Eaton Cooper Power series four-position ring mount loadbreak switch.

 Three-phase, 630 A/400 A/200 A, 50/60 Hz, Ring mount, T-Blade, Cast brass, hotstick operable, Break before make, Individually boxed

Design/production tests The four-position switch has been tested to meet the sequential test requirements described by IEEE Std C37.74™-2003 standard. Tests are also conducted on production switches in accordance with Eaton requirements. • Physical inspection • Turn tested (on/off/on) • Operation torque verification • Resistance testing.

What the four positions mean

A four-position ring-main switch is not a four-pole device. The four positions describe the operating states of a ring network node: both ways closed (normal ring operation), one way closed with the other open (radial feed from either side), and both ways open (isolated, with the earth position available on the cable side). The sequence is break-before-make throughout, which is what allows the switch to be operated under load without an arc reaching the operator.

Four-position switching states

Reading the ratings

The LS4RH3T16B is listed at 630 A, 400 A and 200 A for three-phase service at 50/60 Hz. The three figures correspond to the current rating of the switch body, the rating of the associated cable terminations, and the rating that applies when the switch is used with a reducing tap. Selection follows the lowest of the three that applies to the installed cable, not the highest number on the nameplate.

The T-blade contact arrangement and cast brass body are what give the switch its duty rating. Cast brass holds its shape after repeated fault duty better than a formed sheet contact, which is why the same body can carry a 630 A rating at the distribution voltages these switches are used on. The hotstick-operable handle means the switch can be operated from outside the enclosure without opening the padlockable door.

What the type tests actually confirm

The switch is tested to the sequential test requirements of IEEE Std C37.74. That standard does not test a single operation in isolation; it applies a sequence of make, carry and break operations to the same specimen, because a switch that passes one break may not pass the fifth. Production units are additionally checked for physical condition, a turn test through on-off-on, and operating torque, so a switch that has been sitting in storage can be verified before it is installed.

Production checks applied to every switch