Standards as High as Your Own
NECA Online Help Desk Please leave a message
Re: CQD answer published Wednesday, March 6, 2019 -Existing Installation
I assume that the question is about an older system that is 3 wire 3 phase and no ground. This was used by several local power company's in our area when 480 volt machines were first introduced in our area. We had a 480 volt 3 wire system like this in an egg processing plant. At that time the power company only gave us the 480 volt 3 wire power. One of the machines created a short that did not trip any breakers, but created a corner grounded system. Because the short was in one machine only and they were able to continue to operate they did not call us for several days. One maintenance employee was concerned about the 480 volts to ground on 2 phases, but was ordered to just keep everything running. We were able to correct it by identifying the problem and asked the power company to upgrade the transformers to a 4 wire system. We than added an external ground to every machine in the building. The panels and buses at that time were not designed for grounding. Is this plant in Tuesdays question required to bring every machine up to proper grounding? I would think that any new machine on the line must be properly grounded.
We have another plant that did not have a neutral on the 480 volt system. Someone started to change the lights to 277 volts and I was called when they had problems. (And ruined several new fixtures.) We installed a dry type indoor transformer to correct this. 480 volt 3 wire primary to 480/277 volt 4 wire secondary. We also installed a new 4 wire panel for the lights.
Hey Tom thanks for your follow up question and comments. The NEC is generally understood to be not retroactive, it applies to an installation and is usually done as part of a permit process using the NEC edition that is adopted at the time the permit is obtained. Although Annex H is not mandatory, 80.9 gives some guidance for how this works. If new equipment (machine) is installed it needs to comply with the NEC edition that is adopted in that locality. Whether that is enforced or if the AHJ even knows an installation was made also varies.
As we previously mentioned there are retroactive OSHA requirements and liability issues for employers and owners. It might not be specifically required, by the local municipality, to make an existing installation compliant but if an incident occurs explaining why corrections were not made will be difficult.
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. NEISÃ” 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: email@example.com.
© 1999 – 2014 National Electrical Installation Standards. All rights reserved.
Brought to you by NECA. NECA is the voice of the electrical contracting industry NATIONAL ELECTRICAL INSTALLATION STANDARDS, NEIS and the NEIS logo are registered trademarks of the National Electrical Contractors Association.
Created by Matrix Group International, Inc.