EN 12845 Electric Sprinkler Pump Sets

Independent supplies, direct-on-line starting, short-circuit protection only, PH 90 / E90 fire-resistant cabling, and the overload relay error seen most often on site.

During commissioning at a logistics warehouse, the moment the pump started there was a click from the panel contactor and the electric motor stopped. The operator looked and found the overload relay had tripped. The mechanical contractor said "maybe an earth fault"; the electrical designer said "maybe the motor is undersized". The truth was much simpler: the panel was a general-purpose motor starter with a standard thermal overload inside it. A fire pump panel cannot be built that way. EN 12845 closes this error in one line — but fire pump panels are still drawn to motor-starter logic.

This article covers the electrical side of an electric sprinkler pump set from a site perspective: where the supply comes from, how the main switchboard is labelled, how the cable between panel and motor is run, how the controller logic works, and why there is never an overload device.

The 15 second rule and an always-available supply

The opening requirement is short but sets the philosophy of the whole section: the electric supply system shall be available at all times. The supply feeding the sprinkler pump must not be disabled by any switching operation in the building. That rules out the "the main breaker trips and the pump goes with it" scenario from the start.

The time window follows: from the start signal, the pump must be running at rated capacity within 15 seconds. That may look like a band with room for a soft start or a star-delta transition; it is not. Fifteen seconds is not a run-up allowance but the moment by which design flow and pressure must exist at the valve manifold.

An independent supply

The supply to the sprinkler controller must be dedicated to the sprinkler system and separate from every other connection in the building. Where the local electricity utility permits, it is taken from the input side of the main incoming switch; where not, as a separate feeder immediately downstream of it. The logic is to eliminate a single point of failure: isolating the building supply must not cut the pump.

Two accepted arrangements exist in practice:

• A single supply from the building transformer plus a diesel pump as backup: because the diesel counts as a second drive, one electrical feeder is sufficient. The standard solution on most OH-2 and OH-3 projects.
• Two separate transformers, or a transformer plus a generator: required where two electric pumps are fed. Note: two cables from one transformer do not count as two sources. Two independent medium-voltage feeds, or one transformer and one independent generator, are required.

The standard also requires the backup supply to come from a different compartment or along a route at least 3 m apart. Running two cables side by side in the same containment is not a backup supply; one local fire takes out both.

Direct-on-line starting: why star-delta and VFDs are out

EN 12845 does not write "use DOL" explicitly; but taken together, the 15 second rated-capacity rule, the mandatory AC-3 utilisation category and the prohibition on overload protection leave direct-on-line starting as the only workable method. Approved sprinkler controllers from certification bodies are built on DOL.

Star-delta transition is rejected on site for three reasons:

• Torque dip: at the transition, current and torque fall almost to zero for a few hundred milliseconds. A pump loaded on an open manifold can experience reverse thrust during that dip, and the impeller shakes.
• Two contactors plus a timer: instead of one contactor. Every extra element adds to the failure probability.
• The 15 second margin: the transition typically adds 3–7 seconds, delaying the point at which rated flow begins.

Soft starters and variable frequency drives are equally unsuitable. A soft starter carries control electronics through the transition; a VFD can lock out in an environment of fire currents and harmonics. The basic logic of a sprinkler controller: the least electronics, the shortest chain, the fastest start.

Overcurrent protection: short circuit only, no overload

The requirement is unambiguous: the fuses in the pump controller shall be of high rupturing capacity (HRC) and shall carry the starting current of the sprinkler pump for at least 20 seconds. That fuse provides short circuit protection only. If the winding insulation degrades and the motor runs continuously above rated current, the panel must do nothing.

The philosophy behind that decision is the standard's core priority: the sprinkler pump must not stop during a fire. An overload relay is exactly the device most likely to trip under fire conditions — high water temperature, frequent starting, long running — so it is prohibited from the circuit.

