What means momentary and maintained for push buttons, and what is the difference?
1. What you need to know
A momentary push button holds its contact state only while it is being pressed: release it and the spring returns the actuator, so the contacts revert. A maintained push button latches - press it once and it stays actuated; press it again and the spring returns the actuator. The difference is mechanical and sits in the head, not in the contact block: the same 1 NO block gives a momentary or a maintained function depending on which head is fitted. Momentary is used for start, jog, reset and hold-to-run; maintained for on/off and mode selection, and for emergency stop devices, which latch by design.
2. What the distinction covers
Both types look identical on a panel and share the same Ø22 or Ø30 cut-out, the same contact blocks and the same colour rules. Only the return mechanism inside the head is not the same, which is why the choice is made when the head is specified rather than when the panel is wired.
- The vocabulary varies by supplier and by drawing: spring return and non-latching mean momentary; latching, push-push, push-on/push-off, stay-put and alternate action all mean maintained.
- Do not confuse this with NO / NC, which describes the contact state at rest, not the mechanical action. Any combination is possible - a maintained head with an NC block is common for a stop function.
- Two-position selector switches are the same distinction in selector form: stay put versus spring return.
- Emergency stop devices are always maintained: they latch on actuation and need a deliberate turn, pull or key to release, per ISO 13850 and NFPA 79 for machinery built to US requirements.
- A start function should be momentary so that restoring power cannot restart the machine on its own - a latched start button leaves the command present while the panel is dead.
3. Momentary vs maintained
| Description | Momentary | Maintained |
|---|---|---|
| Mechanical action | Spring return - the actuator moves back as soon as it is released | Latching - the actuator stays where it was put until it is operated again |
| Contact state | Contacts change only while the button is held down | Contacts stay changed after the operator lets go |
| Also called | Spring return, non-latching, momentary contact | Latching, push-push, push-on / push-off, stay-put, alternate action |
| Typical functions | Start, jog, inch, test, reset, hold-to-run | On/off, local/remote, mode selection, emergency stop |
| Behaviour after a power loss | The actuator is already released, so the control circuit decides what happens on restore | The actuator stays latched - the circuit can re-energize on power restore unless the design prevents it |
| When to prefer it | Wherever an unintended restart must be impossible, and for any hold-to-run function | Where the state must remain visible and physically obvious without power |
If the panel must show its state when de-energized, use maintained. If an operator releasing the button must stop the action, use momentary.
4. Schneider Electric references
| Function | Reference | Product description |
|---|---|---|
| Head - momentary, Ø22 | ZB4BA3 / ZB5AA3 | Harmony XB4/XB5 flush head, green, spring return. The last digit sets the colour: 1 white, 2 black, 3 green, 4 red, 5 yellow, 6 blue. |
| Head - maintained, Ø22 | ZB4BH03 / ZB5AH03 | Harmony XB4/XB5 flush head, green, push-push. The latching counterpart of the ZB5AA3, same cut-out and same contact blocks. |
| Illuminated head - maintained, Ø22 | ZB4BH033 / ZB5AH033 | Harmony XB4/XB5 illuminated flush head, green, push-push, universal LED. |
| Module - maintained, Ø30 | 9001K85 | Harmony 9001K push-on / push-off module, converting a Ø30 operator to latching action. |
| Contact block, Ø30 | 9001KA1 | Standard contact block. Identical whether the head is momentary or maintained - the head alone decides the action. |
| Range - Ø22 plastic | Harmony XB5 / ZB5 | Modular Ø22 push buttons, selector switches and pilot lights. XB4 is the metal-bezel equivalent. |
| Range - Ø30 metal | Harmony 9001K | Heavy-duty Ø30 operators for North American panels, in momentary and maintained versions. |
Launch Product Selector on se.com to configure a Harmony selector switch according to your requirements or contact Schneider Electric Technical Support to check a configuration against your control scheme.
Released for: Schneider Electric Vietnam
