Consider 3/4" EMT running from a main panel to a workshop. It has THHN wires for a 240V 30A circuit and a 120V 20A. The EMT is the ground.

In the workshop, the EMT ends at a metal box, and from there on is Romex.

My question is: What gauge should a pigtail from the Romex grounds to the box be? Does this need two pigtails, at least one 10AWG and one 12AWG? Or one that's at least 6 or 8? Or just screw both Romex grounds to the box (though that's less convenient, esp. since you only get one wire per screw)? Or...?

The closest question I found was THHN through EMT - then convert to Romex?, but that doesn't address gauge, just the basic need to ground.

2 Answers 2


One 10 AWG copper pigtail will do. In a shared conduit, (or in this case connecting to a shared conduit) one ground of the largest size is all that's required for all the circuit conductors. It does not need to be larger than that.


The largest

The design presumption is that it's unlikely for two circuits to have a big problem (bolted fault) at the same time.

This only works for ground, however, not any active conductor.

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