The Basics of Connecting Circuits and Pass Through Circuits



In order for devices to connect to a circuit, both the source output circuit and the device input circuit must be the same circuit type.

In the example below we wish to connect the smoke detector on the right to the control panel on the left.


FireCAD provides a dialog and commands for this purpose. 

When the 6820-SD SLC circuit L1 is chosen and the "Connect" button is selected, any compatible devices will become highlighted in green. this tells us that we can connect the device to the circuit provided from the panel.


After the highlighted smoke detector is selected, it is assigned an address and is listed in the connected devices listing.


Following is the explanation of why this connectivity happens:


The panel is configured in the CADGEN database to provide an output circuit of a specific type.

In this case several circuit types are provided by circuit L1:

  • SURGE PROTECTION permits the connection of surge suppressors (which do not receive an address but which can connect to the circuit)
  • JUNCTION PASSTHROUGH permits the connection of junction boxes and other devices such as conduit riser locations (which do not receive an address but which can connect to the circuit)
  • ISO permits the connection of isolator modules (which do not receive an address but which can connect to the circuit)
  • SLC HOCHIKI permits the connection of compatible SLC devices (which receive an address when connected to the circuit)
  • All addressable devices are formatted according to the manufacturer's protocol.



The smoke detector is configured in the CADGEN database to have an input circuit of a specific type.

In this case the SD505-APS detector is compatible with the SLC HOCHIKI circuit type.

It is because of this circuit type compatibility that this connection can be made.

All circuits in FireCAD follow these same rules.



Examples of "PASSTHROUGH" circuits are those that originate at a panel (NAC, AUX POWER, etc. then feed equipment that produces circuits of their own.

  • Example 1:
    · A power supply panel feeds voltage, audio or another type of signal to control modules which each supply one or more discrete output circuits.
    · Typically, each of these circuits can be individually activated from the SLC circuit controlling the control module.
  • Example 2:
    · A power supply panel feeds voltage to control modules which provide an output for the discharge of a suppression system.

The reason for the name "PASSTHROUGH" is that the circuit passes through each of the components on its way to the final component.

Example 2 is shown below.



  • Most panels and devices in the CADGEN database ae configured for you. In spite of that FireCAD users have the ability to change configurations using the Project Device Editor.
  • Because of the uniqueness of passthrough circuits and the variety of devices that can use them, you may need to make changes to your local .atp file using this tool. Below is a brief explanation.

Open your Project Device Editor


  • Below are the settings that the components in your .atp file must have in order to use passthrough circuits.
  • The most important setting is that the same circuit type MUST be used from the beginning to the end of the passthrough circuit.


  • There are critical settings that must be configured for passthrough circuits to provide accurate calculations. Those settings are found on the "Circuit Types" tab of the Project Device Editor.
  • Please look at the red circled check boxes for the circuit(s) you wish to configure for passthrough connections and calculations.


While there are many variables to the settings you will require for your project, this will be your starting point.

As always, you may call our support line or set up an appointment for a one-on-one support session.

Was this article helpful?
0 out of 0 found this helpful