DSL BREAKER

[puckman]

At our plant there is a no racking of breakers by plant personal and this is fine with us. When locking out one of these breakers there has been talk that just locking it out is not safe that it should be racked out into the disconnected position to be considered safe. Can someone expand on the correct way to lock the breaker out to be safe and why ?
At this time we push in the trip button and pull out the lever and place a lock there.
Thanks for any help.

 

[petersonra]

At our plant there is a no racking of breakers by plant personal and this is fine with us. When locking out one of these breakers there has been talk that just locking it out is not safe that it should be racked out into the disconnected position to be considered safe. Can someone expand on the correct way to lock the breaker out to be safe and why ?
At this time we push in the trip button and pull out the lever and place a lock there.
Thanks for any help.

JMNSHO.

I don't see any reason to rack out the breaker as part of a lockout sequence.

You have to test for voltage after you lockout it out anyway. If the CB had somehow failed in the closed position while showing open, the voltage test would show it.

 

[don_resqcapt19]

The plants I have worked in required that the breaker be racked out, not just tripped, for a lockout.

 

[kingpb]

Problem is that racking in/out is the most vulnerable time for failure and thus arc flash. Personnel typically have to stand in front of the breaker and therefore are placed in a precarious position. Proper PPE is a must, but nonetheless, still a potential life threatening situation.

 

[petersonra]

The plants I have worked in required that the breaker be racked out, not just tripped, for a lockout.

any particular reason they require this?

 

[rcwilson]

any particular reason they require this?

Most facilities I have been in require withdrawing the brekaer for lockout. It may have come from the utility "visible-break" philosphy, where it is not considered open unless you can see a break, like an open disconnect.

Some gas insulated switchgear uses cameras to verify the disconnects are open.

 

[zog]

At our plant there is a no racking of breakers by plant personal and this is fine with us. When locking out one of these breakers there has been talk that just locking it out is not safe that it should be racked out into the disconnected position to be considered safe. Can someone expand on the correct way to lock the breaker out to be safe and why ?
At this time we push in the trip button and pull out the lever and place a lock there.
Thanks for any help.

LOTO requires visual verification, which you can't see by just opening the breaker. It should be locked out in the disconnect position, that way you see the breaker disconnect from the stabs. I believe this is covered in the DS instruction manual.

 

[petersonra]

LOTO requires visual verification, which you can't see by just opening the breaker. It should be locked out in the disconnect position, that way you see the breaker disconnect from the stabs. I believe this is covered in the DS instruction manual.

if that is the case how could you ever use a common MCCB as a disconnecting means?

 

[Phil Corso]

Petersonra...

To close the "stab" shutters, thus totally isolating the "live" bus from the CB compartment!

Regards, Phil Corso

 

[Jraef]

if that is the case how could you ever use a common MCCB as a disconnecting means?

One does not buy Metal-Clad Draw Out Switchgear that uses Power Circuit Breakers where an MCCB would be appropriate and vice versa. Hopefully...

As a general rule, PCBs and M-C switchgear is used in very LARGE and coordinated power distribution systems as the last line of defense below the substation. In that role, they are expected to "hold" current during a fault for much longer than an MCCB would be expected to do so, which allows lower level fault protective devices to clear the fault at as low a level as possible.

The way the rack-out requirement issue was explained to me years ago was that a potential consequence of holding that fault current for longer like that may be welding of the contacts. So the backup plan to prevent that possibility, however remote, from killing someone who is working on that circuit is to rack the breaker out, physically removing the breaker's connection to the bus bars with an air gap and a shutter mechanism. That's also why you are supposed to regularly test and exercise your PCB based switchgear by the way.

 

[puckman]

Can the stabs be seen in the disconnected position ? I don't know, this breaker fills the draw pretty good.
When we lock out one of these breakers we confirm open by going to the equipment this dsl feeds and test for lost of power . If this is ok with OSHA OR 70E I don't know.
Is there some chance of this breaker closing as some of us have been led to believe [not here] ?

 

[petersonra]

One does not buy Metal-Clad Draw Out Switchgear that uses Power Circuit Breakers where an MCCB would be appropriate and vice versa. Hopefully...

As a general rule, PCBs and M-C switchgear is used in very LARGE and coordinated power distribution systems as the last line of defense below the substation. In that role, they are expected to "hold" current during a fault for much longer than an MCCB would be expected to do so, which allows lower level fault protective devices to clear the fault at as low a level as possible.

The way the rack-out requirement issue was explained to me years ago was that a potential consequence of holding that fault current for longer like that may be welding of the contacts. So the backup plan to prevent that possibility, however remote, from killing someone who is working on that circuit is to rack the breaker out, physically removing the breaker's connection to the bus bars with an air gap and a shutter mechanism. That's also why you are supposed to regularly test and exercise your PCB based switchgear by the way.

I get that, and do not disagree but why is there any real difference between locking out this kind of CB and a MCCB?

Does the rule of requiring an air gap for LOTO only apply to this kind of CB and not to other LO devices?

 

[jim dungar]

Does the rule of requiring an air gap for LOTO only apply to this kind of CB and not to other LO devices?

There is no 'universal' rule requiring an air gap for LOTO.

Some people get used to their company, or industry, standard procedures and then feel they apply everywhere.

 

[Luketrician]

Racking type DS breakers to the disconnect position disconnects the control power and aux contacts associated with the breaker. With breaker in the tripped but connected position, control power is still present within the breaker.

 

[GoldDigger]

So you are saying that it would directly affect someone working in the breaker enclosure, but only indirectly affect someone working on the load it controlled?
(Hazard only if the breaker malfunctioned? )

Tapatalk...

 

[zog]

Racking type DS breakers to the disconnect position disconnects the control power and aux contacts associated with the breaker. With breaker in the tripped but connected position, control power is still present within the breaker.

Yes, and you are relying on an interlock to prevent the breaker from closing. Just a small metal tab that is easily broken off (We replace them all the time)

 

[puckman]

One last question , can the ds breaker close with a lock attached to the lock out lever of the breaker ?

 

[zog]

One last question , can the ds breaker close with a lock attached to the lock out lever of the breaker ?

The lockout tab prevents opening the racking door and puts the breaker in a trip free condition, so as long as the interlock works right it should prevent the breaker from closing. However, as I mentioned earlier, this relies on a small metal tab that holds the trip bar in the trip position and we see a lot of these broken when we rebuild these in the shop.

 

[JoeStillman]

Racked-out is safer than locked-out.

You can get remote racking devices that have a motorized crank. You stand outside the AF boundary while racking.

 

[Jraef]

Racked-out is safer than locked-out.

You can get remote racking devices that have a motorized crank. You stand outside the AF boundary while racking.

Kudos to Zog for biting his tongue on that issue in respect of the forum rules against self promotion (but I'll do it for him, not my company!). A division of his company makes an excellent system for this, I've seen it in action and highly recommend it.

http://www.cbsarcsafe.com/