Need a 7.5 kW Siemens Contactor with 24V DC Coil? Here's the Part Number (and What Nobody Tells You)
If you're searching for a Siemens contactor to handle a 7.5 kW motor on a 24V DC coil, the most common answer you'll find is the 3RT2017-1BB42 (Sirius series, size S0, 3-pole, 24V DC coil, screw terminals). But that's just the beginning. I've dealt with enough mis-spec'd rush orders to know that copying a part number from a catalog doesn't mean it'll work in your cabinet.
In my role coordinating electrical component sourcing for industrial projects, I've processed over 200 rush orders for Siemens contactors alone. In March 2024, a client called at 4 PM needing a 7.5 kW contactor for a line startup the next morning. Normal lead time from our distributor was five days. We paid $85 in rush fees (on top of the $215 base cost), got it overnight, and the line ran on schedule. The alternative was a $12,000 production delay. That's not unusual—it's the norm when deadlines are tight.
So, What's the Exact Part Number?
3RT2017-1BB42 is the standard Siemens Sirius 3RT contactor for 7.5 kW at 400V AC-3 (7.5 kW / 16 A / 24V DC coil). But there are variations depending on your auxiliary contacts, terminals, and mounting. Here's a quick breakdown:
- 3RT2017-1BB42 – 3-pole, 24V DC, screw terminals, no auxiliary contacts
- 3RT2017-1BB42 + 3RH1911-1FA11 – add a 1NO+1NC auxiliary contact block
- 3RT2017-1AB42 – 24V AC coil (not what you want if you need DC)
People assume you can just swap any 24V coil contactor. The reality is DC coils have different pick-up and hold characteristics—if your control system is 24V DC, you need a DC-rated coil, not an AC coil rectified. I've seen that mistake cost a $600 emergency reorder.
What About the Data Sheet?
The official Siemens data sheet for the 3RT2017 series (product manual 3ZX1012-0RT20-1AA1, as of January 2025) lists:
- Rated operational current: 16 A (AC-3)
- Rated operational power: 7.5 kW at 400V AC
- Coil voltage: 24V DC (range 0.8–1.1 x Uc)
- Mechanical endurance: 30 million operations
Always verify the actual data sheet before ordering. Siemens updates product numbers occasionally—the 3RT2 series superseded the older 3TF series. If you're cross-referencing a legacy part like an old 3TF contactor, the 3RT2 is the drop-in replacement. But don't assume pin-out compatibility without checking the drawings.
Cross-Reference Pitfalls: Not Just a Part Number
It's tempting to think you can just search '7.5 kW 24VDC contactor' and grab the first result. But identical specs from different manufacturers can have wildly different physical sizes, coil power consumption, and terminal layouts. I recall a job where we ordered a 'compatible' alternative that was 15 mm taller—didn't fit the enclosure. Cost us a $250 rush fee to get the correct Siemens.
When cross-referencing, always check:
- Mounting hole pattern – Siemens S0 size is 45 mm wide, 70 mm deep (screw or snap-on rail)
- Coil power – DC coils have a higher inrush current; verify your PLC output card can drive it
- Approvals – CE, UL, CSA (especially for export projects)
Rush Orders: When You Don't Have Time for Trial and Error
From the outside, it looks like vendors just need to work faster. The reality is rush orders often require completely different workflows. For Siemens contactors, your best bet is an authorized distributor who stocks the Sirius series. Many keep S0 and S2 sizes with 24V DC coils on the shelf. In my experience, calling the distributor's counter directly (not the online chat) gets you an answer in 5 minutes vs. 2 hours.
Never expected the biggest bottleneck to be the auxiliary contact block. Turns out many rush orders ship with the contactor but the aux block is backordered. I now spec the entire assembly in one line item: 3RT2017-1BB42 + 3RH1911-1FA11 (or whatever you need). Saves a future headache.
What This Part Number Won't Do
This contactor is rated for AC-3 duty (squirrel cage motors). For inductive DC loads or resistive heating, the ratings change. If you're using it for a DC motor or a transformer, consult the derating table in the data sheet. Also, for safety applications requiring forced-guided contacts (e.g., emergency stop circuits), you need a Siemens Sirius 3SK1 safety contactor, not the standard 3RT.
Bottom line: 3RT2017-1BB42 is your starting point. Verify your control voltage, auxiliary contact needs, and physical constraints before ordering. And if you're in a bind, call—don't email.
