1.) Section 210.8
2.) New text
3.) Exception for A, B, and C above.
(a) Where a stationary appliance or machine is incompatible with ground-fault circuit-interrupter because of normal leakage current, continuous monitoring of the equipment grounding conductor shall be used. The ground check conductor shall connect to the frame of appliance or machine using a silicon diode rated at least 1 ampere and 1,000 volts. As close to the branch circuit cupply as possible the ground check conductor shall be connected to a control relay that looks for the presence of this diode and the control relay shall operate a power relay that connects and disconnects all of the current carrying conductors. The control relay shall lock out the power if the ground check conductor ground faults. The control relay shall be permitted to be of the type that is used in mines for this purpose. The power relay shall be electrically held and shall be permitted to be separately installed or built into the control relay package. Any connecting cord shall not be allowed to lie on the floor or ground.
(b) For mobile loads that run on a fixed track such as trolley hoists and bridge cranes continuous monitoring of the equipment ground as specified above shall be used.
(c) For all other mobile loads or for any load for which which additional protection is desired there shall be 4 protective components:
(c)(1) Continuous monitoring of the equipment ground as specified above.
(c)(2) Ground fault protection of equipment set to trip at up to 50% of the current available from the grounding impedance for both the branch circuit and feeder. The ground fault protection shall be permitted to be a part of the control relay that monitors the equipment ground. The branch circuit and feeder ground fault protection shall deliberately have no cooordination so that a branch circuit ground fault will trip both the branch circuit and feeder ground fault protection.
(c)(3) All conductors including the ground check conductor that are in any cord shall have individual shielding regardless of voltage. The shield strands shall be permitted to be used as the equipment grounding conductor.
(c)(4) The power source shall be impedance grounded using a resistor that is sized to pass 250 milliamperes to 1 ampere. The resistor shall be rated for continuous duty at the highest possible current and voltage. Impedance grounding of single phase or 3-phase power as low as 120 volts phase to phase shall be permitted. For single phase sources the grounding resistor shall be connected to the center tap of the transformer secondary. For 3-phase sources the transformers secondary shall be wye connected and the resistor shall be connected to the secondary neutral. The neutral shall not be used to supply any load other than a ground fault detector. All transformers shall have a grounded shield between primary and secondary. For 120 volts 2-wire single phase systems 2-pole circuit breakers and ground fault protectors rated 120/240 volts shall be permitted.
4.) A lot of existing refrigerators and vending machines have too much leakage current and this leakage current is not any kind of hazard as long as the machine is grounded. For instance, a 480 volt motor **WILL** have a nasty tingle voltage if not grounded.
In some instances such as engine block heaters on trucks excessive leakage current is unavoidable. At 55 miles per hour it is impossible to keep salt water out of the wiring. This is not a hazard as long as the truck is grounded when plugged in.
British coal mines have not had an electrocution since 1964 and they have 1,100 volt and 3,300 volt extension cords. They must be doing something right.
2.) New text
3.) Exception for A, B, and C above.
(a) Where a stationary appliance or machine is incompatible with ground-fault circuit-interrupter because of normal leakage current, continuous monitoring of the equipment grounding conductor shall be used. The ground check conductor shall connect to the frame of appliance or machine using a silicon diode rated at least 1 ampere and 1,000 volts. As close to the branch circuit cupply as possible the ground check conductor shall be connected to a control relay that looks for the presence of this diode and the control relay shall operate a power relay that connects and disconnects all of the current carrying conductors. The control relay shall lock out the power if the ground check conductor ground faults. The control relay shall be permitted to be of the type that is used in mines for this purpose. The power relay shall be electrically held and shall be permitted to be separately installed or built into the control relay package. Any connecting cord shall not be allowed to lie on the floor or ground.
(b) For mobile loads that run on a fixed track such as trolley hoists and bridge cranes continuous monitoring of the equipment ground as specified above shall be used.
(c) For all other mobile loads or for any load for which which additional protection is desired there shall be 4 protective components:
(c)(1) Continuous monitoring of the equipment ground as specified above.
(c)(2) Ground fault protection of equipment set to trip at up to 50% of the current available from the grounding impedance for both the branch circuit and feeder. The ground fault protection shall be permitted to be a part of the control relay that monitors the equipment ground. The branch circuit and feeder ground fault protection shall deliberately have no cooordination so that a branch circuit ground fault will trip both the branch circuit and feeder ground fault protection.
(c)(3) All conductors including the ground check conductor that are in any cord shall have individual shielding regardless of voltage. The shield strands shall be permitted to be used as the equipment grounding conductor.
(c)(4) The power source shall be impedance grounded using a resistor that is sized to pass 250 milliamperes to 1 ampere. The resistor shall be rated for continuous duty at the highest possible current and voltage. Impedance grounding of single phase or 3-phase power as low as 120 volts phase to phase shall be permitted. For single phase sources the grounding resistor shall be connected to the center tap of the transformer secondary. For 3-phase sources the transformers secondary shall be wye connected and the resistor shall be connected to the secondary neutral. The neutral shall not be used to supply any load other than a ground fault detector. All transformers shall have a grounded shield between primary and secondary. For 120 volts 2-wire single phase systems 2-pole circuit breakers and ground fault protectors rated 120/240 volts shall be permitted.
4.) A lot of existing refrigerators and vending machines have too much leakage current and this leakage current is not any kind of hazard as long as the machine is grounded. For instance, a 480 volt motor **WILL** have a nasty tingle voltage if not grounded.
In some instances such as engine block heaters on trucks excessive leakage current is unavoidable. At 55 miles per hour it is impossible to keep salt water out of the wiring. This is not a hazard as long as the truck is grounded when plugged in.
British coal mines have not had an electrocution since 1964 and they have 1,100 volt and 3,300 volt extension cords. They must be doing something right.
