Posted by John T on October 19, 2022 at 09:46:09 from (45.16.200.171):
I observed so much confusion below (plus several threads in over 20 years on here) that I feel compelled to try my best to provide some basic information regarding the current rating of an insulated conductor or what in the trade is referred to as its AMPACITY. What many (not all) lay and even some professional electricians or engineers may fail to understand is as follows:
1) Ampacity is based on the ability of the wire and its insulation to carry X amount of current and to be able to dissipate the heat so generated WITHOUT DAMAGING OR DEGRADING THE INSULATION or the conductor.
2) Ampacity of an insulated conductor is dependent upon several factors such as: a) Size and chemistry of the conductor (aluminum or copper etc) b) Temperature c) Type, Class and chemical make up of the insulator. d) If the conductor is single and in free air it has MUCH MUCH HIGHER ampacity versus MUCH less ampacity if jacketed (rubber, non metallic, romex) or enclosed in a raceway or conduit, and if so how many conductors and in what size conduit.
Dont take my word for it, heres what WIKIPEDIA has to say:
Ampacity is a portmanteau for ampere capacity defined by National Electrical Codes, in some North American countries. Ampacity is defined as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.[1] Also described as current-carrying capacity. The ampacity of a conductor depends on its ability to dissipate heat without damage to the conductor or its insulation. This is a function of the insulation temperature rating, the electrical resistance of the conductor material, the ambient temperature, and the ability of the insulated conductor to dissipate heat to the surrounds. All common electrical conductors have some resistance to the flow of electricity. Electric current flowing through them causes voltage drop and power dissipation, which heats conductors. Copper or aluminum can conduct a large amount of current without damage, but long before conductor damage, insulation would, typically, be damaged by the resultant heat.
A SINGLE CONDUCTOR IN FREE AIR (better ability to dissipate heat) HAS A GREATER AMPACITY and that can explain why if you look inside say a stove or clothes washer/dryer or a welder and see a rats nest of single conductors that are MUCH SMALLER than say some exterior conductors, plus loads are distributed to different wattage heating elements or taps on a transformer etc etc. What ONE input wire conducts may be spread and distributed over MANY different interior wires, explains why some could perhaps possibly be smaller ????
As BOTH an Electrical Engineer plus an Attorney familiar with product liability and those huge risks, I would bet and say for sure the ampacity of wires used inside a tool or appliance HAVE MORE THAN ADEQUATE AMPACITY to conduct current WITHOUT degrading or melting the insulation which could cause a short to case/frame and kill a user !!!!!!!!!!! No way their engineers and lawyers would risk under sizing the internal wiring.
As I posted below trying to help and answer our good friend and my neighbor George plus everyone, back when I practiced the NEC (maybe changed by now it changes every 3 years) prescribed method for selecting the conductors was to compute the Maximum Continuous Current and size the conductor to have a minimum of 125% rating of the MCC. That would apply to the home/shop distribution as well as an appliances interior wiring THE WIRE HAS TO BE BIG ENOUGH TO HANDLE THE CURRENT AND NOT MELT THE INSULATION Well DUH that makes sense to me
HOME AND SHOP ELECTRICAL DISTRIBUTION Back when I practiced and pursuant to the THEN NEC (may be different now it changes every 3 years so no warranty) if I had to design and specify wiring to feed a 50 Amp Receptacle I HAD TO USE 50 AMP RATED WIRE ..No way my boss would have let me get by specifying 12 Gauge to a 50 Amp receptacle. Thats NOT to say how the code today may be different or that a certain tool or appliance may not require as much current and get by with lighter duty electrical service THATS ALL IM SAYING ABOUT THAT
WELDERS as well all know welding at lower amps means less input current while max welding amps would draw much more primary current WELL DUH. If you only weld lower currents you can get by with MUCH LESS primary current. If I were to design the power to feed a welder I would use what is required IF I NEEDED TO WELD AT MAX HIGH CURRENT FOR SUSTAINED TIMES even if smaller cheaper wiring would get me by fine for the lighter welding. I have NO doubt for light duty lower current welding 12 Gauge wire could suffice just fine, but being me I would over engineer and provide adequate enough service/receptacle should I need to upgrade and/or weld at higher currents, Id rather do it now possibly OVER size than have to upgrade later.
There ya go, this is intended to HELP and explain NOT start a feud because I believe anyone has the right to wire as THEY so choose not what anyone here (me included) or the NEC has to say. Being I was trained in, practiced and attended NEC Seminars and Workshops over many years and understand the code and its reasons, I tend to follow it believing doing so may save a life or prevent a fire, but if anyone thinks they know better or have a better way or choose to do otherwise I SUPPORT THEIR RIGHT TO DO SO !!!!!!!!!!!
NOTE theres NO WAY can I explain nor expect anyone to understand in a few sentences what took years of study and practice to comprehend, but hey I try my best to help so cut me some slack if I made mistakes above
Best wishes and God Bless everyone here, be safe now
John T BSEE,JD Long retired n rusty EE but believe this remains true today
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