40 Amp or 30 amp

An inspection on our home (7years old) recently revealed that both our air conditioning units have 40 amp circuit breakers instead of 30 amp (the unit asks for 30 amps). How big of a deal is this? And if so, is it an expensive thing to change?
Thanks in advance.
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I would replace them and its cheap to change provided they are common breakers. putting in the right breaker better protects the units if they malfunction
there are some pricey replacements where the original maker went out of business.
FPE stab lock is one of those, if your unlucky to have their panel change the panel ASAP!! The whole thing is a fire hazard
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Breakers protect the wire...the units motors have internal protection...electric heat has its own protection
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oh yes...Id still change them...just clarifying that breakers dont really protect equipment....they protect the wire.
got a phone while posting that previous post...blah blah blah...hit send....
~:>
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On 22 Feb 2006 15:32:21 -0800, snipped-for-privacy@hotmail.com wrote:

Clueless statement of the month above ^^^ Bubba
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Your house is to new to require any odd, expensive breakers. Garden variety double pole 30 amp breakers run about $15 each

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asco wrote:

No point in changing. The breakers match the wiring as stated earlier. Reducing the breaker size wont do anything, but cost you money. IMHO.
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Breakers protect the conductor, the equipment and the user.
Ahh, but the rating of the equipment on the nameplate does not match the rating of the breaker and that seems to be what the inspector is tripping on. If the appliance is hardwired, you should change the breaker, if it is plugged in, it's your call as long as the breaker is same or smaller than the marking on the receptacle (nod to wire gague as well).
If the nameplate says it uses 30A, a larger breaker is appropriate. If the nameplate says "breaker size" 30A that is much clearer. It may have both ratings or just the first (consumption) if that is the case, 40A is the right size.
In reality on an A/C unit, there are probably no faults that will trip a 30A that wouldn't also trip a 40A breaker. The difference in trip current probably wouldn't make much of a difference because any such fault would likely be due to a dead short. (I suppose a frozen compressor might take a few more seconds to trip it but its toast by then anyway)
Since you had your house inspected, I might guess you are planning to sell. Fix it, so the buyers inspector does not site the same thing. That should be reason enough to act. Up to 1 hour labor plus parts.
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PipeDown wrote:

Wrong. Panel Breakers and fuses protect wiring. A Components internal breakers protect its internal components (motors usually have thermal breakers) GFCI is designed to protect the user.

hardwiring vs. plug makes no difference.

I'm not aware of any nameplate terminology standards!?

In reality, breakers are designed to protect against resistive shorts; Hard shorts are easy. I agree that resistive shorts are rare. Nevertheless, this is what they do.

I wouldn't call it a 'fix.'
--
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dnoyeB wrote:

Under the NEC for motor circuits, like this, the panel fuse/breaker provides short circuit protection for the wires. Protection for the motor is provided by an overload device that matches the current and starting characteristics of the motor - which is a motor starter 'overload unit' or 'thermal protection' in the motor. Fuses/breakers have to withstand the starting current of the motor, and have widely spaced ratings (30, 40 Amp), and as a result don't trip on overloads although as Dan Ackers said they MAY trip on repeated restarts by the 'thermal protector'. In general time delay fuses can be 175% of the motor running amps. The fuses can be larger than the rating of the supply wires and protect them from short circuit - overload protection is provided by the motor overload device. The rules for motors are IMHO rather arcane and should be applied by soomeone who understands them. All of this agrees with dnoyeB. However the panel fuse/breaker also provides some protection for the equipment, and motor starters and other equipment are likely to have a maximum fuse/breaker size.

If equipment comes with a cord and plug it would be reasonable to expect it could be plugged into a matching receptacle. Hardwired equipment has to follow information on the nameplate (but that is also true for cord connnected equipment).

Hardwired compressor units for central air are commonly nameplate marked with "maximum fuse size" or "maximum breaker size". It is a code violation not to follow these ratings and could void a warranty. "Maximum fuse size" requires fuses.

