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Old 07-03-2019, 07:17 PM   #1
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Default Minimum Circuit Ampacity

Another topic in regards to McA and air conditioners.

This mini split has a Nameplate that states
MCA of 25A
And Max overcurrent of 35A

I believe I can run #12 wire to this unit on a 35A breaker l, it sits roughly 50ft away and a co worker says it has to be #10

What are your thoughts?

What would you run?
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Old 07-03-2019, 07:50 PM   #2
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max 35 amp is a max doesnt mean you cant use a 30. if the issue is voltage drop and thats why he is suggesting #10, you would want to know the actual run load amps to calculate voltage drop. # 10 is a safe bet.
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Old 07-03-2019, 08:15 PM   #3
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Your are welcome to install a breaker rated anywhere between the MCA and the Max overcurrent protection rating.

You will need a 25A or 30A breaker. I'd recommend 30A if it were me. As per CEC 14-104 (2), minimum wire size is #10. #12 is only good for a 20A breaker. This is unrelated to voltage drop.

Actual running amps is only about 80% of the MCA -> 20A. 50ft is not long enough to worry about voltage drop. #10 is good to go.
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Old 07-03-2019, 08:22 PM   #4
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Quote:
Originally Posted by 2604Sparky View Post
Another topic in regards to McA and air conditioners.

This mini split has a Nameplate that states
MCA of 25A
And Max overcurrent of 35A

I believe I can run #12 wire to this unit on a 35A breaker l, it sits roughly 50ft away and a co worker says it has to be #10

What are your thoughts?

What would you run?
If the CEC is the same as the NEC you can run 12 AWG for any conducter other than NM (I forget what you guys call it) and UF. Everything else the 75 degree column ampacity is 25A for 12 AWG. And yes, you could put that on a 35A breaker, though a 30 is likely more readily available and probably won't ever be an issue.
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Old 07-03-2019, 08:31 PM   #5
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Your are welcome to install a breaker rated anywhere between the MCA and the Max overcurrent protection rating.

You will need a 25A or 30A breaker. I'd recommend 30A if it were me. As per CEC 14-104 (2), minimum wire size is #10. #12 is only good for a 20A breaker. This is unrelated to voltage drop.

Actual running amps is only about 80% of the MCA -> 20A. 50ft is not long enough to worry about voltage drop. #10 is good to go.

14-104(2) has an exception that refers you to the rule above it 14-104(1) (C)

That states the rating overcurrent rating shall not exceed the ampacity of conductors that they protect except as provided for by other rules of this code

Which section 28 allows for

Am I still wrong or just confused haha
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Old 07-03-2019, 08:54 PM   #6
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14-104(2) has an exception that refers you to the rule above it 14-104(1) (C)

That states the rating overcurrent rating shall not exceed the ampacity of conductors that they protect except as provided for by other rules of this code

Which section 28 allows for

Am I still wrong or just confused haha
You are correct. 14-104 does not apply to equipment like motors, AC units and transformers because they have their own codes for wire size and overcurrent protection.

You are also correct in being able to run 12 awg wire as it is good for 25 amps in table 2 in the 75 degree column as long as the AC unit termination temp is also rated for 75 degrees.
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Old 07-04-2019, 11:58 AM   #7
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You are correct. 14-104 does not apply to equipment like motors, AC units and transformers because they have their own codes for wire size and overcurrent protection.

You are also correct in being able to run 12 awg wire as it is good for 25 amps in table 2 in the 75 degree column as long as the AC unit termination temp is also rated for 75 degrees.
I guess I learn something new every day... but, from a practical point-of-view, isn't #12 wire connected to a 25A or 30A breaker a red flag for an electrical inspector? Rather than having to explain yourself and dig up nameplate data, wouldn't it be easier to run #10? Saving a few bucks on 50ft of wire hardly sounds worth it when you are pushing the maximum limits of the code.

What if the owner changed the A/C unit later and the MCA is 26A?
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Old 07-04-2019, 12:31 PM   #8
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I guess I learn something new every day... but, from a practical point-of-view, isn't #12 wire connected to a 25A or 30A breaker a red flag for an electrical inspector? Rather than having to explain yourself and dig up nameplate data, wouldn't it be easier to run #10? Saving a few bucks on 50ft of wire hardly sounds worth it when you are pushing the maximum limits of the code.

What if the owner changed the A/C unit later and the MCA is 26A?
No red flag, It is common with motors.

for instance, say you had a motor with an FLA of 16 amps.

wire size would be 14awg (16 x 1.25) 28-106(1) and table 2 @ 75 degrees
breaker size would be 40 amp (16 x 2.5) 28-200(3) and Table 29
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Old 07-04-2019, 01:32 PM   #9
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I guess it always comes down to do you like to build to minimum standards or ....since the customer is paying for it ....improve on minimum standards . After all , that's what codes are....minimum acceptable standards .
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Old 07-04-2019, 01:44 PM   #10
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Originally Posted by 908Eng View Post
I guess I learn something new every day... but, from a practical point-of-view, isn't #12 wire connected to a 25A or 30A breaker a red flag for an electrical inspector? Rather than having to explain yourself and dig up nameplate data, wouldn't it be easier to run #10? Saving a few bucks on 50ft of wire hardly sounds worth it when you are pushing the maximum limits of the code.
No, it's common. IMO, running a larger conductor than necessary for an AC unit shows lack of code knowledge and experience. And I have had inspectors agree with that sentiment.

