I Replaced an ABB A16-30-10 Contactor That Wasn't Broken: An $800 Lesson in Testing

If you've ever watched a conveyor stop dead in the middle of a shift, you know the feeling. The line goes quiet. The production manager walks over. It's your problem now.

This is the story of how I replaced an ABB a16-30-10 contactor that wasn't broken. It cost us somewhere around $800 in parts, overtime, and dead production time — and the real culprit was a $15 control relay with a cracked solder joint.

Quick context: I'm a maintenance electrician at a packaging plant in Ohio. I've been doing this for eight years, and I've personally made three significant diagnostic mistakes in that time, totaling roughly $2,600 in wasted budget. I now maintain our team's troubleshooting checklist, mostly so nobody else repeats what I did.

Why the ABB a16 Contactor Was My First Suspect

Line 2 had a 5 HP conveyor motor controlled by an ABB a16 contactor in a corner panel. The unit is a 16-amp, three-pole contactor, AC-3 rated under IEC 60947-4-1, with one normally open aux contact and a 230V coil in our configuration. It's a solid, boring, dependable part. That's why it was annoying when the line started dropping out randomly — this was back in September 2024.

Intermittent faults are the worst because by the time you get to the panel, everything looks fine. The overload relay hadn't tripped. No burned smell. The motor was healthy. So the investigation zeroed in on the contactor. Maybe you've done this too: you see light pitting on the main contacts and declare the part worn. I was so sure that I ordered the replacement before doing any real electrical testing. Then I told anyone who asked that a "new contactor was on the way." Classic.

The "Contactor Is the Problem" Thinking

The belief that a contactor is the most likely failure point has some historical basis. Thirty years ago, contactors running on dirty factory air died young, and the fastest fix was usually to just swap the part. Today, with better enclosures and sealed contact blocks, that default answer is outdated. I keep relearning the same lesson: a contactor that looks bad might be fine, and a relay that looks fine might be failing. The only way to know is to test it.

In my first year on the job — 2017 — I ordered a dozen replacement contactors based on nothing more than the nameplate of a dead one. The winding was open, so I thought the solution was obvious. I was wrong about the root cause then too. That one cost my employer $1,350 and a week of headaches. Apparently I needed a bigger reminder in 2024.

How to Test a Relay With a Multimeter (What I Should've Done First)

When someone on your team looks up how to test relay with multimeter, they usually find the simple version. Some of it applies directly to contactors, because a contactor is basically a big relay.

1. Measure the coil. Set the multimeter to ohms and read across the coil terminals — A1 and A2 — then compare it to the coil label. You're looking for a short (near zero) or an open circuit (OL). A slightly odd resistance reading is not automatically a failure.
2. Energize the coil at rated voltage. Apply the nameplate voltage and listen for a clean click. Then confirm the main contacts actually close. With the coil off, the normally open contacts should read open. With the coil on, they should read near zero.
3. Test under load. This is the step I skipped. Measure the voltage across the closed contact while the downstream load is actually running. A healthy contact reads close to 0V under load. If you see even 1 or 2 volts, that contact is resisting current it shouldn't.

On paper, the old contactor passed all three steps. I only did the first two before I condemned it. And here's the part that stings: the coil was fine, the contacts were fine, and the panel was still dropping out after I installed a brand-new unit.

There's another subtlety with intermittent faults: heat. A failing coil can read perfect at room temperature and drop out when the panel warms up. So if a relay or contactor tests good cold, cycle it twenty times and repeat the test while it's hot. That's what finally caught the relay on our line.

The ABB Contactor Wiring Diagram PDF That Set Me Straight

After the replacement didn't fix anything, I went back to basics. I pulled up ABB's library and found the ABB contactor wiring diagram PDF for the A16-30-10, including the control circuit details. Ten minutes of reading would have saved me a weekend.

