Emergency Stop

[Hoyt]

Hello,

I need to provide an Emergency stop for some existing Busway. Two existing Busways, 1 -400a, 1 -800a

I am already replacing the existing 400/3 c.b. feeding the existing 400a busway? so my thought would be to replace with a 400/3 shunt trip c.b. w/ EM stop.

The existing 800/3 is a large fused switch in the existing switchgear?my thought here would be to place a shunt trip c.b. downstream. This sounds pricy? is there a more economical installation?

Thanks!

 

[Jraef]

You need to check with whomever is requiring the E-Stop. Some authorities do not consider shunt trips as valid E-Stops, because they are not inherently fail-safe. In other words, if the wire opens or shorts, you cannot energize the shunt trip coil so someone hits the E-Stop button and nothing happens. UVRs sometimes work, but that depends on whether or not the AHJ will allow a continuously powered source for the UVR circuit when the breaker is Off, otherwise you can never close the breaker.

The safest bet is to add an electrically held contactor connected to an E-Stop circuit. If your existing breakers are not the type that can have STs or UVRs added in the field, that may be less expensive than buying new breakers anyway. Even if you can remove the breakers and have STs or UVRs added by a service shop, you have to factor in the down time to the cost. Contactors usually win those economic battles if you think it all through.

 

[Hoyt]

Thank you.

 

[petersonra]

It seems to me the critical thing is knowing just why the estop is being put into place.

If it is mostly a way of powering off a machine remotely, a shunt trip makes a lot of sense.

If it is a more traditional estop, than it probably doesn't make sense.

Normally one would associate an estop more closely with the equipment being serviced than to put it on a busway that may serve more than one piece of equipment.

In any case, if you trip the breaker, how convenient is it to reset it? This may be happening multiple times a day.

 

[Hoyt]

The direction was by the Owner - This is a campus setting and teaching lab. They wanted a means of stoping power to the bus duct. I was not part of the early discussions but it may have been as an emergency stop or to stop class perhaps.

 

[weressl]

You need to check with whomever is requiring the E-Stop. Some authorities do not consider shunt trips as valid E-Stops, because they are not inherently fail-safe. In other words, if the wire opens or shorts, you cannot energize the shunt trip coil so someone hits the E-Stop button and nothing happens. UVRs sometimes work, but that depends on whether or not the AHJ will allow a continuously powered source for the UVR circuit when the breaker is Off, otherwise you can never close the breaker.

The safest bet is to add an electrically held contactor connected to an E-Stop circuit. If your existing breakers are not the type that can have STs or UVRs added in the field, that may be less expensive than buying new breakers anyway. Even if you can remove the breakers and have STs or UVRs added by a service shop, you have to factor in the down time to the cost. Contactors usually win those economic battles if you think it all through.

You're right.

Data centers are routinely equipped with shunt breakers yet they do not provide true safety.

Adding a contactor also an additional point of failure so the reliability calc would get skewed for the data center.

It always amazes me that thery spend mega$'s on the data-center hardware, yet they give it to an ordinary architectural firm to construct it instead of a specialized engineering outfit with relability expertise. (If that would have been done, the OP wouldn't exist, nu?)

 

[tshea]

I'm actually in process of doing the same. 600A and 800A bus ducts. we are using shunt trip breakers. This is the most cost effective way to "kill" the power to the bus ducts. The breakers are I-Line.
We have 3 locations set up to heit the "E-stop" buttons. This is primarily for an emergency condition, where going to the bus plug and pulling hte handle OFF would be a safety concern. The power to the entire bus duct can be shutoff.