#10 conductor on a 50amp breaker 220/240VAC

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stickboy1375

Senior Member
Location
Litchfield, CT
Stick has provided a good graphic. I will note one thing about this one it's based on the 2008 and earlier version of the NEC. This would no longer be applicable under the 2011.

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Rob, what changed after 2008? Were still on 2005. :)
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
So the change was 310.16... so 14,12, and 10AWG changed respectively?

Not that I'm worried, I don't think Connecticut will ever advance in NEC code changes... :)

The change was for #14 and #12 conductors at 60? C as well as a few others in Table 310.15(B)(16). It seems that the NEC borrowed this table from the Canadian electrical code and this made them the same.
 

stickboy1375

Senior Member
Location
Litchfield, CT
The change was for #14 and #12 conductors at 60? C as well as a few others in Table 310.15(B)(16). It seems that the NEC borrowed this table from the Canadian electrical code and this made them completely in concert.

Why didn't the Canadian code change theirs instead? :)

Thank you for the input, btw...
 

ritelec

Senior Member
Location
Jersey
Still trying to get my head around this.

Kind of getting the conductor/oc on ac together.

But also trying to locate in 430 how the air handler branch circuit and relative OC is determined as ac.


Just to clarify again...........just when I think I suk at this........I'm always proved right........ :D

working on it.
 

stickboy1375

Senior Member
Location
Litchfield, CT
Still trying to get my head around this.

Kind of getting the conductor/oc on ac together.

But also trying to locate in 430 how the air handler branch circuit and relative OC is determined as ac.


Just to clarify again...........just when I think I suk at this........I'm always proved right........ :D

working on it.

The air handler will have a nameplate, just go by it. Its already been sized by the manufacture.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Still trying to get my head around this.

Kind of getting the conductor/oc on ac together.

But also trying to locate in 430 how the air handler branch circuit and relative OC is determined as ac.


Just to clarify again...........just when I think I suk at this........I'm always proved right........ :D

working on it.

It might be helpful to consider equipment grounding conductors (Table 250.122). Think about their size relative to the branch circuit OCPD. It is the same concept as the A/C unit conductor sizinng as the conductor is only required to carry a high current long enough to open the OCPD in the event of a ground fault or short. The overload unit in the A/C protects the conductors from overload. Also look at Art. 430, similar concepts are in play.
 

stew

Senior Member
multiply the compresser amps which is the largest motor load by 125% and then add the fan current and you will get the MCA> also any unit without this info on the nameplate does not meet NEC requirements and would also probably not be UL listed and approved.
 
from an engineering point of view

from an engineering point of view

I ran into a similar problem with Landscaping transformers when they were too close to the circuit breakers the inrush current would trip the breaker because we we using all 12 guage wire and 20 a breakers (FYI the the solution was to use "hid breakers".) My electrical engineer brother in law explain it to me that we needed to use smaller wire to create resistance to slow the inrush current down. I believe that is why they want us to size the wire to the minumum and fuse to the maximum to prevent nuisance tripping. just my $.02
 

ritelec

Senior Member
Location
Jersey
My electrical engineer brother in law explain it to me that we needed to use smaller wire to create resistance to slow the inrush current down.


Couldn't you also just put a few HARD bends in the wire?



(I don't know about that andyselect........) Say you use the 8's instead of the 12's..........would the unit not work properly because now you have not created that resistance to "slow down" the inrush current.


Just sounds alittle fishy .................intentionally use the wire that way...............
 

kwired

Electron manager
Location
NE Nebraska
Still trying to get my head around this.

Kind of getting the conductor/oc on ac together.

But also trying to locate in 430 how the air handler branch circuit and relative OC is determined as ac.


Just to clarify again...........just when I think I suk at this........I'm always proved right........ :D

working on it.

430 has two sections on overcurrent -

III. Motor and Branch-Circuit Overload Protection: this is your motor overload device - if you protect the motor from overload the branch circuit will never be overloaded. Circuits feeding multiple motors is a little more complicated but you still protect the circuit when you protect the motors.


IV. Motor Branch-Circuit Short-Circuit and Ground-Fault Protection: this is your circuit breaker or fuse at the starting point of the branch circuit and is intended to operate only during a short circuit or ground fault but still allow inrush current necessary to start the motor.

440 tells us to use nameplate MCA and max overcurrent device but in absence of a nameplate with that info you can calculate using methods in 430. The methods in 430 give you the same results that are on nameplate - they have done the calculations for you, all you need to do is read the results.

If the air handler does not contain a hermatic compressor it is not a 440 application. It is also not a 430 application. It is a 422 appliance application but 422 does refer you back to 430 for some motor related information.


It might be helpful to consider equipment grounding conductors (Table 250.122). Think about their size relative to the branch circuit OCPD. It is the same concept as the A/C unit conductor sizinng as the conductor is only required to carry a high current long enough to open the OCPD in the event of a ground fault or short. The overload unit in the A/C protects the conductors from overload. Also look at Art. 430, similar concepts are in play.

Equipment grounding conductors do not need to be larger than ungrounded conductors they are associated with. So a 12 AWG protected by a 40 amp breaker only needs a 12 AWG equipment ground.

Who wants us to use the minimum wire size? and what about voltage drop?
If a short run voltage drop may not be an issue and minimum wire size may be just fine.

Couldn't you also just put a few HARD bends in the wire?



(I don't know about that andyselect........) Say you use the 8's instead of the 12's..........would the unit not work properly because now you have not created that resistance to "slow down" the inrush current.


Just sounds alittle fishy .................intentionally use the wire that way...............

A smaller conductor or even just a longer conductor does limit or choke inrush current because of impedance.

It also can be a voltage drop problem for normal running current, so this type of solution needs a little thought before just doing so.

I run into this with 120 volt chop saws, air compressors, welders, and a few other high starting current equipment. Plug the unit into a receptacle that is close to the source, main panel, etc and it trips breaker frequently when starting. Plug into an extension cord and it never does - the added resistance of the cord chokes the starting current enough the breaker holds. Too long or too small of a cord and you choke it enough it may fail to accelerate to speed.
 

ritelec

Senior Member
Location
Jersey
A smaller conductor or even just a longer conductor does limit or choke inrush current because of impedance.

It also can be a voltage drop problem for normal running current, so this type of solution needs a little thought before just doing so.

I run into this with 120 volt chop saws, air compressors, welders, and a few other high starting current equipment. Plug the unit into a receptacle that is close to the source, main panel, etc and it trips breaker frequently when starting. Plug into an extension cord and it never does - the added resistance of the cord chokes the starting current enough the breaker holds. Too long or too small of a cord and you choke it enough it may fail to accelerate to speed.


Interesting.....
 
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