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Old 07-08-2012, 09:14 PM   #1
thargrav
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Default Wire Size and Current Capacity

A while ago I started a thread about installing a electric water heater element into a stainless steel brew pot. I got chastised about using a 14 gauge power cord to carry what could easily be 17 amps and several quoted that 14 gauge should carry a maximum of 15 amps.

I finally took the time today to chase down the answer about #14 wire and current carrying capacity. And I am correct - #14 wire is perfectly safe for up to 20 amps! But don't believe me, do your own research starting with table 310.16 in the NEC code book.

It is true that #14 wire is used to carry up to 15 amps in house & commercial wiring and #12 wire is used to carry up to 20 amps, and some believe that this means you can only use #14 wire for up to 15 amps. And everywhere you look on the net you see "experts" claiming that #14 wire is only good for up to 15 amps. But it turns out that all of these "experts" are only quoting partial facts, or maybe they are quoting the local "expert" at LOWE'S? Is this is another example of "if it's on the net it must be true"? I don't know but it sure seems so.

But here is the real deal. The same NEC code that specifies that #14 wire can carry no more than 15 amps states that #14 in a branch circuit is good for up to 20 amps (table 310.16 in NEC clearly states the max of 20 amps)! A branch circuit is a circuit run to a single device and this sure reads like a power cord to me, but not a extension cord. In other words, #14 gauge is perfectly safe for 20 amps, they just don't want you to run a string of 20 Amp outlets across your house with #14 wire. And they are correct with this - they are concened about voltage drop across distances.

I dug further into my Engineering books and discovered that #14 wire is actually good for up to 32 amps in chassis wiring.

Also, don't use this info as an excuse to run sub-standard or under size wiring in any of your projects. You still need to brew safe!

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Old 07-08-2012, 09:40 PM   #2
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I'm no 'expert' but as a licensed electrictian, I'll say you have to read the WHOLE chart. The footnote at the bottom clearly says your wrong.


1 The load current rating and the overcurrent protection for conductor types shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG aluminum and copper-clad aluminum after any correction factors for ambient temperature and number of conductors have been applied.

http://lugsdirect.com/WireCurrentAmp...ble-301-16.htm

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Old 07-08-2012, 10:23 PM   #3
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This does not change the current carrying capacity of the wire.

The resistance of #14 copper wire is 0.002525 Ohms per foot and at 20 Amps the voltage drop across a 8 foot power cord (16' total) is only 0.8 Volts. This works out to 16 Watts of power dissipated across the entire length of the cord at 20 Amps - not enough to even get warm. And my brew pot draws 16 Amps (25% less).

Also, do you know how much current needs to pass through #14 wire before it becomes dangerous? I'll give you a clue - the fusing current (the point where the wire goes "poof") of #14 copper wire is 166 Amps.

And 20 Amps is no-where near 166 Amps.

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Old 07-08-2012, 11:47 PM   #4
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The wire doesn't have to go 'poof' to ruin your day. I've been in situations where someone was running a AC unit with 14 wire and it was so hot it was melting the insulation. 166 amps you say? It doesn't matter to me what you do at your own home. I'm just saying that no electrical inspector in any state in this country will allow you to use 14awg wire for 20 Amps. Besides, you have to fuse wires (as well as derate for protection the wire itself ) at 80% of capacity. So actually (per code) you can only put a load of 12amps on 14awg wire and use a 15 amp breaker. Your logic about voltage drop may be valid. But for the cost of a few bucks to use 14 wire, it isn't worth it to me or my home. Just because the wire can physically handle more amperage doesn't make it a smart move. My car speedometer goes to 120mph. Even if it will go that fast (which I doubt), I'm not going to try. I may survive the first time and maybe even the next 10 times. But eventually it'll bite me in the arse. Most safety regulations over do it. But there is a reason for that.

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Old 07-09-2012, 12:28 AM   #5
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You need to understand that I 100% agree with you when it comes to house wiring. And that's what the NEC is for - building wiring, not product wiring. I also understand the derating formula as it applies to house wiring. I also understand that there is a additional derating formula for wires run in a conduit that's based on the conduit size and number of conductors in the conduit that you did not bring up.

But none of this applies to the point I'm trying to make! Matter of fact, we are discussing two different subjects! You are applying building wiring standards to product wiring which includes power cords.

Engineers make decisions about wire & amp carrying capacity in products without referencing NEC every day because building codes do not apply to product safety. They are two different animals with different sets of requirements. Product design uses the same reference materials I use - I've been a Engineer for over 30 years.

I've read most of the electric brewery threads on this site and it's good to know that most are defaulting to the safe side when it comes to wire sizing - you'll note that I never mentioned that a wire can be too large. At least their wire selection will not burn the building down. My purpose of this thread was to point out that a #14 gauge power cord is safe for my 16 Amp electric brew pot and I backed that opinion up with data.

But if you want a real discussion about safety lets discuss the crimp on terminals I see everyone use. From what I see on the outside I suspect that most of the terminal crimps are suspect. But there is a simple test to tell - after you crimp a terminal grab the terminal in one hand and move the wire from side to side with the other. If the wire moves any at all inside the crimp then it's a connection that will get hot and possibly fail.

