UL-2748:2017 pdf free download – STANDARD FOR SAFETY Arcing Fault Quenching Equipment.
9 Grounding
9.1 There shall be provision for grounding all non-current carrying metal parts of the equipment. In addition, the following parts shall be grounded:
a) The metal case of a frame or instrument transformer;
b) The metal case of an instrument, meter or relay: or
c) The secondary circuit of a current or voltage transformer.
9.2 The case of an instrument, relay, meter, or similar device, if mounted on a grounded metal surface
and secured thereto by means of metal screws, is considered to be grounded.
10 Control and Secondary Wiring
10.1 An insulated conductor provided as part of a control circuit or secondary wiring shall be rated for the particular application and shall have an ampacity not less than the continuous current rating of the circuit in which it is connected. Where loads are of an intermittent nature, such as in trip and closing circuits, conductors shall be sized to provide their intended function with respect to voltage drop and mechanical strength.
11 Creepage and Clearance Distance
11.1 Section 12, Spacings, of the Standard for Metal-Enclosed Low-Voltage Power Circuit Breaker Switchgear, UL 1558 applies to the power circuits of low-voltage quenching equipment, other than as noted in 11.3.
11.2 No minimum creepage or clearance distances are specified for medium-voltage circuits in quenching equipment, other than distances sufficient to meet the dielectric requirements specified in this standard for the voltage rating of the equipment.
11.3 No minimum creepage or clearance distances are specified across the contacts of the quenching means when these contacts are contained within a pollution degree 2 microenvironment, and the quenching equipment meets the dielectric test requirements of this standard with the quenching device in the open position.
11.4 Creepage and clearance distances within low-voltage control circuits of quenching devices shall comply with the creepage and clearance distance requirements of the Standard for Industrial Control Equipment, UL 508 or the Standard for Low-Voltage Switchgear and Controlgear — Part 1: General rules, UL 60947-1. Creepage and clearance distances between low-voltage control circuits and medium-voltage circuits shall be no smaller than the creepage and clearance distances required from the medium-voltage circuit to grounded metal, and shall also be sufficient to meet the dielectric requirements specified in this standard for the maximum voltage rating of the equipment, with the control circuits grounded during testing.
11 .5 The pollution degree 2 microenvironment specified in 11.3 need not be maintained during or after the quenching of an arcing fault if servicing of the quenching means is required after an arcing fault event, and the quenching means is marked in accordance with 21.5.
11 .6 For printed wiring boards, the creepage and clearance distances shall comply with requirements of the Standard for Insulation Coordination Including Clearance and Creepage Distances for Electrical Equipment, UL 840. For the purpose of determining required creepage and clearance distances, quenching devices shall be considered to be located within circuits of overvoltage category 3. All quenching devices are considered to be installed in pollution degree 3 environments, except for portions of the device located in a pollution degree 2 microenvironment.