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Discussion Starter · #1 ·
The MDP for a recreation center remodel pictured below. My shop tells me that we're gonna be taking out the existing buckets and and swapping out with new GE molded case circuit breakers? I've never done this before on old switchgear. The only thing is they tell me that they haven't got them approved yet. Was just curious if anyone has ever done anything like this on GE switchgear from the 70s and have anything helpful
 

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Discussion Starter · #3 ·
Also have capacitors hooked into 3 pole. I myself am always learning with almost little help from foreman just talks bout personal life and no useful knowledge. But as long as that breaker is open during a shutdown of the whole system should read no voltage on bus bars? Or would there
 

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Also have capacitors hooked into 3 pole. I myself am always learning with almost little help from foreman just talks bout personal life and no useful knowledge. But as long as that breaker is open during a shutdown of the whole system should read no voltage on bus bars? Or would there

There should be a main breaker for the gear, remember the wires that hit that breaker are always live unless it's shut off by the POCO, always check your self don't take anyone's word for it.
 

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On the surface not a good idea . It looks to me that you would loose all the listing on the gear if your company is not a switchgear rebuilder. On the other hand if your company would but the whole unit and not just the breakers I would not have a problem with that.
For a contractor to put breakers in equipment that is designed for fuses without proper engineering and not having UL look at it NO WAY.

LC
 

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Discussion Starter · #6 ·
Lone Crapshooter said:
On the surface not a good idea . It looks to me that you would loose all the listing on the gear if your company is not a switchgear rebuilder. On the other hand if your company would but the whole unit and not just the breakers I would not have a problem with that. For a contractor to put breakers in equipment that is designed for fuses without proper engineering and not having UL look at it NO WAY. LC
Agreed, all this switchgear is in the basement so I doubt the engineer wanted to change the switchgear cuz you'd have to cut hole and lift en out with a crane. This job has an electrical engineer so you'd think that he'd have good idea how to change these buckets out? Lol funny thing is that this is on a Campus of an engineering college
 

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Discussion Starter · #7 ·
Black Dog said:
There should be a main breaker for the gear, remember the wires that hit that breaker are always live unless it's shut off by the POCO, always check your self don't take anyone's word for it.
That I understand I was planning on a shutdown with campus since this is a state job they run there own high volt. I was mainly concerned with the capacitors whether or not there would be any capacitance in the system when I shut it down were working on and if I should discharge it. And what the capacitors are even for. Cleaner power?
 

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Discussion Starter · #9 ·
Big John said:
If there are capacitors in the system they're likely for power factor correction. There's gotta be a means of isolation in there, be it a disconnect or even just some fuses. I'd pull those to isolate the bank from the system as they absolutely can hold a charge.
Makes sense, itson a 3 pole bucket fuse. A 3 pole bucket were gonna end up changing it to a molded case breaker. What's the proper way to to eliminate that residual charge? Get a hot stick and some grounds? Lol
 

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If this was a designed system and not something somebody just cobbled together then it likely has discharge resistors (I've got some vague memory that capacitors in switchgear are required to have a bleed-down time of less than 5 minutes, but don't hold me to that). If that's the case, test between each set of plates and each plate to ground.

If there's no voltage you bond everything together and ground it. If there is voltage you need a discharge stick, or a carefully selected resistor and some PPE. A solid ground can produce a hell of a flash, in addition it can actually damage some styles of capacitors by causing the plates to deform. So it wouldn't be your first bet if you wanted to re-use these.
 

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Most PFC caps require fuses, not CBs, for protection. What is the thinking behind changing to a CB? Because if it is that the fuses are constantly blowing, that is NOT the way to "fix" it!
 

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Why so? Ive noticed that but never understood why.
The purpose of a fuse in a capacitor is to prevent a catastrophic failure that can be not only messy when the electrolyte oozes out all over everything, but potentially even explosive if the pressure relief on the case fails. By the time a breaker senses and reacts to the rapid rise in current in a failing cap, it's too late.

The issue is, there is no real "load" on a capacitor feed, other than a small amount of "parasitic resistance". So the only time a protective device is necessary is if it ALREADY fails, therefore its purpose is just to limit the collateral damage. That's why replacing the fuses with a CB because the fuses are blowing all the time is such a fallacy. All that is going to do is lead to a more destructive failure.
 

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Discussion Starter · #15 ·
JRaef said:
Most PFC caps require fuses, not CBs, for protection. What is the thinking behind changing to a CB? Because if it is that the fuses are constantly blowing, that is NOT the way to "fix" it!
From what I was told that every circuit in this switchgear was getting swapped. I could be wrong in that it gets swapped but I don't even have approved shop drawings on all this yet. Just says on the print and specs that all circuits get re fed from new molded case CBs. Might be a good question for an engineer when the boss goes on vacation next week lol
 

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Ayuh, those little guys. If you open up the tops of the boxes, they'll look like this:


Just a bunch of daisy-chained electrolytic capacitors. Whether that's even doing an ounce of good is really questionable, because there's no means to switch on or off, they're not variable, and often we see them with no protection or monitoring.

It's not uncommon to open those enclosures and find several bulged out capacitors where they've gone bad or are going bad and nobody has any idea.
 

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Discussion Starter · #19 ·
Well tonight was our first shutdown for this switchgear and had problems with the main breaker opening. Hit the manual trip and only opens up about halfway and still pushing voltage through. Got it to fully open once and it went to close on its own. Kind of strange right so we decided to not proceed with this and told owner rep and it's in there hands I guess. To me this didn't seem normal. Everything I've ever worked on has a tendency to do what I tell it to. This freaked me out beings it 480 and it's old as hell
 

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Well tonight was our first shutdown for this switchgear and had problems with the main breaker opening. Hit the manual trip and only opens up about halfway and still pushing voltage through....This freaked me out beings it 480 and it's old as hell
Fun stuff lol. 480...We had 230 kV electrically operated air switch open and some gears in motor operator decided to get out of alignment half way open, that makes for some excitement!
 
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