ECM Background Information Mobile Generator
36 wc_tx000713gb.fm
4.6 Voltage Display Errors
See Graphic: wc_gr003308
• Single-Phase Display Mode
When operating in the single-phase 120/240V position, line-to-line
voltage will be displayed under P2 (240V). Line-to-neutral voltage
(120V) will be displayed under P1 and P3. This is the normal single-
phase display mode.
• Three-Phase Display Mode
When operating in either three-phase position (208/120V or 480/
277V), the line-to-line voltage will be displayed under P1, P2 and P3 of
the ECM. For example, in the 480/277V position, with the control panel
rheostat adjusted correctly, voltage values will read 480V on all three
phases: P1=480, P2=480, and P3=480. In the 208/120V position,
voltage values will read 208V on all three phases: P1=208, P2=208,
and P3=208.
• If leg 2 (L2) voltage drops below 50V, the ECM is programmed to
switch to its single-phase mode and stay there until the operator
corrects the condition. Two common causes for this condition are:
1) starting the generator with the connection lug door open and
then closing it with the engine still running; 2) starting the genera-
tor in its single-phase position (120/240V), then switching it to a
three-phase position (208/120V or 480/277V) without turning the
generator off first. Both instances will cause the ECM to display a
less than line-to-neutral voltage for P1 and P2, and full line-to-line
voltage for P3. For example, in the 480/277V position P 1 and P2
will read approximately 190V while P3 will read 480V. The volt-
age values displayed in this mode can lead one to conclude that
the generator is not running correctly, when actually it is fine; the
system just needs to be reset. To correct/reset the condition: stop
the engine, make sure the lug door is closed, and then restart the
engine. Allow the generator to cycle through the phases several
times to develop the maximum voltage.
• When in the three-phase mode, if any one of the legs (L1, L2, or
L3) drops out, two of the three phases will automatically also drop
out. For example, if leg 1 drops out, there can be no L1–L2 (P1)
voltage, nor can there be L3–L1 (P3) voltage. (The values dis-
played under P1 and P2 will be residual voltage for the legs them-
selves, not line-to-line voltage. Residual voltage is approximately
36V.) The voltage displayed under P3 will be L2 line-to-neutral
voltage. This condition is known as single-phasing. It is a sign
there is a problem with the generator.
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