Application Note

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Application Note

Walk onto any job site where

electricians are working, and

you’ll probably see some

voltage testers. These handy

devices—which often fit in a

shirt or pants pocket—are

popular because they quickly

give an indication of voltage

presence. That makes them

very handy for general voltage

checks. Thus, voltage testers

are popular with electricians.

Yet, these devices are not all

the same. The differences show

up in safety, reliability, and

convenience.

If you were to look at all the

voltage testers on the market

and note their differences,

you’d quickly see they divide

into two general categories:

solenoid-based testers and

electronic testers. Solenoid-

based testers have a long

tradition—they were the first

voltage testers available and

are still widely in use today.

When voltage passes some

threshold, the tester will indi-

cate a voltage is present. Below

that threshold, the tester won’t

indicate a voltage at all. The

thresholds are markedly differ-

ent between the two catego-

ries of testers—and that fact

carries important implications

for safety and convenience.

Let’s compare voltage testers

in these two categories more

closely, so you can draw your

own conclusions about what to

have in your toolbox—or what

to carry in your pocket.

Solenoid-based

voltage testers

These devices operate, as

their name implies, on solenoid

principles. A solenoid depends

on the movement of a ferrite

core referred to as the slug in

response to the energization

and de-energization of an elec-

tromagnetic coil. The indica-

tion function of these testers

depends on a spring, which

drives a mechanical pointer.

Differences in voltage

testers can be shocking

From the Fluke Digital Library @ www.fluke.com/library

The spring restrains the slug—

which slides to one end of its

chamber or the other, depend-

ing on whether the coil has

enough energy to cause the

slug to overcome the opposing

force of the spring. The amount

of energy required restricts the

sensitivity of solenoid-based

testers. In the US, a useful

solenoid tester will have the

ability to measure voltages up

to 480 V or more. Having the

Figure 1: This solenoid tester experienced a cata-

strophic failure after receiving an impulse. Even

with an MOV (metal oxide varistor) (see A), the unit

will still self-destruct from overheating (see B).

Figure 2: Current-limiting resistors (see C) protect this elec-

tronic tester which results in a predictable failure mechanism

when the tester is exposed to electrical impulses.

Summary of content (3 pages)

PAGE 1
Differences in voltage testers can be shocking Application Note Walk onto any job site where electricians are working, and you’ll probably see some voltage testers. These handy devices—which often fit in a shirt or pants pocket—are popular because they quickly give an indication of voltage presence. That makes them very handy for general voltage checks. Thus, voltage testers are popular with electricians. Yet, these devices are not all the same.
PAGE 2
Electronic testers like this Fluke T+ vibrate, beep, and glow to indicate voltage, giving you the feel of an oldfashioned solenoid in a safer electronic model. ability to measure higher voltages limits the capability to detect voltages below about 100 V due to the poor dynamic range of the magnetics, an unfortunate weakness of solenoid testers. Try using one on 24 V or 48 V control circuits, and you may as well be using a stick of wood.
PAGE 3
false positive. Then again, it can work to your advantage. For one thing, it won’t lull you into a false sense of safety that an energized conductor is de-energized. Suppose the solenoid-based tester doesn’t show you the 80 V sitting on that energized wire, and you grab it—what then? Other considerations Differences occur not just in the testers themselves. Nor is the solenoid vs. electronic issue the only one to resolve. Several other considerations are important for your safety and job performance.