Dueling views over 40-amp breaker covering #10 wire ...

[fliks]

Just a show of hands. How many a permitting everything the do

You brought a smile there, true.

[David Goodman]

Another somewhat random thought.

If you have a chance, and you know how to do it safely, check out the wire sized used for the compressor and condenser fan motor leads.

If there was an instance of one of those motors drawing high amperage without tripping the OCPD, where do you think the overheating of wires and wire failure would occur first? In the condenser unit itself, or the wiring to the unit based on minimum circuit ampacity?

You might decide that you need to rewire the entire condenser unit if you don't trust what the manufacturers have done.

[timebuilder]

Guess what happens if the load exceeds the circuit capacity for long...


The wire gets warm and the breaker trips... from heat.

The wire will indeed experience an increase in temperature...but not for very long.... not enough to melt the insulation.....and certainly not enough to begin any combustion process.....which is why Underwriters Laboratories... the world's premier safety testing organization for electrical devices and appliances.....has approved this method for all listed equipment of this type.

[garyed]

Now you code guys are double talking. You say the wire will not heat up enough to melt the insulation before the breaker will trip. That may be true but that still doesn't mean its just as safe as having the larger wire sized to match the breaker. The code specifically sizes the wire for the breaker to address that problem of the wire overheating already. The whole reason for the exception that allows a smaller wire than the breaker calls for is because of the unit's rated MCA & the assumption that the unit's overload will protect the wire from exceeding its rating from anything except a dead short. Lets face it, you could run over 20 amps off #12 wire all day & never burn it up but that doesn't make it right. So I'm not saying this code is really dangerous but only that it makes no sense when it's supposed to be about safety. The breaker protects the conductor in a standard circuit but in a condenser circuit the condenser protects the conductor & breaker protects the unit I guess. The more I think about it the less sense it makes. I wonder what those code guys were smoking when they came up with this brainstorm.

[timebuilder]

Now you code guys are double talking. You say the wire will not heat up enough to melt the insulation before the breaker will trip. That may be true but that still doesn't mean its just as safe as having the larger wire sized to match the breaker. The code specifically sizes the wire for the breaker to address that problem of the wire overheating already. The whole reason for the exception that allows a smaller wire than the breaker calls for is because of the unit's rated MCA & the assumption that the unit's overload will protect the wire from exceeding its rating from anything except a dead short. Lets face it, you could run over 20 amps off #12 wire all day & never burn it up but that doesn't make it right. So I'm not saying this code is really dangerous but only that it makes no sense when it's supposed to be about safety. The breaker protects the conductor in a standard circuit but in a condenser circuit the condenser protects the conductor & breaker protects the unit I guess. The more I think about it the less sense it makes. I wonder what those code guys were smoking when they came up with this brainstorm.

The code recognizes that the insulation used is sufficient for the purpose.

Those code guys are:

Lifetime electrical experts
Doctorates in electrical engineering
Manufacturer technical experts, also degreed engineers
Electrical equipment manufacturers, all recognizable brand names
Practicing electricians
UL representatives
...and a host of others

Now, I'm not certain why you feel you can't trust these folks, but I have a recommendation or two:

Don't buy food at the store
don't drive
don't fly
don't take any meds
don't use anything electrical
don't use a ladder

ALL of these things require a level of trust in the expertise of a great number of people.... a level of trust that most folks not suffering from a debilitating condition are willing to exercise in the daily pursuit of happiness.

I feel truly sorry for those who are so cautious that they cannot live their lives.

[garyed]

The code recognizes that the insulation used is sufficient for the purpose.

Those code guys are:

Lifetime electrical experts
Doctorates in electrical engineering
Manufacturer technical experts, also degreed engineers
Electrical equipment manufacturers, all recognizable brand names
Practicing electricians
UL representatives
...and a host of others

Now, I'm not certain why you feel you can't trust these folks, but I have a recommendation or two:

Don't buy food at the store
don't drive
don't fly
don't take any meds
don't use anything electrical
don't use a ladder

ALL of these things require a level of trust in the expertise of a great number of people.... a level of trust that most folks not suffering from a debilitating condition are willing to exercise in the daily pursuit of happiness.

I feel truly sorry for those who are so cautious that they cannot live their lives.

It's not that i don't trust these guys because I realize they do a very thorough & good job. I'm only saying they are not perfect & they make mistakes & they have their egos to deal with no different than any of us. I keep trying to understand their logic in this matter & i just can't get passed the part about having the condenser protect the conductor. I can understand it in an industrial setting but it doesn't sound right in a residential setting. Like I said, i'm not worried about a fire but i just don't agree with the logic.

[DOGBOY]

Vendors that install equipment in your house don't have to sleep in that house with you.

There is nothing about the mikeholt video that addresses the possibility that anything could go wrong. The NEC evolved in 1897 as an offshoot of the National Fire Code. This computation method does nothing to address my fears that the overcurrent protection of the device might fail to function.

What happens, in spite of the best efforts of mice and men, when a device fed by #10 wire and protected by a 40 or 50 amp breaker, exceeds 30 amps for an extended period of time?

I think in that event, this interpretation of code is nothing more than hubris.

The real question is this: What risk are you willing to expose your family to?

