Shunt Trip

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KRG9729

Member
Location
New York
We are installing a feed for an x-Ray machine with a shunt trip.
We are feeding a breaker enclosure and the breaker has a 208 volt coil for the shunt trip. Is it permissible to tap off the line side feeders for the 208 volt shunt trip?

What methods would be recommended to accomplish this?
 

luckylerado

Senior Member
We are installing a feed for an x-Ray machine with a shunt trip.
We are feeding a breaker enclosure and the breaker has a 208 volt coil for the shunt trip. Is it permissible to tap off the line side feeders for the 208 volt shunt trip?

What methods would be recommended to accomplish this?

I have done this for an elevator in the past. I just installed a fusible link inside the enclosure on the ungrounded side and protected with a 10 amp cartridge fuse (mine was 120V coil from 208V 3 phase circuit.) I grabbed the load side of the breaker.

I don't have a reference to back it up. Been many years ago.
 

templdl

Senior Member
Location
Wisconsin
We are installing a feed for an x-Ray machine with a shunt trip.
We are feeding a breaker enclosure and the breaker has a 208 volt coil for the shunt trip. Is it permissible to tap off the line side feeders for the 208 volt shunt trip?

What methods would be recommended to accomplish this?
Why use the line side of the breaker as your power source? With the breaker in the on position the load side will be energized and capable of providing power to the ST circuit unless there is a reason to trip the breaker should it be in the off position. By supplying the ST circuit from the load side you will naturally have a way to disconnect power from the ST circuit if required which would be more difficult to do on the line side. Either way the ST actually trips the breaker as Nd tty O close the breaker it as to be latched, reset and closed.
You next concern is "tapping" for power. You simply cannot not slip the wire underneath the existing terminals, they must be listed for it.
Another thought would be if 208v is appropriate. Then you must fuse both line conducters. It is somewhat of a high voltage for control. You need to fuse the 2 line conductors. You could consider 120v or even 24 or 12v.
If you elect to do this you need to supply power to a properly sized CP with a 208 fused primary. You we would fuse one line of the secondary as Nd groung the other line to supply the shunt trip circuit.
Remember that a 208v 3ph supply is normally a Wye then you would have 120v L-N. If available at the breaker that could give you a 120v souce which would commonly require you to use only one fuse on the line condustor.
Of course tty he ST voltage should be the same as the control voltage try ha try to chose.
If you dr o elect to go with 208v there will be 120v from each line to ground also. Depending upon where the ST is activated from and the length of you control circuit is this a safe voltage where a lower voltage would be more appropriate.
This may be a long reply but other things may also need some consideration. I always try to avoid providing an answer that may be like handing someone a loaded gun.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
I agree on the load side, and in fact that's the way it SHOULD be done. If you tap off of the line side, the wires to that coil could be hot when the breaker is off, dangerous for someone who doesn't know that and if the switch contacts controlling it weld, you could burn out the ST coil. It your source comes from the load side of the same breaker, once it trips, the ST circuit is guaranteed dead.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Why use the line side of the breaker as your power source? With the breaker in the on position the load side will be energized and capable of providing power to the ST circuit unless there is a reason to trip the breaker should it be in the off position. By supplying the ST circuit from the load side you will naturally have a way to disconnect power from the ST circuit if required which would be more difficult to do on the line side. Either way the ST actually trips the breaker as Nd tty O close the breaker it as to be latched, reset and closed.
You next concern is "tapping" for power. You simply cannot not slip the wire underneath the existing terminals, they must be listed for it.
Another thought would be if 208v is appropriate. Then you must fuse both line conducters. It is somewhat of a high voltage for control. You need to fuse the 2 line conductors. You could consider 120v or even 24 or 12v.
If you elect to do this you need to supply power to a properly sized CP with a 208 fused primary. You we would fuse one line of the secondary as Nd groung the other line to supply the shunt trip circuit.
Remember that a 208v 3ph supply is normally a Wye then you would have 120v L-N. If available at the breaker that could give you a 120v souce which would commonly require you to use only one fuse on the line condustor.
Of course tty he ST voltage should be the same as the control voltage try ha try to chose.
If you dr o elect to go with 208v there will be 120v from each line to ground also. Depending upon where the ST is activated from and the length of you control circuit is this a safe voltage where a lower voltage would be more appropriate.
This may be a long reply but other things may also need some consideration. I always try to avoid providing an answer that may be like handing someone a loaded gun.

