Posted: 3/10/2017 1:33:40 PM EDT
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I plan to run a 50 amp feeder circuit to several pieces of equipment. The total FLA of all pieces connect will not exceed 50 amps. Further-more, no one piece of equipment will exceed 40 amps. Each piece will be connect through a fusible equipment disconnect. Wire will be THHN 90 degree.
According to NEC, THHN 90 degree table #8 wire is good for 55 amps with no de-rating. However, most connecting devices are only rated to 60 degrees, which would therefore limit the ampacity of the circuit to 40 amps if those devices are used. If each of the connecting devices (disconnect equipment, outlets etc) are each carrying no more than 40 amps by themselves can I use #8 THHN to run that circuit? Stated differently: The wire is good for 55 amps, the outlets are good for only 40 amps. Because any one outlet is not carrying more than 40 amps, but the total circuit may carry up to 50, can I use #8 wire, or do I need to step up to #6? FWIW, I have a friend that is a professional electrician and he is telling me I need to de-rate all my THHN to the 60 degree chart because none of my connecting devices will be rated to 90 degrees. Therefore I would have to run #6, I already bought all the #8 based on the THHN chart not realizing that "you cannot buy UL listed electric connects like wire-nuts & outlets that are rated to 90 degrees". |
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Quoted:
Not an electrician, but if you have an expected 50A load, I believe the circuit breaker needs to be 65A (next size up from 62.5A -> 80% of 62.5A = 50A Load). Expected loads are as follows, semi-permanent (not likely moved) 1 hp motor 9 FLA, semi-permanent 3 hp motor 17 FLA, and the potential for future equipment connection. I have LOTS of wiggle-room, and I want it that way. The reason I want a 50 amp circuit is because I plan to have all 220 outlets in my shop the same 50 amp receptacle so that if I have to connect my welder (40 FLA non-continuous, derates to 30 amp IAW NEC article 630) I can connect it anywhere in the shop. I would never have all the devices connected and drawing load at the same time. The odds of having the welder connected to this circuit is slim to none, but the option is there. My main concern is with the temperature rating of the receptacles etc. If each receptacle is limited to 40 amps or less (ampacity of #8 at 60 degrees) can I still use the #8 for the wiring on that circuit? ETA, worst case scenario I plunk a 40A breaker on the circuit instead of 50A but I would like the capacity for expansion so I'm still curious to the answer. |
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Quoted:
Expected loads are as follows, semi-permanent (not likely moved) 1 hp motor 9 FLA, semi-permanent 3 hp motor 17 FLA, and the potential for future equipment connection. I have LOTS of wiggle-room, and I want it that way. The reason I want a 50 amp circuit is because I plan to have all 220 outlets in my shop the same 50 amp receptacle so that if I have to connect my welder (40 FLA non-continuous, derates to 30 amp IAW NEC article 630) I can connect it anywhere in the shop. I would never have all the devices connected and drawing load at the same time. The odds of having the welder connected to this circuit is slim to none, but the option is there. My main concern is with the temperature rating of the receptacles etc. If each receptacle is limited to 40 amps or less (ampacity of #8 at 60 degrees) can I still use the #8 for the wiring on that circuit? ETA, worst case scenario I plunk a 40A breaker on the circuit instead of 50A but I would like the capacity for expansion so I'm still curious to the answer. Quoted:
Quoted:
Not an electrician, but if you have an expected 50A load, I believe the circuit breaker needs to be 65A (next size up from 62.5A -> 80% of 62.5A = 50A Load). Expected loads are as follows, semi-permanent (not likely moved) 1 hp motor 9 FLA, semi-permanent 3 hp motor 17 FLA, and the potential for future equipment connection. I have LOTS of wiggle-room, and I want it that way. The reason I want a 50 amp circuit is because I plan to have all 220 outlets in my shop the same 50 amp receptacle so that if I have to connect my welder (40 FLA non-continuous, derates to 30 amp IAW NEC article 630) I can connect it anywhere in the shop. I would never have all the devices connected and drawing load at the same time. The odds of having the welder connected to this circuit is slim to none, but the option is there. My main concern is with the temperature rating of the receptacles etc. If each receptacle is limited to 40 amps or less (ampacity of #8 at 60 degrees) can I still use the #8 for the wiring on that circuit? ETA, worst case scenario I plunk a 40A breaker on the circuit instead of 50A but I would like the capacity for expansion so I'm still curious to the answer. Those numbers do not match NEC Table 430-148 Full Load Current Single Phase A/C Motors. This table is used and NOT any markings on the motor. Conductors are 125% of the Full Load Current. Inverse Time Breakers (AKA 'thermal-magnetic) are allowed to be larger to allow for starting without breaker tripping. There is NO requirement to increase the wire size. The breaker is for short circuit protection NOT overload protection. |