Pennsylvania Code › Title 34 - LABOR AND INDUSTRY › Part I - Department of Labor and Industry › Chapter 39 - SAFETY STANDARDS-GENERAL › Subchapter B - ELECTRIC SAFETY › METHODS OF PROTECTIVE GROUNDING › Section 39.69 - Ground resistance

Current through Register Vol. 54, No. 28, July 13, 2024
(a)
Limits.
It is recommended that the combined resistance of the
					 ground wires and connections of any grounded circuit, equipment or lightning
					 arrester should not exceed the values given below, if grounded connections made
					 according to §
											39.66 (relating to nature of
					 ground connection) will sufficiently limit the resistance. It will frequently
					 be impracticable with artificial grounds to obtain resistances in dry or other
					 high resistance soils as low as the values given below for ordinary soils. In
					 such cases two grounds shall be used as defined in §
											39.68 (relating to methods of
					 ground connection), and no requirement shall be made as to resistance.
					 Reference should also be made to §
											39.66. The current stated opposite
					 the different resistances in the table is either the current capacity of a
					 circuit from which leakage may occur to the ground circuit, or the continuous
					 current capacity to which the grounded equipment or arrester is limited by
					 design or by automatic cutouts. If the secondary is exposed only through
					 transformer windings, this current capacity shall be that of the primary fuse
					 of the transformer. If the secondary is exposed by the conductors of
					 conflicting or crossing high voltage circuits, the current capacities shall be
					 those of the automatic cutouts in such circuits. The product of the
					 corresponding numbers in the first and second columns shall never be greater
					 than 150, that is, the potential difference due to the stated current is never
					 greater than 150 volts, if connections are made to water pipes. If more than
					 one ground is made on the same circuit, equipment or arrester, in the same
					 vicinity, all such grounds shall be considered collectively in respect to
					 meeting the requirements of this section:
Amperes
Water pipe grounds (in
								  ohms)
Artificial grounds ordinary soils (in
								  ohms)
less than 10
15
1025
10 to 25
6
25
25 and above
less than 6
25
(b)
Checking.
The resistance
					 of station grounds shall be checked when made. With artificial grounds this
					 check may be made by measuring the voltage between the grounded point of the
					 circuit, or the grounded frame of the equipment or the grounded point of the
					 lightning arrester and an auxiliary metal reference rod or pipe driven into the
					 ground, while a measured current is flowing through the ground connection and
					 any exposed metal piping or other artificial ground in the vicinity, but not
					 within 20 feet. If the station ground is to water piping, the check may be made
					 with current flowing through the water piping and some independent piping
					 system or artificial ground in the vicinity, but not within 20 feet. The
					 auxiliary road or pipe shall be at least ten feet from any artificial ground or
					 piping systems through which the measured current is made to flow. All ground
					 connections shall be inspected periodically. Ground connections on distribution
					 circuits shall, when installed, be tested for resistance unless multiple
					 grounding to water piping systems is used.
This section cited in 34 Pa. Code §
													39.61 (relating to applicability);
						  34 Pa. Code §
													39.62 (relating to scope); 34 Pa.
						  Code §
													39.63 (relating to modification or
						  waiver of provisions); 34 Pa. Code §
													39.65 (relating to ground
						  conductor); 34 Pa. Code §
													39.66 (relating to nature of
						  ground connection); 34 Pa. Code §
													39.67 (relating to attachment of
						  ground conductor); 34 Pa. Code §
													39.103 (relating to protective
						  grounding); 34 Pa. Code §
													39.183 (relating to ground wires);
						  34 Pa. Code §
													39.197 (relating to grounding); 34
						  Pa. Code §
													39.219 (relating to grounding or
						  isolating service conduits); 34 Pa. Code §
													39.292 (relating to grounding
						  noncurrent-carrying parts); and 34 Pa. Code §
													39.304 (relating to grounding of
						  arresters for signaling systems).