Siemens SIRIUS Contactor Coil Identification and Procurement Guide

If you’ve ever opened a panel, stared at a Siemens SIRIUS contactor, and thought, “Which coil voltage is this thing?”—you’re not alone. Drawings go missing, labels fade, and downtime doesn’t wait.

This guide shows how to identify the full Siemens order number (MLFB), read the coil rating and verify the exact product data before ordering. A partial number such as 3RT1056-6..6 does not identify the coil.

1. Why this problem is so common

• The front label shows the base contactor (frame/current ratings) but often hides the exact coil variant.
• SIRIUS 3RT1 coils are replaceable; the coil code appears in the full MLFB on the side label, which is often hard to see.
• U.S. control circuits vary: 24 VAC (HVAC), 24 VDC (PLC), 120 VAC (legacy), or 240 VAC (CPT).

2. Identification workflow

1. Isolate before inspection: follow the site isolation procedure and verify absence of voltage before touching terminals or removing covers.
2. Record the complete MLFB: photograph or transcribe every character on the contactor and coil labels, including additional suffixes. Record the coil’s marked control voltage, AC/DC designation and frequency.
3. Compare drawings and hardware: identify the control transformer or DC supply and any interposing controls. Motor supply voltage is not coil voltage.
4. Look up the exact number: retrieve Siemens’ product data sheet and operating instructions; compare the control supply rating, frequency, operating range and connection arrangement.
5. Resolve a mismatch before procurement: if the label is unreadable or the coil may have been replaced, ask Siemens or an authorized supplier to identify the installed assembly from the available labels and photographs.

3. Verified full-model examples

These examples apply to the full order numbers below. They are not a universal suffix decoder for every SIRIUS family.

• 3RT1056-6AB36: Siemens declares Uc 23–26 V, AC 50–60 Hz/DC.
• 3RT1056-6AF36: Siemens declares Uc 110–127 V, AC 50–60 Hz/DC.
• 3RT1056-6AP36: Siemens declares Uc 220–240 V, AC 50–60 Hz/DC.

The motor-switching current and kW ratings in those descriptions are separate from the coil/control supply. Do not infer a permissible supply from a generic 0.8–1.1 multiplier. Use the exact data sheet’s operating-range conditions and manufacturer confirmation where needed.

From the field: two contactors, identical except for the coil

The coil code I see most often on Siemens contactors in the field is 3RT1056-6AP36. It is also the code that showed me how easily a coil voltage goes wrong, because the contactor looks the same whichever coil is fitted.

On one urgent supply job, the request came with a photo of the contactor and a purchase order for a 230 V coil. We supplied exactly what the order said. The customer’s electrical engineer then compared photos of the installed contactor and the new one and wrote back that the voltage was not the same.

Look at the two labels: the base contactor and its terminals are the same, and only the coil differs, in both the voltage band and the suffix (AV3 against AP3). The right part, with the 380–420 V coil, was available from us at an additional cost, and we sent a revised quotation. That meant a second approval round and extra delay on an order marked urgent, because the coil voltage was not checked against the label before the order went through.

What I do before ordering now:

• Read the coil label on the contactor being replaced, not on a similar one nearby. A photo of a neighbouring unit can carry a different coil.
• Check the voltage band, AC, DC or AC/DC, and the frequency. Coil codes depend on the manufacturer’s own system, so a code that means one thing on a Siemens contactor tells you nothing about another brand’s.
• Put the full coil voltage in the order and compare the quotation, the order and the label photo before anything ships.

If those three agree on paper, a mismatch is caught at the desk. If they don’t, it is found on site, with the old contactor already on the shelf waiting for the part.

4. Ordering checklist

• Complete contactor MLFB and installed coil marking.
• Required control voltage, AC/DC type, frequency and applicable operating range.
• Confirmed spare-coil or complete-contactor part number from Siemens.
• Frame, terminal arrangement, auxiliary contacts, accessories and approved panel requirements.
• Supplier confirmation of compatibility; keep the data sheet with the procurement record.

5. Safety notes

• Follow the site’s lockout/tagout and electrical safe-work procedure. Any energized diagnostic measurement must be justified and performed by a qualified person under that procedure using suitable equipment.
• Verify absence of voltage before touching A1/A2.
• Do not over-voltage a coil “just to test” – it will damage the internal electronics.

FAQ