From: Marne and Associates Inc. []
Sent: Thursday, August 21, 2008 11:39 AM
To: Lazarski, Ann T
Subject: Marne and Associates NESC and OSHA Newsletter - August 20, 2008
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Marne and Associates, Inc.
Experts in Electrical Code

NESC® and OSHA Newsletter August 20, 2008

Marne and Associates NESC and OSHA Newsletter addresses issues relevant to power and communication utilities.

In This Issue:

Question #1:

Is it true that a TIA is changing the Arc Rated Clothing tables in the NESC?

A Tentative Interim Amendment (TIA) has been proposed to make changes to NESC Table 410-2 and is scheduled for vote on September 5. The TIA could pass as written, be delayed for further comments, or be rejected. We will keep you updated via this newsletter when we find out the TIA status. When approved, a TIA is associated with the current edition of the NESC and is considered a change proposal for the next edition.

Fig. 1 shows an example of arc rated clothing. For more information please consider our live web seminar which is offered once a month from August to December on the subject of Arc Flash Hazards and Arc Rated Clothing.

Fig. 1
Photo Courtesy Salisbury
Fig. 1 - Jacket Rated for 11 cal/cm2

Question #2:

I heard that 40 inches was the required clearance from communication attachments to the power above, but the power utility is telling me I need more than 40 inches because the power line operates at 24.9kV. Doesn't the NESC require 40 inches?

The communication worker safety zone does have a "base" value of 40 inches; however, this value is dependant on the voltage involved. NESC Tables 235-5 and 238-1 require an additional 0.4 inches to be added for every kV above 8.7 kV. For the 24.9/14.4 kV line referred to in the question, the NESC would require a communication worker safety zone of

40in + (14.4kV - 8.7kV) * 0.4 in/kV = 43 in

The phase-to-ground voltage (14.4kV) is used in this example as it is assumed that the 24.9/14.4kV line is effectively grounded. The result is rounded up to the nearest inch as required by NESC Rule 230A4. We discuss this and other issues in detail in the NESC Rules for Joint Use Construction 2-day seminar.

News and Upcoming Events:

NESC Rules for Joint Use Construction
More info.

Coming to Dallas, TX (Sept 16-17); Atlanta, GA (Nov 12-13); and Missoula, MT (Dec 3-4).

This NESC® seminar is a two-day class focusing on the joint use construction rules in the National Electrical Safety Code® (NESC®). The class will provide an overview of each part of the NESC® that deals with joint use construction (Day 1). Applying the Code to day-to-day work will be stressed by focusing on practical applications and class attendee questions (Day 2). The class includes ample time for questions and attendees are encouraged to share their NESC® applications with the class. The presentation is rich in graphics. More info.

Arc Flash Hazards and Fire Rated Clothing
More info.

Need help meeting the Jan 1, 2009 deadline for the NESC® arc flash rules? Join our 90-minute live web seminar which is offered once a month from August to December. More info.

NESC Joint Use Rules 2-Day Seminar
NESC Rules for Joint-Use Construction is a 2-day seminar being offered across the country this fall.

Arc Flash for Electric Utilities
Arc Flash Hazards and Arc Rated Clothing is a 90 minute web seminar offered once each month from August through December of 2008.

NESC and NESC Handbook
Purchase McGraw-Hill's NESC 2007 Handbook and current or past editions of the NESC from the Code Store.

Expert Witness Services
Marne and Associates also provides expert witness services relating to the National Electrical Safety Code and OSHA.

If you have a question for our newsletter, please send an email to with a concise description of your NESC or OSHA question. We attempt to answer every question received, but the volume and type of questions limits us.

Disclaimer: The content of this newsletter should be considered general information only. It is not intended to be consulting engineering advice, legal advice, or an official interpretation of the NESC® or OSHA requirements.

619 SW Higgins, Suite C | Missoula, MT 59803 | 406.544.8997 |

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