ABB VFD Breaker?

I have an application where I am using 2 75hp 480vac ABB VFDs, (ACH 550-UH-097A-4) and would like to use molded case circuit breakers. The manual recommends fuses.

I know fuses have advantages, but I want to know for certain if I CAN use breakers.

Thanks for the input.

Stationmaster

yes, as long you size according to 430.52 of the National Electric Code and have overload protection.

Article 430 Motors, Motor Circuits,and Controllers.

ABB recommend to use both but I find the circuit breaker only is sufficient. Fuses on the supply side of the drive are an attempt to protect the downstream device (the drive) and such protection is usually pointless. The fuses blow after the drive has died.

John Gaunt said:

ABB recommend to use both but I find the circuit breaker only is sufficient. Fuses on the supply side of the drive are an attempt to protect the downstream device (the drive) and such protection is usually pointless. The fuses blow after the drive has died.

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I'm thinking the same thing, John. I always have used breakers on another brand of drive I use. And places where other builders have used fuses either get nuisance fuse blows or like you said, the drive blows first.

What I like about breakers is that I can power down one drive for service by flipping off the breaker, without interrupting service to the other drive. Fuses are WAY more cumbersome.

I really don't want to buy "both".

Stationmaster

I have read testimony that basically said semiconductor fuses are fast enough to protect the drive, but if you aren't going to stick with them, you may as well go with MCB (motor circuit breakers) for ease of use.

I don't remember the official specifications of the fuses that can achieve this.

Hopefully the ABB experts (DickDV) can help us learn something here.

If you use the large finger safe fuse holders, you can open them to isolate a drive too, just as quickly and almost as easily as with a breaker.

We've wired a lot of ABB drives and have probably used breakers 99% of the time. Not saying it's right or wrong, but most customers don't like looking for fuses in the middle of the night.

I spec breakers on all drive supplies, EXCEPT where I'm tieing together a common DC bus system. Then I do use semiconductor fuses for each drive on the DC bus.

The problem concerning the use of breakers versus fuses is a little more complicated.

When specifying the overcurrent protective device (be it a fuse or a breaker), the device must be chosen to withstand the full available fault current.

For example, your system can provide 35,000 Amps of fault current, then the fuse or breaker MUST have a AIC withstand rating of at least that amount. The problem then becomes finding a current limiting breaker for that application. That is usually why a $40 fuses is chosen instead of a $1000 breaker.

In addition, just chosing a breaker (or a fuse) and putting it in there can also lead to a lack of co-ordination of protective devices. This will cause problems like the upstream device acting instead of the closest device.

The only bad thing is that most of the designers don't understand or follow the proper design rules - either by ignorance or laziness.



Some good reading:
http://www.littelfuse.com/data/en/S...erature/PF992UsingFusestoIncreaseYourSCCR.pdf


Go here and watch the videos:

http://www.epgco.com/fuses.html


Now, just think of your face being right in front of the starter when it fails (like during troubleshooting).

You must take all this into consideration when designing a circuit.

AND - you must assume that the person who designed the panel that you are working in did NOT take this into consideration.

As a general rule, 460V drives up to about 50hp are not economical to repair if the regulator, power supply, or power circuit has failed. So, for these sizes, I don't see much point in semi-conductor fuses. The drive is toast with or without collateral damage.

Above 50hp, the drive is somewhat repairable and that makes semi-conductor fuses worthwhile. Remember, these fuses are not meant to prevent the first failure. It's the domino effect that they are designed to stop so a single failure doesn't turn into a chunk of carbon.

In the smaller drives, I think the most important consideration with fuses is the warranty. Many manufacturers will not honor their warranty if they find out that the drive is fed from ordinary fuses or circuit breakers.

But then, I start up drives on circuit breakers all of the time and everybody is happy! So, it's probably a free choice, at least on the smaller units.

Also, I think regular circuit breakers are ok. They don't have to be motor start breakers. The drive has a little inrush when first powered but that is far less than DOL inrush.

Thanks all.

Bruce, the "main" disconnect upstream of this VFD controller has fuses (300amp, dual element) and should limit the overall available fault current.

Dick, Does it seem to be ABB's policy to reject warranty clams based on breakers instead of fuses?

Stationmaster

Stationmaster said:

Thanks all.

Bruce, the "main" disconnect upstream of this VFD controller has fuses (300amp, dual element) and should limit the overall available fault current.

Stationmaster

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Well, you are right that it will limit the fault current, but now you have an uncoordinated system. This is where the you will trip the main fuses and shut down everything for a motor fault. On a system with multiple motors, this makes troubleshooting a complete nightmare because the main cabinet fuses blow and the maintenance guys can't tell what is causing it.

When I've seen things like this happen, the first thing a maintenance guys does is up the fuses or worse.

I have a vague memory of ABB VFDs that needed Ultra fast fuses.

brucechase said:

Well, you are right that it will limit the fault current, but now you have an uncoordinated system. This is where the you will trip the main fuses and shut down everything for a motor fault. On a system with multiple motors, this makes troubleshooting a complete nightmare because the main cabinet fuses blow and the maintenance guys can't tell what is causing it.

When I've seen things like this happen, the first thing a maintenance guys does is up the fuses or worse.

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Bruce,

I hear you, But I'm a little unclear. I have two (2) drives each with their own ckt brkr (now engineered at 125amp ea) being fed by one main fusible disconnect with 300 amp fuses. Are you saying that you would expect the 300amp fuse to blow before one of the 125amp breakers trips? I was thinking that the 300amp fuses would act as a last resort to limit maximum fault current, but that a 125 amp breaker would trip for a ground or short, relative to a single drive.

Incidentally, not that it should affect design, but if this outfit blows a 300amp main fuse or fuses, they will call ME, not try to fix it themselves.

Stationmaster

Stationmaster said:

Bruce,

I hear you, But I'm a little unclear. I have two (2) drives each with their own ckt brkr (now engineered at 125amp ea) being fed by one main fusible disconnect with 300 amp fuses. Are you saying that you would expect the 300amp fuse to blow before one of the 125amp breakers trips? I was thinking that the 300amp fuses would act as a last resort to limit maximum fault current, but that a 125 amp breaker would trip for a ground or short, relative to a single drive.

Incidentally, not that it should affect design, but if this outfit blows a 300amp main fuse or fuses, they will call ME, not try to fix it themselves.

Stationmaster

Click to expand...

Yes, I would expect that on a serious fault (thousands of amps), the 300 amp fuses will almost always open BEFORE the 125 amp circuit breaker trips. If you want to see for yourself, you need to get the melt curve on the fuse and the trip curve on the circuit breaker and put them together. You will see in relatively low fault currents that the circuit breaker will trip, then there will be a section of unknown (in which either can trip), and for the higher fault currents, the fuses will act faster or both will actuate together.

Here is an article on selective coordination:

http://www.iaei.org/magazine/2010/0...rcement-overcurrent-protective-device-basics/


If you google selective coordination fuses circuit breakers, there will be a lot of material to digest. Most will explain what I am trying to show.

Stationmaster, ABB requires semi-conductor fusing in the supply to the drive for the warranty to be valid. I suspect that this is the position of most manufacturers. However, the practice in the field lets this slip by more often than not.