Wire Gauge sizes

At 12 volts, you might want to keep the load down to 10 amps on that 10 foot run, else the voltage drop will be excessive and the lights a bit dim.

Remember that a lamp draws about 15 times the rated operating current initially, so 15 amps of lamps are going to try to draw 225 amps. You need relays and switches rated for that tungsten surge or they will be fried rapidly.

The ONLY time a wire is too fat is when it won't go in the connections at the ends. A fat wire saves electrical energy (at the cost of fuel to move it around on the tractor, truck, car, and airplane).

Gerald J.

• voltage drop calculator

You guys got to explain it stupid people terms for some of us.

I've always admired a man who can tell me to go straight square to he!! and at the same time, make me look forward to the trip.

Ya shoulda been a politician! :>)

Allan

No, no! no! You've got it all wrong!

The wires with the barbs are your telephone line.

Geeze! Everyone knows that! :>)

Allan

Mark

First thing I did is went to the radio shop in town and got the AM radio fixed.....had to have those tunes. Now I like peace and quiet.

The vibrator died. Cost $5 parts and labor. For a guy making 50 cents an hour (at a gas station) that was a lot of money.

Mark

You know darned well that they didn't have FM radios in those old 64 Dodge trucks.

(Boy, hope I don't start another arguement)

Allan

Of course it did, silly rabbit!

You were receiving in cattle country.....a very simple deduction. :>)

Allan

Hey! What's all these electricians doing in here anyway? Ha!

Ampacity is the absolute maximum current that can be safely conducted by the wire. It is a function of wire gauge, wire material (copper versus aluminum) and the insulation temperature rating. It also varies by the particular application. The National Electrical Code has tables to determine ampacity for a given conductor in a given application.

Once ampacity has been determined, then voltage drop should be calculated. Generally voltage drop should be no more that 2 or 3 percent of the input voltage. Voltage drop is usually not an issue for short distances. You can look up voltage drop in the NEC tables, or you can calculate it if you know the resistance per foot of the particular conductor, using ohm's law (V=IR, where voltage drop is equal to the current times total resistance). If the voltage drop is excessive, then a larger gauge must be used than is required to meet the ampacity.

Not trying to be argumentative, but it sounds to me like you are either quoting some 6am coffee table chatter, a jeep-load of drunken sailors returning to ship, or quite possibly (and more probable) you are getting your information from off the Internet? :>)

There just is no such word in the English language as “ampacity”. The ability to conduct an electrical current through any given medium is defined as conductance.

When applied to a parallel circuit, voltage drop across any and all legs will always be equal to that of the input voltage. Likewise, across a series circuit, voltage drop will be equal to the sum of its individual component’s voltage drops, but will still always be equal to that of that original input voltage.

Further, Ohm’s Law is written: E=IR.

Have a good one,

Allan

For what it's worth, I had never heard of ampacity until I started reading the NEC. This is in spite of the fact that I've got a piece of paper that says I'm a degreed electrical engineer.

I realize that I should have explained "voltage drop" a little better. I rushed a bit because I needed to get to work. You are correct, the sum of the voltages in the circuit equals zero. If my explanation confused anybody, I'll be happy to give a better one.

As for "E=IR" versus "V=IR", it just depends where you went to school. For electrical engineers, voltage is "V" not "E". (Actually, we use little "v" when we're in the time domain and big "V" when we're in the frequency domain, if you want to get picky. Whatever.) Any chance that you learned your electronics at a little place outside Memphis?

Best regards, mark

Kinda like holes and electrons. Depends on who's doin the talkin.

When in the service, they taught electrons. Made a lot of sense for repair work.

In college, they taught holes which made a lot of since for a person designing something.

So, in technical discussions, I'd either have to figure out what the other guy was talking about or ask him. Hole or electron flow.

Mark

Good point. Is electron flow positive to negative or is it really negative to positive?

A double standard depending on which profession you are in. Never did understand why the academia insisted on teaching both theories.