But equipment, like motor starters, often have a maximum fuse/breaker size which protects the equipment from damage.
bud--
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Did the OP say what was the wire size? I went back and read, and didn't see it.
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dnoyeB wrote:

What? The unit MOP (Maximum Overcurrent Protection) cannot be exceeded, period, no exceptions. In a motor circuit the CB provides the short-circuit and ground-fault protection. The motor overloads are what protect the wire in a motor/compressor circuit. The wire needs to be no larger than the MCA (Minimum Circuit Ampacity). For example, on a condensing unit that has an MCA of 35 amps and an MOP of 60 amps, the wire size need only be a #8 and the maximum breaker can be up to, but not exceeding, 60 amps, as permitted by NEC. As you can see, a 60 amp breaker on a #8 wire is not going to protect against overcurrent. Again, the compressor overloads are what protect the wire IN THE CASE of motors and compressors. The only time that the CB provides short-circuit, ground-fault protection AND overcurrent protection in a motor/compressor circuit is when it is rated at no more than 125% of the motor/compressor Full Load Amps.
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You wrote: "An inspection on our home (7years old) recently revealed that both our air conditioning units have 40 amp circuit breakers instead of 30 amp (the unit asks for 30 amps). How big of a deal is this? And if so, is it an expensive thing to change?" ______________________________________ Re; Assuming you're talking about the compressor power supply breaker, you should replace them and it's not expensive if you do it yourself. The breaker size selection is indeed selected to protect the compressor motor. That's why a maximum breaker ampacity is given on the unit name plate. Even though the compressor has an internal motor protective (IMP) winding temperature limiting device. These IMP devices are last resort current/temperature limiters and tend to operate (open the circuit) at temperatures well above (100F+) normal operating temperature of the windings AND they do reclose only to reopen again if the compressor does not start. They will cycle like this indefinitely if the wrong supply breaker is installed, intermittently "cooking" the windings and greatly reducing the life of the insulation on the windings, until either power is removed or the reason for the stall, such as high head pressure, resolves itself.
Back to the breaker. You should select the breaker amperage rating to be less than the nameplate maximum over-current protection and about twice the compressor running current. My two 2-ton compressors have a running current (RLA) of 11 amps and have 20A breakers for protection. Locked rotor current (LRA) is stated to be 61A. The nameplate calls for max over-current protection to be NO MORE THAN 30 A. You want the breaker to trip as soon as possible to prevent "cooking" the compressor motor windings (even though there is an IMP device) to prevent degradation of the winding insulation that occurs in a long term fail-to-start situation as in the case of a blown starting capacitor.
If the breaker is sized right, it will activate (open) before the IMP does on a stall or start failure.
I hope that helps... Dan Akers
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Dan Akers wrote:

The motors internal protection is not backup protection, but its primary protection as far as the motor engineers are concerned. Motors are damaged by heat, thats why they have thermal breakers. External breakers are not sensitive to the thermal conditions at any point in time, within a motor. The motor itself is adequately protected by its internal breaker is does not get "cooked." The external breaker is necessary to protect the external wiring normally.
The assembly internal wiring should be able to handle motor stall current. But if they are trying to cut costs, they may downsize the wiring then put the onous on the installer to protect the internal wiring by using a smaller external breaker.
So if the faceplate specifically calls for a breaker size he better stick with it. But if it doesen't, he is fine.
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asco wrote:

Depends on whether or not you care about your AC unit being protected from burning up under various fault conditions. See the post by Dan Akers.

