Power Tool Operation & Cord Safety

Power tools do hours of hand work in minutes, and they can injure you just as fast. A circular saw can kick back faster than you can pull away, and a damaged cord in a wet spot can kill. The rules here apply to any power tool, in any trade, along with the operator notes for the tools you will use most. Read the manual for your specific tool, and get hands-on practice from someone experienced. Rules for fixed machines and for nail guns go further than this.

What You Will Be Able to Do

• Inspect a tool before use, and know when to tag it out.
• Explain what causes kickback, and how to prevent it.
• Pick the right blade, bit or wheel.
• Use a grinder and air tools within their limits.
• Choose a cord by gauge and length, and test a GFCI.

Rules for Every Tool

1. Inspect it. Check the cord, plug, housing, switch and guard. The blade or bit should be sharp and tight.
2. Keep guards in place. Never pin, tie or wedge a guard open.
3. Disconnect before you change anything. Unplug it, or take out the battery, before changing bits, blades or wheels, and before clearing a jam.
4. Check the ground. A corded tool must be double insulated or have a working three-prong grounded plug. Never cut off the ground pin.
5. Dress for it. Wear safety glasses, and add a face shield for grinding. Wear hearing protection, since many tools run above 85 decibels. Avoid loose sleeves and jewelry, and tie back long hair.
6. Keep a balanced stance. Keep both feet planted, and never reach over a moving blade.
7. Secure the work. Use clamps or a vise, so that both hands can stay on the tool.
8. Do not carry a tool by the cord, and do not unplug it by yanking the cord.
9. Keep your finger off the trigger until you are ready.

Switches

OSHA's construction rule, 29 CFR 1926.300(d), sets switch types. Handheld circular saws and chainsaws need a constant-pressure switch that shuts off when you let go. Drills, grinders with wheels over 2 inches, reciprocating saws and similar tools need a momentary switch, sometimes called a dead-man switch. They may have a lock-on only if one motion of the same finger turns it off. Do not rig a trigger to stay on, because a tool that is locked on keeps spinning if you drop it or lose your grip.

Circular Saw

Match the blade to the work.

The wrong blade shows fast. A framing blade tears the face off finish plywood, and a fine blade can bind and burn in wet treated lumber.

Set the depth so that no more than one tooth shows below the work. Many saw manuals say less than a full tooth, so follow yours. A deeper setting exposes more blade and raises the risk of kickback.

Kickback happens when the blade binds, and the saw jumps back at you. Common causes are a sagging board that pinches the blade, a saw twisted off line, a nail or knot that grabs the teeth, and plunge-starting a saw not made for it. A dull blade makes all of these worse.

• Support the work, so that the cut opens as you go and the offcut falls away.
• Let the blade reach full speed before you start.
• Feed steadily, and keep the shoe flat on the work.
• Stand beside the cut line, not behind the saw. A saw that kicks back runs straight back along the blade's path.
• Check that the lower guard snaps back before each cut.
• Route the cord over your shoulder or behind the saw, never across the cut line, where the blade can cut it.

Reciprocating Saw

Teeth per inch (TPI) tell you what the blade cuts.

Demolition blades mix tooth patterns and can handle nails in wood. Pruning blades cut green wood, carbide blades cut cast iron and diamond-grit blades cut tile and masonry.

Check what is behind a wall before you cut. Wires, pipes and gas lines hide there, so use a scanner or open up the cavity first. Keep the shoe firmly on the work, and hold the saw with both hands. Use orbital action for fast wood cuts, and turn it off for metal. Blades and clamps get hot, so give them time to cool, and watch for the saw jumping if the blade binds.

Drills and Drivers

Set a drill's clutch low in soft wood, so that it slips before the screw strips. An impact driver has no clutch, so do not use it on small finish screws or fine hardware, because its force can twist the head right off.

Hammer mode pounds the bit along its length. That helps only in concrete and masonry, so turn it off for wood and metal, where it wears out bits and the tool.

Large bits can grab and twist the drill hard. Use the side handle, and brace yourself. Run lower speeds for large bits and metal, and higher speeds for small bits in wood.

Miter Saw

• Let the blade reach full speed before it touches the work.
• Use the hold-down clamp on anything shorter than about 8 inches, instead of holding it by hand, and keep your hands at least 6 inches from the blade path.
• Never cross your arms or reach over the blade.
• Keep the work tight against the fence, and support long pieces.
• After the cut, hold the head down, let go of the trigger and wait for the blade to stop before you raise it.
• Use about 40 teeth for framing and 60 or more for finish work, and never a wood blade on steel.

Angle Grinders

An angle grinder runs at very high speed, and a broken wheel flies out like shrapnel.

• Check the speed rating. The wheel's maximum RPM must meet or exceed the grinder's RPM.
• Use the right wheel. A Type 27 depressed-center wheel is for grinding, and a thin Type 1 wheel is for cutting. Flap discs blend surfaces, diamond blades cut masonry and wire cups strip paint and rust. Do not cut with a grinding wheel or grind with the side of a cut-off wheel, since either can shatter.
• Keep the guard on, and set it between you and the wheel. Use the guard made for your wheel type, since cut-off and grinding wheels can need different guards.
• Inspect the wheel for cracks or chips, and replace it if you find any. Run a new wheel for a moment with nobody in line with it.
• Use two hands, with the side handle in place.
• Wear a face shield over safety glasses.
• Watch your sparks. Sparks can travel 30 feet or more and light sawdust or cardboard. That is why many sites post a fire watch with an extinguisher, and some require a hot work permit.
• Let it stop before you set it down.

