# MCC maintenance



## glen1971

We try and line up MCC cleaning and visuals during scheduled outages, usually every 5 years. We have the latest "hot spot" report from an IR scan on hand, so we have an idea what we are focusing on. We also pull the cubicles and check the bus connections, clean and reassemble. Retorque what we can that is de-energized (cable to bus connections, secondaries, etc). 
Annually, we do the IR scans with as much of a load on as possible. A big part of the scans is also interpreting the readings, so that you aren't chasing a 2 degree temp difference.


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## Wirenuting

What model MCC?


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## kb1jb1

glen1971 said:


> We try and line up MCC cleaning and visuals during scheduled outages, usually every 5 years. We have the latest "hot spot" report from an IR scan on hand, so we have an idea what we are focusing on. We also pull the cubicles and check the bus connections, clean and reassemble. Retorque what we can that is de-energized (cable to bus connections, secondaries, etc).
> Annually, we do the IR scans with as much of a load on as possible. A big part of the scans is also interpreting the readings, so that you aren't chasing a 2 degree temp difference.


One plant I worked at only did the IR scans in the winter. If they did it in the summer then most of the distribution would be in the danger zone. Very little concern for the infrastructure. As long as the floors had a shine and the walls had a fresh coat of paint. I quit that place after two years. A plant electrician should not be painting when equipment needs attention.


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## five.five-six

Wirenuting said:


> What model MCC?


Multi conductor cable, I always thought but I’m here to learn.


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## Wirenuting

five.five-six said:


> Multi conductor cable, I always thought but I’m here to learn.


No, not what kind of SO cord. :vs_mad:

What brand of Motor Control Center. lain:
An old FPE maybe? I liked them. :vs_OMG:


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## Apelectric

Depending on the gear, we clean, check connections, grease, trip and reset breakers about yearly.


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## JRaef

Stab spring weakening on an MCC is generally a result of over heating + time. Sometimes corrosion will attack the stabs themselves, especially if there is a lot of H2S gas (hydrogen sulfide, a byproduct of anything rotting or fermenting, such as sewage). But that is usually happening on all of them at the same time, not just one.

As to the VFD failure: if your MCC was powered down (or the CB feeding the VFD was left open) for over a year, the capacitors inside of the VFD will deteriorate and fail just by being energized for the first time. The trick is that if you are going to decommission something with VFDs but keep it as a backup, energize it once per year for 2 hours or so. You don't need to operate anything with it, just put power to the VFD input. If it has sat for over a year, you need to do what's called a "capacitor reforming procedure" that involves applying low voltage over a long time, slowly increasing it until the capacitors build up their internal layers again (too long to go into).

Most VFDs are not going to be damaged just by getting single phase power. Some may trip, others may just hum along fine until the load is more than 50% of the rating.


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## mburtis

Its a westinghouse 2100 if I remember right. Would be about 25 years old now and I know it has never had anything done to it.

Just to clarify the VFD that is no longer responding was not on back up duty, it has been running. It is part of a three pump skid with VFDs integrated into the motors (grundfos). Typically only one pump runs at a time and it switches pumps every day. Changes speed of motor to match flow while maintaining a set pressure. Works really slick until now. The back up pump does not have a VFD but gets ran weekly anyway to keep the case cleaned out.


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## gpop

You have to consider cause and affect. 

If the spring clip became loose was this the cause of the drive taking a dump or did the motor/drive (presuming this is a all in one) short out and cause the clip to over heat. 

Most vfd's wouldn't care if they drop a phase (some can be fussy about which phase as there controls use 2 phases). This may be something that shows up during one of you future IR pm's when your sent to investigate why 2 fuses are hotter than the third. 

On remote mounted vfd's where you can access the dc bus there are simple test that can be done with the drive disconnected to test the hardware but as your seems to be built onto the motor calling tech support would probably be the best bet to see if they have a testing solution before condemning the unit.


