Don't Be Spooked

1 November 2019


This spooky blog will pair perfectly with the Halloween candy you stole from your kid’s trick-or-treating basket this morning for breakfast. Or if you don’t have children, then today is a great day to stop by the store and get that post-Halloween discounted candy. Like always, we are here for you with great ideas! You probably didn’t think that this was a budget-friendly electrical testing blog, did you?

Anyways, today’s frightening topic is high voltage testing. Except, it’s not as spooky as it sounds, and we’re here to tell you that it’s safe. Gasp. Let’s get to it.

Give us the details.

So, electrical test equipment operates at a medium to high voltage, depending on the tester you are using. This understandably sounds scary, and in general, many folks agree that anything over 50 V is potentially dangerous. However, even your carpet (or your beloved cat after she rolls around on your fluffy rug) can hit you with thousands of volts of static electricity. But we continue to live to tell the tale. How?

Current. This is the real bad guy, monster, villain, evil whatever – you name it. If you’re going to be afraid of something, be afraid of current. It’s this, passing through the human body, that really does the damage. Very small, we’d even go as far to say miniscule, amounts of current are harmless (we’re talking less than 0.5 mA), but anything above 10 mA can cause harm to us humans, primarily through heat. At 50 mA, the outlook is not good. This small amount of current can unfortunately be lethal in certain circumstances.

Now that you understand the vocabulary, you are ready for the truth.

How is high voltage testing actually safe? We still don’t believe you.

Well, an insulation tester is designed with your safety in mind, so it has a built in current-limiting resistor. This gives it just enough current to get the job done without unnecessary or excess current left over. If you are testing insulation that can pass more than a couple of milli-amps, then it’s already struggling. You’ll need to repair or replace the insulation immediately, so there’s no point trying to pump it full of even more current.

If you are dealing with “good” insulation, then you’ll need an instrument that can measure very low levels of current, often down to the nano-amp range. To do this, you need a tester that can deliver well up into the medium voltage zone. Thus, the necessity for higher voltages like 5, 10, or 15 kilo (thousand) volts. Make sense? At such low levels of current, there is minimal risk to the operator, and we can consider it “safe”.

We should also mention that although a few mili-amps won’t cause physical damage to the human body, you should still promote safe practices in the workplace and consider the environment you are testing in. If you are working in a large, open space, a small shock would usually be fine, but if you are on a ladder or working with a motor, the resulting involuntary muscle spasm or twitch could be disastrous. Hence, necessary precautions and a general safety attitude towards high voltage testing should always be implemented.

There’s another player to watch out for though.

Remember, it takes two to tango. While everyone is SO focused on the electrical tester in-hand, we often forget about player 2 – the item under test. This is often the most dangerous part of the whole situation. The item you are testing can store large amounts of static energy in its insulation, which will become polarized by a tester. After a high-stress or high-energy event, humans need to decompress and relax; insulating material requires the same post-testing discharge period to release the capacitance. If you aren’t paying attention, this could occur right through your body, as you attempt to disconnect the test leads. AH!

Luckily, engineers are really on-top of their innovation game, and they’ve essentially solved that problem for you. High-quality testers are now equipped with automatic discharge features. As soon as the test voltage ends, the tester will engage a resistive discharge network. Sounds oh, so fancy. The instrument will also make sounds and flash warnings on the screen to keep the operator up-to-date on the progress (or lack thereof) throughout the discharge process. When it’s at a safe level, the instrument will let you know.

One last thing.

High-pots or dielectric testers are in a field of their own. Insulation testers make quick, careful, and precise measurements, while high-pots generally adopt a “kill the weak” attitude. In this manner, a high-pot will help you identify questionable equipment and take it off-line before it causes damage to personnel or breaks down mid-operation. These are powerful, high voltage instruments that utilize larger levels of current, as well. Typically, high-pots are used to test components, which are a part of a larger piece of equipment and isolated from contact with the operator.

Are you still spooked? We certainly hope not. Now, go share the high voltage truth with a friend or a stranger or a stray black cat. We don’t care who it is. Just get it done.

- Meredith Kenton, Digital Marketing Assistant