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#89681 - 10/13/04 03:48 AM Use of shunt trip CB's?  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
Is the use of shunt trip CB's a design issue or a code issue?

If Code, where?

If design, why?

Seen some used as ground fault trips for equipment panels many times.

Also, seen some that are dropped some loads out of back-up power panels.

And one questionable installation that would drop power for a server, by a computer command.

Has always made me wonder......


Mark Heller
"Well - I oughta....." -Jackie Gleason

2017 / 2014 NEC & Related Books and Study Guides

#89682 - 10/13/04 05:12 AM Re: Use of shunt trip CB's?  
iwire  Offline
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Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I would say they are a design decision.

I can not think of any section in the NEC that directly requires a shunt trip breaker.

This section is a good example.
Quote
645.10 Disconnecting Means.
A means shall be provided to disconnect power to all electronic equipment in the information technology equipment room. There shall also be a similar means to disconnect the power to all dedicated HVAC systems serving the room and cause all required fire/smoke dampers to close. The control for these disconnecting means shall be grouped and identified and shall be readily accessible at the principal exit doors. A single means to control both the electronic equipment and HVAC systems shall be permitted. Where a pushbutton is used as a means to disconnect power, pushing the button in shall disconnect the power.


They do not tell us how to accomplish this but a shunt trip breaker is a common method.

Instead of buying and installing a contactor all you need to do is order a shunt trip kit for the main breaker(s) feeding the space.

I have not seen that application controlled by a computer but they are often controlled by Fire Alarm Systems.

Other areas I have used shunt trips.

1)Commercial Kitchen Equipment, there are codes (Fire?) that require the kitchen equipment under the exhaust hood to be shut down if the fire suppression system is activated.

2)In my area there is still a city that requires buildings to have an outside disconnecting means, they will accept a button outside to trip the main inside.

3)Elevators, we where using shunt trips on elevator feeders to kill the power when a heat detector tripped this was separate and in addition to elevator recall by lobby smoke detectors.

4)Ground fault protection of 277 volt heat trace circuits. We use a 277 volt shunt trip breaker with an external CT donut to provide the required protection.

5)I have not done this but they could certainly be used for load shedding when a generator comes on line that does not have the capacity to run the total load.

In all these cases I believe we could use contactors instead of shunt trip breakers.

But a shunt trip kit in any size is a lot less costly than the cost of a 100, 200, 400 amp 600 volt contactor and installation.

That has been my experience, I am sure others have used them in more applications.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#89683 - 10/13/04 05:17 AM Re: Use of shunt trip CB's?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I forgot that one down fall with the shunt trip breakers is they only trip open, I have never seen one capable of reseting itself.

If you need the circuit to re close then contactors are the only way.

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#89684 - 10/13/04 07:50 AM Re: Use of shunt trip CB's?  
George Corron  Offline
Member
Joined: May 2001
Posts: 717
Lorton, Va USA
Lent my code book to an employee last night.... usually a mistake.

We often use shunt trips for gas pumps, that is a code issue, but there are also other ways to comply.

We also must use them for kitchen equipment as iwire stated above, but only for Type 1 hoods where grease laden foods are prepared (think a fryer of ANY kind) if you have a kitchen with only steamers (or the newer type combi's - they're like microwave/convection ovens) the exhaust will not be grease laden and shunting is not always necessary.


#89685 - 10/13/04 04:32 PM Re: Use of shunt trip CB's?  
mustangelectric  Offline
Member
Joined: Feb 2004
Posts: 494
Bentonville, AR
why is shunt trips a code issue for fueling stations? i never heard of it..

regards

mustang


Electricity has no respect for ignorance!

#89686 - 10/13/04 04:45 PM Re: Use of shunt trip CB's?  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
George

Quote
We often use shunt trips for gas pumps, that is a code issue, but there are also other ways to comply.


Never wired a gas station but how does a shunt trip comply with 514.11?

That section requires the disconnect to open the grounded conductor along with the ungrounded conductors.

Are gas pumps 208 - 240 ?

Bob


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#89687 - 10/13/04 05:39 PM Re: Use of shunt trip CB's?  
trekkie76  Offline
Member
Joined: Jun 2004
Posts: 220
baileyville, maine, usa
I have used shunt trip CB's on elevator pit rooms. The requirements for it are in the Elevator code book, and in 620-51(B), talking about automatically opening it prior to the application of water. It is there to shunt (trip) the breaker in the event of a fire.
on the gas pump issue, could you route the nuetral on one pole of a double pole shunt trip breaker? not sure how you would get it to actuate, but it would open all the conductors.

[This message has been edited by trekkie76 (edited 10-13-2004).]

[This message has been edited by trekkie76 (edited 10-13-2004).]


#89688 - 10/13/04 08:58 PM Re: Use of shunt trip CB's?  
e57  Offline
Member
Joined: May 2003
Posts: 2,876
S.F.,CA USA
I too have used them in commercial Kit's req'ed by design/Spec' of plans. Although, I guess I didn't notice if all the items were under the hoods. And it would make sense as a fire code. But true, also just as effective if done with contactors, I guess.

Thanks for the answers gent's, very informative, as always.

Now that computer controlled one, I mentioned was kind of funny, and maybe some of you will appreciate it. Several years ago, I had to change one shunt trip breaker out that served a server room. As the shunt lead was double lugged I didn't want to pull it out, and drop all the other server rooms that were also connected to the same shunt lead. So I asked around with all the people I was doing the work for, (ya know the geek squad) and no one knew. So in order for me to do it, and not blindly, I needed to know it's operation/purpose. As I could not shut this thing off to change one breaker out of ten, and drop the whole operation. So I start tracking it down, it took almost three hours of digging around in boxes, and gutters to track it down. I find it in a 1 gang box under a desk 3-4 rooms away, with a small $10 relay on it, controlled by a thermostat wire that run out to another box, that was some how controled by a serial cable connected to computer. So I track down all the geeks, and we have a pow wow about it, they have to call some guy in England, and they mumbo jumbo about it. Then they tell me an analogy for what they mumbo jumbo'ed about.

Apparenty, it was a learning experiance for the whole geek squad too. They had some sort of virus software that paged the guy in England in case of a virus, and if he could not shut down the servers due to the virus via the software, he could dial up the modem on that computer on his cell phone, punch in some code, and dropped the whole operation. Pretty neat huh?

In retrospect I thought about it.... The weakest link in the whole operation of this complex network was some 18/2 thermostat wire stapled to the wall, and the cord laid on the floor for a CPU computer sitting under a desk that no one on this side of the world knew what it did.
-----------------------------------------
Oh iwire, nice call on 645..... An often over-looked and rarley enforced set of codes here. Dare I say it I may have over0looked it before! Goood call!

[This message has been edited by e57 (edited 10-14-2004).]


Mark Heller
"Well - I oughta....." -Jackie Gleason

#89689 - 10/14/04 06:45 AM Re: Use of shunt trip CB's?  
walrus  Offline
Member
Joined: Jul 2002
Posts: 680
Bangor Me. USA
Quote
never wired a gas station but how does a shunt trip comply with 514.11?

That section requires the disconnect to open the grounded conductor along with the ungrounded conductors.

Are gas pumps 208 - 240 ?


Shunt trips won't comply. Pumps may be 208,240 but dispensers on the island are generally 120v. I've seen Shunt trips used by fire suppression guys so flow stops when fire station is pulled. on Unattended locations I have used contactors.



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