Monday, January 31, 2011

Wiring the Shop for 220V (bis)

In my previous posting, I went through a lot of detail on wiring a subpanel in my shop.  I had a few questions since then and wanted to clarify here rather than edit something you might have already read.

GFCI Masters and Slaves

Chris asked me about the GFCI sockets that I used since I seemed to have them everywhere.  Actually, for the most part, I do.  Most of my 110V sockets are home-runs to the subpanel on their own circuit; there are no other sockets on that circuit.  The beer-fridge circuit goes to a duplex GFCI socket with just that fridge on it.  The bandsaw DC's circuit similarly goes to a duplex GFCI socket with nothing but DC on it.
GFCI duplex sockets like these (the ones with the test/reset buttons) are called GFCI masters.  The 'line' power comes in one two terminals on the back (hot & neutral).  That's enough to power this master and both sockets are protected.  If you want more sockets GFCI protected, you can chain them to this master by connecting them to the 'load' terminals in the back of the master.  The downstream slave sockets are all protected by this master.
As I mentioned, most of my 110V sockets are home-run circuits to the subpanel; they do not have any downstream sockets.  Except in one case: my "Rockler" circuit has a socket at the ceiling for the extension reel and one below for normal-height people to use.  The socket at normal height is the master with the ceiling socket chained to it for protection (I didn't want to make the wiring easier and need a ladder to reset the circuit should it trip).  So, the line from the subpanel comes in the ceiling conduit to the left of the top socket and goes straight down to the bottom master GFCI socket; that connects to the 'line' terminals of the master.  From there, wires run up from the master's 'load' terminals to the ceiling socket.
You should label downstream GFCI sockets as "GFCI Protected"; a pack of labels comes with the masters.  Mine isn't visible due to the garage door rail.

Socket Blade Orientations

Another question was about the "T" in the socket blades.  Here I show a 220V socket and 110V socket for comparison.  In both cases, the "T" part indicates that this socket is wired to a 20A breaker.  Some tools (so few these days) have a plug with a horizontal blade on that side when they are intended to be used on 20A circuits only.  Regular plugs we're used to seeing have a vertical blade on the left indicating it requires a 15A breaker.  These "20A" sockets accept plugs requiring 15A or 20A. What makes a 220V socket different is the right blade: for 220V, it is horizontal while 110V has it vertical.

Dumb Trivia

Interesting trivia #1: which blade is hot? both for 220V, the right one for 110V (smaller blade).
Interesting trivia #2: why are 110V sockets polarized? To annoy the previous two generations.  Seriously, though, it forces hot and neutral to known wires going to the appliance.  Many appliances simply put the power switch on the hot side so when the appliance is off, there's no shock hazard.  Previously, a switch that flipped both power wires was needed to accomplish this since you could plug in the appliance either way (so a blade could be in neutral or hot).