Device use considerations are based on common sense and sound engineering practices. In many cases, device use remains unregulated, although the NFPA and ISA address many other factors.

The examples here may be presented in the absence of standards. All examples are based on applications that have been installed and proven.

The ultimate responsibility for installation approval, regardless of current regulations, lies with the authority having jurisdiction.

Protruding Devices
Pay close attention to the use of devices that penetrate the surface of a protected enclosure. Protruding devices often contain electrical components that could either be:

• Exposed to the hazardous location, or,
• Isolated from the flow of protective gas

• It is explosion proof
• It is intrinsically safe
• It is proven to emit insufficient energy to ignite the surrounding atmosphere (applies to Division 2 locations only)
• It is constructed so that all electronics within its face are suitably sealed from the surrounding environment and properly ventilated to the protected enclosure, or,
• It is isolated from the surrounding atmosphere by a sealed window or access door that is properly ventilated to the protected enclosure

Protruding Devices
Today's panel mounted instrumentation is almost strictly electronic. The protruding face of these instruments normally contains LEDs, LCDs and incandescent or fluorescent lights.

It is extremely important to isolate all instrumentation from the surrounding atmosphere, unless the face is sealed and all electronics are properly ventilated to the protected enclosure.

Due to the limitations established above, most instruments will require isolation through the use of a sealed access door. However, some end users permit "limited access" to the instruments while maintaining a positive pressure. This allows you to perform maintenance, calibration and adjustment on the instruments.

Limited access may be accomplished by using Pepperl+Fuchs Bebco Rapid Exchange^TM Purging Systems. Special door labeling or purging system automation may also be required.

These designs should be reviewed by all parties, especially the authority having jurisdiction, prior to engineering or fabrication commitments.

Peripheral Devices & Instrument Keypads
Many peripheral devices cannot be pressurized, even if they are Type 4 rated. First, most bar coders and wands feature no internal cavity. Secondly, the membrane assembly of most peripheral keyboards isolates key contacts from the protected gas.

We recommend that peripheral devices not suitable for pressurization be protected by intrinsic safety barriers. Furthermore, the barriers and all intrinsically safe wiring should be mechanically isolated from all other devices and wiring in the protected enclosure. Most peripheral devices can be easily modified with intrinsically safe barriers, however, its not practical to modify panel mounted instrument keypads. These instruments should be placed behind a sealed access door that is properly ventilated to the protected enclosure.

Some end users allow the use of these devices in Division 2 areas without barriers, assuming the normally low energy to these devices will not ignite the surrounding atmosphere. However, the possibility of a ground fault or current overload will always exist without barrier protection. We recommend the use of Intrinsic Safety Barriers.

Operators
Panel mounted operators like push buttons and selector switches should be Type 4 rated or oil-tight and should not contain illumination devices such as incandescent bulbs, unless they are protected as noted below.

A majority of end users permit the use of general purpose illuminated operators in Division 2 areas, if they are isolated from impact with guards.

Pilot Lights
A pilot light is normally unacceptable unless rated for use in the hazardous location. However, some authorities having jurisdiction permit the use of LED clusters and VDC bulbs, after determining they have insufficient power to ignite the surrounding atmosphere. Other concerns include impact resistance and potential power dissipation, unless the pilot light is protected as noted.

Internal Devices
Relays, timers, counters, power supplies and other internally mounted electrical equipment should be ventilated or protected in accordance with the considerations for adjacent and internal enclosures. All devices should not exceed 80% of the flammable or ignitable substance auto-ignition temperature, unless

1. it can be shown by testing that the device will not ignite the surrounding atmosphere
2. the device is enclosed in a hermetically sealed chamber
3. the protected enclosure is equipped with a temperature warning nameplate
4. the device is separately housed and pressurized

Motors
Totally enclosed motors, with NEMA ratings such as TENV, TEFC or TEAO, are best suited for pressurization, but the following factors should also be considered.

1. All motors should have sufficient cavities and openings to permit the flow of protective gas around the windings
2. The gas connections for the supply and return of protective gas should be located at extreme opposite ends of the motor
3. Peripheral devices such as electrical connections, optical encoders and brakes may require a separate housing, purged in series with the motor
4. Pressure within the motor should not exceed the minimum requirement because excessive pressure will force grease out of shaft bearing seals.
5. Class I motors require 10 volume exchanges before energizing power