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

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




wrote in message
ups.com...
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

Maybe the inspector is talking about the size of the conducter on the
breaker? If it's #8, it is correct for the 40A breaker.
If it's smaller, the breaker needs to be changed appropriately.

Bill

wrote in message
ups.com...
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

wrote:
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?


I have a feeling the inspector doesn't have a clue, but...

Is this a new HVAC installation? Is this an existing breaker w/ a new
unit or a new installation for it? Either way, if the unit has been
recently installed, I'd first just check w/ the installers and find out
what they say before anything else. If it is a new installation, you
may well have some information for the unit that describes the required
service feed(s) -- check for that.

As someone else noted, if the service feed to the unit is sized properly
for the existing wiring, it's unlikely the breaker needs to be changed.
The point of breakers in distribution panels is to protect the wiring,
_not_ the device. The unit itself will be protected by internal fusing
or breakers or a combination of both. Thinking a breaker must match a
nameplate load rating for "protection" of the load device is a common
misconception I've found more than one inspector to have (hence my first
comment).

If you don't get a satisfactory response from the HVAC guys or from what
you can learn from the information left w/ the unit (again, assuming
it's new), then if you don't have sufficient expertise to determine for
sure it's time to ask an electrician out to check. I'd think it
unlikely to need that much, but you may have to go that route if the
inspection report has actually gone to the potential buyer to have
sufficient pedigree to satisfy...

Methinks this will turn out to be a tempest in a teapot...

--

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







wrote in message
ups.com...
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

Thank you for your reply dpb, I missed it when I posted a few minutes
ago, I lost a post somewhere, so if this one is a duplicate, my
apologies.

See, I think you could be right about the inspector. I'm sure he's
quite knowledgable, but if he's seen this problem often, I figure hvac
units are installed by certified hvac techs.. who would be more likely
to be the expert? Additionally, the lack of any liability for his
findings/report makes me hesitate to take his word as gospel... if
he's wrong & there's a problem w/the unit after we switch to 15amp,
who is liable? maybe me? I may end up telling the buyers if they
want me to have it changed, I'll have it changed, but I've let them
know I'm not certain it should be done. I'd contact the
manufacturer, but I'm afraid of voiding the warranty.

This is a new unit, installed a few months ago, installer seemed quite
competent and knowledgable.

wrote in message .

See, I think you could be right about the inspector. I'm sure he's
quite knowledgable, but if he's seen this problem often, I figure hvac
units are installed by certified hvac techs.. who would be more likely
to be the expert?

Unfortunately, in my experience in many cases it is the inspector. Many
"certified" HVAC techs take shortcuts if they can get away with it. After
the #1 shortcut (inadequate evacuation prior to system charging), failing to
downsize a breaker when installing a more efficient system is probably the
#2 shortcut taken. Having said this a reduction is breaker size from 40A to
15A seems a bit extreme unless there was a significant change in the system
(for example, the elimination of resistive heat strips in the air handler).

This is a new unit, installed a few months ago, installer seemed quite
competent and knowledgable.

See comment above. Did the installation require a permit in your
municipality? Was one pulled? Did the installation pass the municipality's
final inspection? If no permit was pulled and one is required, the HVAC
installer was probably a hack.

Finally, are we talking about the breaker for the air handler or the
condenser? Does the air handler have heat strips (aka emergency heat)?
What is the make and model of the air handler and condenser, and what are
the specifications for the electrical supply for each (note: should be on
manufacturer's nameplate)?

First time posting so this is a test.

I don't believe it's on a condenser. I think it's an air handler with
heating strips


wrote in message
...
On Sun, 24 Jun 2007 11:36:02 -0400, "RBM" rbm2(remove
wrote:

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

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.

On Sun, 24 Jun 2007 05:03:32 -0700, wrote:

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


I would as why?

Gauge of wire too small, per maker's instructions, etc. Oh, are you
sure you got this right, did you get it on paper or overhead a
conversation. I'm guessing a communication error first.

tom @ www.NoCostAds.com

wrote in message
ups.com...
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


What I have seen done a lot is for the breaker in the main panel to NOT be
changed when a new unit is installed but the correct sized breaker to be
installed in the disconnect box located next to the unit. Assuming the wire
from the breaker to the disconnect box is properly sized this would be fine.
Not something the average home inspector is smart enough to realize.

The final protection for the unit is at the disconnect box. The wiring may
be able to carry 40 amps to the disconnect but if that is a 20 amp breaker
only 20 can pass to the unit.

