Ecmweb 5054 Photo 1
Ecmweb 5054 Photo 1
Ecmweb 5054 Photo 1
Ecmweb 5054 Photo 1
Ecmweb 5054 Photo 1

What’s Wrong Here? Hint: Get Back to Class

July 19, 2012
Can you identify the Code violation(s) in this photo?

How well do you know the Code? Think you can spot violations the original installer either ignored or couldn't identify? Here's your chance to moonlight as an electrical inspector and second-guess someone else's work from the safety of your living room or office. It's your turn to identify the violation.

Hint: It's time to get back to class.

Find the Answer

These fuses (Photo 1 above) were found during an infrared thermal scan inspection of the electrical equipment in a building. A closer look at the fuse holders reveals that Class R (rejection) type fuses should have been used in this installation. These Class H fuses do not have the notch in the blade of the fuse, which would allow it to fit around the post that is built into the fuse holder slot. The notch would allow the fuses to seat completely into the fuse holder. In fact, the cover was clearly labeled "Install Class R Fuses Only" (Photo 2 below), but the installer chose to ignore the instructions.

Section 110.9 of the 2011 NEC requires equipment intended to interrupt current at fault levels to have an interrupting rating not less than the nominal circuit voltage and the current that is available at the line terminals of the equipment. This could have been a serious problem if a fault occurred. The interrupting rating of a Class H fuse is suitable for a maximum of 10,000A of fault current. On the other hand, a Class R fuse may be capable of safely interrupting 200,000A.  That is a difference of 190,000A of energy! The Class H fuses could have exploded and caused serious equipment damage or possibly injured a person.

Photo 3 (above) shows the corrected installation, with appropriate Class R type fuses installed.

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About the Author

Russ LeBlanc | Owner

Russ started in the electrical trade as an apprentice in 1985. He worked his way up to become a Journeyman Electrician and then eventually became a Master Electrician and Licensed Construction Supervisor. In 1999 Russ become an Electrical Instructor for The Peterson School of Engineering in Massachusetts where he developed his passion for teaching, and quickly became Department Head of Electrical Instruction. Russ has taught thousands of apprentices, electricians, engineers, inspectors, and other electrical professionals during his career as an instructor. He continues to provide electrical professionals with Electrical Code seminars, Arc-Flash Awareness training seminars and educational material through his LeBlanc Consulting Services in North Reading, MA whose specialty is educating electricians. He has been an active member of the NFPA Electrical Section and has authored hundreds of National Electrical Code proposals and comments which have become Code rules to improve the safety for the electrical industry. Russ is also an IAEI certified Electrical Inspector.

Please visit www.russleblanc.net for more information.

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