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Engine Room

Engineer’s Angle: Ratings help simplify protection choices


Engineer’s Angle: by JD Anson

Whether battling a ferocious storm at sea or an over-zealous deckhand with a hose nozzle, water and corrosive salt can quickly turn thousands of dollars of equipment into worthless junk. When it comes to protecting valuable and critical equipment, keeping this salt and water out is one of the most important needs. Electrical components are particularly susceptible to damage from the environment in which we use them, thus are most in need of protection.

To help with this, standards have been developed to assist in choosing the best option for the particular use. Most common is the IP, or International Protection Marking code, which is frequently erroneously referred to as Ingress Protection. North America has a similar code called the NEMA rating. These standards gives more detailed information than simply calling something “waterproof.”

The International Protection system markings consist of the letters IP followed by a two-digit numeral. The first digit refers to protection against solid particles entering the equipment or enclosure. This ranges from 0, meaning no protection at all, to 6, which is completely dust-tight. Most yachting equipment is rated with a 2, 5 or 6. A rating of 2 means that nothing larger than 12.5mm can enter. This means fingers. Many pieces of equipment used in the interior or engine room may have a rating of 2. This can include VFDs, contactors, breakers and the like.

A rating of 5 shows that though dust may be able to enter, it would be of such low quantity that it should not interfere with operation. A rating of 6 is completely dust-tight, and is proven by applying a vacuum for up to 8 hours to measure for air flow.

The second digit refers to liquid ingress protection. This is the number most important for exterior use on a yacht, for obvious reasons. This rating ranges from 0 to 9. An item rated at 0 will be completely open to water. The items mentioned before – VFDs, contactors, breakers – usually fall into this category. For this reason, they are normally installed in protective-rated enclosures. Usually, VFDs are rated at IP20, but there are versions available with an IP66 rating if there is a possibility of getting splashed and an enclosure is not viable.

A rating of 4 should be considered the minimum for exterior deck use. This is usually outlet covers and the like, and items with this rating have been shown to be effective against splashing of water or deckies with spray nozzles. Items rated 5 and 6 are protected against increasingly powerful water jets, while those rated 7 and 8 may be submerged with no ill effects, the former up to 1 meter and the latter to 3 meters. Switches, knobs and similar items that are normally exposed to the elements must have a minimum water rating of 5, but of course the higher the better.

The NEMA North American standard combines the two digits into one, but is a bit more complicated to remember. The numerals range from 1-13. Generally, the higher number are better protected. But while 3, 4 and 6 are outdoor rated, 5 is not. The higher numbers do not necessarily pass the lower tests.  For this reason, most manufacturers are shifting their testing to the IP system, though many are using dual ratings as the transition takes place, especially for enclosures.

Each standard may also show an additional letter suffix, such as IP69K or NEMA 4X. These are for specialized uses, such as highly corrosive, high heat or icing conditions and are normally not crucial for use on board yachts.

When installing an enclosure to protect low-rated equipment, the rating of the enclosure is only valid if the openings for the cables are also protected to the same rating. When a low number of cables are penetrating the enclosure, cable glands are a good choice. They are inexpensive and easy to install. When many cables need to be installed, consider using a high-density cable cabinet seal system, such as those offered by Roxtec and MCT Brattberg. These systems, while considerably more costly, do an excellent job of passing many cables through a relatively small space in a neat and well-organized manner.

When it comes to IP and NEMA, complicated choices for protection have been made simpler thanks to these ratings.

JD Anson has over 20 years of experience as a chief engineer on megayachts. He is currently project manager at Fine Line Marine Electric ( in Fort Lauderdale. Comments are welcome below.

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