Electrical Engineering - Racking out of motor starter?? How?

Author

Racking out of motor starter?? How?

spokes

2007-02-20, 9:25 pm

I need to take the overcurrents off a motor starter in an MCC. The
problem I have is that the motor starter is racked into a live 600
Volt bus. I want to know if I can rack out the motor starter without
isolating the whole MCC (there is only 1 bus in the MCC). Is this
usual practice. Any bad experiences when racking the starter back onto
a live bus.

Any rules in any standard on how to do this.

Any web site on how to do this.

Any help would be appreciated.

Thanks,
Blair

Rheilly Phoull

2007-02-20, 9:25 pm

"spokes" <blairlakehead_@hotmail.com> wrote in message
news:1172025264.008170.85980@q2g2000cwa.googlegroups.com...
>I need to take the overcurrents off a motor starter in an MCC. The
> problem I have is that the motor starter is racked into a live 600
> Volt bus. I want to know if I can rack out the motor starter without
> isolating the whole MCC (there is only 1 bus in the MCC). Is this
> usual practice. Any bad experiences when racking the starter back onto
> a live bus.
>
> Any rules in any standard on how to do this.
>
> Any web site on how to do this.
>
> Any help would be appreciated.
>
> Thanks,
> Blair
>
All the mcc's I've racked out have interlocks etc. to prevent the unit being
racked out whilst under load.
There is usually no problems with racking out a properly designed mcc with
the buss live, thats what they're made for :-)
--
Cheers .......... Rheilly P

Long Ranger

2007-02-21, 3:25 am

"spokes" <blairlakehead_@hotmail.com> wrote in message
news:1172025264.008170.85980@q2g2000cwa.googlegroups.com...
>I need to take the overcurrents off a motor starter in an MCC. The
> problem I have is that the motor starter is racked into a live 600
> Volt bus. I want to know if I can rack out the motor starter without
> isolating the whole MCC (there is only 1 bus in the MCC). Is this
> usual practice. Any bad experiences when racking the starter back onto
> a live bus.
>
> Any rules in any standard on how to do this.
>
> Any web site on how to do this.
>
> Any help would be appreciated.
>
> Thanks,
> Blair
>
Just be sure the thing isn't under load. The higher voltages I've worked on
like 4160 have interlocks for that. I saw an interlock fail once though, so
be careful, and take it step by step. Most MCCs are designed to be able to
rack out while the main buss is energized.

Ben Miller

2007-02-21, 9:25 am

"spokes" <blairlakehead_@hotmail.com> wrote in message
news:1172025264.008170.85980@q2g2000cwa.googlegroups.com...
>I need to take the overcurrents off a motor starter in an MCC. The
> problem I have is that the motor starter is racked into a live 600
> Volt bus. I want to know if I can rack out the motor starter without
> isolating the whole MCC (there is only 1 bus in the MCC). Is this
> usual practice. Any bad experiences when racking the starter back onto
> a live bus.
>
> Any rules in any standard on how to do this.
>
> Any web site on how to do this.
>
> Any help would be appreciated.
>
> Thanks,
> Blair
>

-
There is an arc flash hazard, and you need to use appropriate safe work
practices and/or the proper personal protective equipment. Only someone who
is properly trained should do this, and from your questions you obviously do
not have the knowledge. Asking out of curiosity is fine, but I highly
recommend that you not perform this task.

