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When is an electrical panel overcrowded with too much wiring?
Sunday, February 27, 2022
An electrical panel is overcrowded if the jumbled maze of wires makes it impossible to follow the path of a wire from the breaker to where it exits the box. The panel shown above was so jammed with wiring that we had to push the dead front firmly against the top layer of wiring to close the panel. Not good…and not safe.
Filling a panel with too many tandem breakers (the kind that fit two circuits into a single slot, also called duplex or half-high breakers) is the thing that most often causes an overcrowded panel. Manufacturers specify how many tandem breakers are allowed to be installed in a panel, and where they should be located, in the wiring diagram sticker on the inside of the panel door. Newer panels have a lockout device that keeps half-highs from being installed where they are not allowed. But older panels don’t have that safety feature, and there are ways that it can be overridden even in a new panel. See our articles What is the maximum number of circuit breakers allowed in an electric panel? and What is a CTL breaker? for more on this.
Other factors for overcrowding include an original installation that wasn’t planned to minimize running wires from one side of the box to the other, excessive lengths of wire left in panel, and not stripping the sheathing away from NM-cables once they enter the panel box. Panels that have been reconfigured by a homeowner or handyman to connect to a generator panel are another example. We wish all the electrical panels could look like the professional job at right. Many start off life like it, but get added to again and again over the years, instead of installing a subpanel—which is our usual recommendation for repairing an overpacked panel.
The National Electrical Code [NEC 312.8(A)] does have a standard for the maximum amount of wires allowed in wiring space of a panel: they cannot occupy more than 40% of the space cross-section, and the total of wires, splices, and taps cannot exceed 75%. Unfortunately, the problem is often not so much the cross-sectional area as the organization of the wiring in the panel.
The addition of a “plug-on neutral," which provides a neutral bus bar under the breakers, is one feature in newer panels that reduces the amount of wires in the panel. To learn more about it, go to Why are there no neutral pigtails at the AFCI and GFCI breakers in the panel?
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