# 14 AWG allowable ampacity



## MDShunk

Nope. Sorry. Would you like a code reference?


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## shocking

Hi MdShunk...yeah me again..lol

I have the code already(240.4)(D), Im just trying to figure out why they dont allow us to use 20A breakers if the wire is capable of handling that ampacity.


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## MDShunk

shocking said:


> Hi MdShunk...yeah me again..lol
> 
> I have the code already(240.4)(D), Im just trying to figure out why they dont allow us to use 20A breakers if the wire is capable of handling that ampacity.


Beats me. That's the nice thing about the code. We don't have to think too much if we don't want to. We can just follow what it says. :thumbsup:


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## shocking

Maybe then in the '08 NEC, they should just skip the "allowable ampacity" table. Dont tell me the cable can handle more, some of us might remember that instead of the correct overcurrent number. haha. Good nite...


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## raider1

> why cant we have a 20A breaker on 14 AWG wiring if the allowable ampacity states it?


You can install a 20 amp or larger overcurrent protective device on a 14 AWG conductor under some of the specific conductor applications listed in 240.4(G).

For example in a branch circuit feeding an air conditioner you can use the minimum circuit ampacity listed on the nameplate to size the branch circuit conductors and install an overcurrent device sized according to the nameplate of the A/C to protect the branch circuit conductors.

Say I have an A/C with a minimum circuit ampacity of 18 amps and a maximum breaker size of 30 amps. I could use 14 AWG conductors for the branch circuit and install a 30 amp breaker to provide my short-circuit and groundfault protection for the branch circuit.

Chris


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## shocking

Raider,

Using 14 AWG conductors with a 30 amp overcurrent protection would be a violation, since your going beyond a max of 15 amp overcurrent protection.

Once your conductors get near 30 amps, before tripping the breaker, wouldnt they be fried?


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## raider1

shocking said:


> Raider,
> 
> Using 14 AWG conductors with a 30 amp overcurrent protection would be a violation, since your going beyond a max of 15 amp overcurrent protection.
> 
> Once your conductors get near 30 amps, before tripping the breaker, wouldnt they be fried?


It is permissible to use a 30 amp breaker to protect 14 AWG branch circuits for A/C units.

240.4(D) says unless specifically permitted in 240.4(E) or 240.4(G) the overcurrent protection shall not exceed 15 amps for 14 AWG.

240.4(G) gives us specific conductor applications that permit larger overcurrent devices for small conductors. If you look at the list in 240.4(G) you will see Air-conditioning and refrigeration equipment circuit conductors Article 440, Parts III, IV.

Article 440 Part III is titled Branch-circuit short circuit and ground fault protection. We are permitted to follow the requirements of this section which allow the branch circuit short circuit and ground fault protection to be sized no larger than 175% of the motor rated-load current or branch-circuit selection current whichever is greater.

Take a look at Article 440 for sizing your circuits of an A/C unit and you will be suprized by what you can do.

Chris


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## shocking

I see. It also says should not exceed 225% of motor load current.
So if we have 15A, we can go as far as 33.75 amps. 
This also applies to pool pumps I would think, where they draw lots of current initialy.
But all this is not continous load.

Bottom line is stick with 15amp protection for 14 awg.


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## MDShunk

shocking said:


> Bottom line is stick with 15amp protection for 14 awg.


You'll change your tune, in time, when you start dealing with motor loads.


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## raider1

MDShunk said:


> You'll change your tune, in time, when you start dealing with motor loads.


Agreed,

There is no reason on a motor or A/C circuit, not to use the relaxed rules regarding short circuit and ground fault protection and install branch circuit conductors that are rated for the load and not the higher overcurrent device rating.

Chris


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## brian john

additionally for derating


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## macmikeman

Quite a way back the fellows who write the code took romex derating into consideration and required no more than a 15 amp breaker for #14 cable, no more than a 20 amp breaker for #12 and no more than a 30 amp breaker for #10 cables for most purposes. There are exceptions as other posters have noted. The notable part about all this is the fact that nm cables have de-rating factored into them even before you break the seal on the roll of cable. The current trend of increasing the rules about de-rating cables when "bundled" (code still has not properly defined just what that constitutes) for more than 24", when more than two cables are run up thru top plates where firestoping is used, ect, is in my opinion due to a lack of understanding on the part of current code panels on the previous history of the already present de-rating built into the cable to begin with. Soon just having two cables come into contact with each other if buried in thermal insulation will be enough to require further de-rating. Supreme overkill for a problem that did not exist in the first place.


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## Reddy Kilowatt

shocking said:


> Hi MdShunk...yeah me again..lol
> 
> I have the code already(240.4)(D), Im just trying to figure out why they dont allow us to use 20A breakers if the wire is capable of handling that ampacity.


Because they want to leave "head room" for the inevitable situation where a homeowner "fixes" a breaker tripping problem by replacing the breaker with a larger breaker. The fudge factor is there because of stupid homeowners.


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## TOOL_5150

Reddy Kilowatt said:


> The fudge factor is there because of stupid homeowners.



There is a pretty high fudge factor when your helper pushes a fish tape into a live buss on a panel too!  Ok, maybe that is a little different. It sure is quite a sound though.

~Matt


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## kingbob713

also becareful, the most common rating of lugs a termination is 75 degree that changes everything


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## gilbequick

Reddy Kilowatt said:


> Because they want to leave "head room" for the inevitable situation where a homeowner "fixes" a breaker tripping problem by replacing the breaker with a larger breaker. The fudge factor is there because of stupid homeowners.


