Maintenance of explosion proof motors by plant personnel. 10

[electricpete]

We have a very few explosion proof motors at our plant. I'm not very experienced in the requirements related to these motors.

I am aware the motor receives a certification from UL and that motor repair shops can also receive some sort of certification to work on UL motors.

MAIN QUESTION: Are plant personnel (with motor experience but no special UL certification) permitted to disassemble the motor to replace bearings?

Related/contrasting question: Can plant personnel open the terminal box to access connections (it seems to me that it obviously must be allowed for motor installation... removing terminal box cover to access terminations seems somewhat analogous to removing endbells for bearing replacement).


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[djs]

I once was told that if the motor is opened up by an uncertified shop the UL explosion proof sticker must be removed.

 

[waross]

The definitive answer will come from your insurance company.
It really doesn't much matter what others say.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[controlsdude]

I thought the leads or any electrical connection near a motor was potted with explosion proof material which anyone can install or clean out during the install? see below example.

http://na.henkel-adhesives.com/product-search-1554.htm?nodeid=8797959913473

 

[ScottyUK]

Hi ePete,

Under European rules - which probably aren't too dissimilar - any work which disturbs a flamepath must be undertaken by a 'competent person'. Removing an endshield would definitely fall into that category. In UK law 'competent person' has a specific meaning and there are accredited training courses which must be passed in order to gain the 'competent' status.

It is possible for plant personnel to achieve competent status through, for example, AEMT certification, but unless it is a big facility with a lot of motors the economics don't work. In-house overhaul of motors doesn't generally work out at all in the UK, it is almost always contracted out these days.

 

[electricpete]

Thanks for the replies.

I have had opportunity to talk to our insurance rep about a variety of subjects. I don't think this fine level of detail is something they would be involved with or knowledgeable about.

For the UL motors I have seen, the conduit is sealed where it enters the terminal box and the terminal box cover has a machined tight fit for sealing (repair shop identified deviations in that machined fit requiring repair).

Replacing bearings is a routine task for our maintenance folks (for non-explosion proof motors, which are 99% of our motors).

Regardless of what is strictly "required" (if that is even defined), one could argue that it's prudent to use a certified shop to make sure something isn't missed that would compromise the original explosionproof design. I guess I'm leaning that way unless someone is aware of an argument/practice on the other side.


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[ScottyUK]

Hi ePete,

The primary purpose of that precisely machined fit isn't for sealing although that is certainly achieved - the main purpose is to help the casing contain the products of an internal explosion and cool them as they pass through that tight flamepath so by the time they are able to leak out of the casing they have cooled to the point where they are not an ignition risk. Apologies if you already knew this - it wasn't apparent from the post above.

Scratches in a flamepath can have catastrophic consequences which is whay they've been flagged for repair:

https://www.youtube.com/watch?v=MTP1FGZFPKU

 

[SwinnyGG]

I have had opportunity to talk to our insurance rep about a variety of subjects. I don't think this fine level of detail is something they would be involved with or knowledgeable about.

If you have a major claim due to fire or explosion and the source is traced to an ex-proof motor or device of any kind, you can bet your teakettle that the insurance company (which either has a fire protection engineer on staff already, or will contract one as part of their investigation) WILL reject your claim if you have unqualified personnel working on ex-proof equipment.

There is no reason to do it any other way- unless your company enjoys a lot of liability exposure in the event of an accident.

 

[dArsonval]

One of the most informative articles ever written on the subject of UL Follow-Up Service
for Rebuilt Motors and Generators for Use in Hazardous Locations was published in a UL quarterly
news magazine “Lab Data” the Summer of 1978. Written in layman’s terminology by R. C. Valckauski it took
the reader through the various steps of how a motor from a manufacturer was submitted for review,
to the initial UL inspection of a repair shop seeking authorization to repair “explosion proof” motors and so on.
Re-prints of the article were floating around into the late 1990s because while dated, the information
remained very useful and relevant. By the middle 2000’s many repair shops had stopped re-upping for
the program because of shifts in what was actually out there in the field for repair, and the costs required by
repair facilities to keep the repair authorization program active. Reluctantly, I don’t have a suitable copy of
the article to post here because portions of it are missing.

The short answer to electricpete’s main question of, “…Are plant personnel (with motor experience but no special UL certification)
permitted to disassemble the motor to replace bearings?” The answer is NO.

If a motor manufactured for use in a hazardous location has any sign of being dismantled, (match-marks/prick punches etc... not scratched paint)
and it does not have UL’s stainless steel re-built tag riveted to it denoting the repair shop’s active file number and other info
related to its Class/Groups and so on, the motor is deemed no longer [Listed].

