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When did the code first set a limit of one neutral wire (grounded conductor) connection per lug/set-screw in an electric panel?
Friday, June 7, 2019
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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