Motor contactor drop out

[mbrooke]

Then your feeder has not been properly designed. Someone used the absolute minimum, or less, to save money.

:?

 

[ptonsparky]

:?

In post 19, did you use Fig 6 to determine that breakers and feeder protection would not hold?

 

[StarCat]

Refrigeration compressors will stop in 1/4 cycle. I have seen single phase scroll compressors without anti-short cycle protection come back on line running backwards as a consequence of very quick power interruptions.

 

[kwired]

Ok, so reading, it appears that even a breaker at 250% may not hold Even if it does, I can't see the MCC feeder holding. :jawdrop:

Breakers over 150-200 amps often have magnetic trip adjustment.

 

[mbrooke]

In post 19, did you use Fig 6 to determine that breakers and feeder protection would not hold?

Yes. for multiple motors all pulling 2x the starting current.

 

[mbrooke]

Refrigeration compressors will stop in 1/4 cycle. I have seen single phase scroll compressors without anti-short cycle protection come back on line running backwards as a consequence of very quick power interruptions.

Can AC units do this? I've had brief flicks at my home and the outdoor unit will start buzzing/humming very loudly but seems to still be spinning internally. Yes the overload works.

 

[mbrooke]

Breakers over 150-200 amps often have magnetic trip adjustment.

True

Question: why don't breakers below that have adjustable magnetic trip?

 

[Russs57]

Mbrooke, you asked some questions and I'll try to answer them. Not sure I have them all.

First one I'll call "nuisance tripping". Hey, if we knew why it wouldn't be happening! Big ones for me are related to upstream devices having ground fault and downstream devices not having it. Seriously I worked at a hospital in Tenn that had 110/220 duplex receptacles. 3 phases, neutral, and ground. Guys would replace receptacle, not break off a tab, buck phases, and trip the single main breaker to entire place. Got so bad we were stuck on generator power for two days while Square D field rebuilt old bolt lock breaker. I have seen ground faults on 20 amp 120 volt circuits take out 2,000 amp 480 VAC breakers on ground faults. Power blinks are always good for making bad stuff happen. I might go months without any and then have a dozen in an hour. Sometimes seemingly unrelated equipment that suffers a short circuit can cause problems elsewhere. Diode bridges in VFD's don't handle voltage spikes from thunderstorms very well, but then a lot of electronic parts don't.

Second I'll call "why doesn't Goggle have an outage". Best way to avoid problems is to never let the equipment see a disturbance/outage. Think whole facility on-line/double conversion UPS. Think flywheel system to maintain till generators kick in. Oh, and give me at least two of everything (N + 1). Also think spending a lot more money than most are willing to throw at the problem. Don't forget sure suppression and harmonic filtering. Most of us create our own power problems and computers are about the worst offenders.

Third I'll call "why $10,000 breakers become paper weights". I suppose I had a lot of early generation breakers. I love the features and adjustments so I wouldn't stop buying them. Just that I have had some go with little to no warning. Nature of the beast I suppose. On the other hand I have 70 year old Westinghouse and GE breakers still doing fine.

Fourth I'll call " do I need ground fault". If your service is big enough it will be required on the main breakers. If they have it and you experience a downstream fault chances are high you will trip main breakers on occasion. Typical settings on the main will have a delay of 0.1 seconds. Non adjustable small CB's are often capable of about 6-8+ times current rating in that time frame. So yes, IMHO if you have ground fault on the mains you need to have it downstream as well. Not all the way, but at least to the point where you can tolerate dropping out an entire panel board.

You mention Kirk keys but then "rivets?". What I am talking about is a mechanical interlock to prevent two different sources for energizing the same bus.

You mention "install and forget for 30 years" and then what failures I'd most likely find. First just WOW! 30 years huh? Hmmm, I suppose it comes down to what you call a failure. To me maintenance isn't about fixing things. It is about keeping things from ever needing to be fixed. So for me "discovering a failure" involves testing, such as current injection testing of breakers. Historical logs of megger readings is another example. Used to be everything was visually inspected and re-torqued every year. Nowadays they just want to get by with annual infrared scans. So yes, no power out of a breaker is a failure. A breaker that doesn't trip is a FAR larger failure, and sadly, might never become discovered as a failure by some.

