AC wiring question

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Old 01-26-14, 01:18 PM
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AC wiring question

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My model unit is 4TTR4060C1.

Right now this unit is running on a double pole 30 amp breaker and 10/2 wire. Should this unit be on a 60 amp breaker on 6/2 wire ?


Thanks for your help.
 
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Old 01-26-14, 01:38 PM
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Minimum circuit ampacity is 36 amps, and maximum fuse size is 60 amps.
Your wire size should be at least #8 copper and a fuse/circuit breaker no larger than 60 amps. However, your fuse/breaker can't be bigger than the wires are rated for.

If you run:
#8 Romex, it can only be on a 40 amp max.
#8 in conduit it can be on a 50 amp max.
#6 romex can be on a 50 or 60 amp.
#6 in conduit it can be on a 60 amp max.

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Old 01-26-14, 06:41 PM
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However, your fuse/breaker can't be bigger than the wires are rated for.
A breaker or fuse for HVAC can be sized bigger than the wires. Good discussion and code reference here: Breaker size so 60amp breaker on 8 gauge copper wire is what should be. Note Trane document says "fuse" but also has a note that breakers are ok.

My guess is that the compressor was swapped out with a larger unit and the installer didn't want to replace the cable. Probably other problems with the install as well.
 
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Old 01-26-14, 09:17 PM
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However, your fuse/breaker can't be bigger than the wires are rated for.
Sure it can for an A-C unit or a motor load, but I wouldn't if it wasn't necessary.
 
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Old 01-26-14, 10:36 PM
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Hvac

440.22(A) covers short-circuit and ground-fault protection. Can't exceed 175% of motor-compressor load current or branch circuit selection current which ever is greater. If that will not handle the starting current then you can increase to a max of 225%. However 440.22(C) States the device rating cannot exceed the manufactures values. So the manufactures nameplate cannot be exceeded. The branch circuit conductors must be a minimum of 125% of the motor-compressors rated load current. In addition you must meet the requirements of 440.51 and 440.52 for Motor-compressor and branch circuit overload protection. If the manufactures nameplate calls for fuse protection you must provide fuse protection. If the manufactures nameplate calls for HACR or Fuse you can use either. I think the bottom line is the branch circuit can be protected higher than the conductor rating to allow for starting current as with other motor installations and the manufacture specifies protection on the nameplate to protect the unit.
 
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Old 01-27-14, 07:19 AM
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The bottom line, assuming the chart provided by OP is the correct one, the branch circuit wiring should be no smaller than 8-2 NM-B cable. Since the unit is holding on a 30 amp breaker now, I'd probably put it on a 40 amp breaker with a fusible disconnect also fused at 40 amps. If the unit is not drawing FLA, there may be another problem such as a low charge.

Note Trane document says "fuse" but also has a note that breakers are ok.
I don't see that note on the chart provided.
 
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Old 01-27-14, 10:30 PM
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A search for 4TTR4060C1 found the pdf at http://www.blue-phx.com/pdf/Trane%20...%20Product.pdf
Page 4 has footnote 2 which says "Calculated in accordance with N.E.C. Only use HACR circuit breakers or fuses."
 
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Old 01-28-14, 08:37 AM
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A search for 4TTR4060C1 found the pdf at http://www.blue-phx.com/pdf/Trane%20...%20Product.pdf
Page 4 has footnote 2 which says "Calculated in accordance with N.E.C. Only use HACR circuit breakers or fuses."
Then a non-fusible disconnect would be acceptable.
 
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