We were called to an office today to inspect several outlets. The customer complained that when they connected their computers with surge protectors to the outlets that several of the surge strips "popped" and burned up. When measuring the voltage to neutral at all outlets, the readings were normal 120volt, but the voltages to ground were 112 at some outlets and 136 at others. When we checked the voltages at the panel the voltages were all normal.
The circuits are multiwire and installed in EMT conduit to a metal junction box in the attic with a ground wire. After the first junction box, someone installed ENT conduit between the junction box and another section of EMT conduit which disappears into an inaccessible space. The wiring from this junction box going into the ENT conduit does not contain a ground wire. When the wiring reaches the plugs in the office it is type MC cable in metal boxes with bonding screws.
Does anyone have an idea of what the problem is. My first thought is that someone probably connected the ground and neutral wires in some junction box that we can't find and that wherever this connection is, it has come loose...The only reason I second guess this is that I'd expect to have abnormal voltages in the L-N readings at the plugs somewhere if this were true instead of in the ground wire. My other thought was that with the break in the conduit with the small section of ENT and no apparent ground wire, that somewhere there is a fault that is going onto the metal conduits and MC and that because the conduit does not have a solid path it is traveling back to the ground terminal on the screws of the plugs and giving me these readings...the building is wood framing instead of iron and sheetmetal, so the conduits are essentially isolated from a path to ground with the break in the conduit. This break could be causing the lack of the potential and thus not allowing the breaker to trip even though there is a fault.
Any help or ideas would be appreciated. We are going back in the morning and were going to try and turn off the breakers individually while testing the outlets to see if we can find out which circuit is causing the readings and then attempting to track down the problem.....
The circuits are multiwire and installed in EMT conduit to a metal junction box in the attic with a ground wire. After the first junction box, someone installed ENT conduit between the junction box and another section of EMT conduit which disappears into an inaccessible space. The wiring from this junction box going into the ENT conduit does not contain a ground wire. When the wiring reaches the plugs in the office it is type MC cable in metal boxes with bonding screws.
Does anyone have an idea of what the problem is. My first thought is that someone probably connected the ground and neutral wires in some junction box that we can't find and that wherever this connection is, it has come loose...The only reason I second guess this is that I'd expect to have abnormal voltages in the L-N readings at the plugs somewhere if this were true instead of in the ground wire. My other thought was that with the break in the conduit with the small section of ENT and no apparent ground wire, that somewhere there is a fault that is going onto the metal conduits and MC and that because the conduit does not have a solid path it is traveling back to the ground terminal on the screws of the plugs and giving me these readings...the building is wood framing instead of iron and sheetmetal, so the conduits are essentially isolated from a path to ground with the break in the conduit. This break could be causing the lack of the potential and thus not allowing the breaker to trip even though there is a fault.
Any help or ideas would be appreciated. We are going back in the morning and were going to try and turn off the breakers individually while testing the outlets to see if we can find out which circuit is causing the readings and then attempting to track down the problem.....
