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OUr air conditioning system works well until the circuit breaker trips. We added another large return vent in the hall to try to get more air circulating and that didn't work. We just replaced the outdoor airconditioning unit and the circuit trips again. The electrician says the wattage is fine. Any ideas what could be the problem. Everyone is baffled because the house is only 5 years old.

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Current (amps) is voltage (volts) divided by resistance (ohms) or I=v/r. Breakers "trip" when there is too much current flowing through them. This can be caused by wiring that is too small for the application or a short (or a bad breaker, but since you just replaced that).

Cable Size:
The conductors have resistance and heat up when current runs through them. Properly sized conductors allow this heat to be dissipated. Long cable runs or cable runs which are tightly bundled with other cables can prevent this dissipation. Heat adds additional resistance which in turns causes more heat, eventually tripping the breaker to prevent a fire. For a 40 amp breaker, the cable should be a dedicated, 8 gauge wire.

A short (low impedance connection) can be between two conductors or between one conductor and ground (also called a ground fault). Shorts can be tough to track down when they are intermittent. This can be because the insulation was damaged (during installation, by rodents, etc). Moisture can deteriorate insulation or conductors.

It may only be present under certain conditions, so you can try this immediately following a trip. Shut both the breaker and the cutoff at the condenser (you want to isolate the cable), then use a meter to check for bleed between each of the conductors and each other conductor or ground. The neutral eventually connects to ground so it will have zero impedance. If you find there is a connection, you (or your electrician if you don't know what you're doing) will have to track it down and repair it.

It could be a clamp that is too tight where the line enters a jbox or panel, a staple that was driven too far and is biting into the insulation, a bend that is too tight, or a length that isn't supported well and subjected to vibration from a nearby motor .

Other possibilities:
At 40 Amps they'd be really expensive, but are you using a GFI or Arc-Fault breaker? Either of those could cause unwanted tripping.

Good luck with it.
jack g

Posted on Aug 07, 2010

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Hi, you say you installed a new condenser outside, but the unit keeps tripping the breaker? I don't know what all this electrician did, but if the new condenser trips the breaker, its drawing to many amps.Its not the watts that need to be checked, its how many amps the unit draws and compare it to the breaker it has to run it. It will tell you on the data sticker max. and min. circuit size, and compare it to the circuit breaker size. It may be to small. If its max is 35 amps, make sure the breaker is 35 amps. Make sure the connections at the breaker are good and tight also. For that breaker to trip, your problem is in the electrical supply. The breaker may be weak and getting hot causing it ti trip. The electrician needed to put his amp probe on each leg of the breaker with the unit on, and see how many amps it is drawing and compare that to the units amps. Either the breaker is to small, or it is weak, or the 2- wires may be loose. This is your problem for sure, from the breaker to the disconnect box at the condenser. Even though the home is only 5 years old, that main a/c breaker could be burned or what ever, but this is the problem. Look at the amps, 30, 35, or so and compare it to the unit. If its OK, turn the breaker off and pull it out and look it over for hot spots. If you replace that breaker, your mystery will be solved. Please keep me posted and let me know the out come. I know this is your problem as the condenser is new. Please be kind when rating me as I know you will. I will be here if you need me, just get in touch by my user name below. Keep me posted. It has to be from the breaker to the new condenser, so check and replace the breaker. This will solve the problem. I keep records of all of my solutions if I need to go back on them, so get back to me. Thank you and
A/C, Heating, & Refrigeration Contractor

Posted on Aug 06, 2010

  • tasteofthyme Aug 06, 2010

    Actually I used the wrong terminology the electrician checked the amps and they were at 40 the same as the breaker, which is also new. We increased the breaker from 35 to 40 hoping this would solve the problem, but no such luck



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