My brother in law recently had a large garage/shop built and is using a subpanel of sorts for temporary power. The enclosure is that of a subpanel, but it's been modified by adding four 2-gang metal boxes with two duplex receptacles each, and is wired to provide 120V (four receptacles on one phase and four on the other). It has a large cord connected to it, which he plugs into the dryer outlet in the house (through a window). The box lays on the concrete floor in the garage. Everything looks properly wired, except the ground is not connected at the house. This is because he is plugging into the dryer receptacle, which only has 3 slots. I told him it isn't safe to have it wired as such, but he doesn't think it's a big deal. Other than installing an actual sub panel that is mounted permanently to the wall and properly wired to the main panel, what's the simplest thing he can do in the meantime to make it safer? I was thinking he should swap out the 3-prong dryer receptacle with a 4-prong receptacle and/or install a GFCI breaker in the main panel for the dryer receptacle.

 

He could swap out the 3 wire receptacle for a 4 receptacle if all four wires are there. My guess is there is no separate ground.

Installing either a GFI breaker or GFI receptacles would then be a good step for protection.

 

Or if it has a grounded metallic grounding path back to the panel.

 

The house is only 15 years old, so I'm assuming there is a 4-wire in the box. If not, the panel is only a couple feet away.

 

I am sure there are four wires there. The dryer receptacle should have been the 4-wire style when the house was built unless that area was still on a very old version of the NEC. The NEC has required the 4-wire receptacles for dryers and ranges since 1996.