Fire pump inverters and soft starters: This is a common question that arises when designing or verifying a fire suppression pressurization system. Here you’ll find a well-reasoned answer, in the style of “Engineering Insights,” based on the requirements mentioned in the text.
Table of Contents
Dashboard: Where It Should Be and What It Should Do
According to reports, UNI EN 12845 (see section 10.8.5) requires that the pump control panel be located in the same compartment as the electric motor and the pump.
In addition, the electric pump’s control panel must be capable of performing very precise operational functions:
- automatically start the engine when it receives a signal from the pressure switches;
- Start the engine in manual mode;
- Stop the engine only by manual operation (with a specific exception related to fire hydrant networks, discussed below).
These three points are not “details”: they are the framework that shapes everything else, including the choice of any electronic devices.
Automatic Start-up and Pressure Switches: The Key Point
The text focuses on an operational concept: the electric fire pump must start in response to a signal from the pressure switches. This means that the startup logic is not “at the discretion” of a generic control mechanism, but must respond to a specific event (the signal from the pressure switches).
This leads to a practical consequence: any component installed on the line or in the control chain that could alter, delay, or “affect” startup or continuous operation must be evaluated in light of this functional priority.
Brake: Why It Must Be Manual
The text includes several consistent statements regarding continued operation after startup:
- UNI EN 12845:2020 (10.7.5.2): “Once the pump has started, it must continue to operate until it is stopped manually.”
- UNI/TR 11438:2012 (10.2): Once the pump has started operating (regardless of the cause, including at the request of the priming system), it can be stopped only manually by the operator.
The overall logic is clear: the pump must not shut down on its own as a result of automatic interventions that are not strictly intended, especially if these interventions are related to electrical controls that can cut off the power supply.
Fire Pump Inverters and Soft Starters: Why “Off-Line”
This brings us to the question: Can soft starters and/or inverters be installed to control the main fire-fighting electric pumps?
Based on the reasoning presented in the text, the answer is no, because:
- Automatic systems that monitor electrical parameters (such as current draw, ground fault current, phase shifts, etc.) and are capable of intervening to shut down the pump after it has been activated by the pressure switch may not be installed;
- Consequently, electronic systems such as soft starters or inverters cannot be installed on the pump’s power supply line, since “they are equipped with protections that activate automatically” to safeguard the load and/or internal circuits, thereby effectively violating the requirement for continuity until manual shutdown;
- Furthermore, it is pointed out that the presence of electronic components reduces the overall reliability of the system.
In other words: the issue is not “whether the inverter works,” but rather that its standard operating logic (protections and automatic shutdowns) may be incompatible with the requirement to keep the pump running until it is manually shut down.
Electrical Protective Equipment: What Is Allowed and What Isn’t
The text also clarifies a frequently debated operational issue: which circuit-breaking and protective devices are permitted.
- Power failure / stop
It is specified that among the systems for interrupting the electric pump’s power supply there is no device other than the STOP button on the electric pump’s control panel (located in the control unit). It is also specified: no release coil with dedicated button . - Line and load protection
To safeguard the line and the load , only high-breaking capacity fuses are permitted. In support of this theme, the text also cites a circular from the Ministry of the Interior (no. 694/4144 of 23 April 1998), which clarified that the safety objectives imposed by CEI 64-8 must be respected even if they conflict with the specific requirements of UNI 9490 , allowing the use of magnetic switches to protect the power lines of fire pumps, while still guaranteeing the line overload parameters dictated by the same standard.
Finally, the text includes an operational assumption: since UNI 9490 has been fully replaced by UNI EN 12845, it is taken for granted that the circular also applies to the latter standard.
Note on Fire Hydrant Systems and Automatic Shut-Off (Specific Case)
There is a specific condition: if the booster unit is used exclusively to serve a fire hydrant network for activities that are not constantly monitored, the system may shut down automatically, but only after the pressure has remained consistently above the pump’s start-up pressure for at least 20 consecutive minutes (reference to UNI 10779 in the text).
This exception does not alter the general approach of the article: the basic rule remains manual shutdown, except in the specific case described.
Operational Conclusion
To summarize: when it comes to main electric fire pumps, the logic described requires automatic startup via pressure switches, the option for manual startup, and, above all, continuous operation until manually shut down. For this reason, based on the reasoning outlined above, fire pump inverters and soft starters cannot be installed on the pump’s power supply line, as they could trigger automatic interventions that conflict with the requirements.
