Article 210.23

[srasz]

I am having trouble getting past Article 210.23 "In no case shall the load exceed the branch circuit ampere rating", with respect to start up currents. I am using heat trace to heat a sample line. This heat trace requires 35A on a 30A (manufacturer recommended) circuit for a short time (60s, decreases over time to about 11A). Am I not in violation of this article (the CB will hold according to trip curve)? There must be an "out" as there are many devices that have switching power supplies with very high inrush currents (even though the time is very small). Please help.

 

[gregory]

Re: Article 210.23

You should follow the manufacturers installation instructions. Check and make sure that it is UL or ETL or some approved testing lab label affixed to it. Inrush current is for a brief period of time and does not cause undue heating. The manufacturer has electrical engineers who test and submit this equipment for testing. Follow the installation instructions.

 

[charlie b]

Re: Article 210.23

Originally posted by srasz:"In no case shall the load exceed the branch circuit ampere rating"

In this context, the ?load? is the 11 amps. The circuit may carry more current for a short period, just as in the case of a motor. The current in heat tracing remains high for a longer period than is the case for a motor, but the issue-at-hand is the same. The purpose of the article you have quoted is to protect the insulation of the branch circuit conductors.

Look at it this way: If a high current were to remain long enough to threaten the integrity of the cable?s insulation, then the overcurrent protection device would activate, in order to protect the cable. That is its one and only job. It necessarily follows that if the current is not high enough for a long enough period to trip the breaker, then the current (even though it is above the cable?s ?ampacity?) will not damage the insulation.

Gregory is right: go with the manufacturer?s recommendations.