The drawing showed coil terminals A1/A2, main poles 1-2, 3-4, 5-6, and aux contacts 13-14 (NO) and 21-22 (NC). I traced the circuit in the panel and found something unexpected: the wiring didn't match the diagram. The seal-in circuit that keeps the contactor energized after you release the start button was running through the wrong aux contact. And someone had bypassed a control fuse with a jumper wire as a "temporary" repair. (I really should have checked all of this before ordering parts.)

Why was the wiring wrong? Because this panel had a history. A previous contractor had swapped in a Telemecanique contactor in 2019 to keep the line running during an emergency. Nothing wrong with that hardware — it was properly rated for the motor, and Telemecanique makes capable contactors. But whoever adapted the wiring didn't document it, and the official drawing was never updated. Our spare parts list still said ABB, while the machine actually had a Telemecanique contactor installed. Five years later, that undocumented change turned a routine repair into a two-day mystery.

What a "Cheap" Quote Actually Costs

And then there was the purchase order. The production manager wanted a part number that afternoon, so I skipped my normal habit of getting three quotes. I grabbed one from a supply house that looked about 25% cheaper than our usual distributor's price for the same ABB a16 contactor. The salesperson said the lower price was a volume discount and I'd "just need a couple of extra pieces." I didn't ask for a line-item breakdown. I didn't ask what was missing. That was an expensive silence.

The unit arrived with no manual, no wiring diagram, no auxiliary contact block, and not even the little sticker that ABB puts on the side of the product. The terminal layout was slightly different from the unit I was removing. That should have been a red flag.

Final tally for that decision: $187 for the contactor, $38 for the separately shipped aux block, $52 for rush shipping because the aux block arrived three days after the contactor, and roughly six hours of overtime labor. Add the production downtime on top, and the "savings" evaporated quickly.

I've learned to ask what's not included before asking the price. A supplier who lists the contactor, the aux block, the adapter, and the documentation upfront — even if the total looks higher on screen — usually costs less in the end.

The Funniest Side Search: Spark Plug Distributor

Somewhere in the middle of this mess, I searched our inventory system for the vague term "distributor" — I meant an electrical distribution block. The search returned four pages of automotive spark plug distributor components before anything industrial showed up. I spent an embarrassing few minutes looking for a part that didn't exist in our catalog. That's what vague terminology gets you, and it's exactly why I now search by exact catalog numbers instead of plain-English descriptions.

The Real Culprit

The actual failure wasn't the contactor at all. It was a small 24V control relay in the same panel. A cracked solder joint on the relay's base would open as the cabinet warmed up. When the joint opened, the relay dropped out, which de-energized the contactor coil, which stopped the motor. By the time someone reached the panel, everything had cooled down and appeared fine again.

I caught it with the under-load test: while the circuit was running, I measured voltage across the relay's output contacts and watched it climb from near zero to several volts as the joint heated up. That's something a continuity test on a cold bench will never show you.

The ABB a16-30-10 contactor I condemned and replaced was never broken. The "replacement" I installed was still clicking fine on the bench a week later.

The Checklist That Fixed the Process

In October 2024, I wrote a half-page checklist and taped it inside the electrical panel door. The team has been using it since, and it's caught 23 potential mis-orders and misdiagnoses over the past 18 months — not bad for a piece of paper. The checklist is still up there as of April 2025.

• Download the manufacturer's wiring diagram by exact catalog number and compare it to the as-built wiring.
• Measure coil resistance, then energize the coil at rated voltage before condemning the device.
• Perform an under-load voltage drop test on suspected contacts.
• Cycle relays hot and look for intermittent dropouts — heat reveals hidden faults.
• Ask the supplier for a full line-item breakdown before approving the purchase order.
• Order by complete part number, including coil voltage and aux contacts.

Bottom line: a contactor is a simple piece of hardware, but the circuit around it can hide surprises for years. The free ABB contactor wiring diagram PDF is worth more than any discount I could chase. And if you're teaching a new technician how to test a relay with a multimeter, teach them the under-load test, not just the resistance check. That's the difference between diagnosing a problem and guessing at it.

Trust me on this one. I'm the guy who accidentally researched spark plug distributors while looking for a spare part — and the contactor that "failed" is still sitting in a drawer, fully functional.