4.4 Anti-Two Block (A2B) Switch(es)
AT422T cranes are provided with two different configurations of anti-two block switches, i.e.
some having only one switch, and some having two switches. Correct use of the anti-two
block switches must be followed to prevent material damage and serious or even fatal
accidents. The applications under which these switches are used are described below:
a. Primary Anti-Two Block Switch (Mandatory For All Operations)
The Primary (i.e. cab-side) anti-two block switch is used in ALL applications (expect
operation of the Berminghammer pile driver system). For single-hoist working (i.e.
normal lifting operations), always use this switch, with the weight and chain installed
correctly around the main hoist cable (if the crane also has a Secondary (i.e. right-side)
anti-two block switch installed, the secondary switch is used only in operation of the
Linkbelt pile driver system).
For single-hoist working with cranes on which a secondary switch is also installed, the
weight and chain is to be removed from the secondary switch and the by-pass flag
installed. Failure to do this will result in the primary switch being non-functional.
However, if the crane is being used for pile-driving operations, see Paragraph b. below.
b. Secondary Anti-Two Block Switch (Pile Driving Applications Only)
Operation of the Linkbelt pile driver system requires the use of a Secondary (i.e. right-
side) anti-two block switch, as well as the Primary Switch described in Paragraph a.
above. The Secondary Switch must be used with the by-pass flag removed and the
weight and chain attached around the auxiliary hoist cable.
ONLY during operation of the Linkbelt pile driver system is the Secondary Switch used,
because Pile-Driving is the only application in which it is permissible to deploy and
operate both hoists simultaneously.
Operation of the Berminghammer pile driver system uses an impact hammer stop,
installed near the top of the lead tower, to physically prevent the impact hammer from
colliding with the boom nose by limiting its vertical travel. This replaces the anti-two
block function of the Load Moment Indicator (LMI) system.
The PRIMARY (i.e. cab-side) anti-two block switch must be used in ALL
Operations except operation of the Berminghammer pile driver system.
Simultaneous two-hoist working is prohibited in all circumstances other than
operation of the Linkbelt Pile Driver System.