Tile wet saw: water, 120 volts, and a bare blade

The pump on a wet saw sits in a tray of water, and that water runs across the table, down your hands and onto the floor you are standing on. Fifty milliamps across the chest can stop a heart, and a 15-amp breaker will never notice it.

The points

• A cracked pump, a nicked cord or a wet plug puts line voltage into the tray, and you are the path to ground with wet hands. A GFCI trips at about 5 milliamps in a fraction of a second; a breaker trips at 15 amps, three hundred times more than it takes to kill you.
• The rule requires GFCI protection or an assured grounding program on the receptacles a crew uses on a job. A house's bedroom outlet may have neither, so the saw plugs into a GFCI pigtail or a GFCI-protected outlet, every time, and you test it with the button before the first cut.
• The cord runs above the water, not through it, and the plug stays off the floor. Nobody handles the plug, the pump or the switch with wet hands.
• The blade has no guard that covers the cut. Hands stay behind the blade line, narrow strips get a push stick, and small pieces are held against the fence, never pinched free-hand next to the rim.
• Porcelain and stone are silica. The water is what keeps the dust out of your lungs, so the saw runs wet or it does not run, and the dried slurry in the tray gets wiped up wet, never swept.

Why it goes wrong

A wet saw is one of the few tools where you deliberately mix water and electricity for hours. The pump is submerged, the motor is inches from the spray, and the table is a puddle. Every part of that is safe only while the insulation is perfect. A cracked pump housing or a cord that has been dragged over tile edges for a year is not perfect, and the first sign is usually a tingle you talk yourself out of.

Current is what kills, not voltage. Ten milliamps locks your hand on the tool so you cannot let go; 50 to 100 milliamps across the chest can put the heart into fibrillation. The 15-amp breaker in the panel protects the wiring from a fire, not you from a shock. A GFCI compares current going out and coming back and opens the circuit at about 5 milliamps, in as little as a fortieth of a second. That is the only thing on the job that trips before you are hurt.

The rule at 1926.404 requires GFCIs or an assured grounding program on the 120-volt receptacles a crew uses that are not part of the building's permanent wiring. An occupied house is a gray area, because the outlets are permanent and the kitchen and bath may be GFCI-protected while the living room is not. The way to remove the doubt is to carry an inline GFCI pigtail and put every saw and pump through it. Push the test button every morning; a GFCI that does not trip on test is a plug adapter.

Set the saw up where the water can go. A garage with the door open, a driveway, a patio. Not the kitchen, and not a carpeted hall. If it has to be inside, the tray sits in a bigger tray, the floor is covered and the cord is hung so it does not lie in the runoff. Slurry on a smooth subfloor is as slick as ice, and a slip with a hand out toward a spinning rim is how a wet saw takes a finger.

The continuous-rim diamond blade does not have teeth, and people treat it as harmless. It is a grinding wheel spinning at thousands of rpm, and it will grind through a fingertip as easily as through porcelain. Keep hands behind the leading edge of the blade, feed with the tile against the fence, and use a push stick for anything narrower than about 2 inches. A tile that pinches the blade can climb and throw; do not force a cut that has bound.

Cutting porcelain or stone dry on a wet saw to save the mess is the worst trade on the job. The silica rule's Table 1 lists the stationary masonry saw with continuous water to the blade and requires no respirator in that setup. With the water off, the saw is no longer on Table 1, the exposure has to be assessed, and the dust in that room is respirable quartz. The slurry that dries in the tray and on the floor turns into the same dust; wet-wipe or hose it, and never sweep it dry.

Questions for the crew

1. Where is the wet saw set up today, and what is it plugged into?
2. When did somebody last push the test button on that GFCI, and did it trip?
3. What is the narrowest cut on this job, and how is it going to be held?

To close

Today the saw runs through a GFCI that has been tested this morning, with the water on and the cord out of the puddle.