Quote:
What if the owner changed the A/C unit later and the MCA is 26A?
What if you ran #10 and they upgrade the C unit to require 31A? We can what-if all day, but we won't get anywhere.
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Old 07-04-2019, 01:45 PM   #11
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Originally Posted by 908Eng View Post
I guess I learn something new every day... but, from a practical point-of-view, isn't #12 wire connected to a 25A or 30A breaker a red flag for an electrical inspector? Rather than having to explain yourself and dig up nameplate data, wouldn't it be easier to run #10? Saving a few bucks on 50ft of wire hardly sounds worth it when you are pushing the maximum limits of the code.

What if the owner changed the A/C unit later and the MCA is 26A?
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No red flag, It is common with motors.

for instance, say you had a motor with an FLA of 16 amps.

wire size would be 14awg (16 x 1.25) 28-106(1) and table 2 @ 75 degrees
breaker size would be 40 amp (16 x 2.5) 28-200(3) and Table 29

Basically it is very simuair situation to our NEC code on motor appaction so therefore our NEC code art 430 and 440 cover this very well so most of the wording pretty much match up to your CEC codes.

Edit.,,

No the situation as OP describing that is a run of mill item the USA guys been hitting often we just sized the conductor for MCA and max fuse/breaker size and that it.
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Last edited by frenchelectrican; 07-04-2019 at 01:49 PM. Reason: add more info after hackwork posted .,, Thanks Hack.
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Old 07-04-2019, 01:45 PM   #12
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I guess it always comes down to do you like to build to minimum standards or ....since the customer is paying for it ....improve on minimum standards . After all , that's what codes are....minimum acceptable standards .
This is not minimum standards, it's the right way to do it.

It's not different than saying "#10 is better for 20A circuits, so I will run that and tell the customer how much better than code I do my installations".

Running larger conductors for the AC units or other motor loads is in no way making a better installation.
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Old 07-04-2019, 01:55 PM   #13
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This is not minimum standards, it's the right way to do it.

It's not different than saying "#10 is better for 20A circuits, so I will run that and tell the customer how much better than code I do my installations".

Running larger conductors for the AC units or other motor loads is in no way making a better installation.
#6 is so much better than #10. What a jackleg.
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Old 07-04-2019, 02:16 PM   #14
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#6 is so much better than #10. What a jackleg.
Your sarcasm shows how crazy it is to say that code is minimum and using larger wire is somehow better.

Yes, code is the minimum, but there are many things that do not yield any benefit by doing more than that minimum.

I just ran romex thru a basement this morning. Would it give the customer any benefit if I ran rigid? Explosion proof?
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Old 07-04-2019, 03:24 PM   #15
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Your sarcasm shows how crazy it is to say that code is minimum and using larger wire is somehow better.



Yes, code is the minimum, but there are many things that do not yield any benefit by doing more than that minimum.



I just ran romex thru a basement this morning. Would it give the customer any benefit if I ran rigid? Explosion proof?
MI cable or nothing.

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Old 07-04-2019, 03:38 PM   #16
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MI cable or nothing.

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Jesus, what is wrong with you guys? MI cable in rigid is how to do it right.
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Old 07-04-2019, 04:55 PM   #17
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Here I thought we were talking about Motors and Hermetic Compressors ....and the unit nameplate doesn't take into account circuit length or ambient temperature correction factors ...you do that .
So I don't see how upsizing by a wire size is such a huge mistake given the parameters he described ....for motors and compressors.
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Old 07-04-2019, 04:57 PM   #18
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Here I thought we were talking about Motors and Hermetic Compressors ....and the unit nameplate doesn't take into account circuit length or ambient temperature correction factors ...you do that .
So I don't see how upsizing by a wire size is such a huge mistake given the parameters he described ....for motors and compressors.
Because the nameplate and code tell us what to do, and doing more than that is silly.
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Old 07-04-2019, 05:59 PM   #19
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Here I thought we were talking about Motors and Hermetic Compressors ....and the unit nameplate doesn't take into account circuit length or ambient temperature correction factors ...you do that .
So I don't see how upsizing by a wire size is such a huge mistake given the parameters he described ....for motors and compressors.
Of course oversizing is not a huge mistake, I don’t believe anyone said that but it is not required so why do it?

The OP never mentioned ambient temp being over 30 degrees so I doubt that is an issue. And a #12 awg at that ampacity can be run 62 ft at a 3% drop. That is assuming the voltage is 208. If the voltage is 240, it could go 72 feet.
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Old 07-04-2019, 06:18 PM   #20
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What if the owner changed the A/C unit later and the MCA is 26A?
Unless the unit was grossly undersized originally, there is zero chance that will happen. Energy codes are getting stricter every year and a/c units are now more efficient than they have ever been. Changing out units nowadays requires the breaker size to be decreased, not increased.
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