No, it's an easy 5 minute DIY job. Don't be surprised if an electrical contractor wants $75 or $100 to do it though.
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With this amount of information impossible to tell.
The maximum overcurrent device of an air conditioner needs to be adhered to, just good sense. Changing the disconnect at the unit to a fusible pull out is fairly cheap and easy to do. Depending on the length of the circuit just changing the breaker to a 30 may create more problems.
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No recommendation but if you ARE going to change the breaker yourself, make them discuss safety with you, like turning off ALL the power to the breaker box, that is, all the power to the house, bfore you start touching things inside the box.
Remove NOPSAM to email me. Please let me know if you have posted also.
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If the wire is #10 copper or better, there's no reason to change breakers. If it's #12 copper, you should be on 30A breakers. If it's less than #12 copper, you should run new lines. The breaker doesn't care what the power draw of the terminal appliance is.
--Goedjn
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asco wrote:

In case Bud's post isn't clear enough let me explain. There are two ampacities listed on the nameplate of a motor/compressor unit's name plate. One is the circuit selection ampacity. This minimum circuit ampacity is the minimum the circuits conductors must be rated for in table 310.16 of the US NEC. Section 240.4 which limits 14, 12, and 10 gage conductors to certain overcurrent protection values reads in part "240.4 Protection of Conductors. Conductors, other than flexible cords, flexible cables, and fixture wires, shall be protected against overcurrent in accordance with their ampacities specified in 310.15, unless otherwise permitted or required in 240.4(A) through (G). (D) Small Conductors. Unless specifically permitted in 240.4(E) through (G), the overcurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied. (G) Overcurrent Protection for Specific Conductor Applications. Overcurrent protection for the specific conductors shall be permitted to be provided as referenced in Table 240.4(G).
Table 240.4(G) Specific Conductor Applications     Conductor                Article        Section     Air-conditioning and refrigeration    440, equipment circuit conductors        Parts III, VI        
Capacitor circuit conductors         460        460.8(B)and                                     460.25(A)(D)     Control and instrumentation         727        727.9     circuit conductors (Type ITC)    
Electric welder circuit conductors    630        630.12 and                                     630.32      Fire alarm system             760        760.23, 760.24,     circuit conductors                 760.41, and                              Chapter 9,                                     Tables 12(A) and                             12(B)      Motor-operated appliance         422, Part II         circuit conductors
Motor and motor-control         430, Parts III, circuit conductors IV, V, VI, VII
Phase converter supply conductors    455        455.7    
Remote-control, signaling, 725 725.23, 725.24, and power- limited circuit conductors 725.41, and                             Chapter 9,                                     Tables 11(A) and                             11(B)     Secondary tie conductors 450 450.6"
Notice that the first line of Table 240.4(G) covers Air-conditioning and refrigeration equipment circuit conductors. The referenced parts of article 440 provide for the selection of Over Current Protective Devices (OCPD)for air conditioning equipment. Conductors used to supply such equipment are sized by the table 310.16 values and not by the size of the OCPD. The OCPD is sized to allow the compressor to start reliably even under adverse conditions such as already pressurized refrigerant gas piping. The overload protection for both the circuit conductors and the motor itself is provided by overload relays mounted in the motor itself.
The upshot of all of that is that if the conductors are sized so that their table 310.16 ampacity equals or exceeds the minimum circuit ampacity that is on the compressor unit name plate then they are properly sized. Likewise if the supply circuit's OCPD does not exceed the maximum circuit over current protective device value, and type if any, that is shown on the compressor unit name plate it is also properly sized.
This also means that home inspectors should not attempt to do electrical inspections but should leave that work to Master Electricians and certified electrical inspectors.
RANT MODE ON IT ISN'T JUST COLOR TO COLOR PEOPLE! You cannot do safe, competent, nor cost effective electrical work without taking the time to actually learn the craft. IF YOU CANNOT OR WILL NOT TAKE THAT TIME THEN KEEP YOUR HANDS OUT OF ELECTRICAL EQUIPMENT AND KEEP YOUR "THOUGHTS" ABOUT HOW IT SHOULD BE DONE TO YOUR SELF! Incompetent advice is a bigger danger than incompetent work because the bad advise can cause dozens of hazards in multiple places instead of just one or two in one place. I have plenty of experience suppressing and reporting fires of electrical origin, injuries caused by electric shock, and deaths by electrocution. I AND THE REST OF THE NATIONS FIRE AND RESCUE SERVICE DO NOT NEED OR DESIRE ANY MORE! rant mode off.
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