UL 429:2013 pdf download – Electrically Operated Valves
UL 429:2013 pdf download – Electrically Operated Valves.
21.3 Class 2 safety valves and Class 2 safety-control circuits
21.3.1 In a Class 2 safety valve and a safely valve incorporating a Class 2 circuit, the spacing distances of parts in the Class 2 circuit parts shall be as indicated in 21.3.2— 21.3.4, if a short circuit between the parts involved may prevent the valve or controlled device from closing as intended.
21.3.2 The spacing between an uninsulated live part and the wall of a metal enclosure, including fittings for the connection of conduit or cable, shall not be less than 118 inch (3.2 mm), A greater spacing may be required if, because of its size, shape, or the material used, the enclosure is not sufficiently rigid to maintain the required spacing.
21.3.3 The spacing between wiring terminals, regardless of polarity, and between a wiring terminal and a dead metal part (including the enclosure) that may be grounded when the valve is installed, shall not be less than 1/4 inch (6.4 mm).
21.3.4 The spacing between uninsulated live parts, regardless of polarity, and between an uninsulated live part and a dead metal part. other than the enclosure, that may be grounded when the valve is Installed shall not be less than 1132 inch (0.8 mm), if the construction of the parts is such that the spacings will be maintained.
21.4 Other than safety valves and safety-control circuits
21.4.1 The spacing between uninsulated live parts of opposite polarity and between such parts and dead metal that may be grounded in service is not specified for parts of circuits classified as Class 2.
22 Alternate Spacing — Clearances and Creepage Distances
22.1 As indicated in 21.1,4. an alternative approach to the spacing requirements specified in 21.2 and
21.3 may be used to evaluate clearances and creepage distances as described in 22.2 — 22.4.
22.2 Clearance between an uninsulated live part and the walls of a metal enclosure, including tthings for conduit or armored cable, shall be as noted in Table 21.1. The clearance shall be determined by physical measurement.
22.3 The clearance and creepage distance at field•wiring tem,inals shall be in accordance with the requirements in 21.1 —21.4.
Exception: If the design of the fieId’wring terminals is such that it will p’eclude the possibilily of reduced spacing due to stray strands or improper wiring installation, clearances and creepage distances at the field-wiring terminal may be evaluated in accordance with the Standard for Insulation Coordination Including Clearances and Creepage Distances for Electrical Equipment UL 840.
22.4 When conducting an evaluation in accordance with the requirements in the Standard for Insulation Coordination Including Clearances and Creepage Distances for Electrical Equipment. UL 840, the following guidelines shall be used:
a) For clearance:
2) The phase.to.ground rated system voltage used in the determination of clearances shaH be the equipment rated supply voltage rounded to the next highe value (In the table for determining clearances for equipment) for all points on the supply side of an isolating transformer or the entire pioduct when no isolating transformer is piovided. The measured clearance distance used In the evaluation of isolated secondary circuitry shall be interpolated when the secondary voltage occurs between voltages ri the supply voltage column;
3) To determine equivalence with current through-air spacing requirements, an impulse test potential having a value as determined in UL 840 shall be applied.
b) For creepage:
1) Any printed-wiring board, which complies with the requirements in the Standard for
Printed-Wiring Boards. UL 796, piovides a Comparative Tracking Index (CTI) of 100,
and when it complies with the requirements for direct support in UL 796. it provides a
CTI of 175;
2) Unless specified elsewhere in this standard, equipment shall be evaiuated for Pollution Degree 3;
3) Printed-wiring boards are evaluated as Pollution Degree 2 when adjacent conductive material is covered by any coating, such as a solder mask, which provides an uninternipted covering over at least one side and the complete distance up to the other side of conductive material.