Motor in an explosive atmosphere


Thread Starter


I have to install a motor in an explosive atmosphere. The motor should be supplied by a frequency inverter. The motor has the category EExdeIICT4. What are the main things (problems), I have to take care? Could anybody help me or
send me a link to an FAQ site about explosive areas applications?

Thanks Karl
I am not familiar with "EExdeIICT4" but the first thing to do is to go to the "National Eletrical Code" to determine the class and division of your area. Then I would go to a site like "": , they will help with your conduit fittings and locations of seal-off's

david mertens


A good starting point would be, this site has a number of links to various information sources on Ex applications. EExde motors are motors allowed in zone 1 (CENELEC zone classification europe), they are rated flameproof (d) and improved electrically safe (e). The
installation however requires some special considerations, please contact your vendor for detailed information. One of the important items I can remember is the requirement to have a temperature sensor in the motor core that will switch off the motor if it becomes to hot (setting according to your temperature class
T4). This is required on motors with cooling fans fixed to the motor axle when using frequency controllers. This is because at low speeds the fan doesn't produce enough cooling to keep the motor within acceptible temperature. Good luck.

Looks like the motor is already classfied to run in an Explosive Atmosphere, but you will have to site the Frequency Inverter in a "safe" area, unless you can get it in an explosion proof box.
I don't think you will have to make any special considerations in controlling it, except that you may need to shut it down in an emergency (maybe even power-off ?)
There is some more info on Hazardous Area's at

Bob Peterson

This is a European classification.

EExd is flame proof, sort of comparable (but not really) to NEMA7 explosion proof but not allowed in zone 0. The T4 is the temperature rating. I forget what the rest of the stuff is.

Very roughly speaking (but not really):

European Classification US Classification
Zone 0 Division 1
Zone 1,2 Division 2

Using this system in hazardous areas can result in savings BUT:

1) The NEC does not allow you to mix and match NEMA stuff and this European stuff in the same area. Although you can classify a small area to use the European stuff and an adjacent area can still be done to US standards.
2) The NEC says a PE is required to classify the area involved if you want to use the European system.
3) NEMA explosion proof equipment can be used in division 1 areas. The European flame proof stuff cannot be used in zone 0 areas.

Using this stuff takes a fair amount of knowledge. If you insist on going ahead with it, you need to get someone involved who knows a lot more about it then you seem to, or spend the time to get yourself educated.

There seems to be a lot of stuff being imported into the US now, particularly motors, being refered to as "explosion proof" by the sales reps promoting them as "less expensive", but that are actually EEx something. I am not suggesting they present a particular danger if used properly, BUT if misapplied, they just might.

Also, be aware that there is some legitmately explosion proof (as listed by UL) motors coming into the country from overseas that have a cable preattached. These are OK to use BUT as I understand it, UL refuses to list any seals for use with cables, reportedly because once the sealing compound is installed it is no longer possible to replace the cable if it becomes damaged. There is no real fix for this other then to either use an unlisted cable seal, or buy the components for a cable seal and assemble them yourself. This arrangement has to be approved by the "authority having jurisdiction", since it involves the use of unlisted components, or components used for unlisted purposes, but should not present a huge problem.

Bob Peterson

Bruce Durdle

The classification you have states that the motor is certified by a member of the EU. (EEx) The primary method of protection is flameproof with
secondary increased safety (this usually means that the terminal box is Increased Safety rather than flameproof). The motor is designed for use in hydrogen (IIC) and has a maximum surface
temperature exposed to the external atmosphere of 135 degC. With a motor supplied by a frequency inverter, you need to get the motor and inverter certified as a unit. The harmonics etc produced by the inverter can lead to incresed motor losses that will increase the internal temperature.
The main thing is to get a copy of the certification document from the supplier and make sure you comply with all requirements. Also, make sure you get the design checked by someone who is fully familiar with your local requirements.

Viel gluck,