EN 12845 Electrical Flow and Pressure Switches

Flow switches, pressure switches, valve monitoring (tamper) switches, and low level and temperature monitoring: what Clause 16.2, Annex H and Annex I mean on site, typical wiring errors and integration with the fire alarm panel.

An odd picture emerged during the annual panel test at a shopping centre: the ground floor sectional valve was half shut and nobody knew when it had closed. There was a tamper switch; we measured the cable and found an open circuit. During a refurbishment two years earlier the cable had been cut above the ceiling, and not even a fault signal had reached the panel, because the tamper cable ran not to the fire alarm panel but to an old building management (BMS) input card, which logged faults without turning them into alarms. Half the centre had counted as sprinklered on a throttled supply for two years. This article covers how a sprinkler installation must be monitored electrically under EN 12845 Clause 16.2, Annex H (monitoring) and Annex I (transmission of alarms), which switch watches which duty, and where the errors come from.

What Clause 16.2 requires

Clause 16.2.1 recognises two kinds of electrical device for detecting the operation of a sprinkler system: water flow switches conforming to EN 12259-5, or pressure switches. Both are valid; the choice depends on system type and architecture. Clause 16.2.2 sets the critical restriction: water flow alarm switches shall only be used in wet installations. In dry and pre-action systems the pipework is charged with air or inert gas, so a flow switch is not suitable; the alarm is taken from a pressure switch on the alarm valve, and Clause 16.2.3 requires each installation to have a low air/gas pressure alarm giving visual and audible warning in accordance with Annex I.

Clause 16.2.2 also requires a test connection downstream of each flow switch, simulating the operation of a single sprinkler and fitted with a drain. The draw-off pipe is galvanised steel or copper; the pressure/flow characteristic of the fully opened test valve and draw-off pipe equals that of the smallest nominal bore sprinkler supplied through the flow switch. Any orifice plate is at the pipe outlet and is stainless steel or non-ferrous. The outlet is positioned so that the flow can be seen during tests.

Pressure switches around the alarm valve

The pressure switch sits at the nodes of the sprinkler hydraulics. Clause 15.5.1 lists what the 15 mm test valves shall test and from where:

• Wet alarm valve and alternate alarm valve: the hydraulic alarm and any electric alarm pressure switch, by drawing water from the immediate downstream side of the valve (and of any downstream main stop valves).
• Alternate, dry pipe and pre-action alarm valves: the hydraulic alarm and any electric alarm pressure switch, by drawing water downstream of the main water supply stop valve and from the upstream side of the alarm valve, so the alarm circuit is proved without flooding the dry side.
• A water flow alarm switch downstream of the control valve set: by drawing water downstream of the flow alarm.
• An automatic pump set starting device.
• A pump or pressure tank house sprinkler alarm flow switch installed upstream of the control valve set.

Dry and alternate installations additionally have the remote test valve of Clause 15.5.2: at the hydraulically most remote point of a distribution pipe, delivering the flow of a single sprinkler, it is used for the water delivery time test of Clause 11.2.2.

The pressure switches in the pump room are a separate matter. Under Clause 10.7.5.1 two pressure switches are provided to start each pump set, connected so that either switch will start it; the pipe to the switches is at least 15 mm. Under Clause 10.7.5.3, if an isolating valve is installed between the trunk main and a pump starting pressure switch, a non-return valve shall be installed in parallel with it; otherwise, if the valve is closed by mistake, the pressure drop in the trunk main never reaches the switch and the pump never runs. That is the most common answer to "why did the pump never start" after a fire.

Tamper switches: valve position monitoring

Annex H.2.2 and H.2.3 are clear about where valve positions must be monitored. H.2.2: all stop valves whose closing could prevent adequate water flowing to the sprinklers, including water supply valves, control valve sets, subsidiary valves and sectional valves. H.2.3: all stop valves whose closing could prevent the correct operation of an alarm or indicating device (pressure switch, hydraulic alarm, flow switch). One critical rule is often missed in designs:

"For normally open valves, the alarm shall activate once the valve starts to close." (Annex H.2.2 and H.2.3)

So there is no waiting for the valve to close fully; the panel must alarm as soon as the closing movement begins. On site the tamper switch on OS&Y valves is usually set to trip early in the stem travel, and butterfly valves with an integral position switch read the disc angle directly. Always confirm by measurement that a valve returning from service gives a correct fully open signal.

Annex H: what must be continuously monitored

Annex H is one of the most frequently skipped parts of EN 12845. Asked "does the standard require this?", many inspectors look only at Clause 16, when the monitoring obligations are in the annex. In summary:

Annex H.1 adds three general provisions: all monitoring devices have at least IP 54 protection (EN 60529); no more than 15 non-addressable supervisory alarm devices are connected to a common indication; and all signalling and alarm circuits are fully supervised, with a fault alarm on short or open circuit where this corresponds to a fault. In the shopping centre case above, a compliant design would have raised a fault immediately instead of waiting two years.

Annex I: type A and type B alarms

Under Annex I.1 alarms are connected to an alarm panel in the sprinkler control room or pump room and transmitted onwards according to their importance: all alarms go to a permanently attended location, on or off the premises, and type B (technical) alarms may in addition be transmitted to a responsible person (see 20.1) so that immediate corrective action can be taken. Where a direct connection to the fire brigade exists, the transmission procedure should be agreed with the authorities.

• Type A (fire alarm): water flow alarm (16.1.1), water flow detector in the pump room (10.3.2), pump set running, water flow into a zoned installation or zone.
• Type B (technical alarm): low town main pressure, low priming tank level, pump set on demand, start failure, power not available, automatic mode off and common fault, trace heating circuits, low pressure on pre-action and dry systems, partially closed stop valves, liquid levels, low pressure, power failure, low pump room temperature.

