EN 12845 Electrical Flow and Pressure Switches

Flow switches, pressure switches, tamper switches and low level and temperature monitoring: what the electrical monitoring clauses 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 input card, which logged faults without turning them into alarms. Half the centre had counted as sprinklered on half a supply for two years. This article covers how a sprinkler installation must be monitored electrically, which switch watches which duty, and where the errors come from.

What the clause requires

EN 12845 recognises two options for detecting electrically that a sprinkler installation has operated: water flow switches complying with EN 12259-5, or pressure switches. Both are valid; the choice depends on system type and architecture. One critical restriction applies: a paddle-type flow switch is only used on a wet installation. There is no paddle on a dry or pre-action system, because the main medium in the pipe is air; there, a low air or gas pressure alarm and a pressure switch below the alarm valve take over.

A test connection must be run below each flow switch: capable of producing the flow equivalent to one sprinkler of the smallest nominal size opening, discharging compatibly with the drainage system, at a point where the flow can be seen. The test pipe must be galvanised steel or copper; any orifice plate stainless steel or a non-ferrous metal.

Pressure switches around the alarm valve

The pressure switch sits at the nodes of the sprinkler hydraulics. The standard sets out where each is tested from:

• Below a wet alarm valve: a 15 mm test valve draws water from just below the alarm valve, testing both the hydraulic motor gong and the electrical pressure switch.
• Above an alternate alarm valve: from below the main water supply stop valve and above the alternate valve — checking that the switch works in the dry season configuration too.
• Above a dry alarm valve: the remote test valve passes the flow of a single sprinkler from the hydraulically most remote point, simulating a genuine trip.
• The pump room sprinkler branch: a separate test connection for the flow switch on the upstream side of the control valve.

The pressure switch in the pump room is a separate matter. Each pump set is started by two independent pressure switches in parallel logic — either one triggering starts the pump. The pipe to the switch is at least 15 mm. If you put an isolating valve between them, there must be a non-return valve 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

The monitoring annex is clear where tamper switches are mandatory: on every stop valve whose closure would obstruct sprinkler water — the main water supply valve, the control valve set, sectional valves, subsidiary valves — and on isolating valves whose closure would affect an alarm or indicating device. One critical rule is often missed:

For normally open valves, the alarm shall activate once the valve starts to close.

So there is no waiting for the valve to close fully; the panel must alarm as soon as the closing movement begins. The tamper switch on most OS&Y valves is set to trip within the first fifth of the stem travel. 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.

What must be continuously monitored

The monitoring annex is the most frequently skipped part of EN 12845. Asked "does the standard require this?", most inspectors look only at the main clause, when the monitoring obligations are in the annex. In summary:

Monitored quantity	Threshold / rule
Stop valve position (in the water path)	Alarm as soon as closing starts
Stop valves in the alarm or indicating circuit	Alarm as soon as closing starts
Water storage level	Indication before it drops more than 10 % below nominal
Diesel pump fuel tank	Indication before it drops more than 25 %
Pressure tank water level	Indication before it rises more than 10 % above nominal too
Town main pressure	Alarm if it falls below the calculated running pressure
Static pressure of other water supplies	Alarm if it falls more than 20 % below the tested level
Electrical supply	Alarm on loss of one or more phases
Valve and pump room temperature	Alarm if it falls below the required minimum

Three general provisions accompany the list: monitoring devices at least IP54; no more than 15 non-addressable supervisory devices on one common indication; and all signal circuits fully supervised, able to detect short and open circuits. In the shopping centre error above, a compliant design would have raised a fault immediately instead of waiting two years.

Alarm categories

Where does an alarm go once triggered? The standard splits them in two:

• Type A fire alarms: water flow alarm, pump room flow detector, pump running signal, zone flow alarm on a zoned system. Transmitted directly to a continuously staffed centre or the fire service.
• Type B technical alarms: low main pressure, low priming tank level, pump start failure, power not available, pump fault, trace heating fault, low air pressure on pre-action and dry systems, tamper alarms, low water level, low temperature. Sent to the responsible person; the fire service is not called, but action follows immediately.

