Simpson 270 Series - Page 12

Introduction
1.2 DESCRIPTION
1.2.1 Overload Protection
1.2.2 No single protective device nor even a combination of
devices as found in the 270 can fully protect a multi-purpose instru-
ment under all overload conditions. Overloads of such severity as to
damage the Instrument despite all the built-in protection provided
are possible when the Instrument is misused, The fuse/varistor com-
bination in the 270 has been designed to afford maximum instru-
ment protection under foreseeable overload conditions which might
occur within the measuring capabilities of the Instrument; however,
the operator must exercise care to avoid severe Overloads, par-
ticularly when working in high voltage circuits.
a.
1-2
Fuses: Basic overload protection is provided by a small inexpen-
sive and easily obtainable 3 AG type, 1 ampere, quick-blow
fuse. This fuse is rated to interrupt circuit voltages up to 250
volts. A supplemental high energy fuse is provided for addi-
tional protection from severe overloads. This fuse is the
Bussman Type BBS 2A 600 V and has an interruption capacity
of 10,000 amps AC. The Littelfuse Type BLS 2A 600 V with an
interrupt capacity of 100,000 amps AC may also be used.
. For maximum protection it is important to replace the 1A
fuse with the Littelfuse type 312001 only. This will allow the
combination of 1А and 2A fuse to give maximum
protection to the unit and the user under overload conditions
which may occur within the measuring capability of the VOM.
. If the Instrument fails to indicate, the 1 Amp or the 2 Amp
fuse may be burned out. (Refer to paragraph 5.4 for fuse
replacement.) A 1 Amp spare fuse is furnished with each