Wire gauge for given load

Not electronics per se, but it deals with electricity.

I was looking for a site that would tell me which gauge wire to use based on amps and length of wire.

Wanted to run 3 feet for a 15 amp load.

For a 4 amp bench grinder and a room fan.

Thanks, Andy

Reply to
Andy
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15 amp circuits are usually 14 Gauge.

For 3 ft you could go smaller, but then don't put any load other than your 4 amp grinder and a small fan on the circuit. Here are a couple of charts. I'd use 14 gauge.

Mikek

Reply to
amdx

Shouldn't it be based on what the breaker is rated for that feeds the point he wants to connect to?

You would not use 14 ga wire to extend a 20 amp circuit.

Reply to
tom

As Mike said, the NEC says 14Ga but that's assuming a lot longer run and the wires being enclosed in a wall. The real issue, here, is going to be the voltage drop for the motors. Figure out what's acceptable and the resistance of the wire you want to use, and you have your answer. ...then just use 14Ga wire.

Reply to
krw

That's only true if it's part of the building wiring.

You've never used a 16Ga or 18Ga extension cord? You've never plugged a lamp into an outlet? OTOH, it's not clear what he's doing.

Reply to
krw

I took some 14 gauge wire and ran it to an outlet controlled by a standard wall switch.

I thought about incorporating a foot switch, but decided to just extend my setup so I don't have so far to reach to flip the switch.

Hope that makes sense.

Andy

I have a 14 gauge wire supplying to an outlet with a switch.

Reply to
Andy

over 3 feet? You're funny

NT

Reply to
tabbypurr

That's all that matters. He could use 30Ga wire if the drop isn't exceeded. ...unless it's part of the permanent wiring.

Reply to
krw

Why not just buy an 3 foot extension cord rated for air conditioners? With a heavy duty 3-way adapter for the two loads.

Or do the math as shown by previous posters...

John :-#)#

Reply to
John Robertson

What also matters is the current density in the wire & its environment's ability to remove heat. So 30ga probably isn't a good choice, but he doesn't need 14ga either. Just a plain 'ole extension cord will do jus' fine.

Reply to
Bob Engelhardt

If it's permanently wired, by code, you MUST use a 14 gauge wire on a

15A circuit. You can use thicker wire, like 12 gauge, but not thinner. You can NOT use 14 gauge on a 20A breaker. You MUST use 12gauge by code.

If this is just an extension cord, you can probably get by with a

16gauge cord for your needs. But if this is hard wired, you MUST use 14g or heavier wire on a 15A breaker.
Reply to
oldschool

---------------------------

** The point being that you cannot know what someone else may do with your sub standard installation PLUS even the shortest length of underrated cable can overheat and smoke.

.... Phil

Reply to
Phil Allison

I do not worry about length of the wire, as the following wire-size guide has always (>79 years) worked (things stay cold): determine cross-section area in circular mils and use that number for current rating in milliamps (mils --> mils).

Reply to
Robert Baer

e-size

1000 circular mils per amp is the rule that the ARRL handbook quotes for tr ansformers in continuous use.

Cheers

Phil Hobbs

Reply to
pcdhobbs

ed on amps and length of wire.

What wire-size guide? If we're talking about any kind of wire then ampacity is limited by insulation temperature rating before wire gauge. If you go w ith some 300oC rated stuff, you can stuff a 100 A through 20ga. This is how you end up with wiring with small gauge inside an apparatus that is fused at 100A. It would not be practical to require humongous wire throughout or a bunch of different internal interrupters. Generally NEC wants the install ation to limit wire drop to less than 5% at nominal load, and there are thr ee main insulation types in wide use rated at 60oC, 75oC and 90oC which hav e significantly different current ratings for the same gauge.

Reply to
bloggs.fredbloggs.fred

Cooling transformer wire is a little different than wire in free air. There are a lot of unknowns here, so the only answer that's "safe" is "14Ga".

Reply to
krw

Correct. The best source to learn this stuff is the National Electric Code Handbook. It has all sorts of tables concerning wiring. The codes are adopted by all 50 states.

It is available for free online at but you will be required to create a profile to sign in.

Reply to
John S

Exactly. Wire ampacity is about temperature rise. So, the value varies with wire type and installed application parameters.

Current is constant at any node in the path, so current is what wire gets rated on as current determines the temperature rise due to the wire not being a perfect conductor.

It is about keeping the NFPA happy.

Reply to
DecadentLinuxUserNumeroUno

You can also download older versions of the NEC in PDF format. (They are less than 10 years old)

For simple stuff like wire gauge, the older versions are fine. The codes dont change all that much for residential wiring. Commercial codes change more.

Either way, the OP needs to run 3 or 4 feet of wiring on a 15A breaker. Just buy 14 gauge wire and be done with it. Or get 12 gauge which will cost 20 cents more for that short run. This is all he needs to know. (Hopefully he knows how to do the actual wiring properly). [If not, hire an electrician].

Reply to
oldschool

based on amps and length of wire.

ze

acity is limited by insulation temperature rating before wire gauge. If you go with some 300oC rated stuff, you can stuff a 100 A through 20ga. This i s how you end up with wiring with small gauge inside an apparatus that is f used at 100A. It would not be practical to require humongous wire throughou t or a bunch of different internal interrupters. Generally NEC wants the in stallation to limit wire drop to less than 5% at nominal load, and there ar e three main insulation types in wide use rated at 60oC, 75oC and 90oC whic h have significantly different current ratings for the same gauge.

It's about maintaining the integrity of the insulation. If you overstress i t it can melt or embrittle or otherwise lose its insulating value and that means BZZZZZZZT between the conductors.

Reply to
bloggs.fredbloggs.fred

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