I usually enjoy your posts but hard to follow this one.
Please see if you can read what you wrote here because I can't make out half of it.
Is your keyboard messed up?
 

templdl

Senior Member
Location
Wisconsin
I usually enjoy your posts but hard to follow this one.
Please see if you can read what you wrote here because I can't make out half of it.
Is your keyboard messed up?
I use my Nexus tablet what has a touch screen which is a pain sometimes.
You should see it before I go back and clean it up. I'll go over it again.
Thanks.
 

templdl

Senior Member
Location
Wisconsin
I use my Nexus tablet what has a touch screen which is a pain sometimes.
You should see it before I go back and clean it up. I'll go over it again.
Thanks.

I'll try to clean this up and repost it.
Why use the line side of the breaker as your power source? With the breaker in the on position the load side will be energized and capable of providing power to the ST circuit unless there is a reason to trip the breaker should it be in the off position. By supplying the ST circuit from the load side you will naturally have a way to disconnect power for the ST circuit if required which would be more difficult to do on the line side. Either way the ST actually trips the breaker and the breaker needs to latched, reset and then closed.
You next concern is "tapping" for power. You simply cannot just slip the wire underneath the existing terminals as the terminals must be listed for it.
Then you must fuse both line conducters. 208v is somewhat of a high voltage for control and you need to fuse the 2 line conductors. Is 208v is appropriate? 120v or even 24 or 12v should be considered when that circuit leaves the breaker enlosure to a remote location.
If you elect to do this you need to supply power to a properly sized CPT with a 208 fused primary. You would then fuse one line of the secondary grounding the other line to supply the shunt trip circuit.
Remember that a 208v 3ph supply is normally a Wye where you would have 120v L-N. If available at the breaker that could give you a 120v souce which would commonly require you to use only one fuse for the line conductor.
Of course the ST voltage should be the same as the control voltage depending upon what you chose.
Remember if you elect to go with the 208v there will be 120v from each line to ground also. Depending upon what remote location the ST is activated from and the length of your control circuit is this a safe voltage where a lower voltage would be more appropriate.
This may be a long reply but other things may also need some consideration. I always try to avoid providing an answer that may be like handing someone a loaded gun.
I trust that I have caught all of my errors this time.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
I'll try to clean this up and repost it.
Why use the line side of the breaker as your power source? With the breaker in the on position the load side will be energized and capable of providing power to the ST circuit unless there is a reason to trip the breaker should it be in the off position. By supplying the ST circuit from the load side you will naturally have a way to disconnect power for the ST circuit if required which would be more difficult to do on the line side. Either way the ST actually trips the breaker and the breaker needs to latched, reset and then closed.
You next concern is "tapping" for power. You simply cannot just slip the wire underneath the existing terminals as the terminals must be listed for it.
Then you must fuse both line conducters. 208v is somewhat of a high voltage for control and you need to fuse the 2 line conductors. Is 208v is appropriate? 120v or even 24 or 12v should be considered when that circuit leaves the breaker enlosure to a remote location.
If you elect to do this you need to supply power to a properly sized CPT with a 208 fused primary. You would then fuse one line of the secondary grounding the other line to supply the shunt trip circuit.
Remember that a 208v 3ph supply is normally a Wye where you would have 120v L-N. If available at the breaker that could give you a 120v souce which would commonly require you to use only one fuse for the line conductor.
Of course the ST voltage should be the same as the control voltage depending upon what you chose.
Remember if you elect to go with the 208v there will be 120v from each line to ground also. Depending upon what remote location the ST is activated from and the length of your control circuit is this a safe voltage where a lower voltage would be more appropriate.
This may be a long reply but other things may also need some consideration. I always try to avoid providing an answer that may be like handing someone a loaded gun.
I trust that I have caught all of my errors this time.

:thumbsup:
Thanks for doing that but you didn't have to. It looked so good I didn't dare try and pick it apart! (Not that I meant to on the first post)
 

templdl

Senior Member
Location
Wisconsin
:thumbsup:
Thanks for doing that but you didn't have to. It looked so good I didn't dare try and pick it apart! (Not that I meant to on the first post)
No big deal. I shouldn't publish something with those errors. Thanks for pointing it out and certainly there was no offense taken.
 

templdl

Senior Member
Location
Wisconsin
I agree. It would bee great if it simply highlighted the words in question in red. My pro BH lem (problem) has been with my touch screen on my tablet. Note how problem ended up.
 
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