BTW, I love fuses (and anyone that has done current injection testing on breakers will feel the same) but the problem is, will they be kept in stock, and will the proper protection be in place to make sure single phase conditions won't happen......because you can't count on the other fuses blowing (eventually). Nothing will carry it's rating forever and magically trip/blow just above it. A time delay fuse is "required" to carry 500% for at least ten seconds. The large majority of motors run at about 75% so if overload protection is set at 125% you might never get there. I always set OL's for actual running amps. This can change over time, for example as an AHU's coil becomes more of a restriction current will fall and OL relay should be readjusted.

Anyhow, I don't claim to know much but I reckon I do have strong opinions. Not sure if I addressed your questions so ask again if needed. I would add, that some of your goals seem to be at odds with some of your methods (IMHO). Mostly, I would have a MCCB with ground fault module and an electronic overload relay based motor starter in my MCC bucket (assuming there is a full fledged MCC). At the motor end I'd have a fusible disconnect or MCCB. The breakers in a factory built MCC can be mag trip only which you aren't allowed to use otherwise. If no MCC mount a combination motor starter as close as possible to the motor. Either way could remove your liability and could give you series rating.

 

[mbrooke]

You answered most of them well.

I like your support for fuses Does fused switchgear do better than breakers in the long run?

I plan (want, but its open to change) to have everything above 100-225 amps be low peak fuses. Nothing coordinates better than fuses (think how short circuit power varies between gen and utility and system changes).

I also want to ask- have you ever seen the electronics in breakers fail? Or not work from to much voltage dip during a fault?

 

[Russs57]

I would say fused stuff requires more maintenance but is maintainable. You have moving parts exposed to local conditions (I'm next to salt water). You have fuse clips that might get loose, etc.

I prefer fuses when they feed one item. I would not use them to feed an entire panel board, mostly because of the possibility of a single phase condition.

Are you aware of the GE Tri-Break line of MCCB's? I have used a lot of them and they might be just what you are looking for. While it is possible to replace fuses they don't make it easy on purpose and it could very well void UL rating. Not even sure if they still make them. If not maybe someone has something like them.

I couldn't say what causes an electronic breaker to fail. I would be more inclined to suspect high voltage than low. Some, with outboard modules can be repaired (usually larger draw-out types). If obsolete there are places like Satin America that have retrofits. Others, like Micrologic, you toss in the trash.

 

[mbrooke]

I would say fused stuff requires more maintenance but is maintainable. You have moving parts exposed to local conditions (I'm next to salt water). You have fuse clips that might get loose, etc.

Would breakers not require more maintenance since QMQB and similar switches have fewer moving parts?

I prefer fuses when they feed one item. I would not use them to feed an entire panel board, mostly because of the possibility of a single phase condition.

True, but you at least have some power. Though it can be confusing for ICU nurses when the lighted receptacle they just plugged into now starts to dip in voltage.

Are you aware of the GE Tri-Break line of MCCB's? I have used a lot of them and they might be just what you are looking for. While it is possible to replace fuses they don't make it easy on purpose and it could very well void UL rating. Not even sure if they still make them. If not maybe someone has something like them.

Noted.


I

couldn't say what causes an electronic breaker to fail. I would be more inclined to suspect high voltage than low. Some, with outboard modules can be repaired (usually larger draw-out types). If obsolete there are places like Satin America that have retrofits. Others, like Micrologic, you toss in the trash.

One the reasons I want to avoid breakers.

I have in my mind this:

> 225 amps fuses

< 225 amps breakers, or at least < 60amps breakers


This 1) eliminates electronics 2) cheaper / simpler for building users to reset a 15-60 amp breakers when to much gets plugged in or the stove blows an element. 3) faults on >100amp feeders are not likely and may never happen 4) 100% guaranteed coordination with low peak fuses 5) reduced arc flash 6) less that can "stick" if equipment is not touched for 30-60 years

 

[mbrooke]

I would say fused stuff requires more maintenance but is maintainable. You have moving parts exposed to local conditions (I'm next to salt water). You have fuse clips that might get loose, etc.

You might be right after all:

 

[mbrooke]

 

[mbrooke]

Though less so in the higher amp frames:


https://youtu.be/SXe0lkRqkHM?t=415


https://youtu.be/seYXOGHsaS4?t=18


In that case I'll take a fuse/switch combo. Little is gained at the LV level having a breaker, especially as main which is even less likely to call to operate in its in service life.

By rivets I meant a tag. Basically saying something like "Attention: dead tie only, open main on one side before closing this tie breaker" Good enough for me, no kirk key needed.

