Greg

Here is the scenerio; We are building a lift station it has an 800A service going to a fused disconnect, from there to an 800A ATS w/ a 400KW generator. The question is; does it need a shunt trip for the generator? My gut is yes but, I've read the the NEC and can't find find anything saying yea or ney. I know I've over looked some article but can't seem to find it. Any suggestions on where to look?

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BryanMD

It probably needs a master disconnect of some sort, often located remote to the actual gear. This is where the shunt trip device comes into play as a way of accomplishing that need; but not as a code required approach to the situ. That make sense to you?

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nick

iam no nec expert , most jobs we do have one if not two generators paralled like around 1800kw your main service normal power lets say its a 4000amp 480 v service or multi services to the building require a shunt trip button or buttons, we install these for the fire dept in the event of a fire at 7 foot afg, since the generator comes online when your power is out , it is also a service , meaning it is locked or inside of a enclosed room or outside in a generator house in the yard .the building inspector and the electrical inspector need that to final . because you cant get to the generator breaker in a fire or problem or emergency. and its always in our specs on the job ,and shown on the oneline drawns or riser drawns . but i never have found it in the code book . it must be seperated 3 feet away from the normal shunt trip buttons and labeled emergency generator disconnect on a big red name plate white letters ill look at the code book i may have missed it .good question .

micromind

Every installation I've ever done involving a generator had the gen shunt-tripped out as well as the service. Around here, the fire department prefers one button, but will accept two. They must be installed in the middle of a 12" red triangle pointed up.

I don't think this is a national code requirement, it's more of a local thing.

Rob

brian john

I have never seen a shunt trip connected on a generator and we have installed 100's of them and service more.

Some come with shunt coils but have never known of one to be connected.

micromind

The 'shunt trip' on a generator around here is actually a lock-out. When the shunt trip on the building is activated, it opens the E-stop circuit in the generator controls, and prevents it from starting. It doesn't actually trip the generator breaker.

If you think it over a bit, it makes sense to lock out the gen when the building shunt trip is activated. The purpose of a shunt trip on any building is to remove all power to the building; the reason being that most firefighters use water to extinguish flames. Spraying water on a building thats still energized is not the best idea.

If the gen is allowed to run, and the transfer switch goes to source 2, the building is still energized. If the gen breaker is shunt tripped, the engine will start, and the firefighters have no way to know that power is not getting to the building, so they assume that the building is energized.

Rob

nick

that makes sense micromind , i guess the states differ on what the local inspectors need, only reason i think ours is like that is the size of the building it takes up large area like you can drive 1 mile around the building we do hotels / convention centers like opryland hotel down here in central florida , the fire dept wants that generator button seperate . also i think because lots of people would be in big trouble without lites if you had a little fire in that one kitchen out of 6 kitchens on the property , and say that 1400 room twin tower full of guests and had no way to get out do to that shunt generator button . but we do other jobs and they are all the same maybe the fire marshall sells mt k block buttons in orlando .

nick

was that a 800amp ats and 800 amp service at 480volts ,and a 400kw genset,seems that breaker is a little high for that generator or generator is too small?

Greg

Yes 800ATS @ 480vac. I had forgotten about this post since that project is done.

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nick

we came back to see how you made out with the shunt trip button ,we read the post again and saw 400kw gen its 481 amps 3 phase genset , just was thinking that breaker was too large for that gen but i guess you passed inspection so it must be ok .we know the ats is always the next size up meaning larger but what about wire size protection on that did it have a rating plug in breaker , did you go 250%on your protection dont get me wrong iam just learning and asking why , most of our stuff is little bit closer to the wire size protection so thats why i asked we might learn something new or missed something in the nec ? were from orlando just north from you guys.best of luck .

micromind

It's pretty common around here to have a generator that's much smaller than the service.

I just finished a small oil refining plant that has a 1600 amp service, a 1600 amp transfer switch, and a 150 KVA generator. The output of the gen is 180 amps, it is protected by a 250 amp breaker. Since this is not a legally required system, as far as I know, there's no requirement for a minimum generator size. In this case, there's a contact in the transfer switch that tells the PLC to not start the whole plant while on generator power.

Basically, the transfer switch and the switchgear downstream of it must be sized to the larger of A) the generator, or B) the service. There are, as usual, a few exceptions.

Rob

nick

ya thanks for the input micromind, we where thinking the breaker on that generator itself not the main service ,just didnt understand the protection on the feeder size from the generator to the ats switch ,i know normally the emergency load is smaller than the main service load , we where just looking at the wire size from the genset to the 800 amp ats,we were thinking a 600amp ats with 400kw genset and a smaller brk, that would protect the feeder from the genset to the ats would be smaller then 800 amps ,so if 481 amp emergency soucre was used why a 800amp ats if your not using 100% load. its just things i learn about everytime i come online guess there installing for the future ,well thanks for the info best of luck to ya. workin out of town now so i get online early its ruff.