John

Post Script: Ever see a 4000 HP Explosion Proof motor before? I never did either until I had to take one apart one day.
Photo Attached:

http://files.engineering.com/getfile.aspx?folder=621faadf-d42a-47e7-9dc6-1c7d179f9295&file=IMG_8.JPG

 

[electricpete]

So it seems there is clear consensus that personnel replacing bearings require some kind of certification specific to UL motors.

Now, what about removing the terminal box cover (to access connections for testing)…. Can this be done without the UL certification? And if so, how is this any different than removing endbells to change bearings?


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[itsmoked]

A lot of this comes down to a mentality of: If there's an explosion, there will undoubtedly be an investigation. If the investigation reveals compromising work's been done there will be hell to pay (and pay and pay). If the work that's been done was competent then there is no issue what-so-ever who does it.

If while your people replace the bearings they scratch the flanges, leave out bolts, break sealing systems or certification seals, or alter the 'original approved design' and there is an 'event' then you will be found panddleless in a brown smelly river.

No hazardous facility can be 'legislated' into safety, it ultimately comes down to the quality and trust you have in your maintenance staff and safety engineering staff in keeping things safe in a hazardous environment.

Where I'm going in this is changing the bearings in an exp motor is not rocket science and is a normal maintenance task that does not need to shopped out to some fancy outside facility any more than one needs to hire specialists to take the cover off of any other exp enclosure in a facility. It's less of an issue than installing an exp enclosure with the correct feedthroughs, conduiting and the other tasks included.

However, if you have a bunch of monkeys working at your place (which means you're already at risk for a chest full of reasons) or more commonly you have an over burdened and harried staff that operates in a frenetic mode that finds them unable to give 100% concentration to an important task like rebearinging an exp motor then the correct choice is to send the motor out to a facility that can and does focus on the task properly.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[electricpete]

I just noticed the following in EPRI MV motor repair specification 1016679

Hazardous Locations: Where an explosion proof, or dust ignition proof enclosure, as defined in ANSI/NFPA 70 – 2005, Article 500, or CSA Std. C22.1- 1998 is required...

3.2.16 After repair, re-certify explosion proof and dust ignition proof motors to UL674 or CSA Std. C22.1-1998....

7.5 Explosion Proof and Dust Ignition Proof Motors
Explosion proof and dust ignition proof motors shall be repaired only in ANSI/NFPA, or CSA certified shops, per their appropriate procedures. Extra care shall be taken to ensure that joints and flame paths are not damaged during the repair work.

I don't honestly know whether there are legal/code requirements that would require this for our facility, but this is good enough for me to conclude we should not be disassembling these motors for bearing replacement.

I'm still curious what you guys think about removing/reinstalling the terminal box cover to access connections.
Do you guys think this falls in a different category where no certification is required since it is less intrusive?


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[controlsdude]

I think the manu guide below might give you some idea on the questions your asking depending on how your motors are connected. When i was doing explosion proof assembly machines, i did not think that someone had to be qualified worker as it related to connections. As long as you followed manufacturers recommendations on the connection method.

http://www.hubbell-killark.com/literature/2011nec.pdf

 

[braddles90]

We deal with Ex gear for underground mines, and basically every piece of electrical equipment that carries an Ex rating can only be worked on by technicians with proper qualifications.

If your motors are Ex, there should be protection methods around the terminal enclosure as well (either that is another Ex d enclosure, mentioning flame paths, or they're low voltage intrinsically safe connections, something like that - not sure). If that terminal box is Ex d and has flamepath gaps between the lid and enclosure, you should have trained guys working on them.

If there is potential for someone to incorrectly connect something (incorrectly terminated, left a gland out, didn't torque cover bolts to the correct torque, etc), I would want someone trained to work on it. If you don't know what you're looking for, it's easy to miss something.

 

[dArsonval]

Electric Pete should receive all the stars given out so far in this thread.

In reading all the replies over again, and in thinking about how different levels of the discussion
fall in to a very GRAY/Grey area, Pete may have asked a question that technically cannot be
answered within the scope of what can be answered here in this little-ole Internet forum.

Initially, I was going to fire back an answer that YES, the maintenance personnel can
open up the connection box. “For Pete’s Sake”, [to borrow a pun], the motor has to be connected,
and disconnected throughout its useful life in service.

But then I thought about what Keith raised on the subject related to “…if while your people… scratch the
flanges, leave out bolts, break sealing systems…”, and so on.

An electrician may understand and competently disconnect, and reconnect the motor.
But let’s say while the cover to the connection box is resting on a table somewhere as the
motor is being re-connected and along comes someone else who accidently drops a 3 inch diameter
shaft on top of it, nicking the cover’s machined surfaces. The electrician is not going to have a surface
gage with him/her to decide/determine if the cover still passes the required criteria of a [Listed] motor.

