3.5 Combus Operation and Wiring

The Combus is used by the control panel and the modules to

communicate with each other. The four Combus terminals of the

main panel must be connected to the four Combus terminals or

wires of all modules.

Modules can be home run, connected in a daisy chain or T-

tapped anywhere on the Combus.

The following rules MUST be followed when wiring the Combus:

1. The Combus must be run in minimum 22-gauge wire.

2. No module can be more than 1000' (305m) in cable length

from the main control panel.

3. Shielded wire should only be used in areas that present

excessive RF noise or electromagnetic interference. If shielded

wire is used, the maximum distance a module can be located

from the main panel is significantly reduced. Check the

capacitance limit of the wire to calculate the maximum

distance (see “Capacitance Limits” below).

4. The total capacitance of the Combus wiring must not exceed

80nF (see “Capacitance Limits” below).

Line Loss

When current is drawn through a piece of wire, voltage will be

lost due to the wire’s resistance. This voltage loss must be

considered for all installations.

To ensure proper operation, at least 12.5VDC must be applied to

all modules on the system (when AC is applied and the battery is

fully charged). If less than 12.5VDC is applied, system operation

will be adversely affected.

To correct the problem, try any or all of the following:

1. Connect a PC6204 power supply near the module to provide

power to the Combus.

2. Reduce the length of the Combus run to the module.

3. Increase the gauge of wire.

Capacitance Limits

An increase in capacitance on the Combus will affect data

transmission and will cause the system to slow down.

Capacitance will increase for every foot of wire added to the

Combus. The capacitance rating of the wire used will determine

the maximum length of the Combus.

For example, 22-gauge, non-shielded, 4-conductor wire has a

typical capacitance rating of 20 picofarads per foot (which is

20nF/1000’). For every 1000' of wire added – regardless of

where it is run – the capacitance of the Combus will increase by

20nF.

The following chart indicates the total Combus wire allowed

depending on the capacitance rating of the wire used:

Wire Capacitance per

1000'(300m)

TOTAL Combus Wire

Length

15nF 5300'/1616m

20nF 4000'/1220m

25nF 3200'/976m

30nF 2666'/810m

35nF 2280'/693m

40nF 2000'/608m

Wires run in parallel also increase Combus capacitance. For

example, when using 20nF wire, the following would be some of

the combinations allowed:

• Four wire runs at 1000'/305m each

• Six wire runs at 666'/203m each

• Eight wire runs at 500'/152m each

• 10 wire runs at 400'/122m each etc…

NOTE: Contact the wire manufacturer for the capacitance

ratings of the wire being used.

3.6 PC6204 Power Supply

PC6204 power supply modules are required to power additional

modules and devices when the total current from the main panel

is insufficient. A PC6204 should also be used if excessive line loss

is encountered.

PC6204 Current Requirement

AUX - 1.5A available for devices connected to the AUX terminal,

including devices connected to relay outputs and modules

connected for Combus repower (see section 3.5 “Combus

Operation and Wiring”).

Combus Repower

Only Relay 1 on the PC6204 can be used for Combus repower.

The Combus must be wired to the PC6204 according to the

following diagram for Combus repower:

IMPORTANT NOTE: Do not use any power supply other than

the PC6204 to repower the Combus. In the event of a power

surge or transient, a module may lock up and cease to

communicate with the control panel. If the panel loses

communication with the module, it will initiate a module

reset and will power down the Combus for five seconds in an

attempt to reset the problem module. After five seconds, the

panel will reapply power to the Combus and the problem

module should begin to operate as intended.

If a power supply other than the PC6204 is used, the Combus

repower function will not operate as intended.

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