UL Class and Division Encoders

Posted by Brian Winter | View all of Brian's blogs on Jun 11, 2014 4:00:00 PM

In this blog, we'll take a look at encoders that are tested to meet UL Class and Division standards, that is, NEC500 requirements for oil and gas drilling.

Where Do These Encoder Safety Standards Apply?

There are a series of parties that can require encoders in an application to be listed or registered for hazardous applications. Obviously, the end user can determine from his/her application that the area will be deemed continuously hazardous, or intermittently hazardous, or there is a risk of a separate failure causing the area to become hazardous.  Equipment OEMs, such as top drive OEMs, draw works OEMs, etc., can determine that their equipment will be operated in hazardous environments.  Insurers also may have criteria that determine safety requirements and encoder certifications.  These standards may even exceed NEC/UL requirements for encoders in hazardous areas. 

What Encoder Certifications Are Required?

The most typical requirements for rotary encoder hazardous area certifications in North America for oil and gas drilling are Class 1, Division 1, and Class 1, Division 2.  In Canada, cUL CSA or Class 1 Zone 1 certifications may be required.  For example:  many OEMs require draw works encoders to be Class 1, Division 1, while top drives are often Class 1, Division 2.  Nidec Avtron offers encoders with each type of certification. 

Our big advantage that we offer customers is the ability to eliminate bearings and seals in these encoders.  Some example Avtron hazardous duty encoders that offer no-bearings and UL Class and Division ratings are:  XR125 (up to 7 7/8" shaft bore), XR850 (up to 4 1/2" bore), XR56 (up to 3 3/16") bore.


Recognized Encoders vs. Listed Encoders

For OEMs, there are two choices:  They can use a UL_Listed encoder, or they can use a (UL) Recognized encoder.  Let's look at the differences and the advantages of UL Listed encoders vs. UL Recognized encoders:

UL Listed is "simple," that is, UL Listed encoders can be used by OEMs or end-users and applied to a variety of machines.  But, the disadvantage of UL Listed encoders (especially Class I, Division 2) is that there are extremely tight restrictions on connector types.  Often the only available type is a terminal box.  Encoder terminal boxes can require the customer to rewire when the rig is packed up and moved.  Avtron XR encoders are protected against wiring errors so you won't destroy them with wiring errors.  But obviously, if a wiring mistake is made, the customer has to fix the error before drilling can resume.

On the other hand, cRUus (UL Recognized) components can only be installed by an OEM, and the OEM is responsible for evaluating the application requirements and hazard protection.  Often some sort of encoder mechanical protection or overall enclosure may be required.  But many drilling motor applications already have this protection.  Example: the encoder on a top drive is frequently located above the brake and beneath the brake cover.  So no additional enclosure needs to be added.  The great benefit of Recognized encoders is that they can have many more connector options.  So the oil machinery OEM can now make a plug-and-play machine so that rewiring the quadrature encoder is not required--the end user can simply disconnect the mating plug, and reconnect when the rig is relocated. 

Nidec Avtron makes the choice easier:  we offer a full range of hazardous duty XR encoders with both UL Class I, Division 2, Groups A,B,C Listing, as well as UL Recognized Class 1, Division 2, Groups A,B,C encoders.  Here are some example XR4F shafted encoders, showing terminal box and connector options.


Class and Division ratings aren't the end of the safety standard road--in some ways they are the early pioneers.  But they continue to be updated and are a huge part of North American oil and gas drilling requirements for encoders. 

For more information about ultra-reliable encoders for drilling applications, download our white paper series:

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Topics/Tags/Categories: Top Drive Encoders, Oil and Gas Encoders

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