Multiple Rotary Motor Rated Disconnect in single panel

[JBUDA54]

I am working on a project where we have fifteen (15) Sootblowers on a Heat Recovery Steam Generator (HRSG). We are trying to develop a disconnect panel to allow the maintenance personnel to switch the power off of the local sootblower starter to service the local starter or anything that has failed in the local panel without disrupting the other fourteen and keeping 480V from entering the panel. Are there limits to the number of disconnects in a single panel before the alignment becomes a nightmare. Does anyone have experience in designing something similar to this or am I looking at something I should avoid. The previous project had a termination panel where the maintenance personnel had to throw the main disconnect (all sootblower de-energized) and manually de-terming the circuit with with nuts and tape and re-energizing the main once circuit was isolated. I don't want to spend a small fortunate to save a little bit of time, but if the cost of this panel isn't too high I would like to entertain the idea.

The sootblower motor is ~1HP so we are tallking ~20A motor rated switch and #12AWG wire.

The price of this rotary switch is ~$90.

 

[SceneryDriver]

I can imagine 15 operator rods being a nightmare to line up when closing the panel door.

What about something like this; these are UL508 rated disconnects:

http://www.automationdirect.com/adc...nel_Mount_(16-40_Amps,_SD1_Series)/SD1-025-RR

Mount them to the door using DIN rail and standoffs (see attached picture). Cut a rectangular hole the height of the disconnect and as wide as you need, left to right. I'm guessing you'd want to do three rows of five switches. Use tall (15mm height) DIN rail for more rigidity, since you're only holding the rows of disconnects to the back of the panel door at the ends.

http://www.automationdirect.com/adc...locks/DIN_Rails,_Clips_-a-_Brackets/DN-R35HS1

The only caveat with this mounting method is that the disconnects must be wired before they're mounted. Also, make sure to properly bond the door, as there will be line voltage running to devices mounted to it. Also, leave plenty of wiring space between the rows of disconnects so you can mount Panduit to keep things tidy.


SceneryDriver

 

[jraef]

The point where it becomes a potential nightmare to try to align multiple trough-door rotary interlocked handles is 2, because most humans have but 2 hands. If you interlock 3 or more handles with the door, how are you going to over-travel the 3rd handle in order to disengage the interlock?

That is why your other previous program had one main disconnect interlocked with the door, followed by terminals that could be used to isolate one from that system. You could upgrade that concept by adding separate disconnects down stream, but not interlocked with the door. This avoids the second pitfall of now not being allowed to work on live equipment with the door open unless suited up for Arc Flash potential. Even if not interlocked though, my experience is that any more than 3 becomes a logistic nightmare just to get the little tapered mechanisms to slide correctly into the handles because they will likely be in differing states of on-off, and then gravity works against you, making the handles hand in the wrong position one way or the other.

3rd potential pitfall of rotary through-door disconnects if you are in the US, most are NOT listed by UL to be used as a Branch Circuit Disconnect device, they must have another such listed device ahead of them anyway. Be careful on that issue. That means that those UL508 listed rotary switches can ONLY be used as the individual motor disconnects, NOT as the main disconnect ahead of them. That one must be listed under UL98. Many many people do not know this and get burned by inspectors who do.

Were it me, I would use a flange mounted UL98 listed main disconnect, feeding individual IEC style Motor Protection Circuit Breakers (Manual Motor Starters) going to the individual motors. Those can be mounted to the base such that the fronts can extend through the door (if NEMA 1 or IP20 is OK), or better yet an inner door / dead front panel, or or can have a sealed window mounted above them on the door, providing access from the outside to switch or reset them without turning off the main power.

"Will work for (the memory of) salami"

 

[waross]

That would have a hard time passing the Lock-out, Tag-out regulations that are spreading across North America. In our jurisdiction a worker has a legal right and a responsibility to verify that he has locked out the correct motor before working on it. If it is not possible to "bump" the motor a point to point verification is often needed. That means if a mechanic is going to do mechanical repairs he may need an electrician to verify the lock-out. Don't forget the lock provision on each switch.
Much safer is a local disconnect switch at or near each motor. These may be manual motor starter switches.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[dbaird]

Take a look at Siemens Motor Starter Protector/Circuit Breaker Combo for Group Motor installations in the panel. You can individually padlock these in the off position right at the starter.

https://eb.automation.siemens.com/mall/en/WW/Catalog/Products/10047876

http://www.youtube.com/watch?v=Ly0VgjCSDRE

David Baird
Sr Controls Designer
EET degree.

http://www.afctool.com

 

[JBUDA54]

After further investigation, we have decided to forego the quick disconnect option. The project is an EPA type project where there isn't any return on investment.

The Sootblower's have local lockable disconnects at each motor, but we were trying to install the quick disconnects ahead of the local panels so that we would allow each sootblower local panel to be total isolated to work on the local starters. The local starter has a disconnect but the 480V is present on the line side of the disconnect inside of the local panel making the maintenance personnel suit up. The other option would be disconnecting all 15 sootblowers at its main upstream breaker and then disconnecting the specific sootblower feed from a central termination panel and then returning power to the other 14 by turing on the main breaker. The frequency of this event is so rare that installing the disconnects ahead of the local panel elevates the cost too much.

I reviewed the follwoing article and this also influenced me to steer clear of the 508 Disconnects. It's a good resource comparing UL 508 vs UL 98 by Square D.

http://www.barr-thorp.com/wp-content/uploads/2011/06/UL-508-Application-Guide.pdf

Thanks all for your input. Sometimes trying to make life easier for maintenance can lead to design blunders. There is always a price for convenience! The new Arc Flash Safety standards are complicating the design of the way we have to deal with vendor furnished equipment. Back in the old days we woiuldn't think twice to open up a 480V panel to troubleshoot.