Single-Pole Switching; Restrictions On Overhead And Underground Use - S&C Loadbuster Instruction Sheet

Proper Application

Single-Pole Switching

Restrictions on
Overhead and
Underground Use
4 S&C Instruction Sheet 811-505
In single-pole switching of ungrounded-primary three-phase transformers or banks (or
single-phase transform ers connected line to line), circuit connections or parameters
may, in some cases, produce excessive overvoltages. In particular, for the following
applications above 22 kV, single-pole switching by any means—including with the use
of the Load buster tool—should be performed only under the conditions stated in italics:
• Switching unloaded or lightly loaded delta-connected or ungrounded-primary wye-wye
connected three-phase transformers or banks (or line-to-line connected single-phase
transformers), rated 150 kVA or less three-phase, or 50 kVA or less single-phase—
or of any kVA rating when combined with unloaded cables or lines—where the
maximum system operating voltage exceeds 22 kV. (Single-pole switching should be
per formed only if each phase is carrying 5% load or more, or if the transformer or
bank is temporarily grounded at the primary neutral during switching.)
• Switching loaded or unloaded ungrounded-primary wye-delta connected three-phase
transformers or banks—alone or combined with unloaded cables or lines—where
maximum system operating voltage exceeds 22 kV. (Single-pole switching should be
per formed only if each phase is carrying 5% load or more and if the lighting-load
phase is always switched open rst (or switched closed last), or if the trans former
or bank is temporarily grounded at the pri mary neutral during switching.)
The Loadbuster tool must be used only with disconnects, cutouts, power fuses, fuse
limiters, or pad-mounted gear that meet S&C's applicable minimum construction speci ca-
tions found in the latest version of the following publication:
DATA BULLETIN 811-60:
Loadbuster®— Minimum Construction Speci ca tions for
The S&C Loadbreak Tool Disconnects, Cutouts, and Power Fuses
Outdoor Distribution Qualifying for Use with the Loadbuster
(14.4 kV through 34.5 kV) Tool
Loadbuster tool catalog number 5400R3, rated 25/34.5 kV, must not be used with
metal-enclosed switchgear, metal-enclosed switches or fuses, or pad-mounted
gear, of any make.
Although the interrupting ratings of Loadbuster tool catalog number 5400R3, rated
25/34.5 kV, are equally applica ble at lower voltages, the tool must not be used with the
following devices because the fuse tube or blade travel of such devices is too short to
accommodate the Load buster tool's operating stroke:
• Cutouts, power fuses, or fuse limiters of any make, rated 110 kV BIL or less
• Disconnects, cutouts, power fuses, or fuse limiters, of any make rated 7.2/14.4 kV,
7.8/13.8 kV, 8.25 kV, or less
• Disconnects, of any make rated 125 kV BIL or less
• Station-style Type XS Fuse Cutouts, catalog number 189131 (with or without catalog
number sup plements)
Loadbuster tools should not be used for any applications where maximum system
operating voltage exceeds the Loadbuster tool's maximum voltage rating.
NOTICE