I
recently discovered two instances of a false ground where someone connected a
short length of copper from the grounding lug to the neutral lug on electrical
outlets in an older home. Using my three
prong outlet tester, the outlet demonstrated a grounded connection. Not seeing
new conductors in the electrical panel I suspected that something was wrong.
After de-energizing the circuit I discovered this bootleg ground. This act of
de-energizing an electrical circuit is not normally conducted in a home inspection.
The following
are excerpts from the October 2008 ASHI Reporter Issue
Q. Why is a
false ground unsafe at a three-wire (grounded) receptacle outlet?
Answer: The grounding prong of a grounded receptacle outlet should be connected to a separate grounding conductor or grounded raceway system.
Explanation: Sometimes this situation is found when a grounded receptacle is installed in an ungrounded two-wire system. When a false ground (a jumper from the neutral to the ground terminal at an outlet) is made, the grounding prong becomes a parallel path with the neutral. The grounding conductor of the appliance cord is connected to the metal frame of the appliance, which lays out the path from the grounded prong through the cord to the frame. The metal frame becomes a parallel path with the neutral. Any contact between the frame of the appliance and a grounded object can result in current flow. If the contact point is a person, then there is potential for fatal shock.
Answer: The grounding prong of a grounded receptacle outlet should be connected to a separate grounding conductor or grounded raceway system.
Explanation: Sometimes this situation is found when a grounded receptacle is installed in an ungrounded two-wire system. When a false ground (a jumper from the neutral to the ground terminal at an outlet) is made, the grounding prong becomes a parallel path with the neutral. The grounding conductor of the appliance cord is connected to the metal frame of the appliance, which lays out the path from the grounded prong through the cord to the frame. The metal frame becomes a parallel path with the neutral. Any contact between the frame of the appliance and a grounded object can result in current flow. If the contact point is a person, then there is potential for fatal shock.
Q. Why is it
dangerous to use a Nonmetallic-Sheathed cable (NM) grounding conductor as a
neutral?
Answer: Using the grounding conductor as the neutral creates an ungrounded circuit. There is no grounding conductor available for clearing ground faults.
Explanation: Sometimes this is found at retrofit ceiling fan installations or where an outlet has been added at a switch box. Also, it can be found at well pumps and AC disconnects where one leg of a 240-volt circuit is tapped and the grounding conductor is used as a neutral to run a light or 120-volt receptacle. The frame of the fan, yoke of the device and metal box are not grounded (bonded). Just as with the false ground, any contact between these parts and a grounded object will result in current flow. Anyone working on the circuit would not expect neutral current to be flowing on the grounding conductor and could get shocked or electrocuted if he or she disconnected it. In the event of a ground fault on the metallic parts of the connected equipment, there would be no way to clear the fault and the metallic portions of the equipment would become and remain energized, creating a very hazardous condition.
Q. Is it legal to install grounded receptacle outlets on a two wire ungrounded system?
Answer: The National Electrical Code (NEC) allows the installation of grounded receptacles on a two-wire system if a Ground Fault Circuit Interrupter (GFCI) is installed at the beginning of the circuit, either as a breaker or a feed-through receptacle at the first receptacle in the circuit. All receptacle outlets installed downstream must have a label stating that they are GFCI-protected and that there is no equipment ground.
Explanation: A GFCI does not need an equipment ground to function and provide protection. The person using the outlet will be protected, but the equipment will not be grounded. The GFCI will trip if there is an imbalance between the hot and neutral return currents, thereby protecting the circuit.
Answer: Using the grounding conductor as the neutral creates an ungrounded circuit. There is no grounding conductor available for clearing ground faults.
Explanation: Sometimes this is found at retrofit ceiling fan installations or where an outlet has been added at a switch box. Also, it can be found at well pumps and AC disconnects where one leg of a 240-volt circuit is tapped and the grounding conductor is used as a neutral to run a light or 120-volt receptacle. The frame of the fan, yoke of the device and metal box are not grounded (bonded). Just as with the false ground, any contact between these parts and a grounded object will result in current flow. Anyone working on the circuit would not expect neutral current to be flowing on the grounding conductor and could get shocked or electrocuted if he or she disconnected it. In the event of a ground fault on the metallic parts of the connected equipment, there would be no way to clear the fault and the metallic portions of the equipment would become and remain energized, creating a very hazardous condition.
Q. Is it legal to install grounded receptacle outlets on a two wire ungrounded system?
Answer: The National Electrical Code (NEC) allows the installation of grounded receptacles on a two-wire system if a Ground Fault Circuit Interrupter (GFCI) is installed at the beginning of the circuit, either as a breaker or a feed-through receptacle at the first receptacle in the circuit. All receptacle outlets installed downstream must have a label stating that they are GFCI-protected and that there is no equipment ground.
Explanation: A GFCI does not need an equipment ground to function and provide protection. The person using the outlet will be protected, but the equipment will not be grounded. The GFCI will trip if there is an imbalance between the hot and neutral return currents, thereby protecting the circuit.