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Old 07-09-2012, 12:31 AM   #6
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Quote:
Originally Posted by Hammy71 View Post
The wire doesn't have to go 'poof' to ruin your day. I've been in situations where someone was running a AC unit with 14 wire and it was so hot it was melting the insulation.
And BTW, that electrician who ran a AC unit on #14 wire should be shot for putting a 40 Amp circuit on 14 gauge wire!
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Old 07-09-2012, 02:05 AM   #7
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Quote:
Originally Posted by Hammy71 View Post
Besides, you have to fuse wires (as well as derate for protection the wire itself ) at 80% of capacity.
Done by installing a 15A breaker
Quote:
So actually (per code) you can only put a load of 12amps on 14awg wire and use a 15 amp breaker.
You are saying we homeowners have to know our load current to make sure we don't exceed the 12 A limitation?
As long there is a 15 A breaker in my box I should be able to run up to the 15A limit all day long as long the breaker can handle it.
What does NEC recommend how we homeowners should handle the monitoring?

Quote:
I'm just saying that no electrical inspector in any state in this country will allow you to use 14awg wire for 20 Amps.
Just some info.
The NEC 2011 code was first adopted 09/01/2011 in Texas as the minimum standard for all electrical work.
Inside the corporate limits of a municipality, electricians followed the city codes, outside maybe wild wiring went on in some homes.


Cheers,
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Old 07-09-2012, 08:52 PM   #8
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Quote:
Originally Posted by ClaudiusB View Post
Done by installing a 15A breaker

You are saying we homeowners have to know our load current to make sure we don't exceed the 12 A limitation?
As long there is a 15 A breaker in my box I should be able to run up to the 15A limit all day long as long the breaker can handle it.
What does NEC recommend how we homeowners should handle the monitoring?


Just some info.
The NEC 2011 code was first adopted 09/01/2011 in Texas as the minimum standard for all electrical work.
Inside the corporate limits of a municipality, electricians followed the city codes, outside maybe wild wiring went on in some homes.


Cheers,
ClaudiusB
When an electrician wires a house (or anything, be it commercial or whatever), he/she must use calculations in the NEC to basically guesstimate the load that will be used on a circuit. Basically each receptacle is one volt/amp, so at most maybe 12 receptacles on a 15 amp circuit. That's the simplistic answer. So yes, the homeowner should be aware of what they have plugged in. Especially in older homes. Who among us has not at least heard of a neighbor with two teenage daughters using their hair dryers and stereos/tvs blasting in their bedrooms at the same time and the breaker tripping? It happens all the time, especially in older homes. That's why our parents and grandparents used coins to bypass the ole fuse boxes. A 15 amp breaker will eventually stop being able to hold a load and start tripping with an amperage that is 'close' to 15 amps. Hence the lower rating capacity of 12 amps. The NEC is used by most municipalities as a guide line. Whether they choose to follow every recommendation by the NEC is up to their discretion. But I'd be really surprised if 310-16 wasn't one of them.

As far as power cords, every cord in my home that I see (from the microwave to the dryer) is of an appropriate rating for the appliance per 310-16.

Look, I don't really care about 17 amps on a piece of 14 wire. I just felt a need to address the original post that the OP felt he was getting "internet wisdom" when it came to wire size and amperage. I still think it is sound advice not to exceed 12 amps on a piece of 14 wire, whatever the application. At the end of the day we all do what we want, and I guess I'm unaware of any chastising that might have occurred to the OP. But I really think that people mean well and want to help. It's not some kind of d$%K measurement that my wire is bigger than yours, but I think genuine concern.

And since I saw Forrest Gump on TV the other night for the godzillionth time.

That's all I have to say about that.

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Old 07-11-2012, 02:54 AM   #9
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Quote:
Originally Posted by Hammy71 View Post
When an electrician wires a house (or anything, be it commercial or whatever), he/she must use calculations in the NEC to basically guesstimate the load that will be used on a circuit. Basically each receptacle is one volt/amp, so at most maybe 12 receptacles on a 15 amp circuit. That's the simplistic answer. So yes, the homeowner should be aware of what they have plugged in. Especially in older homes. Who among us has not at least heard of a neighbor with two teenage daughters using their hair dryers and stereos/tvs blasting in their bedrooms at the same time and the breaker tripping? It happens all the time, especially in older homes. That's why our parents and grandparents used coins to bypass the ole fuse boxes. A 15 amp breaker will eventually stop being able to hold a load and start tripping with an amperage that is 'close' to 15 amps. Hence the lower rating capacity of 12 amps. The NEC is used by most municipalities as a guide line. Whether they choose to follow every recommendation by the NEC is up to their discretion. But I'd be really surprised if 310-16 wasn't one of them.

As far as power cords, every cord in my home that I see (from the microwave to the dryer) is of an appropriate rating for the appliance per 310-16.

Look, I don't really care about 17 amps on a piece of 14 wire. I just felt a need to address the original post that the OP felt he was getting "internet wisdom" when it came to wire size and amperage. I still think it is sound advice not to exceed 12 amps on a piece of 14 wire, whatever the application. At the end of the day we all do what we want, and I guess I'm unaware of any chastising that might have occurred to the OP. But I really think that people mean well and want to help. It's not some kind of d$%K measurement that my wire is bigger than yours, but I think genuine concern.

And since I saw Forrest Gump on TV the other night for the godzillionth time.

That's all I have to say about that.

Thanks for replying,
ClaudiusB
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Old 07-11-2012, 02:31 PM   #10
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A question popped into my head recently while thinking about power ratings and the like. When a current is specified with regard to a element or whatever in An AC circuit, is this rating rms or peak value.just thought it would be important for selecting write guages and resistor values.

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