Emi/Rfi Considerations; Checking The Earth Ground - Trane Engineered Smoke Control System Application Manual

Chapter 4 Installing the Tracer Summit BMTX BCU
46

EMI/RFI considerations

Take care to isolate HVAC controllers from electromagnetic interference
(EMI) and radio frequency interference (RFI). Such interference can be
caused by radio and TV towers, hospital diagnostic equipment, radar
equipment, electric power transmission equipment, and so on. In addi-
tion, take care to prevent the BMTX BCU from radiating EMI and/or RFI.
The BMTX BCU is equipped with EMI/RFI filters that trap RFI to
ground. In most situations, a good earth ground will reduce EMI/RFI
problems by acting as a drain for EMI and RFI. If the BMTX BCU is
receiving or radiating interference, make sure that the earth ground is
good. Do not assume that the building conduit is an adequate ground.

Checking the earth ground

Though a proper earth ground is especially important in areas of high
EMI or RFI, always check the quality of the ground, regardless of
location.
WARNING
Hazardous voltage!
The cover plate must be in place when the BCU is operating. Failure to
replace the cover plate could result in death or serious injury.
If the earth ground has a voltage of more than 4 Vac, use a different
ground. Failure to do so could result in death or serious injury.
To check the quality of the earth ground:
1. Open the enclosure door.
2. Inside of the enclosure at the top-right corner, remove the high-volt-
age area cover plate.
3. Measure the ac voltage between the earth ground and the neutral ter-
minal, as shown in Figure 20 on page 47.
Ideally, the voltage should be 0 Vac. Find a different ground if the
voltage exceeds 4 Vac. A higher voltage may result in:
Danger to people touching the enclosure
•
Erratic communications
•
Erratic equipment operation (Because noise may affect voltage
•
levels at the inputs—the controller interprets input noise as
changes in temperature, humidity, pressure, and so on.)
4. Replace the cover plate.
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