Mca conductor sizing

Status
Not open for further replies.
USMC1302

USMC1302

Senior Member
Location
NW Indiana
Had a discussion with a restaurant equipment installer regarding the need to re-pull new conductors for a new reefer unit. I asked nameplate and he stated MCA=22A and OCPD=30. He says #10 and was adamant, I say the #12 there is ok, but couldn't find the reference right away. Would appreciate an article number to make sure before I load my "bar" rifle. Thanks.

steve
 
240.4 directs you to 240.4(G) which allows amapcity of conductors realated to Art 440 to be selected from 310.16 without regrad to 240.4(D)(5) (the 20 amp restriction on #12).
You 22 MCA is within the range for a #12
 
The #12 would comply with the NEC but depending on how long the conductors are there could be an issue with voltage drop.
 
USMC1302 said:
Had a discussion with a restaurant equipment installer regarding the need to re-pull new conductors for a new reefer unit. I asked nameplate and he stated MCA=22A and OCPD=30. He says #10 and was adamant, I say the #12 there is ok, but couldn't find the reference right away. Would appreciate an article number to make sure before I load my "bar" rifle. Thanks.
steve
Click to expand...

Might as well give my thoughts. For a/c you can use #12 based on the ampacity in T.310.16. So 25 amps is the key since this is refrigeration and 240.4(G) okays this.

The asterik in the table leads you to 240.4(D) and that takes you to 240.4(G) as stated earlier by Larry.
 
Dennis Alwon said:
Might as well give my thoughts. For a/c you can use #12 based on the ampacity in T.310.16. So 25 amps is the key since this is refrigeration and 240.4(G) okays this.

The asterik in the table leads you to 240.4(D) and that takes you to 240.4(G) as stated earlier by Larry.
Click to expand...

I don't see it that way. 240.4(G) references article 440, parts 3 and 6. Where in those parts does it allow you to do what your speaking of?
 
chevyx92 said:
I don't see it that way. 240.4(G) references article 440, parts 3 and 6. Where in those parts does it allow you to do what your speaking of?
Click to expand...
Chevy, read 240.4(D). It states that unless permitted in 240.4(E) or (G) we must use the info in D1-D7. 240.4(G) tables mention article 440 which involves a/c and refrig. equip. circuit conductors. So if the install involves any of the items under column 1 (conductor) then you are allowed to use the amp. of #10, #12 or #14 at the given ampacity in table 310.16.

This is also true for motors, welders and all the items mentioned in (G).

440 parts 3 references branch circuit short circuit & ground fault and part VI references motor comp. & branch cir. overload protection
 
Last edited:
So many people "know" that #12 copper is rated at 20A. But it is actually rated at 25A, even at 60C. You can use it at that level when 240.4(D) doesn't apply.
 
Mark:
That was pretty much the story here. I run into a lot of "experts" and I know I'm not one. Had a fella(expert) whose son was building a house and they were going to do all the electric work, with the assistance of a friend. He stated they had to install receptacles at least every 6' per "code". I advised they might want to verify that, but of course knew it would fall on deaf ears. I went to see the site one day and there were boxes EVERYWHERE, at which point my accomplice remarked he knew what to get the homeowner for a house warming gift....a one foot extension cord.
 
Dennis Alwon said:
Chevy, read 240.4(D). It states that unless permitted in 240.4(E) or (G) we must use the info in D1-D7. 240.4(G) tables mention article 440 which involves a/c and refrig. equip. circuit conductors. So if the install involves any of the items under column 1 (conductor) then you are allowed to use the amp. of #10, #12 or #14 at the given ampacity in table 310.16.

This is also true for motors, welders and all the items mentioned in (G).

440 parts 3 references branch circuit short circuit & ground fault and part VI references motor comp. & branch cir. overload protection
Click to expand...

I understand it is allowed to be done that way, I do it all the time, the way I was taught. But never actually looked in the NEC to see where it said you could. So from what you're saying when YOU read Table 240.4(G), wheres it says "440, PartsIII, VI", You take it as its saying all of article 440? The way I read it was, article 440 partsIII, and VI. I guess I read it wrong then. But if it implies the entire article 440, then why do they even list "Parts III, VI"???. Because like I said previously partsIII and VI don't give permission to do what you said. Part I gives you the permission.
 
The title of 440 Section II is "Branch-Circuit Short-Circuit and Ground-Fault
Protection". How could this not apply to to breaker sizing on HVAC wires...
 
suemarkp said:
The title of 440 Section II is "Branch-Circuit Short-Circuit and Ground-Fault
Protection". How could this not apply to to breaker sizing on HVAC wires...
Click to expand...

I am assuming you meant 440 Section III. I am not seeing where anyone says it does not. 240.4d limits the OCPD for the smaller wires to a value less than 310.16. 240.4(g) overrides that limitation for use in 440 sec III and IV. The ampacity values of the wire remain the same in both cases. 240.4(g) applies to ref. and air conditioning equip.
 
Last edited:
#12

#12

next to wire rating on 310.16 is an Astrix. this shows the 12 even though rated higher than 20 amps is must not be used for anything more that 20 amps so #10 would be the correct size....
 
Len said:
next to wire rating on 310.16 is an Astrix. this shows the 12 even though rated higher than 20 amps is must not be used for anything more that 20 amps so #10 would be the correct size....
Click to expand...

Len for this application 240.4(D) does not apply, 240.4(G) does.
 
Len said:
next to wire rating on 310.16 is an Astrix. this shows the 12 even though rated higher than 20 amps is must not be used for anything more that 20 amps so #10 would be the correct size....
Click to expand...

No it doesn't. It says see section 240.4(D) which states Unless specifically permitted in 240.4(E) or (G). Air Conditioning equipment (Article 440) is covered under G.
 
Status
Not open for further replies.
Top