# Value of electrical tests vs risk of messing with a stable system



## Flyingsod (Jul 11, 2013)

I’ll go first! It’s a subject near to my heart. I personally think it’s foolish to be messing with things that give you no problem. 
As I said in your other post thermal imagery and vibration analysis are the two most important predictive tests. Maybe because you don’t disconnect anything to do the test, indeed you MUST leave it connected and running to perform these tests. They are non destructive tests. When the test is over the system is in the exact same condition as when the test was performed. 
Other tests as you observantly noted leave the system in a different state than the test was performed on. In such a procedure you don’t KNOW the state of the system you just know what it was before you fiddled with it getting it back together. 

When I worked as a service tech we had some customers who wanted various electrical equipment cleaned. Either dust blowing or vacuuming. I always tried to talk em out of it if it was a control cabinet. Blowing forces dust and debris deeper into electrical apparatuses. When vacuuming you pretty much have to touch everything with the brush. 
It feels like about 20% of the times we cleaned a control cabinet it would cause an issue. A relay knocked loose or debris forced into the contacts. Something you’d have to spend time chasing down. Becuase of this I feel only heatsinks and the like should be cleaned sans a problem. 

Just MY opinion here but most all the testing that requires dismantling of a working electrical system should be reserved for troubleshooting purposes. 


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## just the cowboy (Sep 4, 2013)

As @Flyingsod said I have seen more damaged stuff, than bad stuff found by PM crews. 



mburtis said:


> Take for example megging a three phase transformer, according to the books one is suppose to lift all wires and jumper all the HV winding together and jumper all the LV winding together and then depending on which test you want to do, do whatever is appropriate with the grounds. It seems like if you opened the breakers upstream and downstream you could apply jumpers without necessarily disconnecting anything but regardless.


But for what you said about transformers, I would only feel right just opening breakers or disconnects if I could see connections and was sure there were no taps. 

Cowboy


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## Easy (Oct 18, 2017)

Having a PM program can be quite useful in keeping things running smoothly. Often times it's overdone and will simply waist valuable time. Visual inspections, tightening connections and cleaning are simple and don't take up very much time or much thought and are productive activates. It might be a good idea to keep records of the preventative maintenance that you are going to do so that you know when it was last preformed and you could update the procedures as you go along. Check the manuals for the equipment you have and see if there are recommendations you can follow.


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## just the cowboy (Sep 4, 2013)

Easy said:


> Check the manuals for the equipment you have and see if there are recommendations you can follow.


This is not always a good thing. When I did NC and CNC machine repair the manuals for PM all stated to set the power supplies to XX volts. Well sometimes this effected other things in the system and caused the machines to not run correct. 
Cowboy


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## Easy (Oct 18, 2017)

Most of the PM's that I did were written by some manager that knew nothing about electrical equipment. Some of the equipment was scheduled monthly and some yearly. Often times it was just a way to keep us busy. We had some conventional machines that were loaners from the government and it was ridiculous how often they wanted them inspected by the mechanics and electricians. They would say things like, check contacts for pitting or discoloration. Tighten all connections. Clean all debit inside control cabinet. Sometimes they would be more specific and have you check TDR's with a stop watch. Stupid stuff that was not applicable to the actual equipment. For a long time we were also doing PMs on the 12 kv systems but eventually that was outsourced because we really didn't have the equipment or knowledge to do it safely. The power distribution on the 480 side of things was maintained by us but really there were no actual PM's for that. Often times one of the EE's would determine if something like a transformer needed repair or replacement and also determined what the taps should be set at. Same thing for circuit breakers. The EE would determine properly configured, breaker coordination and have us replace breakers as needed. I think one of the most important part of a PM is visual inspection and cleaning. CNC machines can run into the millions of dollars and should be taken care of but it's also important to maintain the equipment feeding them. You don't really need any special tools to diagnose issues like in this photo.


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## Flyingsod (Jul 11, 2013)

A word about tightening. It’s not all good. Especially with control size wires. Periodic tightening leads to broken wires. I think it’s silly to just stick tools in everywhere for no reason and tighten things.

It makes more sense to check the wire for snugness. If you wiggle it and the lug wiggles with it it’s fine. If the conductor wiggles in the lug then yes it needs tightening. 

What makes more sense than all of that is a good thermal study. If there’s no undue heat being generated then obviously you don’t need to and IMO shouldn’t tighten. 


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## Flyingsod (Jul 11, 2013)

Easy said:


> . I think one of the most important part of a PM is visual inspection and cleaning. You don't really need any special tools to diagnose issues like in this photo.
> 
> View attachment 155875


Well we disagree on cleaning. Unless of course it’s so gross that it’s actually creating a fault path. Then even I have to agree it needs to be cleaned. 


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## just the cowboy (Sep 4, 2013)

Flyingsod said:


> A word about tightening. It’s not all good. Especially with control size wires. Periodic tightening leads to broken wires. I think it’s silly to just stick tools in everywhere for no reason and tighten things.



I agree I do what I call a twenty. I pick 20 random wires and check them, if all are tight I call it good. Yes I could of missed a loose one but I did not strip any screws.
Cowboy


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## mburtis (Sep 1, 2018)

What the....What is that? Plants, spider webs, alien life form...

Long before I was here apparently the entire bottom of one of the MCC was a huge mouse nest, chewed on the main incoming power to the plant as well as everything else. At least regular inspections and cleanings avoid that. 

