Keeping Water and Foreign Objects Out of Electrical Enclosures

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With so many different ratings for ingress protection — from NEMA ratings, to UL standards, to the European IEC ingress protection (IP) ratings appearing more frequently in the U.S.— keeping the standards straight can be challenging. When you consider that each rating is designed to specify the protection required to safeguard your electrical system and protect your workers, you can see that it’s crucial to have a minimum basic understanding of what the different ratings mean.

Here is an overview of the IEC IP ratings, NEMA ratings, and UL standards. 

IEC IP Ratings

IP ratings are specified by the International Electrotechnical Commission (IEC) 60529 standard. They consist of the letters “IP” followed by two numerals, of which the first specifies protection against solid bodies and the second specifies protection against water.

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NEMA Ratings and the Correlation to IP Ratings

While the above IEC IP ratings only cover liquid and solid body ingress protection, National Electrical Manufacturers Association (NEMA) ratings for enclosures, specified in the NEMA 250 standard and corresponding UL Standards 50 and 50E, cover ingress protection and more, including the enclosure design and corrosion protection.

For the purposes of specifying ingress protection only, the following are general translations between NEMA ratings and IEC IP ratings:

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Note: Testing procedures and pass/fail criteria for NEMA and IEC ratings are different. Therefore, these are rough equivalents provided for reference only.

What happens when you make a connection?

Most enclosures that come off a manufacturer’s production floor and are stocked in a distributor’s warehouse are UL® listed, meaning you can be sure they meet a certain UL50/UL50E standard to meet the requirements of your application for ingress protection and more. But as all of us in the industry know, once electrical enclosures are installed and loaded with the equipment they’re meant to protect, they must then be connected to an electrical system to function.

Liquid-tight flexible metallic conduit and liquid-tight fittings can be applied in these circumstances. The standards for liquid-tight conduit and fittings are UL360 and UL514B respectively. In theory, connecting UL360 liquid-tight flexible metallic conduit with UL514B liquid-tight fittings to a UL50E enclosure should maintain ingress protection. In reality, one simply doesn’t know without conducting further testing of the complete assembly.

Learn more about NEMA ratings for enclosures with the free visual guide below.

A Visual Guide to NEMA Ratings for Enclosures


The opinions expressed in this piece are solely Thomas & Betts'. They do not necessarily represent WESCO’s views.