Harris Electrical Safety Tester
Phillip Harris Ltd.
Lynn Lane, Shenstone, Lichfield, Staffs WS14 0EE
Tel 0543 480077, Fax 0543 480068
(schools etc. usually get discounts and free delivery)
This is a brief report on the cheapest answer I've seen to the current (sorry) craze for electrical appliance testing. It's a box about a foot long and six inches high, with a 13A socket, two 4mm plug sockets (plus a long lead with crocodile clip), three pilot lights, and a test button. It checks for earth leakage and earth continuity, the most common problems with portable appliances.
Operation is extremely simple; all the instructions are printed on the front of the unit, and can be summarised as "connect the leads and press the button". This puts 500 volts into the earth cable, to check for leakage to live and neutral, then 10 or 25 amps through the earth lead and casing to ensure that the earth lead won't blow if the equipment goes wrong. The test takes about three seconds, plus time spent plugging and unplugging, connecting the earth lead, etc. A pass results in a green light, a fail in red lights for insulation, earthing, or both.
I've used it for two months, and it's found a few distinctly dodgy items that slipped past a simple resistance test, including a heated cabinet that was happily running while intermittently shorting neutral to earth. It also found three mistakes when we had to wire up nearly a hundred appliances in a hurry.
Drawbacks: It doesn't run some of the more esoteric tests available on its rivals, and is obviously limited to testing equipment with earthed casings; double insulated gadgets will always fail. It's only suitable for use in Britain; Europe may be OK with suitable adaptors, but I wouldn't count on it, and USA at 110V is RIGHT OUT! It's mains powered (and comes without a plug fitted!), so there may be problems if you want to check safety before turning on the mains in a hall or theatre. Finally, it's heavy; about 6 Kg, I think, but I don't have a balance covering that range.
This unit is used by the demonstration team who teach technicians the rudiments of electrical safety, and they have told me that this test, plus a visual inspection and plug check (especially of fuse rating), are enough to comply with existing legislation in schools. I can't say if that makes it OK for convention use. You are strongly advised to check with insurers and/or lawyers if you are in doubt!