National Electrical Installation Standards

Standards as High as Your Own

?
Friday, January 19, 2018

Question:

Hi Charlie,

We have a customer who is feeding an 800 Amp 208/120 V panel with two 400 Amp fused disconnects. The switches are in the same panel, but separate buckets and each is feeding a set of 500 kcmil. This appears to be a violation of 240.8 because the fused disconnect switches are not factory assembled in parallel and listed as a unit. My question is, was this ever legal under an older code? Thanks for your time and for this service you provide.

Regards, Edward M. Barr, P.E.

A

Answer:

Hey Edward thanks for your question. In the 1920's, and possibly before, overcurrent devices were only allowed to be installed "in multiple" if the "ampacity" exceeded the largest available overcurrent device. Back then it is also possible that overcurrent devices were not available (or not available as a tested product) in 800 ampere sizes because the standard cartridge fuse size in the NEC did not exceed 600 amperes. Larger sizes appear to have been added in the 1950's. The wording was changed to "in parallel" for the 1968 NEC and eventually resulted in the wording we have today in 240.8. Depending on when the example you provided was installed, the NEC edition that was adopted there, and what "approved" overcurrent device sizes were available it seems it would need to be somewhere around 1950 for it to be considered acceptable but exact dates are difficult to confirm.

ABOUT CQD: NECA’s Code Question of the Day (CQD) is a leading National Electrical Code® forum for NECA and the industry. The CQD generates a lively dialogue and relative practical and Code-based responses to an ever-increasing and interactive audience.

IMPORTANT NOTICE: All answers are based on the latest edition of the National Electrical Code®, unless the question requests a response based on a specific edition. This correspondence is not a formal interpretation of the NEC®. Any responses expressed to the questions are opinions and do not necessarily represent the official position of NECA, NFPA, or any technical committee. In addition, this correspondence is neither intended, nor should it be relied upon, to provide professional consultation or services.

ABOUT CHARLIE: Charles M. Trout, better known as Charlie, was a nationally known NEC® expert and author. He served on several NEC® technical committees and is past chairman of CMP-12. In 2006 Charlie was awarded the prestigious Coggeshall Award for outstanding contributions to the electrical contracting industry, codes and standards development, and technical training. Charlie was also a member of NECA’s Academy of Electrical Contracting. Charlie’s experienced team of industry experts keep the CQD dialogue and discussions active and informative in the spirit of the man himself, as he wanted.

NECA STANDARDS: NECA publishes the National Electrical Installation Standards™ (NEIS™), a series of ANSI-approved performance and quality standards for electrical construction. Visit NECA-NEIS.org for more information. NEISÔ can be purchased in three formats: as paper books, on CD, or as electronic downloads.

NECA SAFETY PRODUCTS: NECA publishes valuable electrical safety books and CDs for the industry. Visit necanet.org/store to view or purchase NECA safety products.

 CONTACT US: To submit a Code question, subscribe, or unsubscribe from this list, please e-mail: codequestion@necanet.org.