Question: How do you determine which electrical service panels are approved for terminating two neutrals together under one screw terminal, or one neutral and one equipment grounding conductor under one screw terminal, often referred to as “double-lugging”?
Answer: As they say, the devil is in the details. First of all, neutral conductors can never be doubled-up under one terminal; the code has specifically prohibited this practice since 2002. For other terminations, the electrical code has a very basic rule; terminals for more than one conductor must be identified. Space is limited on terminals due to their small size; it’s more important for that precious real estate on a terminal to be marked with the size of conductors, whether it’s approved for copper or aluminum, the temperature rating, etc. There’s not much room left for identifying whether or not the terminal is approved for more than one conductor. Often you have to look at the terminal or circuit breaker packaging, product wiring diagrams, the manufacturer’s label inside the electrical panel, a product specification sheet from the terminal or circuit breaker manufacturer, online at the manufacturer’s website, etc. It inevitably requires some detective work unless the electrical panel or packaging is clearly marked. And different brands of terminals and circuit breakers have different allowances. When in doubt, don’t “double-lug” two conductors under a single terminal. It’s a favorite violation that gets flagged by private home inspectors when homes are being bought and sold.
Always check with your local electrical inspector about the specific code requirements in your area.
Question answered by John Williamson, Chief Electrical Inspector, Minnesota Department of Labor and Industry
John Williamson has been in the electrical industry for 40 years and is a licensed master electrician and certified building official. John has worked for the state of Minnesota for over 23 years and is the Chief Electrical Inspector. For the past 25 years John has also provided electrical code consultation to various book and magazine publishers
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