I have always been told to size the wire on an a/c condenser to its minimum rating.For example:name plate rating states minimum amps 19 with maximum overcurrent 30.The wire size would be #12 on a 30 amp breaker. But I ran accross a condenser stating minimum amps 54, with maximum overcurrent 90. would I still size the wire at 54 amps on a 90 amp breaker? This condenser is a 3 phase 120/240 v. Any help or NEC references would be appreciated.
A/C Wiring
- Thread starter friday
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- Massachusetts
Re: A/C Wiring
14 AWG is rated 20 amps minimum.
Keep in mind code minimums do not take into account circuit length and voltage drop.
Code minimums are not necessarily efficient, convenient, or adequate for good service.
Actually in that example it would be code compliant to use 14 AWG with the 30 amp breaker.
14 AWG is rated 20 amps minimum.
Assuming you have 75 C terminals you could use 6 AWG copper with the 90 amp breaker.
Keep in mind code minimums do not take into account circuit length and voltage drop.
Code minimums are not necessarily efficient, convenient, or adequate for good service.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: A/C Wiring
Bob is correct. You would use the nameplate "minimum circuit ampacity" to size the conductors according to 310.16, and the "maximum fuse or HACR breaker" to size the short circuit and ground fault protection.
Bob is correct. You would use the nameplate "minimum circuit ampacity" to size the conductors according to 310.16, and the "maximum fuse or HACR breaker" to size the short circuit and ground fault protection.
petersonra
Senior Member
- Location
- Northern illinois
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- engineer
Re: A/C Wiring
240.4(D) Small Conductors. Unless specifically permitted in 240.4(E) through (G), the vercurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copperclad aluminum after any correction factors for ambient temperature and number of conductors have been applied.
I don't see anything that seems to amend this in article 440.
what about the note that refers you to 240.4(D) for #14, #12,and #10?
240.4(D) Small Conductors. Unless specifically permitted in 240.4(E) through (G), the vercurrent protection shall not exceed 15 amperes for 14 AWG, 20 amperes for 12 AWG, and 30 amperes for 10 AWG copper; or 15 amperes for 12 AWG and 25 amperes for 10 AWG aluminum and copperclad aluminum after any correction factors for ambient temperature and number of conductors have been applied.
I don't see anything that seems to amend this in article 440.
bphgravity
Senior Member
- Location
- Florida
Re: A/C Wiring
Read the section you just quoted. It states, "Unless specifically permitted in..."
(G) lists Article 440. Again, don't confuse the ground-fault and short-circuit protection as being the same as the overload protection, which is provided elsewhere for the A/C unit.
[ June 05, 2005, 06:05 PM: Message edited by: bphgravity ]
Read the section you just quoted. It states, "Unless specifically permitted in..."
(G) lists Article 440. Again, don't confuse the ground-fault and short-circuit protection as being the same as the overload protection, which is provided elsewhere for the A/C unit.
[ June 05, 2005, 06:05 PM: Message edited by: bphgravity ]
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: A/C Wiring
But it's pretty arguable that an A/C will be on for more than three continuous hours, isn't it?
Just curious about others' thoughts on that point.
But it's pretty arguable that an A/C will be on for more than three continuous hours, isn't it?
Just curious about others' thoughts on that point.
- Location
- Massachusetts
Re: A/C Wiring
All it has to do is stop once every 179 minutes.
An AC should not run continuously for more than 3 hours at a shot if it is sized correctly. The compressor should be cycling.Originally posted by georgestolz:
But it's pretty arguable that an A/C will be on for more than three continuous hours, isn't it?
Just curious about others' thoughts on that point.
All it has to do is stop once every 179 minutes.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: A/C Wiring
In the event of an undersized A/C, though...
In the event of an undersized A/C, though...
- Location
- Massachusetts
Re: A/C Wiring
In that event the extra 25% included in the MCA will cover your back.Originally posted by georgestolz:
In the event of an undersized A/C, though...
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: A/C Wiring
Hmm...I'm sold.
Hmm...I'm sold.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: A/C Wiring
"the size of conductors for equipment covered by this article shall be selected from Tables 310.16 through 310.19 or calculated in accordance with 310.15 as applicable."
Therefore the limitations for small conductors as specified in 240.4(D) do not apply.
240.4(D) directs us to 240.4(G) which directs us to 440.6 Ampacity and Rating, which states that:
"the size of conductors for equipment covered by this article shall be selected from Tables 310.16 through 310.19 or calculated in accordance with 310.15 as applicable."
Therefore the limitations for small conductors as specified in 240.4(D) do not apply.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: A/C Wiring
However, the note refering to another section limiting the ampacity of smaller wires is certainly part of the table. how does one get past that?
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: A/C Wiring
Bob Peterson, even if there were no text regarding ampacity in Article 440, then the small conductor rule would not apply.
The small conductor rule is essentially an exception to 310.16 requiring a smaller OCPD than 310.16 would allow. A focused exception. Air Conditioners are exempt from that exception. So as soon as you find something you're sizing conductors to on the (G) list, (D) flys out the window, before you go any further.
Bob Peterson, even if there were no text regarding ampacity in Article 440, then the small conductor rule would not apply.
Air Conditioners are specifically mentioned in (G), so the small conductor rule doesn't apply.
The small conductor rule is essentially an exception to 310.16 requiring a smaller OCPD than 310.16 would allow. A focused exception. Air Conditioners are exempt from that exception. So as soon as you find something you're sizing conductors to on the (G) list, (D) flys out the window, before you go any further.
Re: A/C Wiring
<---
Ya know,not in trying to pick on anyone..
But I started to interject in thread earlier,then edited-out my own comment after re-reading this post..
He HAD the answer to this question,in his posting.Am I "reading this wrong" or what ?
..did I miss-interpret, this posting?
--->"thar she blows,Captain Ahab"
<---Ya know,not in trying to pick on anyone..
But I started to interject in thread earlier,then edited-out my own comment after re-reading this post..
He HAD the answer to this question,in his posting.Am I "reading this wrong" or what ?
..did I miss-interpret, this posting?
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