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Pressure switch

The pressure switch is another, next to the thermostat, element protecting against the heater's operation in forbidden conditions. It

prevents the heater from being switched on when the pressure generated by the AHU's fan sets is insufficient to ensure safe operation

of the heating elements.

Similarly to the thermostat, the pressure switch is a factory-installed and electrically connected component - connection of the

pressure hoses of the pressure switch should be made in accordance with the following recommendations:

o one of the tubes should be brought out to atmospheric pressure - in the case of installation of the power box on the duct

(outside), the pipe does not need to be connected - there is atmospheric pressure present in the power box

o the second tube should be connected to the overpressure or underpressure in the AHU or in the duct (before or after the air

supply fan)

o in the duct version of the heater, it is allowed to move the pressure switch outside the power box to avoid the need to run

long measuring pipes - recommended position of the pressure switch - horizontal, with a vertical position the reading is 11Pa

higher compared to the actual one

The pressure switch switching threshold is 20 Pa. After connecting to the AHU, check if the pressure switch is working properly for the

lowest AHU airflow available. In the absence of the detected pressure difference, the place of connection of the second pressure hose

to the installation should be changed.

In the opposite case - when for a given pressure switch setting, the pressure difference is detected even when the AHU is turned off

(heater operation is allowed despite the lack of fans operation), the setpoint should be gradually increased until the correct operation

is obtained - its sign is that the electric heater does not work despite the signals from the control device appearing if the pressure

switch does not detect the pressure difference between the measurement channels - the permission should take place only after the

fans are started.

After the pressure switch is fully connected, perform the heater shutdown test. To do so, it is necessary to force the electric heater to

be manually controlled (e.g. by providing heater control signals from the controller) and at the same time to stop the fans. The pressure

switch should prevent the operation of the electric heater (it will be visible e.g. by disconnecting the contactors in the switchgear).

Figure 7 – pressure switch

function

protecting the heater against overheating (fan compression control)

structure

-plastic housing

- two screw terminals

-a membrane connected to a mechanical module

rated work voltage [V DC]

type of output signal

free voltage (switching contact)

measuring range [Pa]

20-300

Table 13 – pressure switch data