Site Wiring Fault
APC UPS
Severity:What Does This Error Mean?
The Site Wiring Fault indicator on an APC UPS means the UPS has detected a problem with the building's mains wiring at the socket it is plugged into. The most common cause is a missing or poor earth (ground) connection. This is a genuine electrical safety issue — do not ignore it. A qualified electrician should inspect the socket and wiring.
Affected Models
- APC Back-UPS series (BE, BX, BVX)
- APC Back-UPS Pro series (BR, BN)
- APC Smart-UPS series
- Any APC model with a wiring fault indicator LED
Common Causes
- Missing or broken earth (ground) wire in the building wiring or socket
- Live and neutral wires reversed at the socket
- Loose or corroded earth connection in the consumer unit (fuse box)
- Extension lead or power strip with a faulty or missing earth conductor
- Old building wiring that was never properly earthed
How to Fix It
-
Try plugging the UPS directly into a different wall socket on a different circuit. If the fault clears, the original socket or its circuit has a wiring fault.
Do not continue using the original socket until it has been inspected. An unearthed socket is a shock and fire hazard — not just a UPS problem.
-
Check whether the UPS is plugged through an extension lead or power strip. If so, try connecting directly to the wall. Cheap extension leads sometimes have poor or missing earth connections.
APC recommends connecting the UPS directly to a wall socket. Extension leads and power strips between the UPS and the wall can also affect the UPS's power conditioning performance.
-
Contact a qualified electrician to test and repair the socket and circuit wiring. Do not attempt to repair mains wiring yourself.
In most countries, mains electrical work must be carried out by a licensed electrician. An earth fault test takes only a few minutes with the right equipment.
Frequently Asked Questions
Is a site wiring fault dangerous?
Yes — a missing earth means that if a fault develops in any connected equipment, the fault current has no safe path to ground. This increases the risk of electric shock and fire. The APC UPS is doing you a favour by detecting and warning about this — have it fixed.