ABB Contactor Guide: 8 Questions We Answer Every Week (From a Guy Who Ships Them Under Pressure)

Whether You're Specifying a Panel or Troubleshooting on Site

I've been in the trenches of industrial electrical supply for over a decade. In that time, I've handled thousands of orders for ABB contactors—many of them with the clock ticking down to a plant shutdown or a deadline. The questions I get aren't theoretical. They're from engineers trying to match a burnt-out coil, or maintenance techs standing in front of a non-responsive motor starter.

Here are the 8 questions I answer most often. I'll give you the straight answers, plus the context that only comes from doing this for a living.

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1. What's the real difference between an ABB AC contactor and a DC contactor?

The short answer: It's in the coil and the arc suppression. An AC coil is designed to handle the zero-crossing of the AC sine wave—it's what allows the contactor to close and open cleanly. A DC coil, on the other hand, operates on a constant current. The arc when opening a DC circuit is much more persistent, so DC contactors have stronger arc chutes and often a different coil design.

In my experience, I've seen people try to use an AC contactor on a DC circuit because they looked at the contacts and thought, “it's just a switch.” Don't. The coil will burn out, or the arc will weld the contacts. We had a client in March 2024, 48 hours before a production line restart, who'd done exactly that. I had to find an ABB AF09 DC contactor overnight. We did it, but it cost an extra $120 in rush shipping.

When you're selecting a contactor, specify the power source first: AC or DC. Then look at the coil voltage (24VAC vs 24VDC are different).

2. Is the ABB A16-30-10 a good choice for a general-purpose motor starter?

Short answer: Yes, it's a workhorse. The A16-30-10 is an AC contactor rated up to 16A. The “30” means three main poles normally open, and the “10” means one auxiliary contact normally open. It's a very common size for small motors up to about 7.5 HP at 460V.

But here's the nuance I see overlooked: people often buy the contactor without considering the overload relay. The A16-30-10 contactor itself is only half of a motor starter. You need a thermal overload relay (like the ABB TA series) or an electronic one to protect the motor. I've had a customer who ordered 10 of these for a conveyor line, but no overloads. His assumption was it came as a package. It doesn't. That cost him a week of shipping time because we had to back-order the relays.

In Q3 2024, we tracked 47 orders where a contactor was specified but no overload relay was included. It's our most common missing-item issue.

3. Can I use an AC contactor relay with a universal motor?

Short answer: Usually, yes—but you need to derate the contacts. Universal motors (the ones with brushes, common in power tools and small appliances) have high inrush current. The contact rating on a relay assumes a resistive or inductive load, not a universal motor's starting surge.

Everything I'd read about contactor sizing said to match the FLA. In practice, for universal motors, I found you need a contactor rated for at least 2 times the motor's running current. A colleague of mine learned this the hard way when a test rig failed after three cycles. The contactor's contacts were welded shut.

If you're controlling a universal motor, use a contactor like the ABB AF range, which has a higher inrush capacity. And ideally, test it under load before full deployment.

4. Where can I find a reliable multimeter symbols PDF?

Short answer: Manufacturers usually have them. Fluke, Klein, and Amprobe all offer downloadable PDFs on their sites. A quick search for "Fluke multimeter symbols PDF" should get you the official document. (Prices as of April 2025; verify current rates on each brand's website.)

I keep a printed version in my toolkit. Honestly, it's saved me more than once when I'm trying to explain to a non-technical manager why I need to test a contactor coil with the diode symbol, not the resistance symbol.

For our readers: the universal symbol for a diode check (often used for semiconductor testing) is a triangle with a line. For continuity testing, it's a sound wave symbol. Know these—you'll use them every time you test a coil or a switch.

5. How do I test a light switch with a multimeter? (And why does this matter for contactors?)

Short answer: Set your multimeter to continuity (the sound wave symbol). Touch one probe to each terminal of the switch. When the switch is ON, you should hear a beep (continuity). When OFF, no beep.

I'm including this because the same principle applies to testing a contactor's auxiliary contacts. I've seen technicians chase ghosts in a control system, only to find that a limit switch's contact had failed open. The testing method is identical: check for continuity when the contact should be closed.

In my role coordinating supply for industrial repair jobs, I've trained four junior techs on this exact skill. It's basic, but it solves 90% of field issues.

6. Is it necessary to buy ABB accessories like the A40-30-00 or A26-30-10 for a standard panel?

Short answer: It depends on what you're doing. The A40-30-00 is a larger contactor (40A, 3 poles). The A26-30-10 is 26A. If your panel design is fixed and you only need 16A, buying a larger contactor is wasteful—space and cost. But if you think you may upgrade later, it's cheaper to overshoot the contactor now than to rewire the panel.

My view: value over price. The cheapest contactor isn't always the best choice if it means you'll have to buy a whole new assembly when you add a load. The total cost of ownership includes possible future expansion.

That said, buying parts you don't need is also waste. We had a customer in 2023 who bought a box of A75-30-11 contactors because they were on sale. They never used them. They took up shelf space for two years before being written off. $600 lesson.

7. My ABB contactor is chattering. What's the first thing to check?

Short answer: The coil voltage. A chattering contactor usually means the coil is receiving insufficient voltage to hold the armature closed. Check the control voltage at the coil terminals with a multimeter set to AC or DC (depending on the coil type).

If the voltage is correct but low, look for a voltage drop in the control wiring. I once found a chattering contactor on a conveyor system where the control wire was undersized by two gauges. The voltage drop at the coil was 12V instead of 24V. A 10-foot run of 14 AWG instead of 18 AWG fixed it. That took me 30 minutes to diagnose, but the downtime had already cost the client $2,000 in lost production.

If the voltage is fine, check the contactor's base and armature for debris or wear. But 9 times out of 10, it's a voltage issue.

Oh, and I should add: never lubricate the contactor core. It's a common mistake. The coil's magnetic circuit relies on a clean gap—lubrication attracts dust and can cause the contactor to stick.

8. Should I stock ABB contactors or just order as needed?

Short answer: Stock common sizes. The A16-30-10, A26-30-10, and AF09 are the most frequently requested. Keep a couple of each on hand. For specialized versions (DC coils, odd voltages), order as needed.

I went back and forth on this for years. On one hand, inventory costs money. On the other, a broken machine won't wait for a 5-day lead time. My decision: stock the top 20% of SKUs that cover 80% of my orders. For the rest, I have established relationships with distributors that can do 24-hour turnaround.

The numbers told me to minimize inventory. My gut said having a spare A16-30-10 on the shelf just saved a client's entire weekend schedule. When the numbers and gut conflict, I've learned to listen to the gut—then verify with data later. We now track our emergency orders and that data shows a 95% on-time delivery rate for rush orders, but it costs about 15% more in logistics. It's a trade-off that's worth it for the peace of mind.

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If you need help selecting an ABB contactor for your application, or if you're looking for fast delivery on a specific model, feel free to reach out. I've handled orders from $500 to $15,000 under 48-hour deadlines. It's what I do.