Appendix C Ground Hook Safety

Engineering Division Electronic Equipment Build Standard Appendix C, Ground Hook Safety
Revision 2

C.1 Introduction
C.1.1 Scope
This policy is written to cover the use of ground hooks on R&D equipment only. A ground hook system places a grounded conductor at the end of the rod between the operator and the electrical hazard. The low impedance ground hook system is not a live line tool and there will not be a voltage potential at the end of the ground hook rod. The integrity of the system will be measured by the performance of the grounding cable. High Z ground hooks may have a voltage potential at the end of the rod and will be held to a stricter standard than low Z ground hooks. High Z ground hooks are used in equipment with >1000 joules energy storage to limit discharge current.

C.1.2 Work Practices
C.1.2.1 Before use of ground hooks LOTO shall be applied. A LOTO procedure shall be written for every ground hook application.
C.1.2.2 Only LBNL QEWs shall apply ground hooks
C.1.2.3 High Energy Discharge
a) A properly installed ground hook must first be connected to the high Z discharge point and then to a low Z discharge point (less than 0.1 ohms) that is identified by a yellow circular marker.
b) Written procedures shall include the discharge time for the circuit and when it is safe to apply the low Z ground hook(s).
c) If there is not a designated high Z discharge point then a high Z ground hook may be used on a low Z discharge point. Limiting the discharge current to 500A also applies to the use of a high Z ground hook.
i) Alternatively a QEW may perform measurements and then apply a ground hook to equipment after it has discharged to <5J and <50V. C.1.2.4 Refer to the Electrical Safety Manual (found in PUB 3000, Chapter 8, Electrical Safety Program) for additional work practices.

C.1.3 Definitions
Z: The letter Z is used as shorthand for impedance. In this document, impedance is equivalent to resistance and is measured in ohms.

Engineering Division Electronic Equipment Build Standard Appendix C, Ground Hook Safety
Revision 2
Low Z Ground Hook: A ground hook with a resistance (cable and ground connection) equal to or less than 0.1 ohms.
High Z Ground Hook: A ground hook with a series resistor to limit the discharge current. The required resistance value should be determined by an electrical engineer or the manufacturer of the equipment.
Hard Ground: A low Z connection measured at less than 0.1 ohms Soft Ground: A high Z connection through a resistance to limit the discharge current