The one-neutral-per-lug rule entered the National Electrical Code at the 2002 edition. Here’s how it is stated in the current edition:

408.41 Grounded Conductor Terminations. Each grounded conductor shall terminate within the panelboard in an individual terminal that is not also used for another conductor.
Exception: Grounded conductors of circuits with parallel conductors shall be permitted to terminate in a single terminal if the terminal is identified for connection of more than the conductor.

    A mantra that we often hear repeated at home inspector electrical seminars is “don’t forget to call out multiple neutrals under the same lug in the panel.” And we do find that defect in many panels installed in the 1990s and earlier. The problem with listing it as a defect in older panels is that it was not specifically prohibited until the 2002 NEC. Plus many juridictions do not adopt the latest NEC edition until several years later.    So it is entirely possible that this code requirement wasn’t in place in your area until 2006 or even later. Why would an inspector call out a defect that wasn’t officially a defect until fairly recently?  We are of the opinion that it should not be, unless the house is newer. 

   Other inspectors see it differently. The code specialist Jerry Peck expressed the second view when we corresponded with him recently about it. "The code required (still does) that listed items be installed and used in accordance with their listing and labeling (which includes installation instructions, etc),” according to Jerry. "While the code itself did not state not to do that, nothing in the listing, labeling, or installation instructions said you could do that.” So the code mandate was added to officially say no in 2002 to something that was never approved to begin with, and also not considered a good practice among electricians for many years.

   For an explanation of why multiple neutrals under one lug are an electrical safety problem, see our blog post Can multiple neutral or ground wires be secured under the same terminal in an electric panel?

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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?

   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.