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Code Question Of The Day
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Friday, September 10, 2010
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Subject: 3 way switching with multiple NM cables
Hi Charlie -
I am an Gary's side with this one. I believe you are WRONG to say that it is o.k. to run multiple two-wire cables instead of a single three wire cable for things such as a three way switch. Article 300.3 (B)(3) says to refer to 300.20(B), which is concerned with inductive heating effects when the conductors are passed into a metallic opening from a nonmetallic or nonmagnetic sheath, such as NM cable or aluminum clad MC.
In very few cases, NM can be used in a structure that has a three-phase service. Are you saying that I could use (2) 14-2 NM cables to carry a three-phase load and not be worried about all of the conductors being grouped because they are not in a metallic sheath? I think not.
Thanks for the service, and the ability to handle the abuse we can cause you...
Andy
IBEW 292
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code question and answer:
Thursday, September 09, 2010
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Subject: Wood vs. Unistrut
I do a lot of low voltage security cameras in business and I have to hang monitors from the ceiling. I used to use a 1 x 6 across the red line but I was told I had to use unistrut. the monitor only weighs 6-8 lbs if that. Is there a code that states no wood is allowed?
Andrew
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Answer:
Hey Andrew, thanks for participating. I have to confess I don’t know what you mean by the red line. However NEC 110.3(B) requires installation of listed equipment to be in accordance with the manufacturers instructions. NEC 110.13(A) requires electrical equipment to be firmly secured to the surface on which it is mounted. Basically I believe that if the 1x6 is securely fastened to the surface it is attached to and the monitor is securely fastened to the 1x6 you are Code compliant. However, if it is the AHJ that is requiring unistrut then it is his approval that must be obtained as to whether or not your installation is securely fastened. Actually, unistrut or a similar product would make installation and removal more easily accomplished.
Note that the type of construction can also restrict the use of wood or other combustible materials in a building or structure.
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Section: 110.3(B), 110.13(A)
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Source: Charlie Trout
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ANSWERS: Answers are the author’s opinions and do not represent formal interpretations of the National Electrical Code.
All answers are based on the latest edition of the NEC, unless the question requests a response based on a specific edition.
CONTACT US: To submit a question, subscribe to Code Question of the Day, or remove yourself from this list, please send an e-mail to
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ABOUT THE AUTHOR: Charlie Trout is a nationally-known NEC expert and author. He served on three different National Electrical Code-Making Panels and is past chairman of CMP-12. He is also a member of the NECA Codes & Standards Committee. In 2006 Charlie Trout won the prestigious Coggeshall Award, given to recognize outstanding contributions to the electrical contracting industry in the technical and training area.
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