A (built in 1987) house that we are under contract to buy has a 30-amp sub-panel in the attached garage. The sub-panel is currently populated by two 120V, 20amp circuits for receptacles in the garage. Upon inspection, I discovered that its electrical supply is as follows:
- 30 amp breaker at main panel, with 8/3 NM-B with ground run to a box with a NEMA 10-30R dryer receptacle in the basement (yes, I'm aware that 10-30R should be replaced with a 14-30R)
- Another 8/3 NM-B with ground running from that box to the garage sub-panel
So it certainly seems that the dryer receptacle and sub-panel share the same 30-amp supply at the main panel. I know that this isn't best practice and will include it in my inspection objections, but can anyone point me to a code reference that would forbid this installation? For example, if they exist, what are the NEC sections requiring a dryer receptacle or subpanel to be on dedicated circuits?
Best Answer
If it goes to a subpanel, it's a feeder.
You cannot put a receptacle on a feeder.
What needs to happen is the dryer receptacle needs to be replaced with a blank junction box cover, and then a new 10/3 cable run from a dryer receptacle in a new box, to either main or sub panel, where it'll land on a 30A breaker. This means the 10/3 cable will be alongside the 8/3 feeder, either to the main panel or to the sub.
You can use 8/3 for this dryer run if you really want to, but I don't see a reason to do that. Dryers won't pull more than 30A (really: <24A) because every dryer manufacturer expects a 30A circuit, and sizes for it.
Once the entire 8/3 feeder is devoid of receptacles, it can be upgraded to a 40A breaker, because that's allowed on 8/3. In practical terms, that will support the dryer and 1 receptacle circuit on each leg of power (so 2 if balanced).
One more thing. If the subpanel came first and the dryer plug was an afterthought, it's possible this was spliced inline, and that probably means the wires in that box are way too short. You need 6" of length past the clamp, or 3" beyond the surface of the box. In that case, move the box so one end has enough length, and re-run the other end. Better, leave the "enough length" side as the dryer branch circuit, scrap the other end, and run a whole new feeder in 6AWG, bypassing the box entirely. 6AWG gives you 60A at the subpanel.