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 39.67 - Attachment of ground conductor

(a) Direct current distributing systems. The neutral of three-wire direct current systems shall be grounded at one or more supply stations, but not at individual services nor within buildings served. One side of a two-wire direct current system may be grounded, but at one station only. In three-wire systems the neutrals entering any junction box should be bonded together, but the box should not be specially grounded. In two-wire systems the grounded side of the circuit should be insulated from ground except at the station ground connection.

(b) Alternating current distribution systems. All secondary distribution systems shall be grounded at the building services or near the transformer (or transformers) either by direct ground connection or by the use of a system ground wire to which are connected the grounded conductors of many secondary mains and which is itself effectually grounded at intervals which fulfill, for any secondary utilizing the system ground wire, the resistance and current carrying requirements of § 39.69 (relating to ground resistance). Single-phase, three-wire distribution systems shall be grounded at the neutral conductor. Two-wire, single-phase systems shall be grounded at the neutral point or on either conductor. Two-wire, single-phase and two or three phase systems shall, in general, be grounded at that point of the system which brings about the lowest voltage from ground of unguarded current carrying parts of connected devices and also permits most convenient grounding. If one phase of a two or three phase system is used for lighting, that phase should be grounded and at the neutral conductor, if one is used. In the absence of direct grounds at all building services, ground connections shall be made to the grounded neutral or other grounded conductor of a secondary system supplying more than one utilization equipment, at intervals that will fulfill the resistance and current-carrying requirements of § 39.69. If the secondaries of transformers are supplying a common set of mains, the fuses shall be installed only at such points as will not cause the loss of the ground connections after the fuses in the transformer circuits or mains have been blown. Multiple grounds are preferable in all cases, because of the assurance provided against loss of the protection afforded by the chance disconnection of any ground connection. Grounds other than the single ground connection at the building service shall not be made to alternating current secondaries within buildings. Reference should be made to § 39.66 (relating to nature of ground connection).

(c) Lightning arresters. The connection to a lightning arrester shall be at such a point that its ground conductor is as short and straight as practicable. Ground conductors for lightning arresters shall not pass through iron or steel conduits unless electrically connected to both ends of such conduits.

(d) Equipment and wire runways. The point at which the ground conductor is attached to equipment or wire runways shall, if practicable, be readily accessible.