I'm thinking about re-siding a house within a next year or two. It is 2-unit house, 3 floors. The third floor outlets do not have ground. Can electric wires be ran under the siding? Is this common and/or up to code?

Alternative is to 'snake' wires but that will require a lot of dry-wall destruction.


Keep in mind that while you may choose to replace the entire cable for other reasons... It is now legal to retrofit ground wires.

The ground wires need to be large enough for the circuit (same size wire) and need to return ultimately to the same [sub?]panel. Grounds need to be installed using proper wiring methods, but do not need to follow the same path as the conductors. A ground can be chained off other grounds, i.e. it only needs to reach a point with a large enough path back to the same panel.

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  • Does a ground wire need to reach the panel with enough current-carrying capacity to handle simultaneous max-current fault on all involved circuits simultaneously, or simply the largest? Would that be affected by whether the circuits are guarded with GFCI or AFCI devices? – supercat Apr 10 '18 at 20:08
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    @supercat -- a retrofit ground handling multiple circuits would be sized to the largest circuit that it handles. – ThreePhaseEel Apr 10 '18 at 23:04
  • @superman what TPE says. Current only flows during faults, and they don't expect two things to bolt faults at once. – Harper - Reinstate Monica Apr 11 '18 at 21:19

You can't run it directly under the siding.

However, depending on how much siding you will remove during the process, it could be easier/cleaner to cut through the exterior sheathing to run new wiring. The cuts you make in the sheathing only have to be sealed against airflow and ambient moisture, unlike drywall which has to look good, too. There is much less work needed to repair exterior sheathing.

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