Chapter 5 Installing the Tracer MP581 programmable controller
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 Tracer MP581 controller from radiating EMI and/or RFI.
The Tracer MP581 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 Tracer MP581 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 controller is operating. Fail- ure 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
3.Measure the ac voltage between the earth ground and the neutral ter- minal, as shown in Figure 31 on page 63.
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
4.Replace the cover plate.
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