Thermal imaging or even trending of the critical location temperatures seems like a wiser use of time than blindly checking things with a torque wrench or screwdriver. In my mind if the connection is good why would i risk "breaking the seal" by checking it. Now if there is evidence of a potential issue such as excess heat, heavy corrosion etc, then that's different. 

As far as control cabinets go. I've been planning to go through once a year or so and just due a basic inspection, try to organize the wires to keep them from getting out of control, and vacuum the bottom of the cabinets. Lately been thinking of vacuuming the transformer winding and enclosure once a year. MCC buckets probably just vacuum out the bottom. Thoughts?


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## Flyingsod (Jul 11, 2013)

mburtis said:


> What the....What is that? Plants, spider webs, alien life form...
> 
> As far as control cabinets go. I've been planning to go through once a year or so and just due a basic inspection, try to organize the wires to keep them from getting out of control, and vacuum the bottom of the cabinets.


My first thought was someone spilled their spaghetti. 


For the bottom of the control cabinets, throw out those damn blown fuses! Every place has at least one control cab with blown fuses in the bottom. 


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## gpop (May 14, 2018)

Like i have pointed out before its more to do with history and the environment you work in. I worked in a juice plant with thousands of electrical parts including over 600 motors. On the good side we only ran 9 months of the year which meant we had 3 months to carry out a lot of pm's. On the bad side everything in a juice plant gets washed down many times a week.

We installed 2 x IR windows and one clear window in our 25kv to 480v transformers. IR and ultra-sound were done once a month and temp, levels were checked once a week. Yearly oil samples were taken. The oil samples dictated what maintenance to carry out including filtering the oil or replacing the transformer. 

Opening pecker heads and re terminating the motors was cost effective and saved many small problems from become major problems. yes we did cause problems especially on small motors where the bolts would snap but on paper it saved a bunch of money. Tripping breakers yearly also lead to problems but it better to find a problem during a down period then it was to discover the problem during the running period. 

As for tightening wires you really have to do it once and make sure its done correctly. In my new job in utilities im 20 panels in on a 140+ and every panel has wire nips, loose wires, splayed wires, over stripped and generally old abandoned or caped wires. Once the panels have been done correctly then yearly it should be a quick check rather than a major job. (unfortunately it takes planning to shut the panel down and there's no 3 month break from other problems in this job)


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## mburtis (Sep 1, 2018)

Flyingsod said:


> For the bottom of the control cabinets, throw out those damn blown fuses! Every place has at least one control cab with blown fuses in the bottom.


But if I do that how is anyone going to ever going to figure out what the original fuse size was....
Does that also go for the 400 zipties that have gotten cut off and thrown in the bottom of the cabinet over the years. I'm hoping once I get through the PLC cabinets once they won't need anything except for actual modification. I got lots of ignored ones that have been monkeyed with over the years plus the fact they are always built by the lowest bidder so typically are a nightmare even when new. 

I'm going to have to do some investigation into IR windows and other inspection port type add ons. Open to suggestions. That would make it a lot easier and safer to take temp readings or scans, and other inspection type tasks. Most of our stuff has pretty small incident energy ratings and my everyday uniform is arc rated but I still don't open doors or remove covers with it energized and don't particularly like turning stuff back on with the doors open. Door mounted voltage and current readouts would be pretty dang slick too. Been planning on starting to exercise our breakers once a year or so, I bet there are some that haven't been turned off for close to 30 years. I don't think Ill ever have a way to actually trip test them but at least if I operate them once a year I know the contacts are welded shut.


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## splatz (May 23, 2015)

Flyingsod said:


> When I worked as a service tech we had some customers who wanted various electrical equipment cleaned. Either dust blowing or vacuuming. I always tried to talk em out of it if it was a control cabinet. Blowing forces dust and debris deeper into electrical apparatuses. When vacuuming you pretty much have to touch everything with the brush.
> 
> It feels like about 20% of the times we cleaned a control cabinet it would cause an issue. A relay knocked loose or debris forced into the contacts. Something you’d have to spend time chasing down. Becuase of this I feel only heatsinks and the like should be cleaned sans a problem.


I think the same way. I have seen seen things run dirty for a very long time without any trouble then the day they're cleaned, bam. 

I will vacuum things but without a brush and without actually touching the components, it's not nearly as thorough but blowing them out forces dirt into places it would never get. The brush can do that too, plus possible static if there's electronics exposed. 

I know that people do this quite a bit as busy work when things are slow and take pride in a neat and clean appearance but in most cases there are a lot of better things to do with what little time is available.


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## Easy (Oct 18, 2017)

I agree with the fact that using an air hose to clean out control cabinets is a bad thing. Overtightening terminal strips is also a bad thing.
Cleaning switch gear and large transformers with vacuums and wiping down insulators or checking connections is a good thing. There is really not much you can do to make repairs to a transformer. The only real things you can do on a dry-type transformer is look for discoloration or listen for vibration. You could also make sure the cooling fans are operating and the gages are working properly. Some transformers are in areas that are damp and they might have heaters so they should be checked as well. Look for missing bolts on the covers and replace them. Check the condition of the signage and replace as needed. I'm not sure how important it is but we eventually went around to all the gear and installed labels for voltages. 480v and 12,500 equipment. I guess some guys just could not understand the difference and just opened covers on stuff without checking first. View ports and a thermal imaging camera is great if it's in the hands of a qualified person. Most of the guys I see using them are not properly trained in thermography.


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