Vent on electrical ratings

I have seen many questions on wire sizes. It is important to understand that the NEC and other codes state the MINIMUM requirements, and must be upsized if necessary. The BREAKER protects the wiring, and thermal overloads protect the motor.

It does not matter what someone thinks will work, the codes state what will work safely.

There are so many factors to be considered. One that comes to mind if a pipe nipple is 24 inches or less there is no derating and alot more fill allowed. I noticed in a question [from Tooltalk] about wire size so I plugged the number into a voltage drop calculator which automatically corrected wire size before giving the VD. Then another guy posted an online VD calculator stated to rum too small a wire size. It takes five years of school to become an electrician . Another thing is the fill into some of the pipe allowed by code is very tight and it may behoove one to step up a pipe size for ease of wire installation. It's not rocket science but you have to spend some time with the code.

VERY GOOD Great Post

A) I (long retired EE) have also advised the NEC calls out MINIMUM acceptable standards to protect life and property but that DOES NOT MEAN one cant exceed those standards. In fact, if things ever got "close" I, as a conservative designer, would opt for an upgrade or even bigger wire etc just to err on the safe and conservative side, thats just how Im WIRED lol

B) YES its NOT what anyone here (including yours truly) says or thinks that matters regardless if their opinion is lay or trained professional, ITS WHAT THE LOCAL AUTHORITY SAYS that counts the most. HOWEVER, if the local authority suggests something LESS then what the NEC calls for as a minimum standard THAT WOULD MAKE ME NERVOUS...........

C) As far as protecting motors and motor branch circuits YES YOURE RIGHT. The purpose of a circuit breaker in the motor branch circuit is to protect the feeders. The purpose of the thermal overload protection device (perhaps integral to motor or inside a motor starter or combination strter) IS TO PROTECT THE MOTOR FROM OVERHEAT AND OVERCURRENT. NOTE there are certain limited situations and exceptions in which the circuit breaker may be sized bigger then normal if necessary to allow the motor to start.

NOWWWWWWWWWW AS FAR AS WIRE SIZES they way I approached it as a conservative designer was as follows:

1) You FIRST compute the max continuous load

2) You size the wire so the load is no greater then 80% of the max continuous load

3) You size the overcurrent protection device to match and protect the wires ampacity i.e. if you use 20 amp rated wire, you use no bigger then a 20 amp breaker WELL DUHHHHHHHH

AND

You calculate VOLTAGE DROP and if the voltage drop is excessive then you increase the wire size unitl the drop is acceptable.

SUBJECT TO SOME EXCEPTIONS FOR WELDERS AND DUTY CYCLES ETC

NOTE if you do all the above and the wire is properly protected and the voltage drop is within limits, all will work and theres really no need to go wild and double or triple the wire sizes like some lay persons may suggest, but hey if that turns your crank or floats your boat or your dad did it that way HEY IM NOT STOPPING YOU its your house and your money so go for it. Im ONLY saying if you apply the NEC minimum standards and compute loads and dont exceed 80% of the max load current in the wires rating and if voltage drop is within limits THAT WILL WORK FINE AND SATISFY THE NEC AND MOST LOCAL AUTHORITY but feel free to do as yall please and double or triple wire if you have a need..

PS many people look at short hand versions or incomplete wire ampacity charts and dont realize those ratings depend on MANY VARIABLES SUCH AS............. Temperature,,,,,,,,,,Conductors in free air or enclosed,,,,,,,,,If enclosed (or buried in earth) how many conductors in what enclosures,,,,,,,,,,The class of insulation

Sooooooooooo you have been so advised

FUN chat, great post, thanks

John T

The breaker on a motor feeder is for ground fault / short circuit protection. The overloads of the controller are what really protects the motor AND feeder. The breaker for a motor feeder is often 250% of the motor nameplate full amperage, and that will typically be well above the raiting of the wire to feed the motor.....that is where the overloads come into play....

The NEC is not law nor required everywhere and it is written by imperfect people. There have been times when the NEC has been wrong and fire and deaths resulted. Remember their first recommendations on aluminum wiring back 40-50 years ago?

In my opinion, anybody doing wiring ought to use his/her common sense along with outside reading and research besides what is "suggested" in the code. If not capable of that, maybe the person shouldn't be wiring anyway. I would never stake MY life on anything in the code-book. Some is WAY overboard and some is too understated.

The NEC is the guideline that most agencies use as a minimum baseline. John T spoke it correct when he stated that local authorities should be the ones that make the call, not anyone on this board.

That was my experience as an EE over forty years, THE LOCAL AUTHORITES are the ones who sign off or reject the work REGARDLESS OF WHAT ANY NEC OR ME OR FOR SURE WHAT ANYONE THINKS HERE

Also in all my years and NEC Seminars and in the field experiences Id for sure trust my familys life in what the NEC thought versus any lay or even less qualified professionals may think and for sure anyone here if they disagreed. You pay your money and take your chances, Id take mine on the NEC experts versus any lay persons butttttttttttt you must temper that with the fact Im also trained and experienced so I dont just take what they say blindly ya know, Id think it over first then decide to believe the NEC or myself or others.

Fun Chat

John T

Make the "call" for who? When I'm working on my own properties, I make the call. If it's someone else - it's up to them if they want to delegate responsibility to some government official who may , or may not be competent.

From what I've seen here on these forums - posters ask questions and get responses, not "calls' that dictate anyone's behavior.

But yes, government agencies usually rely on some sort of written "fits all" code with allowance for discression and lee-way by the code enforcement officer. Many states take part of the NEC and then add their own stuff to it (or subtract).

The current NEC code if followed is safe. It is also ridiculous in some areas. I was just required to hard-wire AC smoke/fire alarms in a cabin that has NO AC electricity and never will.

As far as this thread based on some sort of "vent" due to minimum specs? I don't get it. When it comes to voltage drop, wire insulation types, wire ampacity, alloy conductivity, the code book is very clear.