CheckItOut Posted May 12, 2010 Report Share Posted May 12, 2010 I have not found a maximum ampacity for multi-stranded wire but know that it can carry more than single strand. This HVAC unit had a 40 amp breaker and a 12 gauge multi-strand copper wire. Wire from unit to breaker panel was only a few feet. I think this may be ok but would like to find a chart for ampacity of multi-strand. Anyone? Quote Link to comment Share on other sites More sharing options...
Brandon Whitmore Posted May 12, 2010 Report Share Posted May 12, 2010 12 gauge is 12 gauge. What was the data plates ampacity and OCPD rating? Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 12, 2010 Report Share Posted May 12, 2010 I have not found a maximum ampacity for multi-stranded wire but know that it can carry more than single strand. This HVAC unit had a 40 amp breaker and a 12 gauge multi-strand copper wire. Wire from unit to breaker panel was only a few feet. I think this may be ok but would like to find a chart for ampacity of multi-strand. Anyone? The NEC doesn't give stranded wire and greater ampacity than solid wire. The type of insulation on the wire makes a difference though, in terms of its temperature rating and will affect the ampacity. Just use table 310.16 as you would for solid wire. Remember that, in an air conditioning circuit, the breaker isn't there to provide overcurrent protection. The AC data plate will list the minimum necessary ampacity of the wire and the maximum breaker or fuse size. It might be fine to have a circuit with a #12 wire and a 40-amp breaker. There are two key questions: What does the data plate require? What kind of stranded wire was it, and what is its temperature rating? - Jim Katen, Oregon Quote Link to comment Share on other sites More sharing options...
Brandon Whitmore Posted May 12, 2010 Report Share Posted May 12, 2010 As usual, Jim's answer may be a little better than mine. [:-paperba Quote Link to comment Share on other sites More sharing options...
CheckItOut Posted May 12, 2010 Author Report Share Posted May 12, 2010 Thanks guys. The plate calls for a minimum of a 25.6 amp circuit. I read the insulation rating, took a pic but can't recall the rating and it did not show in the pic. Quote Link to comment Share on other sites More sharing options...
Chad Fabry Posted May 12, 2010 Report Share Posted May 12, 2010 Thanks guys. The plate calls for a minimum of a 25.6 amp circuit. I read the insulation rating, took a pic but can't recall the rating and it did not show in the pic. Then the wire needs to be at least 10 gauge. Quote Link to comment Share on other sites More sharing options...
CheckItOut Posted May 12, 2010 Author Report Share Posted May 12, 2010 [quo Remember that, in an air conditioning circuit, the breaker isn't there to provide overcurrent protection. - Jim Katen, Oregon Jim, Can you explain that? What would happen if the data plate listed a max fuse rating of 25 AMPS and they had a 40 AMP breaker (see this all of the time on older houses that have had systems replaced). I would think this could cause a problem but maybe I am missing something. I always give them 5 AMPS for compressor load (start up) draw and that is commonly done around here. Quote Link to comment Share on other sites More sharing options...
Jim Katen Posted May 12, 2010 Report Share Posted May 12, 2010 Jim, Can you explain that? What would happen if the data plate listed a max fuse rating of 25 AMPS and they had a 40 AMP breaker (see this all of the time on older houses that have had systems replaced). I would think this could cause a problem but maybe I am missing something. I always give them 5 AMPS for compressor load (start up) draw and that is commonly done around here. Forget the 5-amp thing. It's meaningless. Just go by the data plate. With an air conditioning compressor -- as with lots of large motor loads -- the compressor motor itself has overload protection built in. That'll protect the wire from overloads. The required breaker is only there to protect against short circuits & ground faults. Why then, you may ask, does the size of the breaker matter? If it's only there to protect against faults, wouldn't any larger breaker size do? And if you were to ask those questions, they'd be good ones. The answer is that smaller breakers have steeper trip curves, even for faults, so they provide slightly (ever so slightly) better protection. - Jim Katen, Oregon Quote Link to comment Share on other sites More sharing options...
Nolan Kienitz Posted May 12, 2010 Report Share Posted May 12, 2010 Just follow the requirements noted on the data plate. If it says that the MAX Fuse/Breaker size is: 40-amps ... Then that is what you need to see in the panelboard. I just went through an 8-hour CE session on electrical this past Friday and the electrical consultant was adamant about following the rules. He more than once commented that you need to follow the data plate per the manufacturer's requirements. He noted that most electrical guys do things in a certain way as "that's the way we've always done it" ... does not make it the "right" way. Quote Link to comment Share on other sites More sharing options...
CheckItOut Posted May 12, 2010 Author Report Share Posted May 12, 2010 Jim, Can you explain that? What would happen if the data plate listed a max fuse rating of 25 AMPS and they had a 40 AMP breaker (see this all of the time on older houses that have had systems replaced). I would think this could cause a problem but maybe I am missing something. I always give them 5 AMPS for compressor load (start up) draw and that is commonly done around here. Forget the 5-amp thing. It's meaningless. Just go by the data plate. With an air conditioning compressor -- as with lots of large motor loads -- the compressor motor itself has overload protection built in. That'll protect the wire from overloads. The required breaker is only there to protect against short circuits & ground faults. Why then, you may ask, does the size of the breaker matter? If it's only there to protect against faults, wouldn't any larger breaker size do? And if you were to ask those questions, they'd be good ones. The answer is that smaller breakers have steeper trip curves, even for faults, so they provide slightly (ever so slightly) better protection. - Jim Katen, Oregon Thank you Jim! Quote Link to comment Share on other sites More sharing options...
plummen Posted May 20, 2010 Report Share Posted May 20, 2010 Jim, Can you explain that? What would happen if the data plate listed a max fuse rating of 25 AMPS and they had a 40 AMP breaker (see this all of the time on older houses that have had systems replaced). I would think this could cause a problem but maybe I am missing something. I always give them 5 AMPS for compressor load (start up) draw and that is commonly done around here. Forget the 5-amp thing. It's meaningless. Just go by the data plate. With an air conditioning compressor -- as with lots of large motor loads -- the compressor motor itself has overload protection built in. That'll protect the wire from overloads. The required breaker is only there to protect against short circuits & ground faults. Why then, you may ask, does the size of the breaker matter? If it's only there to protect against faults, wouldn't any larger breaker size do? And if you were to ask those questions, they'd be good ones. The answer is that smaller breakers have steeper trip curves, even for faults, so they provide slightly (ever so slightly) better protection. - Jim Katen, Oregon Motor wiring is supposed to be sized to 125% of rated load,10gauge wire is actually a little less than required but most inspectors would accept it.As far as the breaker size if it is just used as a disconect in the box outside by the unit it doesnt really matter if its oversized,the breaker feeding the circuit in the panel is what matters. Quote Link to comment Share on other sites More sharing options...
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