Narrative:

This was a first lesson for the student and we were just about to wrap it up and head back in. We were starting to head back to the airport when the lights on the comms started to flicker. One by one each item shut off on my comm/nav panel. I lost the GPS; comms; navs; transponder; basically anything electric. The intercom; however; kept going in and out. It would work for a few minutes and then cut out for a few minutes throughout the whole event.I followed the procedure of turning off all equipment and only trying to turn back on the comms. That didn't work; so I checked the circuit breakers and none were popped. They weren't the push/pull type so I couldn't try resetting them. I also tried turning off the master for a few minutes to let the battery charge; but that didn't help either. The only really weird thing was that I kept getting a vac light failure. However; after 20 minutes into the event; the vacuum gauges were still operable; and the ai was still erect. As a last ditch effort; I tried calling the tower directly via cell phone; but unfortunately I couldn't hear them over the loud engine and didn't have a way to connect it to my headset. I followed standard lost comm procedure and entered the delta airspace from the east (never much traffic on that side) and set myself up for a right downwind to runway 32; the runway in use. When I saw an opening; I fell in to the traffic pattern and spaced myself appropriately from the aircraft in front of me. I was looking for light gun signals; but never did see them. I followed the aircraft in front of me on an extended downwind to the inner shore line and followed him to base. When I turned final; the aircraft in front of me turned off to the left and I could see the controller was clearing the way for me to land. Upon landing and taking the turn-off; I called the tower again and explained the situation and to get a taxi clearance back to the parking spot. The controller completely understood and had explained that they had a feeling it was something like that and tried their best to get me in safely. After the mechanic's inspection; the end result was that a ground wire had come loose. The mechanic told me it wasn't caused by anything I did and that there was nothing I could do to fix it in flight.

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Original NASA ASRS Text

Title: A C172 lost electrical power due to a loose ground wire and made a NORDO landing at a Towered airport.

Narrative: This was a first lesson for the student and we were just about to wrap it up and head back in. We were starting to head back to the airport when the lights on the Comms started to flicker. One by one each item shut off on my Comm/Nav panel. I lost the GPS; Comms; Navs; Transponder; basically anything electric. The intercom; however; kept going in and out. It would work for a few minutes and then cut out for a few minutes throughout the whole event.I followed the procedure of turning off all equipment and only trying to turn back on the Comms. That didn't work; so I checked the circuit breakers and none were popped. They weren't the push/pull type so I couldn't try resetting them. I also tried turning off the master for a few minutes to let the battery charge; but that didn't help either. The only really weird thing was that I kept getting a VAC light failure. However; after 20 minutes into the event; the vacuum gauges were still operable; and the AI was still erect. As a last ditch effort; I tried calling the Tower directly via cell phone; but unfortunately I couldn't hear them over the loud engine and didn't have a way to connect it to my headset. I followed standard Lost Comm procedure and entered the Delta airspace from the East (never much traffic on that side) and set myself up for a right downwind to Runway 32; the runway in use. When I saw an opening; I fell in to the traffic pattern and spaced myself appropriately from the aircraft in front of me. I was looking for light gun signals; but never did see them. I followed the aircraft in front of me on an extended downwind to the inner shore line and followed him to base. When I turned final; the aircraft in front of me turned off to the left and I could see the Controller was clearing the way for me to land. Upon landing and taking the turn-off; I called the Tower again and explained the situation and to get a taxi clearance back to the parking spot. The Controller completely understood and had explained that they had a feeling it was something like that and tried their best to get me in safely. After the mechanic's inspection; the end result was that a ground wire had come loose. The mechanic told me it wasn't caused by anything I did and that there was nothing I could do to fix it in flight.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.