TELEPHONE AND OTHER SIGNAL APPARATUS ON CIRCUITS
EXPOSED BY SUPPLY LINES
§ 39.301. Guarding noncurrent-carrying parts.
(a) If telephone or other signal apparatus, not included under subsection (b) of this section, which is necessarily handled by persons is permanently connected, except for portable telephones, to overhead signal circuits exposed by supply lines over 400 volts to ground, provision shall be made by one of the following methods against shock to persons handling apparatus:
(1) The use of suitable protective devices, including fuses and arresters.
(2) The grounding of exposed noncurrent-carrying metal parts and the suitable guarding of ungrounded current-carrying parts. Reference should also be made to § 39.302 (relating to guarding current-carrying parts).
(3) The arrangement of apparatus in such a way that persons using it will be obliged to stand on a suitably insulated platform, in a suitably insulated booth or on other insulating surfaces. This paragraph shall apply where apparatus is accessible to authorized persons only.
(4) The arrangement of apparatus on signal circuits exposed to supply lines of more than 750 volts to ground as to have no exposed current-carrying parts exceeding two square inches in area with which a person is liable to come in contact and the use of suitable protective devices, including fuses and arresters or other means.
(b) The signaling devices as fire and police alarm boxes and telegraph test boxes, if connected to overhead signal circuits exposed by supply lines over 400 volts to ground, should have the accessible noncurrent-carrying metal parts permanently grounded whenever the character of service gives valid objection to the use of arresters or transformers on the signal circuit. Police alarm boxes if connected to overhead police alarm circuits should usually be protectd by arresters operating at 400 volts to ground, placed in the connecting leads outside the box. Fire alarm boxes connected to overhead circuits, if not protected by arresters, should be provided with suitable insulating material between the circuit within and the exposed frame and operating hook, this insulation to be capable of withstanding the highest voltage of the supply circuits to which the fire-alarm circuit is exposed up to 7,500 volts.
Cross References This section cited in 34 Pa. Code § 39.192 (relating to scope).
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