need to downgrade breaker (from 40amp to 15amp) for new hvac?

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Hello, I recently had a home inspection in preparation for selling my house. The inspector informed the buyer that I need to downgrade the circuit breaker (from 40amp to 15amp) for new hvac? He said he sees this problem a lot. My father, who does a lot of DIY including some electrical, says that if we change to 15amp when the hvac switches to aux. heat it will blow the breaker?
I need to find out if this really needs to be changed, the inspector warned the hvac unit could be damaged if this isn't changed. But I don't want to have the change done if it will cause problems when the unit goes to aux heat.
I'd call the hvac installer, but, clearly, they didn't think it was necessary to change the breaker & I'd really like an independent opinion on this.
ALSO, is changing a breaker best left to an electrician or might this be something we could do ourselves?
Thanks in advance for any input. WJ
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If the unit has an electric heating element in it that requires a 40 amp feeder, you don't want to change it. It may be possible that two feeds are required, one for the blower and a separate one for the heater and your father installed an improper jumper to feed both. I would call a local electrician to give a look

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Thank you for your responses.
We didn't do any of the wiring ourselves, the breaker is the same from the prior HVAC unit (ca. 1987), I'm fairly certain the contractor who installed the hvac a few months ago didn't make any change to the breaker(s). He seemed quite competent and earnest, so I'm a little reluctant to accept the inspector's word as gospel. Either way, I'm concerned about a liability situation down the road, so I'm trying to research this prior to having someone in to make a change.
The inspector stood in front of the breaker box pointing to the 40amp breaker when he made the statement, so I'm pretty certain he's referring to the breaker. The buyer read aloud a liability disclaimer based upon the inspector's report.
I read all of the literature that came with the unit - an electric heat pump/air conditioning unit w/air handler.
I did find this within the paperwork for the new unit (not sure if this is relative): <i> This unit is designed for single-phase electrical supply. DO NOT OPERATE ON A THREE-PHASE POWER SUPPLY. Measure the power supply to the unit. The supply voltage must be in agreement with the unit nameplate power requirements and within the range shown in: Nominal Input 208/240 Minimum Voltage 187 Maximum Voltage 253 </i> I don't mind saying this is pretty much greek to me, but does this mean if I check the plate on the unit I'll be able to tell what kind of breaker is best (based upon the range info above)?
I plan on having someone come in to make the change, if it's necessary, but I'd like to have an idea of whether it needs to be done before 'going there.'
Again, thank you so much for any input.
WJ
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Yes, but what Bill Allerman posted is important as well. The feeder cable must be sized for a 40 amp breaker, which would be at least #8. Look on the unit's name plate for an amperage rating or even a recommended circuit breaker size. The full load amperage will determine the size wire and breaker required

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On Sun, 24 Jun 2007 11:36:02 -0400, "RBM" <rbm2(remove

Nope, not on an HVAC condenser. Read the label on the condenser and size the breaker/wire accordingly You should see miminum circuit ampacity, that is the wire size based on 301.16 (not 240.4(D) so 12ga is good for 25a, 14ga 20a. Then look at maximum branch circuit over protection size and that is the breaker you can use. It will NOT be what you would think. This is for short circuit protection, not overload protection, that is internal in the compressor as a general rule. You can very well see a 40a breaker on 14 ga wire.
All that said you still have to wire and protect the heater strips in the air handler like a regular circuit, using the 310.16 rating on the wire. Again that will be in the installation instructions as to what wire and breaker combo you need for each heater option size.
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I don't believe it's on a condenser. I think it's an air handler with heating strips
wrote:

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wrote:

??????????????????????????????????????????????????
It is a violation of code to put a 20a breaker on 14ga wire! 12ga is required!!!!!!!

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Mike Dobony wrote:

For motors the rules change. The breaker protects the wire from short circuits, not overloads, as gfretwell said. Rather arcane rules for motors are among the reasons why electricians have licenses.
It is not possible to give an answer to the OP's question without nameplate information for the equipment connected and wire size. I wouldn't necessarily trust a home inspector apply the rules. I also wouldn't necessarily trust an installer to do the electrical right - particularly if the electrical was not done by an electrician.
-- bud--

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wrote:

Exactly right Bud. In fact there is a question on every inspector exam I have taken about a 115v 1HP motor with internal overload protection (16a FLA) and the correct answer is "40a breaker, 14 ga wire". I understand this is an anomally using all the exceptions and "round up" rules but it is NEC compliant.
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Really?
That's plain nuts!
Your run of the mill CB takes seconds to trip just from FLA currents. There just isn't any need to put a 40 amp breaker on a motor circuit.
If there is something about the motor the keeps it from coming up to speed in a second or two then fix that. But don't put a 40 amp breaker on #14 wire.
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wrote:

I suppose I could walk you through it all but this is what the code allows The short answer is 16a FLA from the nameplate is 20a, Article 430 (motors) is one of the exceptions to 240.4(D) (the 14a rule) in 240.4(G) 310.16 (the wire ampacity table) lists 14 ga copper at 20a in the 60c column. If you have internal overload protection you can use table 430.52 to size the branch circuit O/C device. If that is an inverse time breaker it can be 250% of FLA (16 x 2,5 @a)
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John Gilmer wrote:

