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What are the requirements for NM-cables entering an electric panel box?

Saturday, July 7, 2018

NM-cables must be securely fastened where they enter an electric panel, so that tugging on a cable from outside the box will not pull wires loose from their terminations inside.  This is usually accomplished by installation of an NM-connector at the knockout that is secured to the box from both sides and clamps down on the cable. Most NM-connectors are approved for securing only one or two cables, but there are connectors listed to handle even more. 

    The configuration shown above, where a cluster of wires enters the top of the box through a single opening, is called a chase nipple. It is a fast and easy way to pull NM-cables into a box, but not code approved. 

    The photo below shows NM-cables entering the top of a box through NM-connectors (except that one is missing, with a cable poking through it, and will need repair).

    Also, shown below is a typical NM-connector—viewed from the side that typically would be on the outside of the panel.

    The National Electrical Code [NEC 312.5 (C)] allows one exception to the requirement for securely fastening NM-cables at panel entry, as long as the cables enter the top of a surface-mounted panel box through a non-flexible raceway that is between 18-inches and 10-feet long, and meet the following additional requirements:

  1. Each cable is fastened within 12-inches of the outer end of the raceway.
  2. The raceway extends directly above the panel and does not penetrate a structural ceiling.
  3. A fitting is installed at each end of the raceway to avoid abrasion of the cable jacket and fitting remain accessible after installation.
  4. The raceway is sealed at the outer end.
  5. The cable sheathing is continuous through the raceway and extends a minimum of 1/4” into box enclosure.
  6. The raceway is securely fastened at outer end.
  7. Where installed as conduit, the allowable cable fill should not exceed permitted level in Table 1 of Chapter 9 of NEC Code, approximately 60%.

• • • • • • • • • • • • • • • • • • • • • • • • • • 

Here’s links to a collection of our other blog posts about ELECTRIC PANELS:

What causes copper wires to turn green or black in an electric panel?  

What is the maximum number of circuit breakers allowed in an electric panel?

When should a corroded or damaged electric panel cabinet or disconnect box be replaced? 

What is a tandem circuit breaker? 

When did arc fault circuit interrupter (AFCI) breakers first become required?

Can an electric panel be located in a closet? 

Can an electric panel be located in a bathroom? 

What are the requirements for NM-cables entering an electric panel box?

Why is a fuse box/panel an insurance problem for homebuyers? 

Why is bundled wiring in an electric panel a defect?

What is the difference between GFCI and AFCI circuit breakers? 

Why are old electrical components not always "grandfathered" as acceptable by home inspectors?

My circuit breaker won't reset. What's wrong? 

Why do some breakers in my electric panel have a "TEST" button on them?

What is the right size electric panel for a house? 

• What do I need to know about buying a whole house surge protector? 

What is the maximum allowed height of a circuit breaker (OCPD) above the floor?

• What is the maximum height you can mount an electric panel above the floor? 

• What is the code required clearance in front of an electric panel?

What is the main bonding jumper and where do it find it in an electric panel? 

   Visit our ELECTRIC PANELS page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.

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