I'll be honest: for the first few years of my career, I didn't think much about how a contactor and overload relay were packaged. It was either a Siemens 3RT contactor on a shelf, or a 3RA2 starter with the overload built in. Grab the part number, plug it in, move on. It wasn't until I started handling rush orders—where a mis-picked part can cost a $15,000 line to sit idle—that I realized the "standalone vs. bundled" decision is way more nuanced than the catalog makes it look.
This is a comparison of two approaches to the same function: motor switching and protection. The standalone path is a Siemens 3RT contactor plus a separate 3RU overload relay. The bundled path is a Siemens 3RA2 or 3RA13 starter (contactor + overload in one). Both do the job. But they optimize for completely different priorities—and which one is "better" depends entirely on how much time you have and who's wiring it.
The Frame: Two Paths to the Same Goal
There are three main comparison dimensions I want to hit. We're not going to get into every single spec—the Siemens datasheets cover that. What matters is the real-world difference when you're on the clock:
- Wiring Speed & Complexity – How fast can you get this operational?
- Replacement Flexibility – When something fails, what happens next?
- Inventory & Stocking Strategy – What makes sense to keep on the shelf?
If you're expecting me to say the bundled starter is always better for speed and the standalone is always better for flexibility, you're right—mostly. But there's a twist in dimension three that caught me off guard.
Dimension 1: Wiring Speed & Complexity
The Bundled Starter (3RA2) wins this one. No contest.
With a 3RA2, the overload relay and contactor are already wired together internally. The control wiring for the overload auxiliary contacts is done at the factory. You mount it, you wire your three-phase power in and out, you run your coil voltage, and you're done. Total time if you know what you're doing: maybe 15 minutes. Faster if you've done it before.
With the standalone approach—a Siemens 3RT contactor plus a 3RU overload relay—you need to:
- Mount both separately (or buy a mounting kit to stack them)
- Wire the main contacts from contactor to overload
- Wire the overload's NC (95-96) and NO (97-98) contacts into your control circuit
- Set the overload trip current manually
That's 20-30 minutes on a good day. In a rush scenario where every minute counts, the bundled starter is the clear winner.
But here's the thing nobody talks about: the bundled starter's overload is often harder to test quickly. The test button is tucked in, and if you accidentally jog the contactor during testing, you can reset the overload without meaning to. I've had that happen. It's annoying.
Verdict: Bundled wins if speed is your only metric. But standalone is not as bad as the marketing suggests if you have the experience.
Dimension 2: Replacement Flexibility (The Surprise)
Standalone wins this one. And here's the twist that surprised me.
Conventional wisdom says: "If the overload fails on a bundled starter, you replace the whole thing. If it fails on a standalone setup, you just replace the overload." That's true. But in the real world, the contactor fails far more often than the overload. I want to say about 70% of field failures I've seen are contactor-related (welded contacts, coil burnout). Only about 30% are overload issues.
In March 2024, I had a client call on a Tuesday at 3:00 PM. They had a 3RT103 contactor that welded its contacts closed on a conveyor drive. Motor wouldn't stop. It was a production-critical line. The overload was fine. But because they had a standalone setup, I could ship them just the contactor from stock—$180 part, standard ground shipping, next-day arrival. Done.
If they had a bundled starter, I would have had to ship a whole new 3RA2—$280, plus the same shipping. Silghtly more cost, but also, the replacement takes longer because you have to re-run the control wiring for the new starter.
So the counter-intuitive finding: if you expect more contactor failures than overload failures (which is common in high-cycling applications), standalone actually gives you a faster, cheaper fix. The bundled starter only wins on first-install speed, not on repair speed.
Verdict: Standalone for repairability. Bundled for first-time installation speed. Which one matters more depends on your maintenance strategy.
Dimension 3: Inventory & Stocking Strategy (Where I Changed My Mind)
I used to think that stocking bundled starters was the smart move for warehouses. One SKU. Covers a range of FLA settings with the adjustable overload. Seems efficient.
Then I looked at our actual data. Over 47 rush orders from Q3 2023 to Q2 2024, here's what happened:
- 14 orders for standalone contactors (different sizes)
- 9 orders for standalone overload relays (different sizes)
- 12 orders for bundled starters
- 12 orders for other stuff (auxiliary contacts, etc.)
The demand for standalone was roughly split between contactors and overloads, which means you need to stock both to serve the standalone customer. But the demand for bundled starters was concentrated in only two frame sizes (S0 and S2).
The takeaway: If you're stocking for a plant with a lot of existing Siemens gear, you probably already have both. But if you're choosing a new plant design, the inventory complexity actually favors the bundled starter—because one SKU covers the most common failure scenario (contactor + overload). But only if you can accept the slight premium on replacement cost.
Honestly, I'm not sure there's a universal right answer here. It depends on your failure modes and your budget for inventory. If you have high-cycling machines, standalone gives you cheaper repairs. If you have steady-state loads where contactors rarely fail, bundled gives you simpler stocking.
Verdict: Bundled wins for inventory simplicity if your failure rate is low. Standalone wins if you repair often.
So, What Should You Do?
Here's my rule of thumb, based on about 200 interactions with these parts (give or take a few dozen):
- Choose the bundled starter (3RA2) if you're building new panels or machines where installation speed matters, and you have low cycling (less than 100 operations per day). The convenience is real.
- Choose the standalone (3RT + 3RU) if you're maintaining existing equipment, especially in high-cycling environments (conveyor lines, presses, frequent starts/stops). The repair flexibility is worth the extra 15 minutes on first install.
- In a rush situation where you're replacing a failed part on a running machine, go with whichever is in stock. A 24-hour wait for the "right" configuration is worse than a 1-hour swap with a different one.
One more thing: the pricing difference isn't as big as you might think. In January 2025, a 3RT103 contactor + 3RU103 overload relay runs maybe $200-230 combined. The equivalent 3RA2 starter is about $240-270. The bundled premium is maybe 15-20%, not 50%. For the installation time saved, that's often worth it.
Unless you are in a rush repair scenario. Then it is NOT worth it.
