AOV Controls Explained: Key Switch vs Push Button vs Fire Alarm Input (Plus Commissioning Checklist)

This guide is written to reduce site call-backs and the usual email ping-pong by helping you:

• choose the right local control (key switch vs push button)
• define what a fire alarm input/interface actually needs
• understand what “reset” means in practice (and why it’s frequently misunderstood)
• commission the system with a repeatable checklist

Important: This page is a coordination guide, not a fire strategy. Always follow the project fire strategy, approved cause-and-effect, and the specific wiring diagram/manual issued for the installed control panel.

Quick answer: which control is for what?

• Key switch: typically used to restrict manual operation to authorised users (maintenance/testing/controlled override).
• Push button: typically used for everyday local operation where permitted (often described as daily/comfort ventilation).
• Fire alarm input/interface: the link that triggers the smoke vent control panel into fire mode (must be defined by cause-and-effect).
• Break glass / MCP: a manual emergency trigger point (commonly the root cause of “it won’t reset” issues on site).
• Fireman’s switch (Firefighter’s Priority Switch): a dedicated firefighter control point where required by design, and distinct from a general maintenance key switch.

Looking for product information and downloads? Start here: AOV Smoke Vents and the Smoke Vent Resources page.

Typical AOV control architecture (what connects to what)

Most “wiring diagram” confusion comes from not separating three things:

1. The vent/actuator (roof hardware)
2. The control panel/control centre (power + logic + monitoring)
3. The inputs (key switch, push button, fire alarm interface, smoke detector, etc.)

Surespan AOV smoke vents are designed to meet BS EN 12101-2 performance requirements and are CE-marked (and, for the GB market, UKCA-marked where applicable). Always verify the current certification for the exact product variant and project documentation.

Example product pages (for context and downloads):

• Smoke Vent with Access (SRHP-AOV)
• Bespoke Smoke Vent (SRHE-AOV)

Power and battery backup: don’t assume the requirement

On many projects, the control centre is specified with a 24VDC control panel with 72-hour battery back up (this is common where there is no life-safety generator). Where a suitable backup generator is provided, standby requirements can be reduced (commonly to around 4 hours), but this must be confirmed against the project fire strategy and the applicable power supply standard (BS EN 12101-10) for the installed system.

Practical takeaway: two sites can use “the same vent” but have different panel and standby requirements. Always work from the issued wiring diagram and project cause-and-effect.

Key switch vs push button vs fire alarm input: comparison table

Use this table to sanity-check what you are trying to achieve before you start wiring.

Key switches: what you must define (not just “key switch”)

Two common phrases we see are “internal key switch” and “external key switch”. Location matters, but it is not enough. The wiring (and even the correct accessory choice) depends on the intended behaviour.

Define the behaviour up front

• Maintained or momentary (spring return)?
• Open only, or open/close, or open/stop/close?
• Is it for daily operation, maintenance/testing, or a priority override?
• What must it override (if anything) and what must override it (e.g., fire alarm always takes priority)?

Rule of thumb: if you cannot answer the questions above, you do not yet have enough defined to request “the wiring diagram”, because there may be multiple correct wiring variants depending on intent.

Push buttons: where they fit (and where they do not)

Push buttons are typically simplest when used for daily/comfort ventilation or straightforward local operation in controlled areas. In Surespan documentation, this is commonly described as push button comfort (daily) air ventilation where configured.

Push buttons work best when:

• the fire strategy allows day-to-day operation and it is clearly separated from fire mode
• users have appropriate access and the device location is sensible
• priority logic is defined if multiple inputs exist (push button, key switch, fire alarm input, MCP)

Push buttons cause issues when:

• operation should be restricted (a key switch or controlled interface is more appropriate)
• they are expected to act as a “system reset”
• they are installed alongside emergency inputs with no agreed priorities

Fire alarm input and interfaces: define it before you energise

Many projects stall at commissioning because the term “fire alarm interface” is used without defining what it means on that specific job.

Minimum information to confirm with the fire alarm contractor

• Who is providing the interface (fire alarm contractor vs smoke vent contractor)?
• What output type is being provided to the smoke vent control panel (and is it monitored/supervised)?
• What happens on activation (which vents/zones open, any delays, any indications)?
• What is the required reset sequence and who is responsible for each step?

