Ask Lewis Bass: A Question About Field Labeling Reports

Ask Lewis Bass: A Question About Field Labeling Reports

Welcome to another blog in our ongoing series, Ask Lewis Bass!

This series features actual submitted questions from companies in the industries we provide engineering safety consulting services to.

Topics covered include those associated with our work in 3rd party field labeling, SEMI S2/S8/EMC/F47 testing and design, CE Marking evaluations, and general engineering safety consulting questions.


Hi Lewis Bass,

I operate a company that designs and manufactures custom injection molding machines for the aerospace industry.

From time to time I have been asked to include third party field labeling sourcing and pricing as part of my quotes for my clients as their jurisdiction/AHJ is requesting it.

This last month, a new client of mine asked me to find a third party to conduct a full NFPA 79 evaluation of one of my machines.

I did some research and found NFPA 79, NFPA 790, and NFPA 791 standards and I can’t quite wrap my head around why my client is specifically asking for NFPA 79.

Does NFPA 790/791 allow for the same type of acceptable field labeling procedures as NFPA 79?

Asked by Michael in Santa Clara, CA


Lewis Bass:

Hello Michael,

You are correct in that this can get very confusing for the layperson when diving into the language of these three separate standards provided by the NFPA.

So, let’s start off with definitions of each of these standards along with an interpretation of what each means according to field labeling processes:

1) NFPA 79

The definition of NFPA 79: Known as the “Electrical Standards for Industrial Machinery” is the code that provides safeguards for industrial machinery to protect operators, equipment, facilities, and work-in-progress from fire and electrical hazards. NFPA 79 encompasses all of the machines’ electrical and electronic elements operating at 600V or less.

Our interpretation of NFPA 79: NFPA 79 provides the fundamental criteria by which unlisted equipment should or shall be evaluated according to a step-by-step list of codes that cover every aspect of the machinery’s electrical design and functionality.

2) NFPA 790

The definition of NFPA 790: Known as “The Standard for Competency of Third-Party Field Evaluation Bodies” is the code that gives guidance for evaluating installed electrical equipment that has not been previously certified, listed, recognized, or classified undergo a “field evaluation” to ensure compliance. This standard provides qualifications and competencies for third parties performing field evaluations and specifies how they are to be completed.

Our interpretation of NFPA 790: NFPA 790 guides a Field Evaluation Body’s corporate management process with regards to how it performs its evaluations of unlisted equipment.

3) NFPA 791

The definition of NFPA 791: Known as “Recommended Practice and Procedures for Unlabeled Electrical Equipment Evaluation” is the code that covers recommended procedures for evaluating unlabeled electrical equipment for compliance with nationally recognized standards.

Our interpretation of NFPA 791: NFPA 791 is the code that guides a Field Evaluation Body’s evaluation processes for unlisted equipment in-line with NPFA 79 standards.

Now that we have definitions of each code base, let’s touch base on your question below:

Does NFPA 790/791 allow for the same type of acceptable field labeling procedures as NFPA 79?

Yes, it does. In fact, the local AHJ in your city or county is the one that defines what type of report is acceptable in their jurisdiction to establish confidence in a third party’s review of an unlisted machine. A report that is prepared in accordance with NFPA 790/791 may be at most 4-5 pages of testing results, details on its installation, and background on the machine’s compliance or non-compliance to the tests performed on it.

An NFPA 79 report can be in excess of 90 pages and is extremely comprehensive. This is owing to the fact that every single line item in the code base is being evaluated against the machine in a pass/fail/NA manner in addition to including the shoulds (recommended but not required) and the shalls (tests that must be performed). The evaluation starts at section 4.4 “Electrical Supply” and goes all the way to section to the 19.3 “Servo Drive System Conductors” section! While most tests may not be applicable to the machine (no lasers used for instance) they still have to be marked pass/fail/NA.

In closing, most AHJs are very accepting of the briefer reporting format of NFPA 790/791, but in cases where machinery can be seen as mission critical or is of a semiconductor type, NFPA 79 reports may be requested by the clients themselves to ensure that every single potential test that may be applicable is performed for their own liability purposes.


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