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## mburtis

Im waiting on tech support to get back to me on further troubleshooting the drive. And yes its integrated into the motor, I opened up the drive and couldn't see any obvious spots where the smoke and fire escaped. I also couldn't get any 24VDC readings making me think something in the control/signal circuitry is fried. 

As far as which is the chicken and which is the egg I'm not sure. When the skid shut down the pump shut off and the screen on the control cabinet shut off, (second hand info as I wasn't there). I found one of the 1 amp fuses on the control circuit was blown, and the overload for one of the pumps was tripped (the pump that now wont do anything). Replacing the fuse brought the screen back. 

Its entirely possible that the motor/drive shorted first although there is enough protection in the control cabinet that i would think it would have tripped before overheating the MCC clip. On the other hand there is enough protection in the control cabinet that dropping the phase shouldn't have been able to hurt the drive. 

Getting back to the original question, when tripping breakers, is it just manually cycling the breaker or is there a better way to actually test the breakers? Is the basic point of cycling them to make sure the contacts aren't stuck and to hopefully remove oxidation on the contact surfaces? What would need greasing inside of an MCC (big breaker linkages ?)?


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## kb1jb1

I had a problem with drives breaking down because the workers were turning the machines on and off by the 60 amp disconnect switch and not an orderly shut down by using the control panel. They were using the drive for speed control only. No more problems after they started to shut down the machines the right way. Maybe the drive burnt out because the feeder faulted while the drive was under load. Newer drives have safe guards.


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## gpop

mburtis said:


> Getting back to the original question, when tripping breakers, is it just manually cycling the breaker or is there a better way to actually test the breakers? Is the basic point of cycling them to make sure the contacts aren't stuck and to hopefully remove oxidation on the contact surfaces? What would need greasing inside of an MCC (big breaker linkages ?)?


You are only dealing with small sealed breakers so there's no greasing. If you have a test button push that and make sure the breaker trips, Confirm the breaker trips on all 3 legs then reset and confirm the breaker makes on all 3 legs. If you can power the bank down safely you can do a resistance test but that really requires a low resistance meter. 

Wear PPE when testing, Only do one breaker at a time as some breaker may fail and if you only stock one its better to stop once you find a bad until you get another spare. Larger sub and main breakers should be contracted out to people who have all the toys to test them.


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## mburtis

gpop said:


> You are only dealing with small sealed breakers so there's no greasing. If you have a test button push that and make sure the breaker trips, Confirm the breaker trips on all 3 legs then reset and confirm the breaker makes on all 3 legs. If you can power the bank down safely you can do a resistance test but that really requires a low resistance meter.
> 
> Wear PPE when testing, Only do one breaker at a time as some breaker may fail and if you only stock one its better to stop once you find a bad until you get another spare. Larger sub and main breakers should be contracted out to people who have all the toys to test them.


Thanks for the input. None of our stuff is set up with any way to test it, will have to keep researching that. I'm the first person in the history of the plant to really look into any of this kind of maintenance so lots of development work to do. Our stuff is pretty small and basically designed to be set and forget but figure I might as well attempt to do what I can as far as maintenance.


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## Wirenuting

kb1jb1 said:


> I had a problem with drives breaking down because the workers were turning the machines on and off by the 60 amp disconnect switch and not an orderly shut down by using the control panel. They were using the drive for speed control only. No more problems after they started to shut down the machines the right way. Maybe the drive burnt out because the feeder faulted while the drive was under load. Newer drives have safe guards.


If the disconnect is after the drive output, it should have aux contacts in it to shut the drive down before the blades open. That spike is a killer to drives over time. 
There is a couple of threads were it’s been discussed.


