Siemens Low-Voltage Code Decoder — 3RT, 3RV, 3RU, 3VA, 5SL and 3SU Explained

What the leading groups in Siemens low-voltage order numbers mean — 3RT2 contactors, 3RV motor-protection breakers, 3RU/3RB overload relays, 3VA moulded-case breakers with their 3VA9 accessories, 5SL miniature breakers and 3SU1 pushbuttons — with worked examples from the catalogue and the checks that prevent a wrong panel part.

The family prefixes

Siemens LV order numbers (MLFB codes) start with a family group that instantly places the device:

Worked examples

5SL6363-7 reads as: 5SL = MCB; 6 = the 6 kA breaking-capacity series; the next digits carry pole count and rating — this one is a C-curve 63 A three-pole, exactly as the catalogue row states. Siemens' 5SL4 and 5SL7 siblings shift the breaking capacity (10 kA class and higher) while keeping the logic.
3VA9263-0JA12: 3VA9 marks a SENTRON accessory; the digits that follow bind it to a frame — here a box terminal for the 3VA2 250 A frame, 25–185 mm² (a number so often mistyped as "3VA9463" that the catalogue page lists the misprint). Breaker-side, 3VA1/3VA2 encode frame and breaking class before the trip-unit digits.
3RT2 contactors scale through frame sizes S00–S3 and beyond: the two digits after 3RT2 fix frame and AC-3 rating, the following group the contact complement, and the final letters the coil voltage — always read the coil code from the old unit, not assumed from the panel voltage.

Checks before ordering a replacement

• Full MLFB from the device face — dash suffixes change coils, terminals and auxiliaries.
• Coil voltage group on contactors; AC and DC coils are different part numbers.
• Accessory compatibility by frame: a 3VA9 accessory fits only its stated 3VA frame; the same is true of 3RU overloads on 3RT2 frames.
• Breaking capacity class on 5SL/3VA must meet the board's prospective fault current — see the selectivity guide.

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Frequently asked questions

What does 5SL63 mean on a Siemens MCB?

5SL = miniature circuit breaker, 6 = the 6 kA series; the following digits give poles and rating — 5SL6363-7 is the C-curve 63 A three-pole in that series.

What is the difference between 3RT and 3RH?

3RT2 are power contactors for motor and load switching; 3RH2 are auxiliary contactors for control logic — same SIRIUS platform, different duty.

Which overload relay fits a 3RT2 contactor?

A 3RU (thermal) or 3RB (electronic) sized to the same SIRIUS frame — frame match first, then the current setting range around the motor's rated current.

What does 3VA9 mean?

Accessory for the SENTRON 3VA breaker family — terminals, locks, auxiliaries — each bound to a specific frame size stated in its description.

Can I order from a partial Siemens number?

Send what the nameplate shows: the family group usually survives even on worn labels, and the quotation confirms the full MLFB against frame, coil and accessory data.

Compiled by cBallast for identification and cross-reference. Part numbers, designations and trademarks belong to their respective manufacturers. Confirm ratings and dimensions against the manufacturer's current documentation and the nameplate of the installed equipment before ordering or installation.