The first decision in fire pump selection is the drive type, and it affects everything from the tank room to the electrical design. There is no single right answer to electric or diesel; but where a superior or duplicate water supply has more than one pump, at most one may be electric.
Side by side
| Criterion | Electric motor | Diesel engine |
|---|---|---|
| Mains dependence | Total | None (independent on batteries) |
| First cost | Low | High (engine, fuel, exhaust, batteries) |
| Pump room area | Small | Large (ventilation, exhaust, fuel) |
| Ventilation | Ordinary | Combustion plus cooling plus radiator air |
| Room temperature (EN 12845 10.3.3) | At least 4 °C | At least 10 °C |
| Pump room fire resistance | At least 60 min (EN 12845 10.3.1) | At least 60 min (EN 12845 10.3.1) |
| Weekly test (EN 12845 20.2.2) | Automatic start by reducing pressure; starting pressure recorded (20.2.2.4) | Automatic start, run for 20 min (or the supplier's recommended time), then restart with the manual start test button (20.2.2.5) |
| Maintenance burden | Low | High (oil, filters, batteries, fuel turnover) |
| Fuel management | None | Tank, turnover, water separation, level alarm |
| Noise | Low | High; silencer and insulation needed |
| Redundancy role | Duty pump | Standby pump (typical) |
The rule: only one electric pump on a duplicate supply
EN 12845 10.2 is explicit: where more than one pump forms part of a superior or duplicate water supply, at most one may be driven by an electric motor; the rest must be diesel. The reasoning is one sentence — a mains outage is a single point of failure. If two electric pumps are fed from the same transformer, both fall when that transformer does.
The rule is absolute: even with a second electrical source such as another transformer or a generator, EN 12845 10.2 does not permit a second electric pump. Where the electric pump itself is fed from two power sources, the cables to the controller are to be laid at least 3 m apart (10.8.2).
The hidden costs of diesel
- Ventilation free area. EN 12845 10.3.4 requires adequate ventilation in accordance with the supplier's recommendations and gives no fixed figure. A 50 to 100 kW diesel pump typically needs 1.2 m² of net free area for combustion, cooling and radiator air. If that is not in the architectural plan from the start, a facade has to be cut open later.
- Exhaust. Fitted with a silencer, insulated and discharged outside so that exhaust gases cannot re-enter the pump room (EN 12845:2015+A2:2026 10.9.1, which refers diesel pump sets and ancillaries to EN 17451); in practice at high level with a rain cap. Discharging into the room or an internal courtyard heats the room quickly and damages the batteries and sensors.
- Fuel and tank. EN 12845:2015+A2:2026 gives no separate duration for the fuel tank; Clause 10.9.1 requires diesel driven pump sets and their ancillaries to be in accordance with EN 17451. Diesel has a shelf life, so an annual turnover and water separation routine is needed.
- Test discipline. Once a week, 20 minutes of running (or the supplier's recommended time) followed by a manual restart (EN 12845 20.2.2.5). Where that routine slips, the diesel will not run at a real alarm — the most common failure I see on site.
The hidden risks of electric
- Supply independence. The supply to the pump controller serves the sprinkler system only; where the electricity utility permits, it is taken from the input side of the main incoming switch, otherwise by a connection from the main switch (EN 12845 10.8.2). Isolating other services must not isolate the pump supply (10.8.3.1).
- Cable class. Where a protected route cannot be achieved, E 90 fire-resistant cable becomes mandatory (EN 12845 10.8.2), and the cost difference is significant.
- Labelling. Every switch in the supply must carry the label "SPRINKLER PUMP MOTOR SUPPLY – NOT TO BE SWITCHED OFF IN THE EVENT OF FIRE" (white letters at least 10 mm high on red) and be locked (EN 12845 10.8.3.2). It is the item most often sent back at inspection.
- Overload relay. If the panel was built from a general-purpose motor starter it contains an overload device, and that is a direct non-conformity: EN 12845 10.7.5.2 requires the pump, once started, to run until stopped manually.
The practical arrangement: on OH2 and OH3 projects in Turkey, the most common solution is a single electric duty pump plus a diesel standby. That satisfies the one-electric rule and brings a second drive independent of the mains.
Frequently Asked Questions
Can I use two electric pumps on a duplicate supply?
No. EN 12845 permits at most one electric motor driven pump within a superior or duplicate supply; the rest must be diesel. A mains outage counts as a single point of failure.
How much ventilation does a diesel pump room need?
EN 12845 10.3.4 requires adequate ventilation in accordance with the supplier's recommendations and gives no fixed figure. A 50 to 100 kW diesel pump typically needs at least 1.2 m² of net free area for combustion, cooling and radiator air; take the exact figure from the engine manufacturer's table.
What temperature must the pump room be?
Under EN 12845 10.3.3, at least 4 °C for an electric motor pump and at least 10 °C for a diesel. The difference is for oil viscosity and battery performance.
Which cable is used for an electric pump?
Under EN 12845 10.8.2, flame-retardant cable is sufficient on a protected route (buried at least 70 cm deep, in concrete with at least 10 cm cover, in the pump room, or in a sprinklered main switchboard room). Where that cannot be achieved, E 90 fire-resistant cable becomes mandatory.
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Download MEP Calc on the App StoreNFPA 20 Standard for the Installation of Stationary Pumps for Fire Protection (2025). EN 12845:2015+A2:2026 pump clauses. EN 17451 (sprinkler pump sets). FM Global DS 3-7. Values are for information only.