By the same logic, the controller output contactor contacts must be certified to utilisation category AC-3 under EN 60947 — the class covering repeated making and breaking of squirrel-cage motor starting and running currents.

Item	General motor panel	Sprinkler pump panel
Overload protection	Thermal relay fitted	None
Short circuit protection	MCB or fuse	HRC fuse carrying starting current for 20 s or more
Starting method	Star-delta, VFD or DOL	DOL only, from the 15 second rule
Contactor class	AC-1 or AC-3	AC-3 mandatory
Stop function	Automatic or manual	Manual stop only
Panel to motor distance	Flexible	Same compartment mandatory

The main switchboard and the "do not switch off" label

The main switchboard must sit in a fire compartment used only for electrical distribution. Its circuit arrangement must ensure the sprinkler pump supply is not disabled when other services are isolated.

Every switch in the sprinkler pump supply carries the following label:

SPRINKLER PUMP MOTOR SUPPLY — NOT TO BE SWITCHED OFF IN THE EVENT OF FIRE

Minimum letter height 10 mm, white on red. The switch is physically locked, by key or padlock. On Turkish sites a Turkish version is added alongside; the English original must remain, because certification inspections look for the original wording.

Sizing the cable between panel and pump

The cable from the main switchboard to the pump controller is sized for 150 % of the greatest possible full load current. That keeps the voltage drop within a sensible band at starting and compensates for the long-term derating from the cable's operating temperature.

A worked example: a 75 kW motor at 400 V with a power factor of 0.85 draws roughly 135 A. The sizing basis is 135 × 1.5 = 202.5 A, from which an XLPE copper cross-section is chosen from the IEC 60364 tables. In practice 4 × 70 mm² or 4 × 95 mm² copper is typical for a 75 kW pump; do not forget the derating factor for a fire-resistant cable type.

Cable that survives the fire: PH 90 / E90

The cable to the pump motor terminal block must be in one continuous length. Between the switchgear outside the sprinkler equipment room and the pump motor there may be no joint whatsoever — no junction box, terminal or splice. On a dual-source system, a terminal box near the motor is accepted only where the cables from the two sources are neither buried nor run together outside.

The minimum conductor size is 2.5 mm² copper, and the cable must be flame retardant to EN 60332. Two routing options are given:

Option 1 — flame retardant cable on a protected route:

• Buried at least 70 cm underground;
• In floors or walls of non-combustible material, with at least 10 cm of concrete cover;
• Within the sprinkler pump room;
• Within a sprinklered or otherwise compliant main switchroom.

Option 2 — fire-resistant E 90 (PH 90) cable: where the above cannot be met, the cable must be E 90 class, additionally tested by a certification body for operation under water spray and mechanical impact, and installed on approved supports. Where it runs within a suspended ceiling it goes immediately below the structural soffit, in a non-combustible shaft or in fully enclosed non-combustible containment.

Where there are two supplies, the two cables must be at least 3 m apart, so that a local fire or mechanical impact cannot take out both. On site, separate containment routes count; stacking them on one tray does not.

In Turkey, fire-resistant cable (PH 90 / E90, tested to IEC 60331 and EN 50200) has become standard in line with BYKHY. Despite the cost, E 90 ends up mandatory on most projects because option 1 is hard to achieve in practice.

Pump controller logic

The controller must be able to do three things:

• Start the motor automatically on a signal from the pressure switches;
• Start the motor from a manual button;
• Stop the motor manually only.

Automatic stopping is prohibited. Once a sprinkler has operated, the response team sees the water, assesses the cause, shuts off the flow at a valve and only then stops the pump by hand. Logic that says "pressure dropped, let the pump stop and start again" is a disaster during a fire — the pump cycles up and down as pressure swings, and wears out mechanically.

The controller carries an ammeter; where a submersible pump is used, a label with the pump characteristics (flow, pressure and current points) is fixed to the panel. Panel and motor sit in the same compartment, submersible pumps excepted.