Bench grinders have their own limits. The work rest stays within 1/8 inch of the wheel, and the tongue guard within 1/4 inch. Before mounting, inspect a new wheel and ring test it by tapping it lightly. A clear ring is good. A dead sound means a crack.

Air Tools

Compressed air stores a lot of energy.

• Attach tools with a secure connection, so that they cannot come loose.
• Use a whip check at hose couplings where your site requires it. Hoses over 1/2 inch inside diameter need a safety device at the source or branch line to reduce pressure if a hose fails.
• Do not hoist or lower tools by the hose.
• Shut off the air and bleed the line before disconnecting a hose.
• Do not use compressed air for cleaning unless it is reduced to under 30 psi, with effective chip guarding and PPE. Never point it at anyone.
• For nailers, disconnect the air or remove the battery before clearing a jam, keep your finger off the trigger when not nailing, and never point one at anyone.

Cord Safety

Before You Plug In

• Look for cuts, crushed spots and exposed copper.
• Check that the ground pin is there and straight.
• Check that the cord's jacket is firmly held at both ends.
• Use three-wire cords rated for hard or extra-hard use. Look for types such as SJTW or SJOOW. Do not use light household cords on a job site.

Size for the Load

A smaller AWG number means thicker wire. A long or thin cord drops voltage, which makes the tool labor and the cord heat up.

Use these as rules of thumb, and follow the tool's manual if it says more.

Worked example: A 20-amp tool sits 75 feet from the outlet. A 12 AWG cord stops at 50 feet, so use 10 AWG. An undersized cord runs hot, and the tool bogs down.

Routing

• Do not run cords through doorways or windows, where they can be pinched.
• Keep them out of water, and away from heat, oil and sharp edges.
• Do not fasten them with staples, nails or wire, or hang them over rebar or pipe edges.
• Use weatherproof connections on outdoor runs.
• Cover or lift them over walkways, so that they are not a trip hazard or crushed by vehicles.

Repairs

Take a damaged cord out of service. Wrapping tape around a cut does not count as a repair. OSHA permits a repair to hard-service cords of 12 AWG or larger only if the splice keeps the cord's original insulation and strength, and many employers ban field repairs entirely. Replace the plug with a proper one, or replace the cord.

GFCIs

A ground-fault circuit interrupter (GFCI) cuts power in a fraction of a second when current leaks to where it should not be, such as through you.

On construction sites, OSHA requires GFCIs on 120-volt, 15- and 20-amp receptacles that are not part of the permanent wiring, or a written assured equipment grounding conductor program. The program requires a competent person, daily visual checks, and tests before first use, after repairs, after possible damage, and at least every 3 months. Most sites simply use GFCIs. If an outlet is not protected, use a portable GFCI, such as a GFCI cord set, at the source end of the cord. Use one wherever you work in wet or damp places.

Testing a GFCI

1. Plug in a small load, such as a work light.
2. Press TEST. The light should go out, and the RESET button should pop.
3. Press RESET. The light should come back on.
4. If it does not trip or reset, take it out of service.

Test it before the first use of each shift, or as your employer requires. A GFCI that keeps tripping is telling you something. Find the fault rather than bypass it.

When to Stop

Stop using a tool, tag it DO NOT USE and tell your supervisor if:

• A guard is missing or does not work.
• The cord, plug or ground pin is damaged.
• The switch sticks or will not turn the tool off.
• It smokes, sparks or smells of burning.
• The blade or wheel is cracked or wobbles.
• It has been dropped hard, such as onto concrete. The damage can stay hidden until the tool fails.

Common Mistakes

Check Your Understanding

1. Your circular saw jerked back at the end of a cut through a sagging plywood sheet. What caused it, and how do you stop it?

The sheet sagged and pinched the blade. Support the sheet so that the kerf opens as you cut.

2. The plate on your grinder says 12,200 RPM. The wheel in the bin is marked 9,000 RPM. Can you use it?

No. It would spin faster than its rating and could burst.

3. A GFCI cuts your work light at the TEST button, but RESET will not bring it back. What now?

Take it out of service, and tag it. Use a working one.

4. A coworker has taped a cut in an extension cord on the slab and says it is fixed. What do you do?

Have it taken out of service and replaced. Tape does not restore the jacket, and the site is often wet.

5. A 3-prong plug has no ground pin, but the tool still runs. Is it OK?

No. Without the ground, a fault can energize the tool's case. Replace the plug or the cord.

Key Takeaways

• Inspect tools before use, and keep guards working.
• Disconnect power before you change a blade, bit or wheel, or clear a jam.
• Support the work and stand out of line to avoid kickback.
• Match the wheel to the task, and the wheel's RPM to the grinder.
• Use three-wire hard-use cords, sized for the load and distance.
• Use and test GFCIs, especially on construction sites and in wet places.
• If in doubt, tag the tool and report it.