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Pepperl+Fuchs Blog

Visualization with HMI Systems in Class I, Division 2 Areas

Posted by Mike Mendicino on Fri, Aug 02, 2013

Our recommended connection scheme

We receive numerous requests for information on how to connect visualization devices (industrial computers, HMI systems, remote monitors, etc.,) in Division 2 hazardous locations.

Here is a “cookbook” approach on how to facilitate Division 2 connections as we understand National Fire Protection Association guideline NFPA 70. Please consult your local authority on the connection of equipment in hazardous locations before proceeding with your own project.

Fixed mounting options

Most visualization installations in process environments are fixed mounted. Perhaps on a pedestal as shown above, or a wall arm, wall bracket, or motion arm. In general, the optional adapters, wiring, and components apply to any of the standard mounting methods shown at the end of this post.

Our understanding of NFPA 70

NFPA 70 on Wiring Methods, Class I, Division 2 General deals with the importance of installing cable in a way that avoids placing tensile stress on termination fittings.

(B) Class I, Division 2.

(1) General. In Class I, Division 2 locations, the following wiring methods shall be permitted:
(1) All wiring methods permitted in 501.10 (A).
(2) Threaded rigid metal conduit, threaded steel intermediate conduit.
(3) Enclosed gasketed busways, enclosed gasketed wireways.
(4) Type PLTC cable in accordance with the provisions of Article 725, or in cable tray systems. PLTC shall be installed in a manner to avoid tensile stress at the termination fittings.

The above is excerpted from the NFPA 70: National Electrical Code®

Article 725.154 describes adequate support and mechanical protection for cables intended for hazardous areas.

PLTC Cable

(1) Type PLTC: Cables installed in hazardous (classified) locations shall be Type PLTC. Where the use of Type PLTC cable is permitted by 501.10 (B), and 504.20, the cable shall be installed in cable trays, in raceways, supported and mechanically protected by angles, struts, channels, or mechanical means...

The above is excerpted from the NFPA 70: National Electrical Code®

So according to NFPA 70, PLTC cable mechanically supported to avoid stress at both the termination ends and along the cable itself meets the requirements for installation of cabling in a hazardous location Division 2 area.

As far as terminating the cable so that the termination is stress relieved, all Pepperl+Fuchs free standing visualization systems come with cable glands. The gland secures the cable to the unit, and the electrical connections are made separately in the terminal box at the rear of the unit.  The unsupported cable length from exiting a mechanical means and the next supported point is 6 feet. So if our gland-to-gland distance is small, we can make the connection directly between the two glands as the sole means of mechanical support.

VESA cable feedthrough

In this image, the total distance between the two glands is approximately 16 inches. This distance provides plenty of room for a wire loop, so none of the connections are stressed, yet not so much that wiring is hanging in the way.

Sandwiched between the pedestal mount (same applies for the wall arm) is a 1-inch thick plate with a standard 100 mm VESA pattern and two glands. This adapter (VESA CABLE FEEDTHROUGH) provides the stress-relief termination at the opposite end of the cable where it feeds into the pedestal. The same provision is made at the bottom of the pedestal or wall arm to transition to the next support mechanism.

Pedestal mountTHE VESA CABLE FEEDTHROUGH gland plate is an optional component for mounting systems for those types of products.

There are several other mounting accessories that may be helpful in installing an HMI in specific situations.

Mounting accessories for HMI

The VESA TILTMOUNT is a hinged unit that can be mounted either vertically (up-down) or horizontally (right-left) tilt/rotate. You can use them in pairs for for up/down and right/left movement simultaneously.

Using a PMK-2 pipe mounting kit, you can connect the HMI directly to a pipe or other support apparatus.

Which HMI Solution is Right for You? Click and find out!

Topics: Industrial Monitors/ HMI

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