What must be monitored

The following must be indicated audibly and visually in the pump room and at a location under human supervision, such as a control room:

• Power available at the motor, on all three phases for AC;
• Pump on demand;
• Pump running;
• Start failure.

The fault indication must be yellow; the audible signal at least 75 dB and silenceable. A manual lamp test button is mandatory — and the missing lamp test button is the most common inspection shortfall on site.

The most common error: leaving the overload relay in circuit

Electrical teams often think "what harm is a small overload device" in order to keep the motor healthy for years. Their logic: if the motor burns out, the pump is down to a spare part and it is expensive. The standard's logic is the reverse: the motor is expensive and the pump more so, but losing the building and its occupants during a fire costs many times either. That is why EN 12845 prohibits overload protection outright.

The practical way to catch this on site: open the panel door, and if there is a bimetallic overload device on L1-L2-L3 at the contactor output, that relay must be removed and links fitted. In some panels the overload is integral to the contactor body and bypassing requires a manufacturer-approved kit; there, replacing the panel is the only correct route. The fuse remains as HRC short-circuit protection only.

Comparison with NFPA 20

NFPA 20 (Centrifugal Fire Pumps) shares the same philosophy; the differences are practical:

• NFPA 20 distinguishes limited service from full service controllers; EN 12845 defines a single controller class.
• NFPA 20 also prohibits overload protection, reaching the same result through the individual motor branch circuit concept.
• NFPA 20 lists reduced voltage starting (star-delta, soft starter, autotransformer) as permitted options, but certified panels are sold as DOL in practice — the same point on site.
• NFPA 20 defines the automatic transfer switch in detail; EN 12845 leaves that to local regulation, the two-independent-sources philosophy being sufficient.

Turkish context

BYKHY uses the general phrase "fire-resistant cable" for the sprinkler pump supply, leaving the class to the EN and IEC references. In practice, fire brigade and municipal project reviews require PH 90 (IEC 60331 plus EN 50200). The two points most often sent back on the panel side:

• Labelling not provided bilingually in Turkish and English;
• Overload relays still physically wired in the panel — sometimes left with a note saying "disabled", which inspection rejects; they must be removed.

Specifying a certified sprinkler controller (LPCB, VdS or FM Approved) at procurement closes this standard-versus-site argument from the start. A declaration from a general motor panel builder that "we can make it EN 12845 compliant" is a risky promise without a certificate in the inspection file.

Frequently asked questions

Why can a sprinkler pump not be star-delta started?

Rated capacity is required within 15 seconds of the start signal. The torque dip and transition time of a star-delta start put that window at risk. Approved sprinkler controllers come as DOL as standard.

Why is there no overload relay?

Only HRC short circuit protection is permitted. Overload protection is deliberately absent, so that the motor does not stop during a fire. Adding an overload device is a risky comfort measure, not a control.

What fire class must the pump cable be?

Either a flame retardant cable on a protected route — buried, in concrete, in the pump room or in a protected switchroom — or a fire-resistant E 90 (PH 90) cable on approved supports. E 90 has become the norm on Turkish sites.

What counts as two independent supplies?

Two separate transformers, or one transformer plus an independent generator. Two cables from one transformer do not count, and the two cables must be run at least 3 m apart.

Can the panel and motor be in different rooms?

No. Apart from submersible pumps, the panel and motor must be in the same compartment.

Frequently Asked Questions

Why is there no overload relay in a fire pump panel?

Because the pump must not stop during a fire. Only HRC short-circuit protection is permitted; an overload device is exactly what would trip under fire conditions.

Why direct-on-line starting?

Rated capacity is required within 15 seconds of the start signal, and a star-delta torque dip and transition time put that window at risk.

What cable is required between panel and motor?

One continuous length with no joints, minimum 2.5 mm² copper, either flame retardant on a protected route or fire-resistant E 90 on approved supports.

Can the pump be stopped automatically?

No. Starting may be automatic or manual, but stopping is manual only, after the flow has been shut off at a valve.

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