Cause-and-effect is not optional

In real-world “wiring diagram” and “commissioning” enquiries, the details that actually determine the wiring variant are frequently missing — especially zoning intent and cause-and-effect. If you want a fast technical response, provide the cause-and-effect and device schedule up front.

What “reset” actually means (and why it is not one button)

“Reset” is one of the most expensive misunderstandings because it leads to return visits. On site, reset may involve multiple systems and multiple devices.

In practice, “reset” may include:

1. Resetting the initiating device (for example, an MCP/break glass if it is latched)
2. Clearing the fire alarm condition (where applicable)
3. Restoring the smoke vent control panel back to normal mode (per the panel manual)
4. Confirming comfort/daily controls are reinstated (where permitted)

Common reasons “it won’t reset”: a device remains latched, the alarm condition has not been cleared, an override is still active, or the wiring intent does not match the approved cause-and-effect.

Commissioning checklist (site-friendly, reduces call-backs)

This sequence aligns with the principles of BS 7346-8 (Code of practice for planning, design, installation, commissioning and maintenance of smoke control systems). Always follow the project documentation and the specific control panel manual for the installed equipment.

1) Pre-power checks

• Confirm correct vent type and locations against the schedule
• Confirm actuators are installed correctly and vents operate freely
• Check containment, segregation, labelling and terminations
• Confirm local devices are installed as shown (key switch, push button, MCP)
• Ensure you have the latest wiring diagram and device schedule on site

2) Power-up checks

• Confirm the correct panel supply and protection (do not assume)
• Confirm batteries are present/connected where specified
• Where specified, note battery standby requirement (e.g., 72-hour battery back up is common where no generator exists; confirm project-specific requirements)
• Check for fault indications before functional testing

3) Functional testing (record results)

• Test each input independently first (push button, key switch, MCP/break glass)
• Test fire alarm input/interface against the approved cause-and-effect
• Confirm vents achieve intended open position and close correctly
• Confirm priorities behave as intended (fire mode vs local controls)

4) Backup / standby behaviour (where specified)

• Simulate mains loss safely using site procedures and isolation
• Confirm the system behaves as required by the specification
• Restore supply and confirm normal mode returns

5) Handover pack (what should be in it)

• As-built schematics / wiring mark-ups
• Device location plan (what is actually installed)
• Final approved cause-and-effect
• Commissioning record (tests performed, results, snags)
• O&M pack and resource links

Before you request a wiring diagram: copy/paste checklist

If you send the items below in your first message, you’ll avoid most delays and misinterpretations.

Downloads and next steps

• Start with the resource hub: Smoke Vent Resources
• Browse products: AOV Smoke Vents
• Common reference: Smoke Vent with Access (SRHP-AOV)

Recommended next step: Download the relevant wiring diagram(s) and then submit your cause-and-effect and device schedule for review before energising. This is the fastest way to prevent wiring assumptions turning into a commissioning failure on the day.

FAQs

What does a key switch do on an AOV?

It typically provides authorised manual control and helps restrict operation to trained or approved users. The exact behaviour depends on how the control panel is configured.

Key switch vs push button: which should I use?

Use a key switch where access needs to be controlled (maintenance/testing/authorised operation). Use a push button for daily local operation where the fire strategy permits comfort ventilation and priorities are clearly defined.

What is a fire alarm input/interface on a smoke vent system?

It is the connection that allows the fire alarm system (or an interface module) to trigger the smoke vent control panel into fire mode. It must be defined by the approved cause-and-effect and the panel wiring diagram.

Why won’t my AOV reset?

Because “reset” often involves more than one device/system: an MCP may be latched, the fire alarm condition may still be active, or an override may still be engaged. Reset steps must follow the panel manual and project cause-and-effect.

What should be tested during commissioning?

Pre-power checks, power-up checks, each input independently (push button, key switch, MCP), fire alarm interface activation, and standby/backup behaviour where specified. Record results for handover.

What information is usually missing from wiring diagram requests?

Zoning intent, approved cause-and-effect, who supplies the fire alarm interface, and the required behaviour of the key switch (maintained vs momentary; open only vs open/close).