I think there are some conflicting opinions on this. There can be an interpretation that the motor and inverter needs testing in combination, which clearly suits those companies that make and sell both motors AND invertors. Those that just do motors OR invertors tend to have a different interpretation.

Oh the joys of the ATEX Directive ..... ■

The ratings of an existing motor will change when fed by a VSD, because it will be exposed to a new "environment": variables frequency and voltage. Both factors will stress the motor insulation.

Additionally, its cooler fan - designed for the use with full speed - will operate sometimes in lower speeds, what would put the motor in temperatures above the ideal point, contributing even more to the insulation stress.

As these situations were not evaluated by the testing station, the Ex certificate will be no longer valid, and the user will be the only responsible for all consequences of doing this modification. ■

True, but we shouldn't assume that he's not capable of doing this himself. ■

Do the existing motors have a thermistor switch in the windings? The switch should connect to the VFD and remove power in a motor overtemperature condition.

It is my understanding the thermistor will prevent the skin temperature from exceeding the rated value, so should be acceptable for your area classification. ■

For motors using VSD it is necessary to take into consideration some facts. One of them is overtemperature: thermistor switches can be used. Another is internal sparking. No information was given about the type of motor, nor about its nominal voltage level.

It is recommended to work together with the motor manufacturer to garantee that all adequate protective measures will be taken, especially because the motor is installed in a hazardous location.

More information about this issue can be obtained in:

http://www.drives.co.uk/news/uknews/newsuknews457.htm

P.S.:

To view the Frank Lienesch article referred in the url above, use this link (it was updated):

http://www.r-stahl.com/fileadmin/Dat...drivesen.pdf ■

We all probably have our run-ins with Atex and sometimes love it and sometimes hate it.

Antoin,

What is the Atex zone where your motor is mounted? The beauty of Atex is that it goes with skin temperature of your equipment. So you may be able to pass with your existing motor without modifications.

What motor brand and model is the motor? It often helps to contact the OEM in getting valid information. ■

The important thing about ATEX is the risk assessment. The trouble is many people are used to just applying "rules" and not the logical thinking necessary for risk assessments and this causes uncertainty.

Uncertaintly breeds over zoneing and over specification, especially if done by "consultants" needing to cover their backs and maximise their income. ■