By doing it this way the HVAC contractor has not messed with your wiring or
your breaker box and is only liable for the disconnect and the unit. It is
a CYA (his A) type of thing.

If that is the case a simple letter from the HVAC contractor should be
enough to satisfy the "repair requirements" of the home inspection. You
should offer to pay the HVAC for the time to write the letter. Most will
not charge.

I have never seen a home inspector argue with a licensed person who is
willing to commit something to writing.

Colbyt

Travis Jordan wrote:
wrote in message .
See, I think you could be right about the inspector. I'm sure he's
quite knowledgable, but if he's seen this problem often, I figure hvac
units are installed by certified hvac techs.. who would be more likely
to be the expert?

Unfortunately, in my experience in many cases it is the inspector. Many
"certified" HVAC techs take shortcuts if they can get away with it. After
the #1 shortcut (inadequate evacuation prior to system charging), failing to
downsize a breaker when installing a more efficient system is probably the
#2 shortcut taken. ....

What, precisely, is the "shortcut"? If the existing wiring is sized for
40A, the circuit breaker isn't intended to do anything but protect the
wiring from short circuit faults, _NOT_ the load device, whatever it is.

--

wrote:
...

See, I think you could be right about the inspector. I'm sure he's
quite knowledgable, but if he's seen this problem often, I figure hvac
units are installed by certified hvac techs.. who would be more likely
to be the expert?

I'm not that confident in his expertise... In fact, I'm giving
pretty low odds that he is right on this and, conversely, the other way
'round that he has the misconception of the breaker supposedly
protecting the device...I fully expect that the vendor requirement will
be for a _minimum_ of some value and as long as the original circuit
wasn't miswired the larger breaker is perfectly find for its intended
purpose.

Additionally, the lack of any liability for his
findings/report makes me hesitate to take his word as gospel... if
he's wrong & there's a problem w/the unit after we switch to 15amp,
who is liable? maybe me? I may end up telling the buyers if they
want me to have it changed, I'll have it changed, but I've let them
know I'm not certain it should be done.

The worst that can happen is the unit will trip so guess you could just
leave them w/ the problem. My understanding of the disclosure rules is
you make a disclosure of existing conditions, it's up to the buyer to
agree/reject/negotiate.

...I'd contact the
manufacturer, but I'm afraid of voiding the warranty.

No how, no way can simply asking a question affect the warranty.

This is a new unit, installed a few months ago, installer seemed quite
competent and knowledgable.

And I'd wager they probably were/are. If you haven't, I'd check w/ them
and get an explanation of their understanding of the inspector's
concern. If it makes sense (as I suspect it will) I'd give it to the
buyer and go on. If not, then you can decide whether an independent
opinion is worth the $$ or not.

OBTW, changing a breaker is pretty simple. Of course, be sure to turn
the feeder breaker off...

--

wrote in message
ups.com...
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.


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 read all of the literature that came with the unit - an electric
heat pump/air conditioning unit w/air handler.


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!

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

wrote in message
...
On Sun, 24 Jun 2007 11:36:02 -0400, "RBM" rbm2(remove
wrote:

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

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.

??????????????????????????????????????????????????

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


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.

Travis J beat me to the puch on the question: Is this breaker for the
outside condensing unit, or for the inside air handler? Very few
condensing units call for a 15amp breaker. I have only seen a
couple--certain brands of 1.5 and possibly 2 ton units. Regardless, the
unit will have a maximum breaker size on the data plate, and some brands
list a minimum as well. Go with whatever it says, making sure the wire
is large enough. Larger wire than necessary is fine. If it is the air
handler you are referring to, even the smallest heat strips made will
require a lot more than 15 amps. The problem is that the airhandlers are
usually ordered without heat strips, and they are ordered separately and
installed when the unit is installed. You have to first know what size
heat strips you have ---they can be from 3KW to 20 KW. They are sized
according to the amount of heat desired, and the available power. Call
the installer and get all the info from them. They may be willing to
talk to the inspector and get this resolved over the phone. Our service
mgr gets involved with things like this from time to time. Good luck
Larry

"dpb" wrote in message:
What, precisely, is the "shortcut"? If the existing wiring is sized for
40A, the circuit breaker isn't intended to do anything but protect the
wiring from short circuit faults, _NOT_ the load device, whatever it is.

The circuit breaker is there to protect the load device and the wiring. The
shortcut is that some installers don't downsize the breaker when installing
a more efficient system. The NEC, most state building codes require
appropriate sizing. Most HVAC manufacturers specify the maximum fuse size
(MFS) and maximum circuit breaker size (MCB) for protection of their
equipment. Of course the wire size has to be large enough for the intended
load.

