Is ampacity overkill by NEC standards?

[mbrooke]

I agree to some extent on some of your installation examples. I do feel there are some continuous loads in some dwellings though that do need to take extra heating because of continuous load into consideration - in particlular heating or cooling loads.

That's true, but in a resi panel the breakers around then are not likely to have a continuous load. A resi panel has enough load diversity that heat can dissipate to lightly loaded/unloaded breakers.

I can go to some commercial/industrial sites and notice some heat in panelboards because of loading conditions, but go to a dwelling and you seldom notice that but if you do it is usually either a breaker supplying an air conditioner that has been running most of the day or on an electric heat circuit that has been running continuous or near continuous.

In commercial and industrial if all 42 spaces are under full load heat build up does get extreme, but in a resi application that just doesn't happen to such a degree.

GFP lags the rest of the world because they (the CMP's) got stuck (more like bought by the AFCI manufacturers) on AFCI's instead.

Im with you on this. We got stuck with AFCIs :happysad:

Of course our society demands a lot of these requirements not only because the owners/users need a safe installation, but the installers need a standard to follow to help prevent or minimize lawsuits when something does go wrong. Prove that you followed the standard in court and it will bring your liability potential down much faster then if you didn't follow the standard - have an inspection program affirm that your install met the standard helps you even more. That leads to if you are going to have a standard, what good does it do if you continually let people modify it as they see fit? Bad enough we have AHJ's every where that make modifications to the standard as it is, just makes it harder for the installers that work in more then one AHJ area to make sure they keep up with what is essentially a new standard in every jurisdiction.

True, but a lot of what the NEC mandates is to protect unqualified personnel. In most parts of the world single fixed loads are treated much like a motor or AC unit, the breaker can be larger than the wire because in theory the load will not draw more than its rating. In turn the circuit only needs short circuit and ground fault protection. But in the US a DIY could easily swap a 2kw heater for a 10kw heater creating a danger with their reason being if the breaker says 30amps then the wire must be good for that to. Ditto for handle ties on MWBC. There is nothing dangerous about not having handle ties, but unqualified personnel where opening neutrals under load unaware that a neutral could be shared. Luminaire disconnects, arc flash, ect ect, all to protect the untrained.


IMO the NEC should not make leeway for unqualified personnel. As Iwire once said "If idiots where the only thing we had to consider working on electrical systems we would have to shut down the entire power grid because idiots can screw up a 2 wire lamp cord."

 

[kwired]

In a 90C ambient temperature, we'd all be dead.

That's true, but in a resi panel the breakers around then are not likely to have a continuous load. A resi panel has enough load diversity that heat can dissipate to lightly loaded/unloaded breakers.






In commercial and industrial if all 42 spaces are under full load heat build up does get extreme, but in a resi application that just doesn't happen to such a degree.





Im with you on this. We got stuck with AFCIs :happysad:






True, but a lot of what the NEC mandates is to protect unqualified personnel. In most parts of the world single fixed loads are treated much like a motor or AC unit, the breaker can be larger than the wire because in theory the load will not draw more than its rating. In turn the circuit only needs short circuit and ground fault protection. But in the US a DIY could easily swap a 2kw heater for a 10kw heater creating a danger with their reason being if the breaker says 30amps then the wire must be good for that to. Ditto for handle ties on MWBC. There is nothing dangerous about not having handle ties, but unqualified personnel where opening neutrals under load unaware that a neutral could be shared. Luminaire disconnects, arc flash, ect ect, all to protect the untrained.


IMO the NEC should not make leeway for unqualified personnel. As Iwire once said "If idiots where the only thing we had to consider working on electrical systems we would have to shut down the entire power grid because idiots can screw up a 2 wire lamp cord."

I think the luminaire disconnects rule was mostly because of "qualified" people getting electrocuted when making ballast changes without turning off power to the luminaire.

NEC doesn't have too many rules directly related to arc flash - but have added a few more in last couple editions, the bulk of arc flash rules are there because of OSHA - and even they don't have specific rules so much as they require a safety rules standard to be in place - and it is easier to just say we will use 70E then it is to try to write your own standard and cover everything as well as 70E does, but then you do have to follow it if it is your chosen safety standard.

 

[mbrooke]

I think the luminaire disconnects rule was mostly because of "qualified" people getting electrocuted when making ballast changes without turning off power to the luminaire.

Not qualified in my book. glove up or shut down.



NEC doesn't have too many rules directly related to arc flash - but have added a few more in last couple editions, the bulk of arc flash rules are there because of OSHA - and even they don't have specific rules so much as they require a safety rules standard to be in place - and it is easier to just say we will use 70E then it is to try to write your own standard and cover everything as well as 70E does, but then you do have to follow it if it is your chosen safety standard.[/QUOTE]


Still think selective interlocking/differential/other approved means are not necessary when people shut down and lock out imo.

 

[kwired]

Not qualified in my book. glove up or shut down.



NEC doesn't have too many rules directly related to arc flash - but have added a few more in last couple editions, the bulk of arc flash rules are there because of OSHA - and even they don't have specific rules so much as they require a safety rules standard to be in place - and it is easier to just say we will use 70E then it is to try to write your own standard and cover everything as well as 70E does, but then you do have to follow it if it is your chosen safety standard.

Still think selective interlocking/differential/other approved means are not necessary when people shut down and lock out imo.[/QUOTE]Makes sense, but not qualified don't understand the hazards in the first place and are not going to have proper gloves or other appropriate PPE and they don't know LOTO either - if they did know any of those things they are much more likely to be considered qualified.