Why Your Best Technicians Are Still Missing Faults: The Continuity Test Trap in Process Control Systems

Key Highlights

• The continuity beep threshold varies by meter model—most trigger around 60 ohms or less, missing critical resistance problems.
• Contact resistance as low as 0.01 ohms can prevent safety solenoids and motor starters from operating correctly.
• Parallel loads like solenoid coils (100+ ohms) won't trigger continuity beeps, leading to false conclusions during troubleshooting.
• ISA studies show technicians introduce errors approximately 17% of the time when using improper verification methods.

• Best practice: Always read the actual resistance value rather than relying on the audible beep.

The Continuity Beep That Lied to You : Wasting hours in troubleshooting?..

If you’ve been following along in this series on data integrity and measurement accuracy in process control, you already know the pattern:

Most failures don’t look like failures.
They hide in plain sight and they often hide behind tools that feel “easy.”

Today, I want to cover one of the most common troubleshooting traps I’ve seen in industrial electrical and controls work:

Continuity testing.

It’s one of the first things people learn. It’s also one of the easiest ways to get fooled — even when you’re doing everything “by the book.”

This mistake sends technicians in circles…

Video Timestamp: 0:00–0:28

Continuity mode feels like a shortcut.

You touch two points, and if the meter sees resistance low enough…

Beep.
You move on.
“Circuit’s good.”

But that beep isn’t actually proving the circuit is healthy.

It’s only proving one thing:

✅ the resistance is below a preset threshold.

And here’s the part most people miss:

that threshold changes depending on the meter.

Some meters will beep at surprisingly high values, high enough to completely hide a real problem.

Even 0.01 ohms can stop an 800-amp starter

Video Timestamp: 1:23–2:02

Let’s talk about what “small resistance” really means in the real world.

People hear “ohms” and assume:

• if it’s not huge, it’s not a big deal

But on high-current paths, that thinking breaks instantly.

The easiest analogy is a car starter:
If you develop even 0.1 ohm of resistance between your battery terminal and cable…

That fully charged battery can fail to crank the starter.

You get the annoying click-click-click, but no turnover.

Why?

Because the starter motor needs extremely low resistance to allow hundreds of amps to flow cleanly.

Industrial systems are the same:

• relay coils need clean low-resistance contacts to pull in reliably

• motor starters need solid contact paths for inrush current

• shutdown circuits need predictable energy delivery every time

So even if a tiny resistance values in the wrong place, it can cause intermittent failures that send techs chasing ghosts

The classic failure: The relay that “passed” but wasn’t good

Here’s the most common scenario I see:

A technician checks relay contacts in a control circuit, this could be an interlock, starter, shutdown path, or permissive.

Meter goes to continuity mode.
Contacts close.

Beep.

The assumption becomes:
✅ “Contacts are good.”

But here’s the catch:

That meter might actually be reading something like 45 ohms, and still beeping.

That’s low enough to pass continuity mode…
but it’s absolutely not low enough for reliable performance in many applications.

Contacts can degrade slowly due to:

• corrosion and contamination

• arc damage

• oxidation

• wear/age

So the circuit isn’t “open”…
it’s degraded and that’s often worse because it fails intermittently.

Why your solenoid won’t beep! and why that’s a problem

Video Timestamp: 2:42–3:19

Continuity testing doesn’t only fool people one way.

It can fool you in the opposite direction too.

Sometimes the meter doesn’t beep, and the technician assumes:

❌ open circuit

But the circuit may actually contain a normal load path with resistance above the beep threshold.

Example:
You’re checking a circuit with a solenoid coil in it.

A solenoid coil may measure something like 122 ohms (totally normal).

Continuity mode won’t beep at that value.

So you get silence and assume the path is broken, even when the coil is intact.

Don’t just listen.. look at the number!

Video Timestamp: 4:01–4:37

This is the rule I want people to walk away with:

Stop troubleshooting with your ears.

The beep is a convenience feature, not a diagnostic conclusion.

The only way to do this right is to:
✅ switch to ohms mode
✅ read the number on the display
✅ decide whether it makes sense for the application

For contact resistance checks, you generally want values as close to zero as possible:

• often under 1 ohm for many relay contacts

• often much lower for high-current paths

And if you’re working in safety-critical circuits, don’t just check once and move on — document and trend it over time.

If resistance creeps upward over successive checks, that’s actionable information.

Why this matters in safety and shutdown circuits

In safety-instrumented or shutdown functions, you’re not just “verifying a signal.”

You’re validating the entire chain will work on demand:
sensor → logic solver → final element

If a circuit is degraded and you miss it because continuity mode gave you a reassuring beep…

You can sign off a system that won’t perform when it matters.

And that’s the part that makes this issue worth calling out.

Final takeaway

Continuity mode is useful.

But it can also create false confidence.

So the next time your meter beeps and you’re tempted to move on…

Pause.

Because the number tells the truth. The beep only tells you you’re below a threshold.

And that threshold might not mean what you think it means.

Want to sharpen your team's troubleshooting skills? Explore Orion's hands-on I&C training programs or contact us for technician assessments.