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## JRaef

Exercising a breaker is just turning it on and off a couple of times, and that's fine. The only way to test a breaker that doesn't have a "Test" button is to do a current injection test. That's not really recommended on Molded Case Circuit Breakers (MCCBs) because that tests the breaker by actually making it carry trip current until it trips, just using low voltage so as to limit any damage to the contacts. But there is also the aspect of the trip elements getting stressed. Current injection testing is generally done on large air-break POWER Circuit Breakers (PCBs), not on MCCBs. PCBs are designed to be tested periodically and can be rebuilt. MCCBs are designed differently and you can wear out the trip system by doing injection testing too much, then they cannot be rebuilt, they are throw-away. The UL test standard only require that they can be tripped and reset so many times Yes, breaker houses claim to sell "refurbished" MCCBs, but all they can actually do is clean them and test them, and in the testing they actually consume some of the component life.


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## VELOCI3

Last job I did used Eaton contactors in the MCC buckets. The contactor monitors voltage, phase loss, on off condition. They trip out in the event of those conditions to protect the load.


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## cam_maint

I don't have very many machines at work, so during my monthly PMs, I do a thermographic survey and just compare what I see to memory. Problems show up better in the winter months. I have seen some wires through raceway covers when they had current draw too high. Nothing was wrong in the circuit, so I added another wire in parallel and never had any issues.


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## controlsengineer5779

I worked at a water utility out west. As electricians, we were scheduled with PM's for all electrical equipment. Maintenance engineering developed the schedules. It actually worked out well. We did IR surveys twice a year. Any suspicious reading and the station was taken down and the condition was checked/corrected. We caught several loose connections that would have resulted in failures eventually, mostly on the 5kv gear and transformers. We also used an ultrasonic probe (microphone) to pick up arcing. We got several hits using that on the 480 gear; saved us a lot of failures.


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## Quickservice

kb1jb1 said:


> One plant I worked at only did the IR scans in the winter. If they did it in the summer then most of the distribution would be in the danger zone. Very little concern for the infrastructure. As long as the floors had a shine and the walls had a fresh coat of paint. I quit that place after two years. * A plant electrician should not be painting when equipment needs attention.*




Amen!! Reminds me of the funny guy who asked ME if I did any plumbing. NOT


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## Quickservice

VELOCI3 said:


> Last job I did used Eaton contactors in the MCC buckets. The contactor monitors voltage, phase loss, on off condition. They trip out in the event of those conditions to protect the load.


I worked for an Eaton/Cutler-Hammer distributor. We had great success with their contactors per MCC applications. Biggest job was a tier 2 plant that fed Nissan.


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## gpop

controlsengineer5779 said:


> I worked at a water utility out west. As electricians, we were scheduled with PM's for all electrical equipment. Maintenance engineering developed the schedules. It actually worked out well. We did IR surveys twice a year. Any suspicious reading and the station was taken down and the condition was checked/corrected. We caught several loose connections that would have resulted in failures eventually, mostly on the 5kv gear and transformers. We also used an ultrasonic probe (microphone) to pick up arcing. We got several hits using that on the 480 gear; saved us a lot of failures.


Please tell me you are using a parabolic mic and not a probe. 

We had to unlock the 25kv transformers for a engineer to do ultra sonic testing.
Engineer puts on full flash then pulls out a ultra sonic wand. I told him he didn't need PPE as we was not going to allow him to carry on. He went on a rant then finally asked me why. 

I told him you have a wand connected with a cable to a box on your side which is then connected to headphones. If there is a leak from the cable its going to jump to the wand then to the head phones and blow your head off. 
Poor guy stood there for a minute white as a sheet. Turns out this wasn't the first high voltage transformer he had tested by holding the wand next to the cables.


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## just the cowboy

I had a engineer wipe off the dust on a 4160 volt cable to read the type number once. We had just shut it down and he did not wait for us to discharge the cable to ground, and put on clamps.
He discharged the capacitance charge quick. Bet he never did that again.


