TOPIC: electrical

A couple times per week I will note #10 wire to a forty amp breaker, I will recommend a licenced elect. eval.I do this based on the understanding that #8 wire is always (rope type)or( stranded)So when I see the solid copper wire it screams wrong to me.I see this situation in both- new,& -older homes. It seems odd that brand new construction with recent APPROVED labels on them would be incorrect.... In what ? if any? situations does this become good enough to walk past ? Thank You.

I believe that this can be acceptable for an appliance like an air conditioner. The data plate on the air conditioner exterior condensor states the wire minimum ampacity.

This is old from the 2003 IRC

IRC 2003, E3602.11 Branch circuits for air-conditioning and heat pump equipment. The ampacity of the conductors supplying multi motor and combination load equipment shall not be less than the minimum circuit ampacity marked on the equipment. The branch-circuit overcurrent device rating shall be the size and type marked on the appliance and shall be listed for the specific purpose.

David nailed it. 
Most 40A breakers I run across are typically controlling HVAC equipment.  You would have to look at the data tag on the HVAC unit to determine the minimum ampacity circuit rating and the maximum allowable amp rating for the overcurrent protection device.  If you look at the next data tag you come across, you will see they are different and don't necessarily match wire size to breaker amperage.

If you look at the photo I attached, the data tag indicates Minimum circuit amps at 23.6A (which would be 12ga conductor) and Maximum Fuse or HVACR breaker rating at 40A.  This is what you must base your assessments upon of the breakers and conductors in the panel.  In this case, if you called out a 12ga conductor on a 40A breaker protecting the air conditioner... you would be incorrect in calling it out.

That does not compute Bill. Help me understand? Why would they allow 12g wire and then allow 40a breaker? There is no way that would support the load and the wire would glow before the breaker tripped.

WIres should be sized to handle the amp ratings shouldn't they?

It boils down to cost Sean.

The primary reason for the allowance with A/C units is that the sustainable load while the unit is operating will never reach 40amps... it may surge upon start-up near that, but the sustainable load will be around the minimum ampacity rating on the data tag.

I think the problem with this is as HVAC units age they tend to draw more amps plus if a compressor or condensing fan seizes
for a short time you could be cooking your 12 gage.