ABB Contactor FAQ: A40-30-10, A95-30, VFD Motor Setups, and Multimeter Testing

I'm not an electrical engineer. I'm the office administrator who orders parts for a mid-size facilities company—about 60-80 orders a year across a few dozen vendors. When I took over purchasing in 2020, one of the first things I had to learn was how to buy an ABB contactor without getting burned. If you search 'abb-contactor' online, you'll get the full A-line and AF-line range, but you still need to know which one fits your job. This FAQ covers what comes up on every order request:

• Which ABB contactor should I order for a VFD motor setup?
• What do the model numbers actually mean?
• How do I test a light switch with a multimeter—and can I use the same trick on a contactor?
• Why am I so picky about genuine ABB parts?
• What can go wrong when buying ABB contactors online?
• The DJI Mini 4 Pro battery charger question nobody wanted to ask.

Which ABB Contactor Should I Order for a VFD Motor Setup?

For a VFD motor circuit, I start with the ABB AF series. Actually, let me correct myself—I start with the spec sheet, then I pick the AF series when the panel's control voltage is uncertain. The AF line—AF09, AF12, AF16, all the way up to AF96—has an electronically controlled coil that handles a wider control voltage range. That matters on drive panels where the control supply can dip. I don't have hard data on failure rates, but based on five years of ordering contactors, coil burnout is the most common field failure. Giving up coil margin to save $20 is a dumb trade.

If your design puts the contactor on the input side of the drive, a standard A-line contactor like the ABB A40-30-10 contactor can work. The key is not to put a standard contactor between the drive output and the motor unless the drive is off and the application is designed for it. ABB's application guide makes that point, and so does the plant electrician who had to clean up after a previous contractor ignored it.

For a 95A input circuit, you would be looking at the ABB A95-30 contactor or possibly an AF96 if you need the coil flexibility. I tell a vendor 'I need a 95A AC-3 contactor' and let them help instead of guessing from horsepower alone. According to ABB's contactor selection guide (ABB Control Products, 2024), the AC-3 rating from IEC 60947-4-1 is the number to use for motor switching.

What's the Difference Between the ABB A40-30-10 Contactor and the ABB A95-30 Contactor?

The short answer is current rating and auxiliary contacts. The ABB A40-30-10 contactor is a 40A frame with three main poles and one N/O auxiliary contact. The 30-10 part of the name tells you that: 30 means three poles, 10 means one normally open aux. The ABB A95-30 contactor is a 95A frame with three poles. If you don't need auxiliary contacts, you'll often see it written as A95-30-00. I want to say the A95-30 is the frame we use for 75A-plus services, but don't quote me on that—check the motor nameplate current.

As of early 2025, both part numbers are current in ABB's catalog, but don't trust a search result from 2021. Part numbers change when coil voltages or accessory options change. I learned this the hard way when I ordered the wrong coil for a 24V system because I assumed the item title was enough.

From the outside, a big contactor looks like a small contactor with extra plastic. The reality is inside: contact gap, arc extinguishing, terminal capacity, and heat dissipation are different. If the motor load is above the A40's AC-3 rating, don't convince yourself that it will be fine because the motor only runs for five seconds. That's how contacts weld.

How Do I Test a Light Switch with a Multimeter—and Does the Same Trick Work on a Contactor?

Yes, the same principle works. First, how to test a light switch with a multimeter: turn off the power at the breaker, pull the switch out, set the meter to continuity/ohms, and touch the probes to the two screw terminals. With the switch off, the meter should show OL or no beep. Flip it on; it should show near zero ohms. On a three-way switch, test common against each traveler separately.

For a contactor, I do two checks with power off. First, coil: put the probes on A1 and A2. A good coil will show some resistance—usually hundreds to a few thousand ohms depending on the coil. Open circuit means the coil is dead. Second, main contacts: press the contactor's armature or use the manual override to close it, then measure L1-T1, L2-T2, L3-T3. Each should read near zero ohms. If one leg reads high, the contacts aren't closing evenly.

I keep a multimeter in my desk (mental note: I really should buy a second one for the office). It saves a lot of finger-pointing when a supplier says the part tested fine.

Why Am I So Picky About Genuine ABB Parts?

When I started, I didn't care about brand. I cared about price and delivery. Then I ordered a 'compatible' contactor for a compressor panel. It tested fine on the bench, and it failed two days later. The client didn't complain about the contactor—they complained that our company looked sloppy. Our maintenance team swapped it on a Saturday. The part cost $50 less than a genuine ABB A95-30 contactor. The callback cost a lot more.

I'm not saying every non-ABB part is garbage. I'm saying the part inside the panel is an extension of your brand. If you put a no-name box in an ABB-labeled panel, the opinion of your company goes down even if the failure isn't your fault. For me, quality perception is the reason I order genuine ABB contactors for anything that touches a VFD motor or a critical load.

Honestly, I wish I had tracked every field failure more carefully. What I can say anecdotally is that after 60-80 orders a year, the pattern is clear.

What Can Go Wrong When Buying ABB Contactors Online?

A few years ago I found a great price on a batch of contactors from a new supplier. The price was about 30% lower than our regular distributor. The units looked right, but the seller couldn't produce a proper invoice. Finance rejected the expense report, and I ate the cost from the department budget. That's when I learned to verify three things before ordering:

• Is the seller on ABB's authorized distributor list?
• Does the quoted part number match ABB's official catalog?
• Can they provide a normal commercial invoice with a stated warranty?

If the answer to any of those is no, I move on. It's not worth the process headaches, even if the boxes look identical.

Another thing I look for: gray market units from overseas. They may be genuine, but they may not have the UL/IEC markings required by the local inspector. If the authority having jurisdiction sees a contactor without the right markings, it holds up the whole panel. That's a compliance headache that follows the purchase order, not the electrician.

What Does a DJI Mini 4 Pro Battery Charger Have to Do with ABB Contactors?

Nothing. A DJI Mini 4 Pro battery charger is a low-voltage DC charger, not a contactor accessory. If you landed here because you're building a workbench with a VFD motor and a drone charger on the same bench, keep them on separate circuits. Don't put a contactor in line with the charger. The charger has its own protection circuitry; adding a contactor doesn't make it safer and can cause voltage drop.

If the charger stopped working, use your multimeter to check the wall outlet and the charger's input, then buy a genuine replacement charger. I don't know your drone model's charging specs, and I won't pretend to. This was accurate as of early 2025; check current recommendations from DJI before buying anything.