The first time I ran up against the transistor gates on a schematic and after dealing with the Raytheon stuff for so long, it really threw me for a loop…It is hard to adjust one’s thinking into looking at it (and accepting it) in a totally backwards fashion.

Just life, I guess.

Allan

But 36 years of it solved the problem.

Mark

Yep, I read ya on that score, but I 'taint about to delve into that one, as they'd probably stone me or some such thing. :>)

Allan

Geez we're all Einsteins, just like Pappy said.....a bunch of smart a..... .es. Grin

Oh missed one. The "true rms" value of the AC current is equal to the heating effect of the DC. Course when you get to microwave frequencies, ya gotta consider "skin effect" and stuff like dat.

Mark

E=IR vs V=IR is kind of petty.

On the plus side, you are completely correct on Kirchof's laws.

Ya mean I should have had my coffee first before engaging my mouth? Darn, I did it again! :>)

Now about this word: "ampacity". Must be some kind of an industry 'insider' word then; I dunno, I don't work in your line of business.

I do however, have access to every English language dictionary ever printed and pay something on the order of $700 a year on real-time spell checkers because this is "my" line of work (neat, correct, clear and comprehensible documents).

If "Ampacity" is indeed a word, I sure can't find the dude and further, having been to almost every electronic school under the sun, I’ve sure never heard of the term.

Must be an electrician thing or something? :>)

Like I say tho, I’m old too. Thanks for the heads up,

Allan

The following is a definition from the National Electrical Code-1990 Handbook, NFPA, Pg. 11 Article 100(my latest copy)

"Ampacity: The current in amperes a conductor can carry continuously under the conditions of use without exceeding its temperature rating".

They also have Ampacity tables in Article 310 of the same book for reference.

This was my bible for several years and before I acquired it I had nothing but grief trying to get machinery built for use in Ford Transmission plants.

Vern

from:
Standard Handbook for Electrical Engineers
Fink & Carroll Tenth Edition 1969
McGraw Hill ISBN 07-020973-1

Current-carrying Capacity (Ampacity). As the conductors of an electrical wiring system offer some resistance, a current-carrying conductor dissipates heat. Under practical conditions of installation and operation the temperatures reached must not result in the destruction of the insulation or risk to surrounding materials.

snip, they show tables taken from the NEC here

Allowable ampacities for insulated conductors are based upon an allowable temperature rise above an ambient of 30°C, 86°F.
Allowable ampacities for copper conductors and aluminum conductors in accordance with the temperature rating of the insulation are given for installation in conduit and for installation in free air.

Guess it goes to show you, old pfarts need to step aside for the later generation.

Oh well!

Mark

(60 more work days and a wake up. Yeeeeehoooo!)

• Ampacity

Yes, I get the message.

And, obviously from all the feedback thrown my way, this is an “in house” term that you boys use in your profession.

Guess I should have been aware of the jargon before popping off. :>)

Have a good one,

Allan

But so what!

Mark

(Just checked in my "Standard Handbook for Electrical Engineers", Ninth Edition, McGraw Hill, 1957..... not there.)

• More

BTW, the answer is 10 amps. I have a slick chart for 12V wire sizes, but it's a word document. Don't know how to post it here.

Here you go!! A DC wire table.

T_Bone

• DC Wire Table

Mark

With all the gadgets people dream up, be nice to have something to pack you kill back to the camp.

So what's a Canadian, out of country, two week hunting license (and stamp) for moose worth?

Mark

The outfitters are hurting after the bunny huggers banned the spring bear hunt. And reduced the number of moose tags due to both anti-hunters within the government and the higher bear population eating more moose calves.

Now tell me that it makes sense to take a quick kill on a game animal vs let it die a slow death of starvation.

Grrrrr rrrrr rrrrr rrrrr rrrrr .

Mark

With only 10 feet I think I would ignore the voltage drop and the difference in isulating properties. I'd get the THWN wire cause IIRC it stands up better to harsh environments. I'd think it was good for 15 Amps and forget it.

Of course you could splurge and run #12. It couldn't make a dollars difference, could it?

steveormary