operated from a location where the operator is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be ar- ranged to be locked in the open position. Metal-enclosed
switches shall be operable from outside the enclosure.
(5) Stored Energy for Opening. The stored-energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch.
(6) Supply Terminals. The supply terminals of fused in- terrupter switches shall be installed at the top of the switch enclosure, or, if the terminals are located elsewhere, the equipment shall have barriers installed so as to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts.
490.22 Isolating Means. Means shall be provided to com- pletely isolate an item of equipment. The use of isolating switches shall not be required where there are other ways of de-energizing the equipment for inspection and repairs, such as draw-out-type metal-enclosed switchgear units and removable truck panels.
Isolating switches not interlocked with an approved circuit-interrupting device shall be provided with a sign warning against opening them under load.
A fuseholder and fuse, designed for the purpose, shall be permitted as an isolating switch.
Table 490.24 Minimum Clearance of Live Parts
Minimum Clearance of Live Parts
Nominal Impulse Withstand,
Phase-to-Phase Phase-to-Ground
Voltage B.I.L (kV) Indoors Outdoors Indoors Outdoors
Rating -
(kV) Indoors Outdoors mm in. nun in. mm in. mm in.
2.4-4.16 60 95 115 4.5 180 7 80 3.0 155 6
7.2 75 95 140 5.5 180 7 105 4.0 155 6
13.8 95 110 195 7.5 305 12 130 5.0 180 7
14.4 110 230 9.0
23 125 150 270 10.5
34.5 150 150 320 12.5
200 200 460 18.0 460 18 335 13.0 335 13
46 — 200 — — 460 18 — — 335 13
— 250 — — 535 21 — — 435 17
69 — 250 — — 535 21 — — 435 17
— 350 — — 790 31 — — 635 25
115 — 550 — — 1350 53 — — 1070 42
138 — 550 — — 1350 53 — — 1070 42
— 650 — — 1605 63 — — 1270 50
161 — 650 — — 1605 63 — — 1270 50
— 750 — — 1830 72 — — 1475 58
230 — 750 — — 1830 72 — — 1475 58
— 900 — — 2265 89 — — 1805 71
— 1050 — — 2670 105 — — 2110 83
Note: The values given are the minimum clearance for rigid parts and bare conductors under favorable service conditions. They shall be increased for conductor movement or under unfavorable service conditions or wherever space limitations permit. The selection of the associated impulse withstand voltage for a particular system voltage is determined by the characteristics of the surge protective equipment.