I believe you have been showed the code and you are not getting the answer YOU want. I highlighted what I believe is the problem. If you have a short the breaker will trip even with #10 wire.

Ask this question to us. How many of you have seen a 30 to 60 amp circuit trip a 200a main breaker before the 30 to 60 amp breaker tripped. I for one have.

[vstech]

Now you code guys are double talking. You say the wire will not heat up enough to melt the insulation before the breaker will trip. That may be true but that still doesn't mean its just as safe as having the larger wire sized to match the breaker. The code specifically sizes the wire for the breaker to address that problem of the wire overheating already. The whole reason for the exception that allows a smaller wire than the breaker calls for is because of the unit's rated MCA & the assumption that the unit's overload will protect the wire from exceeding its rating from anything except a dead short. Lets face it, you could run over 20 amps off #12 wire all day & never burn it up but that doesn't make it right. So I'm not saying this code is really dangerous but only that it makes no sense when it's supposed to be about safety. The breaker protects the conductor in a standard circuit but in a condenser circuit the condenser protects the conductor & breaker protects the unit I guess. The more I think about it the less sense it makes. I wonder what those code guys were smoking when they came up with this brainstorm.

Look...

It is correct.

The actual load on a unit with a MCA of say 20 is going to be around 16 or less 99% of the time.

ALL BREAKERS ARE RATED AT 60C FOR A REASON... it is because the conductors if overloaded, will cause the breaker to trip from heat.

An inductive load has a high starting requirement. For less than 5 seconds...

And under the rest of the powered operation of the appliance, the load is substantially less than the conductor can handle...

Don't argue about it here... contact the NEC and argue with them.

[lasitter]

It is worth noting to those not versed in these ideas the the typical insulation listing is 90 C. A 40 amp breaker will open (clear the fault) before the conductor can be sufficiently heated to even cause melting of that insulation, much less to cause any combustion.

I finally did the conversion on this: 194 degrees Fahrenheit?

So if the 40 Amp breaker trips at 60C, it does so because it is picking up heat from the copper wires it is protecting, which are up to 194 degrees Farenheit?

Thanks for helping me understand what makes a breaker trip.

[timebuilder]

I finally did the conversion on this: 194 degrees Fahrenheit?

So if the 40 Amp breaker trips at 60C, it does so because it is picking up heat from the copper wires it is protecting, which are up to 194 degrees Farenheit?

Thanks for helping me understand what makes a breaker trip.

Not quite.

I mentioned the insulation to illustrate how very hot the insulation CAN become, without a problem as a result of its heating.

The breaker (early style) used a thermal element to actuate the trip. You won't find many of these still in use today.

Modern breakers use a magnetic element, which gives the mechanism a very close indication of the amount of current a circuit can draw at any moment. In addition, this breaker type is an "inverse time" design.

So no, the wire does not make the breaker trip because it gets warm.

http://www.schneider-electric.us/en/faqs/FA115818/

[BALloyd]

This right from Schneider's documentation on Square D circuit breakers.

"
Trip Curves

The tripping characteristics of QO and QOB circuit breakers can be represented by a characteristic
tripping curve that plots tripping time versus current level. The curve shows the amount of time required by a circuit breaker to trip at a given overcurrent level. The curve has a performance band that is bound by a minimum and a maximum value of clearing time. Total clearing time is the sum of the sensing time, unlatching time, mechanical operating time and arcing time of the circuit breaker. For currents in excess of 135% of the circuit breaker rating at rated ambient temperature (40°C), the circuit breaker will automatically open the circuit within limits specified by the band.


Thermal Tripping Characteristics

The upper left portion of each trip curve displays the thermal response of the circuit breaker. On low-fault current levels, up to the magnetic tripping level, thermal tripping occurs when a bimetal in the circuit breaker responds to heat associated with the overcurrent. The bimetal deflects, unlatching the mechanism and mechanically causing the circuit breaker to trip and open the circuit. The greater the overcurrent, the faster the circuit breaker will operate to clear the circuit.


Magnetic Tripping Characteristics

The lower right portion of each trip curve displays the magnetic tripping response of the circuit breaker.
This takes place when overcurrents of sufficient magnitude operate in an internal magnetic armature which unlatches the mechanism. Magnetic tripping occurs with no intentional time delay."

http://download.schneider-electric.c...0730CT9801.pdf

Sent from my SM-N910W8 using Tapatalk

[David Goodman]

I finally did the conversion on this: 194 degrees Fahrenheit?

So if the 40 Amp breaker trips at 60C, it does so because it is picking up heat from the copper wires it is protecting, which are up to 194 degrees Farenheit?

Thanks for helping me understand what makes a breaker trip.

I believe 60˚C is only 140˚F.

[timebuilder]

Magnetic Tripping Characteristics

The lower right portion of each trip curve displays the magnetic tripping response of the circuit breaker.
This takes place when overcurrents of sufficient magnitude operate in an internal magnetic armature which unlatches the mechanism. Magnetic tripping occurs with no intentional time delay."

This is the function of a breaker being used in the protection task in article 440.

Since the overloads provide conductor protection, the breaker provides ground fault and short circuit protection, which are characteristic of the magnetic trip function.

Years ago, a thermal mechanism was all that was available, and many manufacturers specified the use of fuses for the branch circuit for a condensing unit.