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What does the Site Wiring Fault Indicator LED on my UPS or Surge Arrestor represent?

What does the Site Wiring Fault Indicator LED on my UPS / Surge Arrestor represent?

Product Line:
All Back-UPS and SurgeArrest products

All Back-UPS and SurgeArrest products equipped with a Site or Building Wiring Fault indicator

The Site Wiring Fault (SWF) LED light is only present on 120V UPS and Surge products. On APC UPS products this indicator is typically on the rear panel. The purpose of this indicator light is to warn you that there are problems with your building wiring that may result in a shock hazard.

APC recommends that you have a qualified electrician inspect your wiring for one or more of the conditions listed below.

Reasons why the Site Wiring Fault (SWF) LED light will illuminate:

1. Overloaded neutral wire (>5vac measured between Neutral and Ground).

2. Reversed polarity (hot and neutral wires are reversed).

3. Missing ground wire. (Note: this also includes using a 3 prong to 2 prong adapter)

If the outlet that the APC UPS unit is plugged into is not properly grounded or properly wired, the unit will attempt to absorb the excess voltage instead of redirecting it to ground. It would be like attempting to catch a bullet with a catcher mit, where as if the light is not on it would be able to redirect the excess voltage to ground. Therefore, in order to maintain your warranty and protection under APC's Equipment Protection Policy, be sure that the APC unit is only plugged into a properly grounded outlet where the Site Wiring Fault Indicator (SWFI) light is not illuminated.

All of APC's UPSs with the exception of the Matrix-UPS and the Symmetra Power Array have a small red LED light that is called a SWFI. On some UPS models, this LED is referred to as the Building Wiring Fault Indicator. Both have the same function. On most UPS models, the light is located on the rear of the unit near where the output receptacles are located.
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