Siemens LMV5 Quick Start Manual page 34

Grounds
The LMV5 has three different types of grounds. They are:
Protective Earth
Functional Earth
Reference Ground
Protective Earth
Protective Earth (PE) or chassis ground should always be connected to the control panel
grounding lug. One wire from the secondary side of the control panel's main step-down
transformer should also be connected to the control panel grounding lug.
All of the PE terminals on the front of the LMV5 casing are common.
Functional Earth
Functional Earth (FE) connections are found on the CANBus terminals as well as other low
voltage connections.
The sole purpose of the FE is for termination of low voltage cable shields.
The FE is bonded to the Reference Ground through capacitors on the LMV5 circuit board with
the exception of the CANBus where it is bonded directly.
Reference Ground
The last type of ground is the Reference Ground. These are found on the low voltage
connections.
The purpose of the Reference Ground is to serve as a datum to measure other voltages.
The Reference Ground is bonded to the FE on the CANBus circuit board through pins 2 and 3
on the AGG5 transformer.
Note: Pin 3 on the AGG5 transformer is also connected to the control panel grounding lug
(PE), so that all three grounds are eventually bonded together.
Summary:
0 & PE are bonded together at the transformer (connect X52.4 & SEK2 pin 3 to panel ground)
FE is bonded to 0 & PE, for the CANBus ONLY, directly on the circuit board
FE is bonded to 0 & PE everywhere else through a capacitor on the circuit board
LMV5 QSG Rev 4
(marked as PE on the LMV5)
(marked as FE on the LMV5)
(marked as 0, M or GND on the LMV5, hereafter referred to as 0)
Sec 3 Pg 2 www.scccombustion.com