The Hammond enclosure shown in Figure 1 is a deceptively simple enclosure. The complexity is revealed when we analyze the enclosure through the lens of Underwriters Laboratories (UL) and the UL 508A Industrial Control Panels Standard for Safety. Recall that UL 508A is an American standard harmonized with Canadian standards describing how to safely construct industrial control panels.
Note that this Type 4 Eclipse Junior series Hammond enclosure is dual certified with the Canadian Standards Association (CSA) LR21001 marking. CSA is analogous to UL. This engineering brief is focused on UL 508A.
Figure 1: Image of a Hammond type EJ863LG enclosure along with the internal label.
Tech Tip: This article draws heavily from UL Product iQ. Recommend you establish a free account so that you may follow along.
What is the UL 508A standard?
Part of the answer is implied in the name “Underwriters Laboratories.” An underwriter is traditionally defined as an agent hired by an insurance company or government agency. They provide the technical expertise so that an insurance company can better understand what they are getting into. The word laboratory recognizes that the underwriter’s work is conducted in a controlled environment.
An example is UL 489, which is used to evaluate the circuit breakers as used in the feeder and branch circuits of a control panel. In this case, circuit breakers are evaluated in a laboratory to determine compliance with the standard. Only UL-listed circuit breakers may carry the UL stamp of approval indicating suitability and safety when used within the prescribed limits of the standard. Note that there are two UL markings including UL-Listed and UL-Recognized (the backward UR symbol). The distinction is important but beyond the scope of this article.
UL 508A is a North American (United States and Canada) standard to which a control panel is evaluated for conformity with attention to fire and safety risks. A panel constructed in accordance with the standard may be listed with UL. The underwriter’s stamp of approval is a green flag demonstrating that the panel was constructed to UL standards under the watchful eye of knowledgeable UL inspectors. Your control panel fits within a larger regulatory ecosystem involving OSHA, NFPA, and insurance.
Tech Tip: The Manufacturer’s Technical Representative (MTR) is a key player for UL 508A compliance. The MTR is a senior technician or engineer who works at a commercial panel shop, ensuring that each control panel is designed and constructed for UL 508A compliance. Note that the MTR’s work is routinely inspected by a local UL field engineer.
Navigation within the UL Product iQ
Decoding UL’s classification scheme can be a challenge. It appears to be a hierarchical system, yet the naming conventions are not clear. For example, industrial controls are identified using the UL Category Control Number (CCN) NIMX. Industrial control panels are classified as NITW, industrial switches are classified as NRNT.
There are multiple “.GuideInfo” documents within the system. The trick is to find the high-level documents containing the references to other pages. Personally, I find these two links to be most useful:
With respect to the Hammond box, we can follow links to arrive at AALZ.GuideInfo - Electrical Equipment for Use in Ordinary Locations. This is the page that describes the enclosure type.
Enclosure classification
As shown in Figure 1, the Hammond enclosure is identified as Type 4, Type 13, and Type 12. According to UL’s AALZ.GuideInfo document, the enclosure is rated as:
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Type 4: Outdoor use, splashing water, windblown dust, hose-directed water, undamaged by the formation of ice on the enclosure**
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Type 13: Indoor use, dust, spraying water, oil and noncorrosive coolants
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Type 12: Indoor use, dust, dripping noncorrosive liquids
Note that outdoor type enclosures provide a degree of protection against rain, snow and sleet. Outdoor enclosures are also suitable for use indoors if they meet the environmental conditions present.
The document goes further suggesting that the Hammond enclosure could be marked as Watertight, Dusttight, and Driptight.
UL Certification for the enclosure
From figure 1, we see that this product is listed with UL under the number E65324. We search for this term in UL Product iQ, leading to the NITW.E65324 document.
- We recognize the NITW CCN for industrial control panels
- The suffix E65324 is the Hammond-specific listing
Parting thoughts
Carefully consider each and every component that goes into your UL 508A-listed control panel. The Hammond enclosure described in this engineering brief provides a solid starting point.
Best wishes,
APDahlen
Related Information
Please follow these links to related and useful information:
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DigiKey’s product selection guides for a comprehensive index into DigiKey’s product families.
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With regards to UL508A, be sure to follow manufacturers recommendations for wire crimps. In each case, the crimp, wire, crimp tool, and receiving socket must be properly matched. Refer to the engineering brief for additional information. Failure to demonstrate the correct procedure may require considerable rework or result in the loss of the UL listing.
About this author
Aaron Dahlen, LCDR USCG (Ret.), serves as an application engineer at DigiKey. He has a unique electronics and automation foundation built over a 27-year military career as a technician and engineer which was further enhanced by 12 years of teaching (interwoven). With an MSEE degree from Minnesota State University, Mankato, Dahlen has taught in an ABET-accredited EE program, served as the program coordinator for an EET program, and taught component-level repair to military electronics technicians. Dahlen has returned to his Northern Minnesota home and thoroughly enjoys researching and writing articles such as this.