No swelling or shorting between the terminals. Interesting though, it is not registering any voltage (I assume it does not have the opportunity because of the issue described above.)

What do think??? I really appreciate all of your help!!!

Nestor_Kelebay 05-31-2009 03:04 PM

Quote:

Originally Posted by mjpogue (Post 30956)
I have two wires that originate from the compressor (yellow and black). These wires connect to the contractor at the opposite poles. When I put my meter on them to check for resistance, I get a beep which indicates a short. This leaves me to believe that the compressor is bad.

I presume you meant to say: "These wires connect to the CAPACITOR at the opposite poles."

I would agree with you ONLY if the compressor motor was running at the time you checked the resistance across those wires. Otherwise, to my way of thinking, you should have gotten that beep because you're essentially measuring the resistance of a short circuit. Here, go to this page:
Single-Phase Hermetic Motors
and take a look at Figure 14-26.

That diagram shows a typical capacitor start motor wiring diagram. If the motor was not running at the time you checked the resistance between the yellow and black wires, then the start relay would have been closed, thereby including the start capacitor and the motor's start winding in the circuit.
(Once the motor gets up to speed, that start relay cuts the start capacitor and start winding out, and the motor continues operating on the run winding alone.)

Inspection of Figure 14-26 shows that measuring the resistance across the yellow and black wires will give you the resistance of the start relay coil, the run winding and the start winding all in series. You can see how a multimeter which operates on DC voltage and current could misinterpret this as a short circuit. It's just a long wire looped into three different coils, and it only makes sense and works properly with AC voltage and current. To a DC tester, it looks like a short circuit.

To properly check your compressor's motor for a short circuit, you need to access and remove the electrical connector that plugs into the side of the compressor. Once you remove that connector, you should see THREE electrical terminals of some type. One terminal goes to the start winding, and the end of the start winding wire goes to the "Common" terminal. Another terminal will go to the run winding and the other end of the run winding wire will go to that same "Common" terminal. And, the third terminal you see will be that "Common" terminal. Thus, inside the motor the start and run windings are connected in parallel to the common terminal. The electricity goes into the motor through the first two terminals, and the wire that connects to that common terminal takes the electricity back to the generating station (to use a hydraulic analogy).

The way you test your motor for short circuits is to measure the resistance between each of the three PAIR of terminals (S to C), (R to C) and (S to R). Two of those resistance measurements should exactly add up to the third. If they do, then there are no short circuits in your motor's windings. That's simply saying that measuring the resistance of the start winding individually and the resistance of the run winding individually should add up to the resistance of the start and run windings in series.

Also, check to ensure you don't have continuity between any of the terminals and ground. That's a problem for sure.

But, you'll need a multimeter that can measure small resistances without presuming it's a short circuit.

If the resistances measured this way don't add up, THEN you can legitimately conclude there's an electrical problem in the motor.

Also, hermetically sealed electric motors (that is, motors that are inside an airtight container) used in air conditioning and refrigeration will often use something called a "permanent split phase motor", which will use a run capacitor on the start winding, and that start winding will remain in the circuit all the time, not just while the motor is starting. Go to:
Split-Phase Hermetic Motor Windings and Terminals
and take a look at Figure 14-28.

Since the start winding remains in the circuit all the time the motor is running, permanent split phase motors don't have a start relay to cut the start capacitor and start winding out of the circuit once the motor gets up to speed. (This figure more clearly explains why measuring the resistance between the black and yellow wires may give you a low resistance, but it's certainly not a short circuit for AC voltage and current.)

So, phone up the company that made your air conditioner, or their local factory authorized service depot, and ask them if that's a "start" capacitor the yellow and black wires go to (in which case you have a capacitor start motor) or if it's a "run" capacitor the yellow and black wires go to (in which case you have a permanent split phase motor). And, while your talking to them, ask what you need to do to access the Start, Run and Common terminals to the motor on the compressor housing so you can check to see if the resistances through the motor windings add up, and so you can test for shorts to ground on it.

Quote:

Also, I checked the capacitor and it appears to be fine. No swelling or shorting between the terminals. Interesting though, it is not registering any voltage.
You can't "check" a capacitor visually. I'd take it to any place that repairs electronics and ask them to check the capacitance on it to see if it's still good or not. A bad capacitor on a capacitor start motor WILL cause the circuit breaker tripping problem you're having, so it's critical that we have confirmation that the capacitor is good before proceeding. It's the most likely suspect here.

Also, be careful with capacitors, especially on television sets and CRT type computer monitors. These capacitors are very strong and can hold enough of a charge to give you a real good shock (and potentially kill you if Murphy's Law has any say in the matter).


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