Lennox EL280UHE Series Service Literature page 28

I- Proper Ground and Voltage
Furnace must be properly grounded for proper perfor-
mance. Use the following procedure to check for ground
and voltage to the integrated control.
1 - Measure the AC voltage between Line Neutral
(spade terminals) and "C" terminal (low voltage
terminal block) on the integrated control. See figure
20. A wide variation in the voltage between Line
Neutral and "C" as a function of load indicates a
poor or partial ground. Compare the readings to the
table below. If the readings exceed the maximum
shown in table 16, make repairs before operating
the furnace.
CHECK VOLTAGE BETWEEN LINE NEUTRAL
AND LOW VOLTAGE "C" TERMINAL
2 - In addition, measure the AC voltage from Line Hot
to Line Neutral (spade terminals) on the integrated
control. See figure 20. This voltage should be in the
range of 97 to 132 Vac.
Furnace Status
Power On Furnace Idle
CAI / Ignitor Energized
Indoor Blower Energized
CHECK VOLTAGE BETWEEN LINE HOT
AND LINE NEUTRAL
FIGURE 20
Page 28
TABLE 16
Measurement VAC
Expected Maximum
0.3
0.75
Less than 2
2
5
10