MC Cable
- Thread starter lektrik33
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- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: MC Cable
When you say, ?what does that mean,? are you asking (1) What is MC cable?, or (2) What is an overall jacket?, or (3) What is the Exception all about?
The answer to the first would be from 330.2: ?Definition. Metal Clad Cable, Type MC. A factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated metallic sheath.?
The answer to the second would be that an MC cable can have a jacket made of rubber (or is it plastic ? someone else many have to correct me here) surrounding the interlocking metal tape.
The answer to the third would come from the fact that the only reason for derating any conductor is to protect the insulation system from damage due to overheating. If you have more than one current-carrying conductors in a conduit, the heat generated by each would cause the temperature to rise on all the others. The ampacity tables are based on three or fewer current-carrying conductors, so if you have more than four, you can?t use the full ampacity shown in the tables. My opinion is that the insulation systems of the conductors within the MC cable?s metal tape would be protected from the heat generated by other nearby MC cables, through the ability of metal to carry heat away from the source. So if you had a rubber (or plastic, or whatever) jacket surrounding the metal tape, the metal could no longer carry heat away as well. Thus, if an MC cable with the overall jacket has more than three current-carrying conductors, you need to derate.
When you say, ?what does that mean,? are you asking (1) What is MC cable?, or (2) What is an overall jacket?, or (3) What is the Exception all about?
The answer to the first would be from 330.2: ?Definition. Metal Clad Cable, Type MC. A factory assembly of one or more insulated circuit conductors with or without optical fiber members enclosed in an armor of interlocking metal tape, or a smooth or corrugated metallic sheath.?
The answer to the second would be that an MC cable can have a jacket made of rubber (or is it plastic ? someone else many have to correct me here) surrounding the interlocking metal tape.
The answer to the third would come from the fact that the only reason for derating any conductor is to protect the insulation system from damage due to overheating. If you have more than one current-carrying conductors in a conduit, the heat generated by each would cause the temperature to rise on all the others. The ampacity tables are based on three or fewer current-carrying conductors, so if you have more than four, you can?t use the full ampacity shown in the tables. My opinion is that the insulation systems of the conductors within the MC cable?s metal tape would be protected from the heat generated by other nearby MC cables, through the ability of metal to carry heat away from the source. So if you had a rubber (or plastic, or whatever) jacket surrounding the metal tape, the metal could no longer carry heat away as well. Thus, if an MC cable with the overall jacket has more than three current-carrying conductors, you need to derate.
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