 

[paulengr]

Maybe I’m missing something here but pull in is normally around 85 V with 120 V coils and drop out is around 60-75 V based on testing. But more importantly who cares. Once the aux contact drops out the starting circuit drops out in standard 3 wire design. Even 2 wire (PLC) designs are supposed to emulate this. Most PLCs if they drop out turn off outputs on startup.

The biggest problem I see with main breakers is lack of coordination, failed feeder breakers that no longer trip, and somebody didn’t use ground fault in feeder breakers or especially starters. The NEC changes with respect to ground faults and arc flash settings fail to account for coordination so I see a lot of dumb things like having ground fault on the main of an MCC but skipping it in the overloads (cheap to do right, expensive to fix), or instantaneous everywhere (no coordination). The other issue is when you have one huge motor and not much of anything else. Typically the main gets set to 125% of the current while the motor protection is set much higher for obvious reasons so the coordination issue gets missed until startup.

 

[mbrooke]

Maybe I’m missing something here but pull in is normally around 85 V with 120 V coils and drop out is around 60-75 V based on testing. But more importantly who cares. Once the aux contact drops out the starting circuit drops out in standard 3 wire design. Even 2 wire (PLC) designs are supposed to emulate this. Most PLCs if they drop out turn off outputs on startup.

The biggest problem I see with main breakers is lack of coordination, failed feeder breakers that no longer trip, and somebody didn’t use ground fault in feeder breakers or especially starters. The NEC changes with respect to ground faults and arc flash settings fail to account for coordination so I see a lot of dumb things like having ground fault on the main of an MCC but skipping it in the overloads (cheap to do right, expensive to fix), or instantaneous everywhere (no coordination). The other issue is when you have one huge motor and not much of anything else. Typically the main gets set to 125% of the current while the motor protection is set much higher for obvious reasons so the coordination issue gets missed until startup.

Most buildings are not coordinated. Breakers are left at their factor setting dials and thats it.

I'll also go on a limb and say that a breaker which has not opened in 20 years might take an extra cycle to fully open.

 

[Besoeker3]

Normal power up does not involve the inrush of every motor in a building.

Wouldn't each motor have its own overcurrent protection?
And would they all automatically restart?

 

[jim dungar]

Most buildings are not coordinated. Breakers are left at their factor setting dials and thats it.

I'll also go on a limb and say that a breaker which has not opened in 20 years might take an extra cycle to fully open.

In a hospital environment you are required to have at least two levels of ground fault protection. It is expensive to add GF trip function to fusible switches below 800A.
The NEC will be requiring 1000A and larger fusible switches to be provided with some type of Arc Flash Energy Reduction switch, it seems many manufacturers will be moving towards incorporating electronics into their fusible switches.
Historically 1000A and larger fusible switches require regular (every 3-5 years) operation and maintenance or else the grease, on their moving parts, tends to seize up preventing the switch from opening. A switch stuck in a partially open position can be catastrophic, particularly when trying to clear a single phase event.

For fuses to coordinate, you usually must maintain at least a 2:1 ratio but in other cases it can be as high as 8:1 and the fuses must be from the same manufacturer. What safe guards would be implemented to prevent someone from purchasing 'cheaper' replacement fuses, much less ones from a different manufacturer?

 

[mbrooke]

In a hospital environment you are required to have at least two levels of ground fault protection. It is expensive to add GF trip function to fusible switches below 800A.

Even 120/208 and 138/240?

The NEC will be requiring 1000A and larger fusible switches to be provided with some type of Arc Flash Energy Reduction switch, it seems many manufacturers will be moving towards incorporating electronics into their fusible switches

.

A low peak current limiting fuse is not enough?

Historically 1000A and larger fusible switches require regular (every 3-5 years) operation and maintenance or else the grease, on their moving parts, tends to seize up preventing the switch from opening. A switch stuck in a partially open position can be catastrophic, particularly when trying to clear a single phase event.

For fuses to coordinate, you usually must maintain at least a 2:1 ratio but in other cases it can be as high as 8:1 and the fuses must be from the same manufacturer. What safe guards would be implemented to prevent someone from purchasing 'cheaper' replacement fuses, much less ones from a different manufacturer?

About the same safeguards as someone closing a breaker into a fault.

Key is knowing regardless of the system at hand.

 

[mbrooke]

Wouldn't each motor have its own overcurrent protection?
And would they all automatically restart?

Yes, but imagine a power dip for a few cycles... where the contactor does not drop out. Its possible to have a significant current inrush afterwards.