Welcome to the forum wec.
wec said:
Due to my biomedical engineering experience, I find myself being very conservative in my work.
Well that is good, I would hate to think that type of equipment was being designed 'on the edge'.
When dealing with AC power mains I find myself questioning some of the assumptions made by the NEC...
Now do not be offended but in my opinion your background in biomedical engineering does not begin to make you qualified to make assumptions about NEC requirements.
The NEC is a work in progress that is modified as needed every three years, the code is created by a wide range of people directly in the industry who are in a better position to decide what will and will not be acceptable.
such as the 15 amp rating on AC receptacles found in homes yet acceptable to utilize a 20 amp breaker.
Again this is all part of the listing process.
The internal parts of 15 amp duplex receptacle are in fact required by the listing to be capable of use on 20 amp branch circuits.
Imagine a 15 amp duplex on a 15 amp circuit, I can 'overload' that duplex by simply plugging in two loads that have a combined total above 15 amps.
As long as I have followed the NEC the circuit is still safe although it will likely trip out soon dependent on the amount of overload.
In my own home I utilized 12 AWG NM-B and placed 15 amp circuit breakers in those areas where I used '15 amp rated' plugs...
I have to ask why?
If the distances are long than perhaps 12 AWG on the 15 amp circuits will provide better serviceability (less voltage drop).
But it is really not safer by any appreciable amount.
14/2 NM is actually rated
20 amps, but like you the NEC is also conservative so there is an additional rule.
240.4(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.
12 AWG NM is actually rated 25 amps.
That being the case in my opinion unless you have unusually long circuit lengths using 25 amp rated conductors for 15 amp circuits is both wasteful of material and labor.
in the kitchen area or appliance area I choose to install 20 AMP rated plugs and then and only then did I place 20 Amp circuit breakers in the panel.
Again IMO this was an additional cost that actually provided
no increase in safety.
If you go and buy 15 and a 20 amp duplex receptacles from the same manufacturer and of the same grade than you where to take them apart you would find that the internal construction is entirely interchangeable.
The
only difference between a 15 or 20 duplex of the same manufacture and grade is the face that allows a 20 amp plug to be inserted in the 20 amp duplex.
Do you have any appliances in your house that have a 20 amp plug on them?
The above picture is a 120 volt 20 amp plug, I highly doubt you have a single appliance that has this plug.
Now again I am not saying any of what you have done is wrong, just unnecessary.
The money spent on those items could have been better spent IMO on more individual circuits, GFCIs, CO or smoke detectors etc.
Feel free to ask as many questions as you like here, there are many here much more familiar with the listing requirements of electrical products than I am.
Bob
