# Capacitor bank



## Ryan6864 (Feb 18, 2016)

Question about safest way to disconnect power. Haveelectric company coming out to disconnect power so I can get in gear to add some breakers. There is a capacitor bank tied in. This building is about 50 years old already had huge problems with breakers and contractors not coming back up after loss of power. Would the safest way be to throw disconnect on capacitor bank then have electric company kill power at pull. Then on reconnect have electric company kick power on pole on then throw disconnect on capacitor bank? My main concern is capacitor bank discharging through gear after main power was cut.


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## Ryan6864 (Feb 18, 2016)

Sorry hate iPad with autocorrect you get what I mean though


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## bkmichael65 (Mar 25, 2013)

I think most of them have internal discharging resistors. Should be able to just wait a couple of minutes after cutting power for them to discharge.


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## telsa (May 22, 2015)

Without ANY electrical figures...

I wouldn't hazard a guess as to which way to go.

Usually such banks are used to pull up the power factor for a plant larded with inductive loads.

You are telling us the facility is very poorly maintained.

Right off, that brings big concerns as to what's transpired.

Are you dealing with a "tank circuit" ?

{ LC circuit }


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## Ryan6864 (Feb 18, 2016)

The building is beyond bad shape it's a giant rats nest. Half the motor starters are all jumpered out to force run in auto. I accidentally shorted out some old MC that ended up dropping power to half the building. Restored power and none of the air handlers would come back up as all the contactors wouldn't suck back in. Most of the junk here hasn't been powered down in who knows how many years. 

I'm adding a 225A breaker on the main gear to feed a high voltage pannel, 75kva transformer and two low voltage pannels.

Any markings or ID tags are long gone on the capacator bank. Which I'm assuming was for power factor correction. Was told the gear was installed in late 60s. Just trying to decide what safest route would be as far as isolating capacitor bank for when I get in the gear.


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## Bird dog (Oct 27, 2015)

A meter to make sure the caps are actually discharged? I would think a shorting stick would be too dangerous. Ask your POCO for their procedure if they had to do it.


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## telsa (May 22, 2015)

Keep the capacitor bank connected while the Poco kills line power.

The capacitor bank will dump what energy it has into the connected resistive loads all across the facility.

You're dealing with a *super scaled* version of shutting down a capacitor start, capacitor run motor.

So, if I read you right, you've got nothing to do.

If it's not going to bleed off via connected loads -- it's too big, they're too small -- then you'll need to wait for it...

Bleeding resistors should've been designed in -- way back when. I'd throw the disconnect last... and only if the voltage refuses to decay.

Based upon your post, everything in the plant is a trip wire for electricians.

So the less you touch, the less you break.


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## joebanana (Dec 21, 2010)

Bird dog said:


> A meter to make sure the caps are actually discharged? I would think a shorting stick would be too dangerous. Ask your POCO for their procedure if they had to do it.


I think a "short stick" with a 1 megohm wirewound rsistor would be fine.


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## Ryan6864 (Feb 18, 2016)

Well I found out the hard way. I opened up all my breakers power company went to pull fuses and it started to back feed. Needless to say they weren't happy. I isolated the bank and all was good.

Of course there had to be issues. One of existing 400A breakers was arcing out where the finger kit landed on bus. Guess it worked loose over time. When I went to throw the 400A sparks were flying everywhere. That woke me up. Called the guy who signs my checks he said screw see if it will hold.

Tossed it again same thing. Had to drill out bolts that were literally welded to bus. Install new bolt clean through bus.


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## B-Nabs (Jun 4, 2014)

Ryan6864 said:


> Well I found out the hard way. I opened up all my breakers power company went to pull fuses and it started to back feed. Needless to say they weren't happy. I isolated the bank and all was good.
> 
> Of course there had to be issues. One of existing 400A breakers was arcing out where the finger kit landed on bus. Guess it worked loose over time. When I went to throw the 400A sparks were flying everywhere. That woke me up. Called the guy who signs my checks he said screw see if it will hold.
> 
> Tossed it again same thing. Had to drill out bolts that were literally welded to bus. Install new bolt clean through bus.


Sounds like the guy who signs your cheques needs to give his head a shake. Easy to say screw it when it's somebody else's life on the line I guess.

Sent from my SM-G920W8 using Tapatalk


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## circuitman1 (Mar 14, 2013)

like b nabs said, it isn't his life on the line. bet that was a scary sight!glad all is well.


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