FLA (full load amps) are not the problem. Starting current/LRA (locked rotor amps) are. I presume this was a typo on your part.
As a rule of thumb a motor draws a current (LRA) of about 6x its FLA when it starts.
Looking at a SquareD current - trip-time curve, at 6x the rated breaker current a breaker may be in it's "instantaneous" trip region - no time delay.
If the motor was rated 80% of the breaker rating (more likely) the starting current is (0.8)x(6) = 5.4x the breaker rating. The trip time can be 0.3 to 2.5 seconds - not reliable.
Obviously the motor current goes down as the motor accelerates. But that doesn't help in the instantaneous trip region. And in the 0.3 to 2.5 sec range there is no guarantee the motor will start. If turn up a thermostat then turn it down a refrigeration compressor it will likely not restart immediately. That causes the LRA until the motor protector opens the circuit. You would generally not want the circuit breaker to open. And high inertia motor loads increase the time to start.
The NEC is really quite pragmatic. Rules like this come from field experience as well as engineering considerations. Not only can a circuit breaker be 250% of FLA, as in gfretwell's example - if the breaker does not permit the motor to start the breaker can be increased to 300 or 400% of the FLA.
And as has been a couple times, the breaker provides short circuit protection for the wire, not overload protection.
-- bud
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I have one issue with your otherwise excellent post -- this last sentence:

The breaker provides *overcurrent* protection for the wire -- IOW, the breaker is sized to open if more current is flowing through the wire than it can safely handle. This does not occur solely through short circuits, but can result from overload as well (e.g. fifty 60W incandescent light bulbs on a single 15A circuit is supposed to pop the breaker, even though there is no short).
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

Note that gfretwell and I agree on this.
This is a motor circuit, not light bulbs. The rules are in article 430.
The circuit breaker provides *short circuit* protection - 430 part 5.
*Overload protection* is typically provided by thermal overload units in, or attached to, the motor. - or motor starter (contactor) overload units - 430 part 4. (Note that the overload protection is near the motor, not the panel.)
Wire size is 430 part 2.
gfretwell's nice 'worst case' example gave code citations for his calculations - would be a good place to start.
IMHO article 430 is of similar difficulty to article 230 - grounding. Article 230 is the most difficult of the commonly used articles. As I wrote earlier, there is a reason why electricians are required to have licenses (in many jurisdictions).
If you (and John) are appalled by the 'oversizing' of the breakers for motors make sure you don't read article 630 - welders. Particularly for low duty cycle welders.
-- bud--
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Right, I know -- I'm objecting to what appeared, at least, to be a general statement that breakers provide only short-circuit protection. In the specific cases you cited, that's correct, but as a general rule, it's not.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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On Wed, 27 Jun 2007 15:43:25 GMT, snipped-for-privacy@milmac.com (Doug Miller) wrote:

Doug I think the point was that in the case of motors on dedicated circuits the rules are different. You are right that in general lighting circuits the breaker provides overload protection as well as overcurrent protection. The installer has no control over what the user will plug in. That is the reason why we have atrticle 240.4(D) that gives us the familiar rule of thumb 14gaa, 12ga a, 10ga0a This includes the other general rule of thumb that you shouldn't load a circuit more than 80%. The 80% is built into this limit when you look at what 310.16 says the wire is really good for. (14ga a) NFPA knows the typical user will keep loading a circuit until the breaker trips and then unplug the clock if that is all it takes to make it hold.
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Right, I know that. I just wanted to make sure it was understood that as a _general_ rule, breakers are there to provide overcurrent protection generally, which is not the same as short circuit protection.
--
Regards,
Doug Miller (alphageek at milmac dot com)
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Doug Miller wrote:

My post was in the context of motors.
Your response was general - it would have helped if it was limited to non-motors.
-- bud--
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On Sun, 24 Jun 2007 19:13:09 -0500, "Mike Dobony"

Read article 440 and 430, then get back to me. You are citing 240.4(D) and is says
(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.
HVAC units are one of the exceptions in (G)
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Then change the breaker and add into the purchase agreement a disclaimer for the inadequate breaker and lay hte blame on future breaker trips on the incompetent inspector. Include power requirements (amp draw) of the HVAC unit. Your attorney should know how to word it and lay the blame and liability squarely upon the inspector's report. Be absolutely certain to include the SIGNED (the inspector and buyer's signatures) inspection report in the closing of the house. Have fun finding a 15 amp 240 breaker! 20 is about the smallest I have seen and if you do find one, the wires might be too big to fit them into the breaker! All you need to do to replace it is to shut if off, take off the breaker box cover, unscrew the wires, pull out the breaker, put the new one in, connect the wires, replace the cover, and turn it back on. Simple job!

I can guarantee that it draws MUCH more than 15 amps unless it is a micro .25 ton unit! My 2 ton requires a 25 amp breaker and it also needs the furnace! An electric heat pump plus aux heat requires even more amperage!

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