Brian Erga, CUSP
The minimum approach distance (MAD) is the closest distance a worker is permitted to approach an exposed energized conductor. When we think of MADs, we normally think of qualified electrical workers, and this discussion will cover what a MAD is, how it is developed, how it is to be applied and how it is often misapplied. There is also a second MAD for nonqualified electrical workers known as the 10-foot rule. Nonqualified electrical workers, subject to federal OSHA regulations, must remain a minimum of 10 feet away from any exposed energized conductors or equipment up to 50 kV, plus an additional 4 inches for every 10 kV above 50 kV.
The changes to Section 444.D, “Employee’s protective grounds,” and Section 445.A & B, “Protective grounds,” in the National Electrical Safety Code (NESC) 2012 were approved by NESC Subcommittee 8 after reviewing change proposals (CP) 3050 and 3051, respectively.
In prior iP articles we have discussed effective methods of applying personal protective grounding to both overhead and underground electric utility systems. Proper application of the equipotential grounding method will ensure worker protection during an accidental re-energization or backfeed of the electric utility system. But what does your personal protective grounding practice do to reduce the hazards of induction? Is it possible your personal protective grounding practice is actually increasing the effects of induction? Let’s look at what we call induction, or what electrical engineers refer to as electric field induction and magnetic field induction.
This article is a continuation of the discussion published in the August 2011 issue of Incident Prevention, which covered personal protective grounding of overhead distribution and transmission systems. As with overhead grounding, there are three industry-accepted work methods that allow qualified employees to work with de-energized underground distribution cables and equipment. They are:
• Personal protective grounding, also known as equipotential grounding or EPZ
Personal protective grounding of overhead distribution and transmission lines and equipment is one of three industry-accepted work methods that allow qualified employees to work with de-energized lines and equipment. The other two methods are insulation and isolation. Following are descriptions of all three.
The wide variety of cover-up equipment currently available to the qualified electrical worker allows energized live-line work methods to be performed safety and productively. Cover-up equipment comes in several styles and voltage ratings for use in many different live-line applications. Flexible line hose, plastic guards and covers, rubber insulating blankets and sheathing allow the qualified electrical worker to install temporary insulation between themselves and energized conductors and devices.
OSHA 1910.269(m) – “De-energizing Lines and Equipment for Employee Protection” – covers de-energizing a section of an electric utility’s transmission and distribution (T&D) system, and the transfer of that section’s control from the system operator to the employee in charge. What does that mean? Simply put, paragraph (m) covers your company’s required written T&D switching and clearance procedure.
The current state of FR clothing for qualified electrical workers seems to be still greatly misunderstood. However, the current FR clothing requirement is very straightforward once you decide what side of the fence you’re on – the National Electric Safety Code (NESC) or the National Fire Protection Association (NFPA).
Many questions arise in the minds of electrical workers when the discussion turns to safely operating high-voltage, gang-operated disconnect switches while standing on the ground. These questions often include:
• Should the steel operating rod connecting the switch handle to the switch have an insulator (insulated insert)?
• Should the switch handle and operating rod be grounded to a ground rod?
• Should I wear rated rubber gloves?
• Should I be standing on a ground mat?
A tree falls through a 7.2 kV, single-phase, overhead lateral, taking the tree, the phase conductor and common neutral to the ground. The electric utility sends a crew of qualified electrical workers to the site to re-install the overhead conductors.
The crew first goes to the upstream protective device (the cutout) protecting the lateral; let’s say it is Switch #1234. The crew will most likely find the cutout door open and the fuse blown. If the utility has a system operator on duty, the designated employee (normally the lead worker of the crew) will request permission from the system operator to open the upstream cutout, if it is not already open, and request a clearance from Switch #1234 to the end of the line.