Siemens Contactor Reviews: An Emergency Specialist's Honest Take on Performance, Pitfalls, & True Cost
Let's be real: if you're here reading Siemens contactor reviews, you're probably not just killing time. You've got a spec to meet, a panel to build, or—more likely—a problem to solve before yesterday. In my role coordinating industrial control components for an automation integrator, I've handled hundreds of rush orders for Siemens contactors alone, including a nightmare last March where a client's entire production line upgrade hinged on getting the right 3RT2 series unit in 36 hours.
This FAQ breaks down what I've learned the hard way about selecting, installing, and budgeting for Siemens contactors, focusing on the stuff that actually matters when the deadline is tight and the budget is real.
Are Siemens contactors worth the premium price?
My short answer is: it depends on your total cost calculation, not just the unit price. I've seen project managers save $40 on a generic contactor only to burn $300 in technician troubleshooting time because the coil voltage tolerance was garbage, or worse, it welded shut during the first test cycle.
A Siemens Sirius 3RT2 contactor, for example, costs more upfront. But in my experience, the spec compliance and documentation alone save you during commissioning. When a plant engineer asks for the contactor's utilization category (AC-3 vs AC-4) and pickup power consumption, you have a catalog page ready, not a shrug. Over 200+ orders, I'd estimate the premium is recovered in reduced field service calls 60% of the time.
What is the difference between Sirius 3RT2 and 3RT1 contactors?
This is one of the most confused topics I deal with. The 3RT1 series was essentially the 'classic' line, while the 3RT2 series is the newer Sirius modular platform.
Key difference: The 3RT2 has a much wider set of add-on components—auxiliary switches, surge suppressors, and timer modules—that clip directly onto the device without needing tools. The 3RT1 line uses older screw-terminal auxiliary blocks that are more tedious to install and often require a specific socket. For a project I did in 2022, swapping from a 3RT1 to a 3RT2 spec saved the installer about 20 minutes per panel. On a 10-panel job, that's over 3 hours of labor saved.
When to pick one over the other? If you're buying new for a panel, get the 3RT2. If it's a replacement for an existing 3RT1 setup, double check the mechanical and electrical dimensions—the footprint is often similar, but the contactor's control circuit layout changed.
What does a 'Siemens Lighting Contactor' actually do differently?
A standard contactor, like a 3RT2, is rated for motor starting which sees high inrush currents. A lighting contactor (like the Siemens 5TT or ECG series) is optimized for switching lighting loads—tungsten, fluorescent, and LED ballasts.
The major design difference? It's quieter. Seriously. Standard contactors produce a loud 'thunk' when they close, which can be annoying in an office or school. Siemens lighting contactors use a snap-action mechanism to reduce noise and provide a cleaner contact surface for capacitive loads. They are also designed for continuous duty over long periods (lights on for 10+ hours).
In my experience, using a standard motor contactor for lighting often works... until it doesn't. I once had a customer who used a 3RT2 for a 20A lighting circuit. After 6 months of hourly cycling (a motion-sensor office), the contacts chattered and failed. The lighting contactor was rated for 50,000 cycles; the motor contactor was rated for maybe 3,000 at that load. That's a $100 learning experience.
How do I test a contactor with a multimeter?
You don't need a lot of tools, but you need to be methodical. I follow this process—and I'd suggest you do too, especially during a rush fix.
- Power OFF. Isolate the circuit. Verify with the multimeter set to AC volts that the load side is dead.
- Check the coil. Measure resistance across terminals A1 and A2. A good 24V AC coil on a 3RT2 might read between 7 and 15 ohms. A completely open loop (OL) means a burnt coil.
- Check the main contacts (NC). Set your multimeter to resistance (ohms). Measure between L1–T1, L2–T2, L3–T3. You should see very low resistance (near 0 ohms) when the contactor is NOT energized.
- Check the auxiliary contacts. Same process for the 13-14 (NO) and 21-22 (NC) terminals.
- Energize the coil. Apply control voltage. Listen for the distinct click. Now measure again. The main contacts (L1-T1 etc.) should now read near 0 ohms. The NC auxiliary (21-22) should go open. If you get weird resistance values or no change, the contactor is mechanically faulty.
Pro tip: I've skipped step 5 before, just checking resistance de-energized and assuming. That was the time a contactor had a mechanically stuck armature but perfect static resistance. Don't assume.
Will a reversing contactor work for a generator application (50 Amp)?
Not directly, but I understand why you're asking. A reversing contactor is designed to swap two phases to reverse a three-phase motor. A generator transfer switch (like for a quiet generator with a 50 amp plug) is a different beast—it needs to mechanically or electrically isolate one source from the other (grid vs. generator) to prevent backfeeding.
Using a standard reversing contactor for mains transfer is a serious safety violation. They lack the positive air gap required for disconnection. I've seen integrators try to 'get creative' with this. It's not worth the fire risk or the code violation. Get a proper UL-listed automatic transfer switch.
What maintenance does a contactor need?
From my experience, the most common failure isn't the contacts—it's the coil. Dirt, moisture, or a weak power supply kills contactor coils. Here's my simple checklist for a quarterly PM:
- Visual check: Look for charring, melted plastic, or dust buildup on the arc chutes.
- Check the coil voltage. Use your multimeter across A1 and A2 while the contactor is energized. It should be within +/-10% of rated. If you see 18V on a 24V coil, you have a bad power supply or a voltage drop issue in the control wiring.
- Listen for chatter. A buzzing sound usually means a loose mounting screw or a degraded magnet core.
- Clean the dust. Use compressed air, not a brush. Dust conducts electricity and can create tracking paths.
Honestly, I've only replaced main contacts once in 8 years. The rest of the time, it's been coils or auxiliary blocks.
Can I use an auxiliary contact block on any Siemens contactor?
No, and this mistake cost a client a weekend. The 3RT2 series uses a specific auxiliary contact block (3RH2) that clips onto the front or side. The older 3RT1 uses a different mechanical interface (3RH1). Physically, a 3RH2 block won't latch onto a 3RT1 base. Also, the electrical ratings differ: the 3RH2 blocks are rated for DC switching applications much better than the old 3RH1 series.
Always check the catalog number. If you're ordering a contactor and an auxiliary block independently, verify they are from the same 'family' (3RT2 = 3RH2, 3RT1 = 3RH1). Mismatching them is a classic rookie mistake that you'll only make once, because you'll waste a whole afternoon trying to force them together.
Final thought from the trenches
I don't think Siemens contactors are magic. I've had 3RT2 units fail within a year due to a bad batch of pilot relays that cooked the coils. But when you factor in the reliability of the specification, the ease of installation, and the support ecosystem, they are consistently the lowest-total-cost option for industrial work. A $40 savings on a generic contactor that takes an hour to install and has no documentation? That's a false economy. You pay for that time during the first rush fix.