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## controlsengineer5779

gpop said:


> Please tell me you are using a parabolic mic and not a probe.
> 
> We had to unlock the 25kv transformers for a engineer to do ultra sonic testing.
> Engineer puts on full flash then pulls out a ultra sonic wand. I told him he didn't need PPE as we was not going to allow him to carry on. He went on a rant then finally asked me why.
> 
> I told him you have a wand connected with a cable to a box on your side which is then connected to headphones. If there is a leak from the cable its going to jump to the wand then to the head phones and blow your head off.
> Poor guy stood there for a minute white as a sheet. Turns out this wasn't the first high voltage transformer he had tested by holding the wand next to the cables.


Yes, it was a parabolic mic. I was kind of remembering that our planner had always said "ultrasonic probe" on the work orders. 
That was last decade, and PPE and arc flash stuff was just getting serious. We had flash suits, but we would remove 5kv transformer covers all the time, same with the 12.4 to 480 or 5kv and shoot the connections. We had non-contact testers that could be used on a hot stick, plus a contact meter that would go to 25kv if we absolutely needed it.
On some of our old GE disconnects, a blade would not disengage from the contacts (prongs). Had to be careful with those, thus the testers.
We also did all the splices on the 5kv submersible wells. After sitting all winter, I got a good idea why that little sticker of that very angry electricity god on the front of the enclosure looked like that. We had several "pooms!" when we called ops for a start. Pretty cool stuff.


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## controlsengineer5779

just the cowboy said:


> I had a engineer wipe off the dust on a 4160 volt cable to read the type number once. We had just shut it down and he did not wait for us to discharge the cable to ground, and put on clamps.
> He discharged the capacitance charge quick. Bet he never did that again.


When I was in the IBEW out west, my foreman walked by a 5kv cable with a bare end lying at about mid-calf level. An electrician on the other end was Hi-potting it. He drew an arc and it burned a hole through his jeans, into his calf and out his heel through his boot. Customer spec on Hi-potting was 3 times line voltage. Nice little 15kv zap.
He had gone under the red tape without asking. Hmm.:wallbash:


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## JRaef

I was troubleshooting some 5kV soft starters once that kept shorting out the SCRs. We could hear a ticking sound through the closed door, like something arcing to ground inside. But when we killed power and opened it, we couldn't find anything. So we opened the door, set up a high speed video camera, turned off the lights, then energized it while standing about 15 feet back. What we saw and recorded was an eerie spider web like phenomenon, crawling across the surface of the conductors used inside. It looked like is was alive, searching for something. Then eventually it crawled across all of the cables and found a point close enough to a bolt head to make the jump, and that was the ticking sound we heard. Turned out that the factory had over tightened some straps and compressed the rubber insulation too much, causing corona discharge. then they had also forgotten to wipe down the cables after installing them, so they were covered with a thin film of dust that was conductive enough to allow tracking of the corona until it found a ground point. 



I wish I had a copy of that video, but the guy who owned the camera quit right after that.


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## paulengr

Had a 4160 enclosure explode with so much force we never found the door. When we cut open the terminations the contractor never removed the semicon and it took two weeks to fail.

Lots of “3 year” terminations. That’s where someone cuts everythjng back but no termination.

Saw one in Georgia where the guy changing out 5 kV MV-105 didn’t know how to do it. So he cut the jacket, shield, insulation off very straight and flat then butted it up tight so the shield was loosely against the mechanical lug. After six months it had eaten about 18” of cable on both ends without failing catastrophically yet.

Recently saw a “home made” splice. Everything was mostly cut back. They wrapped a piece of #8 loosely around the shield. Then wrapped everything in 130C. Then a layer of some off brand silicone tape (70). Then put on two heavy wall adhesive heat shrink jackets, one over the other, then vinyl tape over everythjng for good measure. No stress relief.

I understand medium voltage can do strange things but every “strange” situation I’ve ever seen comes down to the same simple issues. The same guys that screw it up are the same ones that try hydraulic repairs with a rag and hose clamps. MV is the point where you have to use high electron pressure practices.


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## Benjamin1014

We do yearly IR scans of all our MCCS. We’ve identified loose clips this way. We also regularaly vacuum our MCCs because of combustible dust rules. We often find things needing repair during our routine cleaning.


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