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

In This Issue:

• Question 1: Changes to NESC Arc Rated Clothing Tables
• Question 2: Greater Than 40" for Joint Use Clearance
• Public Seminar: NESC Rules for Joint Use Construction (2 Day)
• Live Web Seminar: Arc Flash Hazards and Fire Rated Clothing

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.

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

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.

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.