Power Tools and Equipment
This domain tests safe selection, inspection and operation of drills, grinders, saws, mixers, vibrators and compactors, plus the simple calculations that go with them.
Before you start
Check plug, cable and body for damage; confirm 230 V single-phase supply; use an RCCB or ELCB; keep cables off wet ground and out of walkways; never bypass a guard. Unplug before changing a blade, bit or disc. Loose clothing, jewellery and long hair get caught in rotating parts.
The speed rating rule
Every disc or blade has a maximum safe speed. The tool no-load speed must be equal to or lower than that rating. A 180 mm disc rated at 6,000 rpm fitted to an 11,000 rpm grinder is a burst hazard, not a shortcut.
Common equipment
Concrete mixer: charge cement, sand and aggregate dry, then add water; never put hands or a shovel inside a running drum. Needle vibrator: insert vertically, withdraw slowly, do not drag it sideways. Plate compactor: keep feet clear. Circular saw: let the blade reach full speed, clamp the workpiece, and watch for kickback. Use dust extraction or wet methods to control silica.
Worked example
A mixer gives 0.2 m3 output per batch on a 1:2:4 mix. With a dry volume factor of 1.52, dry volume = 0.2 x 1.52 = 0.304 m3, so cement = 0.304 x 1/7 = 0.043 m3, about 63 kg or one and a quarter bags. Loading two bags would over-cement the mix and waste money.
Traps
Mixing up rated speed and operating speed, using a cutting disc for grinding, fitting a larger disc than the guard allows, and ignoring the current rating of extension leads and generators.