Equipotential Grounding

EquipotentialGrounding

Jim McGrailCity of NapervilleSafety &Training Instructor

Engineering & Operations Technical ConferenceApril 13-18,2007

Introduction

• Definition - Equipotential Grounding

• Regulatory Agencies

• Some benefits of Equipotential Grounding

• Other considerations…

What is equipotential ?

An identical state of electrical potential for two or more items.

For the purposes of protective grounding a near identical state of electrical potential-*

*IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003

OSHA says…

“General.” For the employee to work lines or equipment deenergized, the lines or equipment shall be deenergized under the provisions of paragraph (m) of this section and shall be grounded as specified in paragraphs (n) (3) through (n)(9) of this section.*

*OSHA 1910.269(n)(2)

OSHA - 1910.269(n)(3) continued

“Equipotential zone.” Temporary protective grounds shall be arraigned in such a manner as to prevent each employee from being exposed to hazardous differences in electrical potential.*

*OSHA 1910.269(n)(2)

National Electrical Safety Code C2-2007

444D Employee’s protective grounds

…”Grounds shall be placed at each side of the work location and as close as practical to the work location ,or a worksite ground shall be placed at the work location.”

IEEE Std.1048-2003

6.2.4 Worksite versus bracket grounding sets

In general ,the use of worksite grounding sets will result in the minimum obtainable impedance path in parallel with the workers body, and thus , the minimum body intercept voltage for the worker.

APPA Safety Manual Rev.13,2004

615 Grounding—General (f) Grounds shall be placed between

work location and all sources of energy and as close as practicable to the work location ,or grounds shall be placed at the work location…Temporary protective grounds shall be placed at equipotential zones and arranged in a manner to prevent exposure to hazardous differences in electrical potential.

APPA safety manual - continued

616 Equal Potential Grounding

(f) When it is not practical to use single point grounding at the pole where work is to be performed ,such as when wires are down ,grounds shall be installed on both sides of the work location but not further than adjacent structures.

Definitions -

Bracket Grounding: A grounding method where temporary ground sets are installed on both sides of the worksite. Syn. adjacent structure grounding.

IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003

Definitions - continued

Worksite grounds: A technique where either the ground set is installed at the structure where the work is to be performed. Syn. personal ground; working ground; ground stick; personal protective ground.*

IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003

Reasons For Grounding -

• Circuit is accidentally energized from source

• Energized from another circuit

(Top circuit contacts lower circuit)

• Induction

• Lightning Strikes

Unintended Induced Current Loop

Energized 138 Kv.

12.7 Kv

NeutralBracket Grounds

Source Circuit

Induced circuit

Equal Potential Grounding -per “APPA Safety Manual”

a) A chain binder ,with provisions for attaching a personal protective ground, shall be tightened around the pole at a position below where the lineman place his feet

Equal Potential Grounding -per “APPA Safety Manual”

b) A personal protective ground shall be attached to the chain binder and extended to the system neutral. If the neutral is not present or cannot be approached safely ,refer to Paragraphs 615-h and 615-I for alternate grounding

Equal Potential Grounding -per “APPA Safety Manual”

c) Personal protective grounds shall be extended from the chain binder to each phase conductor or from the chain binder to a single phase, and from that phase to the other phases.

Equal Potential Grounding -per “APPA Safety Manual”

d) When work is completed ,the personal protective grounds shall be removed in reverse order of installation.

Equal Potential Grounding -per “APPA Safety Manual”

e) When a circuit is to be opened (e.g., opening jumpers at a junction pole or cutting slack), a temporary jumper shall be installed across the open point.

Other Considerations

Start with fundamentals…

1. Verify equipment is de-energized

2. Grounding equipment is in good condition (proper size and style)

3. Install and remove in correct order

4. Make sure connection points are clean and tight

Other Considerations - continued

Ground personnel should be aware if there is fault current on the system a possibility for step and touch potential could be present at the base of the structure.

Conclusion:

OSHA 1910.269(n)(3) Refers to establishing a “Equipotential zone”

IEEE Std.1048-2003 talks about worksite grounding and the minimum body intercept voltage for the worker.

APPA Safety Manual also supports the use of Equal potential grounding.

Resources

OSHA 29 CFR 1910.269

IEEE Guide for Protective Grounding of Power lines IEEE STD 1048-2003

APPA Safety Manual

National Electrical Safety Code C2-2007

“Why Single- Point Grounding Works” by Jim Vaughn, iP Volume 2 Issue 3 May/June 2005