Ben Miller

-
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com

spokes

2007-02-21, 1:25 pm

On Feb 21, 9:04 am, "Ben Miller" <benmil...@worldnet.att.net> wrote:
> "spokes" <blairlakehe...@hotmail.com> wrote in message
>
> news:1172025264.008170.85980@q2g2000cwa.googlegroups.com...
>
>
>
>
>
>
>
>
>
>
> -
> There is an arc flash hazard, and you need to use appropriate safe work
> practices and/or the proper personal protective equipment. Only someone who
> is properly trained should do this, and from your questions you obviously do
> not have the knowledge. Asking out of curiosity is fine, but I highly
> recommend that you not perform this task.
>
> Ben Miller
>
> -
> Benjamin D. Miller, PE
> B. MILLER ENGINEERINGwww.bmillerengineering.com- Hide quoted text -
>
> - Show quoted text -

I'm not doing it but I will be getting guys to do it. I have racked
out many breakers but they were on a dead bus. The guys are highly
trained and have done it before. I wanted to know if it was regular
industry practice. It appears they will be racking it out for
maintenance. Proper PPE will be worn I assure you.

Rheilly Phoull

2007-02-21, 9:25 pm

"spokes" <blairlakehead_@hotmail.com> wrote in message
news:1172077818.932331.234810@s48g2000cws.googlegroups.com...
> On Feb 21, 9:04 am, "Ben Miller" <benmil...@worldnet.att.net> wrote:
>
> I'm not doing it but I will be getting guys to do it. I have racked
> out many breakers but they were on a dead bus. The guys are highly
> trained and have done it before. I wanted to know if it was regular
> industry practice. It appears they will be racking it out for
> maintenance. Proper PPE will be worn I assure you.

Probably be best to ask the guys doing it, no doubt they will require
certain conditions to carry out the work.
--
Cheers .......... Rheilly P

Bob Ferapples

2007-02-26, 9:25 am

On 21 Feb 2007 09:10:18 -0800, "spokes" <blairlakehead_@hotmail.com>
wrote:

>On Feb 21, 9:04 am, "Ben Miller" <benmil...@worldnet.att.net> wrote:
>
>I'm not doing it but I will be getting guys to do it. I have racked
>out many breakers but they were on a dead bus. The guys are highly
>trained and have done it before. I wanted to know if it was regular
>industry practice. It appears they will be racking it out for
>maintenance. Proper PPE will be worn I assure you.

As others have said, MCCs are specifically s=designed for this
purpose, otherwise you could just put a bunch of starters in a box.

In order to open the door, you will need to turn off the disconnect or
breaker in that bucket. Once off (open) the load is disconnected and
the bucket can be pulled out. most good MCC designes have a vertical
ground bus and each bucket stabs on to that bus. When pulling the
bucket out, the ground stab will be the last one to disengage, meaning
the bucket is still grounded until after the main bus has been
cleared.

Still, not something to be undertaken by novices.

Matthew Beasley

2007-02-26, 1:25 pm

"Bob Ferapples" <licku45@yqahoo.com> wrote in message
news:lvg5u2lh0g76nsq39ifl8v25r7tpshg7ol@4ax.com...

> As others have said, MCCs are specifically s=designed for this
> purpose, otherwise you could just put a bunch of starters in a box.
>
> In order to open the door, you will need to turn off the disconnect or
> breaker in that bucket. Once off (open) the load is disconnected and
> the bucket can be pulled out. most good MCC designes have a vertical
> ground bus and each bucket stabs on to that bus. When pulling the
> bucket out, the ground stab will be the last one to disengage, meaning
> the bucket is still grounded until after the main bus has been
> cleared.
>
> Still, not something to be undertaken by novices.

I know an electrician who sports some nasty scars on his arm from racking
out a 480V MCC breaker. He was the safety man, and was about 20 feet away.
The two doing the work were in full PPE. One stabs broke and twisted
sideways at disconnect, causing a line to ground fault and then a full three
phase fault. The MCC main did trip very fast, but there was quite a bit of
damage done in the few cycles of the fault. The two men doing the work
suffered no injury. But the guy I know got hit with some of the flying
molten copper and steel. Nothing life threatening and most fortunately none
in the face and especially eyes, but painful nonetheless.

If you're watching, give them a lost of room. A long sleeve cotton shirt
and blue jeans would be a good idea if you're not wearing full fire
retardant clothing.

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