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ATS U2 Low Voltage Warning

Publication Date:  2015-01-13 Views:  146 Downloads:  0
Issue Description
When U1 input off, U2 input is power on, but the breaker cannot transfer to the U2 input, the indicator shows breaker doesn’t transfer from U1 to U2, Manual operation is also invalid, and with the alarm bee sounding all the time.
Alarm Information

U2 Volt. Low

Handling Process

We have thought many methods to confirm that the ATS’ function is normal, but the alarm information always exists.

After we reset the ATS by power off, the alarm information would disappear, and the ATS’ breaker can transfer from U1 to U2 normally.

So, because of the ATS has alarm locked lead to the ATS’ breaker cannot transfer from U1 to U2 normally until the alarm clear by manual operation.

The manual operation is that: take out the NO.34 cables(Located the rear of ATS board) out, then the ATS will power off, after that put the cable back to the NO.34 connector and fasten again, ATS power on again, restart is accomplishment.

We confirmed this issue and solution many times on site.

So, from above analyzing, the ATS is normal, what caused this issue is the unstable main input.

Root Cause
The local grid is very abnormal, at daylight, the volatage is high, but at night, the voltage will decrease sharply, even lower than the limited value of ATS, and this directly lead to alarm and ATS warning locked.

Remove the power supply cables of ATS,put cables back again, then ATS will restart, and alarm bee disappear, the function of ATS is normal.


1.Configure the input scope more wider;

2. before the PDU in the power supply system to avoid the unstable national power supply grid.