In practice, bringing both levels out as volt-free contacts into one address pool is a common shortcut. Type A relays go to the fire alarm input and type B relays to the supervisory input, separately. 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 says "alarm panel", located in the sprinkler control room or the pump room. In Turkish practice that role goes to an EN 54 certified fire alarm panel. Sending information to a building management system is not forbidden, but the BMS can never be the primary alarm path, because EN 54 fault tolerance, redundant power and audible/visual outputs are required, and a generic BMS does not provide them.

Typical wiring:

1. Field device (flow, pressure or tamper) → volt-free contact → fire panel supervisory input.
2. The fire panel routes type A alarms directly to the fire service or monitoring centre, and type B alarms to the responsible person by message.
3. BMS monitoring is a parallel second contact or a fieldbus connection — for reporting, not as the primary path.

Comparison with NFPA 72

On the NFPA side, monitoring falls under NFPA 72, which corresponds to the combination of the EN 12845 monitoring and alarm annexes. Three important differences:

• NFPA 72 defines supervisory circuit categories as Class A, B and X; EN 12845 does not go to that detail, saying only "fully supervised".
• NFPA states tamper actuation at one fifth of valve travel explicitly; EN 12845 says only "as soon as closing starts", with no ratio.
• Flow switch retard time — typically 30 to 60 seconds to filter surge alarms — appears in the NFPA text, while EN 12845 leaves it to the device manufacturer's calibration.

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

Turkish context

BYKHY makes sprinkler installations mandatory by reference to TS EN 12845, and points to EN 54 for fire detection and alarm systems. On site, the EN 12845 monitoring list, the EN 54 panel certification and the BYKHY requirement for automatic transmission to the fire service all combine. A practical checklist:

• Are all valves in the water path fitted with tamper switches? (The first item an inspection asks about.)
• Does every wet alarm valve have an electrical pressure switch, with the test valve piped?
• Is the water tank low level switch wired to the panel, set at the 10 % threshold?
• Is there a pump room temperature sensor? Critical in basement and external pump rooms at risk of freezing.
• Are the two pump start pressure switches genuinely independent, on separate contacts?

Five errors seen on site

1. A paddle flow switch on a dry installation. A paddle does not work in air — it gives either constant false alarms or none at all. The fix: a pressure switch below the alarm valve plus a low air pressure alarm.
2. A single pump start switch. Two are required. Pump sets delivered with one switch always get upgraded to two.
3. Tamper cable wired to the BMS instead of the fire panel. The shopping centre error. Wiring it to the fire panel as a supervisory input is required by both EN 12845 and EN 54.
4. No test valve fitted. A test facility is required on every electrical alarm circuit. Without one, there is no way to tell at the annual test whether the switch works.
5. Low temperature switch forgotten. It is mandatory. In a pump room falling to −5 °C the diesel will not start and wet mains freeze; with no temperature alarm nobody notices until morning.

A quick design check

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

Question	Expected
Does the wet alarm valve have an electrical switch?	Pressure or flow switch
Low air pressure alarm on dry and pre-action?	Present, type B
Tamper switches on all stop valves?	Yes, normally open
Two pump start pressure switches?	Independent, either-one logic
Water tank low level switch?	10 % threshold
Pump room minimum temperature alarm?	Present
Phase failure monitoring?	At the pump controller
Volt-free contacts to the fire panel?	Yes, separate type A and B inputs
Circuits fully supervised?	Short and open circuit faults reported
Device ingress protection?	IP54 or better

If every answer is yes, the electrical monitoring is compliant. If one is in doubt, you have to go and measure that circuit — the design on paper is often not the same thing as the cable on site.

Frequently Asked Questions

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

No. A paddle works only on a wet installation. Dry and pre-action systems use a pressure switch below the alarm valve plus a low air pressure alarm.

When must a tamper switch alarm?

As soon as a normally open valve starts to close — not when it is fully shut. Most OS&Y switches trip within the first fifth of stem travel.

How many pressure switches start a pump?

Two independent switches in either-one logic. Any isolating valve in the sensing line needs a non-return valve in parallel with it.

Can a BMS be the primary alarm path?

No. The alarm panel must be an EN 54 certified fire alarm panel; BMS monitoring runs in parallel for reporting only.

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