Generally the calculation is:
MCB = 2.25 x largest motor amps (FLA or RLA) + the sum of the remaining
motor amps.

Mike Dobony wrote:
wrote in message
...
On Sun, 24 Jun 2007 11:36:02 -0400, "RBM" rbm2(remove
wrote:

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

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.

??????????????????????????????????????????????????

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


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--




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.

Travis Jordan wrote:
"dpb" wrote in message:
What, precisely, is the "shortcut"? If the existing wiring is sized for
40A, the circuit breaker isn't intended to do anything but protect the
wiring from short circuit faults, _NOT_ the load device, whatever it is.

The circuit breaker is there to protect the load device and the wiring. The
shortcut is that some installers don't downsize the breaker when installing
a more efficient system. ...

40A to 15A more efficient???? Now THAT is one efficient system...

I ain't buyin', sorry.

--

wrote in message
...
On Mon, 25 Jun 2007 10:00:27 -0500, Bud--
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.


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.

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.

"dpb" wrote...

40A to 15A more efficient???? Now THAT is one efficient system...

I ain't buyin', sorry.

Normally I'd agree, but if a resistive heat air handler was changed out for
a variable speed heatpump only air handler, it would be completely logical.
Or maybe the original breaker was oversized.

Travis Jordan" wrote...
"dpb" wrote...

40A to 15A more efficient???? Now THAT is one efficient system...

I ain't buyin', sorry.

Normally I'd agree, but if a resistive heat air handler was changed out
for a variable speed heatpump only air handler, it would be completely
logical. Or maybe the original breaker was oversized.

I just checked Trane's documentation and all of their 1.5T and smaller heat
pump systems state a MCB of 15A. It is quite possible the old system (1987
vintage, probably twice the load) had an oversized breaker installed also.

John Gilmer wrote:
wrote in message
...
On Mon, 25 Jun 2007 10:00:27 -0500, Bud--
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.

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.

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.


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

In article , Bud-- wrote:

I have one issue with your otherwise excellent post -- this last sentence:

And as has been a couple times, the breaker provides short circuit
protection for the wire, not overload protection.

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)

It's time to throw all their damned tea in the harbor again.

Travis Jordan wrote:
"dpb" wrote...

40A to 15A more efficient???? Now THAT is one efficient system...

I ain't buyin', sorry.

Normally I'd agree, but if a resistive heat air handler was changed out for
a variable speed heatpump only air handler, it would be completely logical.

Except OP specifically spoke of "emergency heat" kicking on which seems
to preclude that -- or, of course, could be he just does not know what
he just bought and paid for and had installed...

Or maybe the original breaker was oversized.

In about the same category as the above...

imo, ymmv, $0.02, etc., etc., ...

--

Doug Miller wrote:
In article , Bud-- wrote:

I have one issue with your otherwise excellent post -- this last sentence:

And as has been a couple times, the breaker provides short circuit
protection for the wire, not overload protection.

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).


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--

In article , Bud-- wrote:
Doug Miller wrote:
In article , Bud--
wrote:

I have one issue with your otherwise excellent post -- this last sentence:

And as has been a couple times, the breaker provides short circuit
protection for the wire, not overload protection.

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).


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.

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)

It's time to throw all their damned tea in the harbor again.

In article , wrote:
On Wed, 27 Jun 2007 15:43:25 GMT, (Doug Miller)
wrote:

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.

Doug I think the point was that in the case of motors on dedicated
circuits the rules are different.

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)

It's time to throw all their damned tea in the harbor again.

If the unit has aux heat, it may very well need 40 amps. Read the
manual.

If you have to ask, you don't have the skills. I wouldn't
reccomend to open a panel box unless you've seen it done several
times, and have someone experienced working with you.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
..

wrote in message
ups.com...
: 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
:

See if the paper work mentions the word amp, or ampacity.

Since this is greek, please leave the panel box closed. For your
safety, you see.

--

Christopher A. Young
You can't shout down a troll.
You have to starve them.
..

wrote in message
ups.com...
: 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
:
:

Doug Miller wrote:
In article , Bud-- wrote:
Doug Miller wrote:
In article , Bud--
wrote:
I have one issue with your otherwise excellent post -- this last sentence:

And as has been a couple times, the breaker provides short circuit
protection for the wire, not overload protection.

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).



This is a motor circuit, not light bulbs. The rules are in article 430.



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.


My post was in the context of motors.

Your response was general - it would have helped if it was limited to
non-motors.

--
bud--