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? 

Can you add circuit breakers by different manufacturers to an electric panel if they fit?

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

What is a split bus electric panel?

How do I identify a combination AFCI (CAFCI) circuit breaker? 

What does a circuit breaker with a yellow or white test button indicate? 

What is the maximum gap allowed between the front of a recessed electric panel box and the wall surface surrounding it? 

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?

What happens when you press the "TEST" button on a circuit breaker in an electric panel?

What is a Dual Function Circuit Interrupter (DFCI)? 

What is the difference between a Combination Arc Fault Circuit Interrupter (CAFCI) and an Arc Fault Circuit Interrupter (AFCI) circuit breaker?  

What is the difference between "grounded" and "grounding" electrical conductors? 

What does it mean when a wire is "overstripped" at a circuit breaker?

Why is an old fuse panel dangerous?  

Who is the manufacturer of those "bad" electric panels?

Why is the circuit breaker stuck in the middle? 

What is a double tap at a circuit breaker?

What is the right electric wire size for a circuit breaker in an electric panel?

What is the life expectancy of a circuit breaker? 

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. 

How To Look At A House

McGarry and Madsen's home inspection blog for buyers of  

site-built, mobile/manfuactured and modular homes






Air Conditioner & Furnace Age/Size




Aging in Place


Click Below  

for Links

to Collections

of Blog Posts

by Subject


Doors and Windows


Energy Efficiency

Fireplaces and Chimneys

Heating and Air Conditioning

Home Inspection

Hurricane Resistance

Electrical Receptacle Outlets

Electrical Panels

Garages and Carports

Common Problems

Exterior Walls & Structures



Life Expectancy

Mobile/Manufactured Homes

Older and

Historic Houses

Mold, Lead & Other Contaminants

Modular Homes

Metal Roofs



Pool and Spa

Roof and Attic




"Should I Buy A..."


Termites, Wood Rot

& Pests

Structure and Rooms


Water Heaters

Water Heater Age

Septic Tank Systems

Plumbing Pipes


When It First

Became Code

Park Model Homes

Shingle Roofs


Wind Mitigation Form

"Does A Home


"What Is The Difference Between..."


Concrete and

Concrete Block


Rain Gutters


Crawl Spaces

Building Permits

Clay Soil




HUD-Code for

Mobile Homes

Flat (Low Slope) Roofs

Sprinkler Systems

4-Point Inspections

Frequently Asked Questions (FAQ)

Building Codes

Inspector Licensing

& Standards

Washers and Dryers



Electrical Wiring

Plumbing Drains

and Traps

Smoke & CO Alarms

Top 5 results given instantly.

Click on magnifying glass

for all search results.



Electrical Switches


Water Intrusion

Electrical - Old

and Obsolete

Foundation Certifications

Tiny Houses