Under Annex I.2 a pump running signal may, subject to local conditions, alternatively be treated as a trouble alarm. In practice type A and type B signals should go to separate inputs: type A relays to the fire alarm input, type B relays to the supervisory input. Wire them all in parallel on one cable and you cannot tell them apart; a technical fault becomes a fire call, or the reverse.

Building management system or fire alarm panel?

A question EN 12845 does not answer but every project raises. The standard requires an alarm panel in the sprinkler control room or the pump room (Annex I.1), and Annex H.1 requires control and indicating equipment to follow the provisions valid in the country of use. In Turkey that role goes to a fire detection panel conforming to TS EN 54 (BYKHY Article 74(1)). Sending information to a BMS is not forbidden, but the BMS should not be the primary alarm path (engineering comment).

Typical wiring:

• Field device (flow, pressure or tamper switch) → volt-free contact → fire panel input.
• The fire panel routes type A alarms to the permanently attended centre or the fire service connection, and type B alarms to the same centre and additionally to the responsible person.
• BMS monitoring is a parallel second contact or a Modbus/BACnet connection, for reporting, not as the primary path.

Comparison with NFPA 72

On the NFPA side, monitoring falls under NFPA 72 (National Fire Alarm and Signaling Code), which corresponds to the combination of Annex H and Annex I of EN 12845. Three important differences (the NFPA 72 text is not available to us, so this paragraph could not be verified):

• NFPA 72-2022 Section 12.3 designates pathway classes by performance as Class A, B, C, D, E, N and X; EN 12845 does not go into that detail, requiring only fully supervised circuits.
• NFPA states tamper actuation at one fifth of valve travel explicitly; EN 12845 says only "once the valve starts to close", with no ratio.
• NFPA 72-2022 Section 17.13.2 requires the flow switch to activate within 90 seconds of a flow equal to or greater than that from a single sprinkler of the smallest orifice size installed in the system, and Section 17.13.3 requires that water movement due to waste, surges or variable pressure not initiate an alarm; it gives no specific retard range. EN 12845 leaves the retard time to the device manufacturer's setting.

The conclusion: the two standards agree on which switches to fit, but NFPA 72 is more detailed on documentation discipline and circuit supervision.

Turkish context

BYKHY Article 96 sets where sprinkler systems are mandatory and requires their design to TS EN 12845 (96(5)); Article 74(1) requires fire detection systems to conform to TS EN 54. On site the EN 12845 monitoring list, the EN 54 panel certification and the BYKHY provisions combine: under Article 78(1), where the building has automatic detection, sprinkler alarm stations and flow switches are connected to the fire alarm system, and the supervisory switches of stop valves and other fault contacts are continuously monitored by it; Article 76(1)(c) requires the fire service to be alerted through direct lines or other data communication. A practical checklist:

• Are all valves in the water path fitted with tamper switches? (One of the first items an inspection asks about.)
• Does every wet alarm valve have an electrical pressure switch and a test valve?
• Is the water tank low level switch wired to the panel and set to the 10 % threshold?
• Is the pump room temperature monitored? Critical in basement and external pump rooms at risk of freezing.
• Are there two starting pressure switches per pump set, each able to start the pump on its own?

Five errors seen on site

1. A flow switch on a dry installation: a breach of Clause 16.2.2; water flow alarm switches are for wet installations only. The fix: a pressure switch on the alarm valve plus a low air pressure alarm to 16.2.3.
2. A single pump start switch: Clause 10.7.5.1 requires two. Pump sets delivered with one switch always get a second one.
3. Tamper cable wired to the BMS instead of the fire panel: the shopping centre error. Annex H.1 requires fully supervised circuits, and BYKHY Article 78(1) requires these contacts to be continuously monitored by the fire alarm system.
4. No test valve fitted: Clause 15.5.1 requires 15 mm test valves for the alarm devices and 16.2.2 a test connection for every flow switch. Without them there is no way to tell at the periodic test whether the switch works.
5. Temperature monitoring forgotten: Annex H.2.7 makes it mandatory. Clause 10.3.3 requires a diesel pump room to be kept at 10 °C or above; without a temperature alarm a heating failure can go unnoticed until morning, wet mains can freeze and the engine will be hard to start.

A quick design check

The list used to review the monitoring design of an installation in a few minutes:

If every answer is yes, the electrical monitoring is compliant with EN 12845 on these points. If one is in doubt, open that circuit and measure it; the design on paper is often not the same as the cable on site.

Frequently Asked Questions

Can a water flow switch be used on a dry system?

No. Clause 16.2.2 allows water flow alarm switches only in wet installations. Dry and pre-action systems use a pressure switch on the alarm valve, and Clause 16.2.3 requires a low air/gas pressure alarm.

When must a tamper switch alarm?

As soon as a normally open valve starts to close, not when it is fully shut (Annex H.2.2 and H.2.3). In field practice most OS&Y switches trip within the first fifth of stem travel.

How many pressure switches start a pump?

Two, connected so that either switch will start the pump set (Clause 10.7.5.1). If an isolating valve is fitted between the trunk main and a starting pressure switch, a non-return valve shall be installed in parallel with it (Clause 10.7.5.3).

Can a BMS be the primary alarm path?

It should not be. EN 12845 requires an alarm panel in the sprinkler control room or pump room (Annex I.1) and control and indicating equipment to national provisions (Annex H.1); in Turkey fire detection systems must conform to TS EN 54 (BYKHY Article 74(1)), and Article 78(1) requires sprinkler alarm contacts to be supervised by the fire alarm system. BMS monitoring runs in parallel, for reporting only.

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