That's it. It's a built in safety. 
You think that wire is going to burn at 21A? Nope, just built in safety factors.


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## FJSchrank

You shouldn't use too small of a conductor anywhere, especially not on a motor like a air conditioning compressor. The reason being is when the compressor first starts the usual amperage is close to the LRA of the compressor for a very short period. If the conductor is undersized, even if there is an exception in the code for it, it's not a good idea.

Why? When that compressor firsts starts up a large current is going to flow through the wires, if they're undersized then they generate heat. The creation of heat has to come from somewhere, and it's coming from a voltage drop created. Compressors can be hard enough to start sometimes, but if you introduce a voltage drop at start-up you're going to find that the compressor has a premature life, cooks capacitors too quickly or has starting problems.

In general it's not good to get away with the bare minimum conductor because your trade off will always be heat and a drop in voltage. Your wire becomes a resistor if you will.


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## erics37

It's always the n00bs :laughing:


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## FJSchrank

erics37 said:


> It's always the n00bs :laughing:


Eric, yes but still searchable on Google which is how I found it. It's a rather important subject so I joined to post that much needed reply. "Noob"? Maybe to the forum but I am speaking from a long established background in electrical engineering.


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## BBQ

Well thanks for letting us know what voltage drop is and that compressors can be hard to start. :jester:


Ball breaking aside, welcome to the forum. 

I think if you hang around a bit you will find most of the members here very knowledgeable.


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## 360max

erics37 said:


> It's always the n00bs :laughing:


...they are here to learn :thumbup:


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## 360max

FJSchrank said:


> You shouldn't use too small of a conductor anywhere, especially not on a motor like a air conditioning compressor. The reason being is when the compressor first starts the usual amperage is close to the LRA of the compressor for a very short period. If the conductor is undersized, even if there is an exception in the code for it, it's not a good idea.
> 
> Why? When that compressor firsts starts up a large current is going to flow through the wires, if they're undersized then they generate heat. The creation of heat has to come from somewhere, and it's coming from a voltage drop created. Compressors can be hard enough to start sometimes, but if you introduce a voltage drop at start-up you're going to find that the compressor has a premature life, cooks capacitors too quickly or has starting problems.
> 
> In general it's not good to get away with the bare minimum conductor because your trade off will always be heat and a drop in voltage. Your wire becomes a resistor if you will.


It may appear undersized when you look at a #14 wire on a 30A breaker, but the branch circuit conductors are protected against overloads by the overload device, which is sized between 115-125% of the motor nameplate current rating.(430.32, 240.4(G) NEC '08)


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## FJSchrank

Thank you for the welcome BBQ...

Even if it's allowed, depending on the LRA of the compressor it could still be undersized. Forgetting everything except ohms law...

If you have a 30' run of 14 awg cu, and the LRA is say for example 30 amps the voltage drop is fairly large of about 4.7% so 120V becomes 114 (about). Agreed, the drop is quick, but it's noticeable.

30' @ 20A = 3.2% drop
50' @ 25A = 6.5% drop

Allowed sure, but I'm speaking purely about the performance of the compressor. From a code and safety stand point, no argument. The code doesn't take in to account compressor starting performance.


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## NolaTigaBait

Yep sounds like an engineer...lets use 4/0 copper where #12 would suffice...Or my personal favorite is when they spec 1/0 copper for the GEC portion for the ground rods


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## bkmichael65

FJSchrank said:


> Thank you for the welcome BBQ...
> 
> Even if it's allowed, depending on the LRA of the compressor it could still be undersized. Forgetting everything except ohms law...
> 
> If you have a 30' run of 14 awg cu, and the LRA is say for example 30 amps the voltage drop is fairly large of about 4.7% so 120V becomes 114 (about). Agreed, the drop is quick, but it's noticeable.
> 
> 30' @ 20A = 3.2% drop
> 50' @ 25A = 6.5% drop
> 
> Allowed sure, but I'm speaking purely about the performance of the compressor. From a code and safety stand point, no argument. The code doesn't take in to account compressor starting performance.


Locked rotor current lasts a fraction of a second. Let's not get carried away with conductor sizes


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## FJSchrank

bkmichael65 said:


> Locked rotor current lasts a fraction of a second. Let's not get carried away with conductor sizes


Might be accurate except the voltage drop occurs just as fast and the voltage drop will extend the start up time (and add stress to the compressor).


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## FJSchrank

NolaTigaBait said:


> Yep sounds like an engineer...lets use 4/0 copper where #12 would suffice...Or my personal favorite is when they spec 1/0 copper for the GEC portion for the ground rods


4/0 is a bit too much here...


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## Jlarson

I like this guy. He should move here and open up shop so we can bid against him and win all the time. :laughing:


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## BBQ

I smell troll poop


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## Jlarson

BBQ said:


> I smell troll poop


Most likely that smell is really the undersized wire going to your HVAC unit burning. :laughing:


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## Speedy Petey

FJSchrank said:


> Eric, yes but still searchable on Google which is how I found it. It's a rather important subject so I joined to post that much needed reply.


Much needed reply?? To a nearly six YEAR old thread? 
So you just go around Googling for ancient threads to reply to?

Sorry, digging up a 5+ year old thread to state the obvious really is poor forum etiquette.


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