The thread gets tangled more.
Another reader is contributing, or tying in the Bureau of Mine Safety into the topic.
We might as well have the auto industry, ships, and railroad people chime in here as well.

One could cut and paste the wording out of the National Electric Code of those having jurisdiction
and authority, but I bet ’cha that same authority would refer you to UL.
Well, let’s say the motor is one listed by Factory Mutual? Now what?
Let’s call EASA, they have all the answers… they’ll know.

No they won’t.

Call EASA up and ask them about what varnish to use in rewinding your motor.
They will tell you to refer your question to the varnish manufacturer.

The “untangled” answer to Pete’s question is likely; yes… a competent plant personnel electrician can
open up a connection box on a motor for use in a hazardous location, disconnect it, and reconnect it again for service.

If one really wanted to cover the job fully, a technician familiar with UL’s Follow-Up Service Procedure
(from a EASA member repair shop) could accompany a licensed/competent plant electrician as the work is performed.

Have a great holiday weekend everyone!

John

 

[controlsdude]

I think its stating what I mean by complying with manufacturer's recommended installation instructions. Usually what happens is a distributor of the explosion proof product will demo how its implemented, to me this is what is explained below. Its kind of funny how we get wrapped up in who qualifies what in what circumstances. To me its that simply and lets not get wrapped up in the sematics.

https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=9976

what does it mean?
Qualified person. One who has received training in and has demonstrated skills and knowledge in the construction and operation of electric equipment and installations and the hazards involved.

Note 1 to the definition of "qualified person:" Whether an employee is considered to be a "qualified person" will depend upon various circumstances in the workplace. For example, it is possible and, in fact, likely for an individual to be considered "qualified" with regard to certain equipment in the workplace, but "unqualified" as to other equipment. (See 1910.332(b)(3) for training requirements that specifically apply to qualified persons.)

Note 2 to the definition of "qualified person:" An employee who is undergoing on-the-job training and who, in the course of such training, has demonstrated an ability to perform duties safely at his or her level of training and who is under the direct supervision of a qualified person is considered to be a qualified person for the performance of those duties.

 

[ScottyUK]

Over here in the UK we have the COMPEX scheme which is a nationally-recognised qualification for those who install and inspect hazardous area equipment. The COMPEX course covers the various types of hazardous area protection and upon completion of the course the trainee should have enough knowledge to recognise any damage with the potential to compromise safety such as a scratched flamepath. In this context 'install and inspect' would not extend to stripping and rebuilding the motor itself but would certainly cover opening up the temrinal chamber and connecting it up. We have a separate set of requirements for strip & rebuild of the motor itself which probably mirror the FM / UL requirements in the US; ours are published by AEMT and BEAMA.

 

[electricpete]

In this context 'install and inspect' would not extend to stripping and rebuilding the motor itself but would certainly cover opening up the temrinal chamber and connecting it up

This is an aspect I'd like to explore (how is removing/reinstalling the terminal box cover different than removing/reinstalling the endbells with respect to preserving explosion proof status).

Attached is a photo of the terminal boxes from one of our hazardous location motors currently at a shop. I'm not savvy enough to know, does this terminal box cover mating surface constitute a flame path? or a critical surface for maintaining explosion proof enclosure? In what way is it different than the endbell mounting surface?



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[itsmoked]

The makers pick a surface that is predictable in creating a cooling flame path and big enough to limit the explosive over-pressure in the product so it doesn't crack open or grenade. Typically that's the cover. On all regular enclosures it's just the cover. I suspect it's the terminal box cover on motors because while a motor is large in volume the rotor takes up almost every bit of that volume so the fuel volume is actually quite small. It's likely the cover. The end-bell is part of the motor structure that has to resist and support the shaft rigidly so I doubt it is also doing flame path cooling. One more reason changing the bearings is not a big issue.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Hi Pete;
I sympathize with your problem.
In the jurisdiction that I work in, only a licensed electrician may remove the cover of an explosion proof enclosure.
A licensed electrician may connect or disconnect the motor. Depending on the local trade jurisdictions an electrician or a millwright may remove and replace the motor.
Bearing replacement will be done in a qualified shop.
What is the answer in your jurisdiction?
The answer to that is getting more stringent as the MBA (sometimes referred to as CYA) influence increases.
The proper procedure is a matter of liability as determined by the level of risk that your firm is willing to accept and the ruling of the AHJ and of your insurance carrier.




Bill
--------------------
"Why not the best?"
Jimmy Carter