NEMA 4X & 7 Enclosure


Thread Starter


Hi All,

Can anyone clarify my doubt about above subject.

If i am buying an Instrument which is to be installed in Explossion proof area.If the selected Instrument (For Example Ultrasonic Level Instrument)is FM Certified for the required Electrical classification with Enclosure as
NEMA 4X then whethere it is Technically Acceptable.

Thanks in Advance.

Control System Engineer
Saudi Arabian Bechtel Co.
P.O. Box 1840, Al Khobar 31952
Kingdom of Saudi Arabia
*Tel. (966-3) 882-5288 Ext. 1677
*Fax. (966-3) 882-5234
*E-mail: [email protected]
Nema 4 is an environmental designation that does not relate to Hazardous Area Classification.

If the device is FM approved for the appropriate area classification, the entire device is approved...including the enclosure.

So, as an example, if your ultrasonic level transmitter is FM-approved suitable for use in Class 1 Division 1, Groups C and D, _and_ is FM-approved NEMA 4X, then you can use it in that hazardous area classification, outdoors without further protection.

Some "explosion proof enclosures" are NEMA4/7 or NEMA4/7/9 for the same reason.

FM approves the entire instrument as presented to them, not the enclosure or the circuitry alone.

Walt Boyes
Hi -

Many intrinsically safe barriers are available that render selected products intrinsically safe in explosion proof locations. Search the web for this device in your area. SPST to programmable units are available. Several types of level switches work with the units check with the supplier. This would allow your box to conform.

Thanks Bob Hogg

For an electrical/instrument device to placed into service it must meet two separate requirements, environmental and hazardous area rating. The environmental rating is the ability to survive in the environment the device will be installed in and is in the U.S. and NEC using countries typically rated by National Electrical Manufacturers Association(NEMA) per NEMA 250,
"Enclosures for Electrical Equipment(1000 Volts Maximum)." Canada also has similar rating to NEMA. IEC or European countries use IEC 529(IP ratings).

NEMA 4x is basically weather proof, corrosion resistant(note corrosion resistance ability may vary).

For the hazardous area rating, the equipment must meet the requirements for the specific area classification it will be installed in and is typically listed(UL), approved(FM), or rated by some other national recognized testing laboratory(NRTL) for the hazardous area classification. NEMA also has enclosure ratings for hazardous areas which also meet NEMA requirements for the enclosure. These are NEMA 7, 8, 9, & 10. NEMA 7 is indoor explosion-proof Group A,B, C, or D or a combination of these. Since NEMA 7 is an indoor rating, it is not suitable for outdoor service(though commonly incorrectly used outdoors) and should also have a NEMA 4 or 4x rating.

Therefore a NEMA 4x & 7 enclosure can go into a environment requiring a weather-proof, corrosion resistant enclosure in a hazardous area which
requires an explosion-proof enclosure for which it is approved for.

If FM approved your instrument for a hazardous area and NEMA 4x, then the instrument is good for the hazardous area it is approved for and for areas that the NEMA 4x is suitable for.

Bill Mostia
William(Bill) L. Mostia, Jr. PE
Independent I &E Consultant
WLM Engineering Co.
P.O. Box 1129
Kemah, TX 77565
[email protected]
These opinions are my own and are offered on the basis of Caveat Emptor.