Main Gear Expansion

Status
Not open for further replies.

statedogg

Member
This could possibly be a UL, Safety, or engineering quetsion but I'll go here.
I couldn't find much using search, my key words: tap, bus, and, bar were too common.

Anyway we have a 12,750 - 277/480 xfmr (not sure of the rating yet) supplying switchgear with a 1200A main, and 6 400/3 switches. 6 switches is all the space the gear has. The facility is requesting an additional service of 400A. The facility electrician has told them we can tap the bus and hang a 400/3 disconnect on the end of the gear. The panel is lightly loaded approx 25% and working clearance would not be an issue. I don't like this idea and feel like its a sub par installation, but I can't find a reason to say we can't do it. I am getting a lot of pressure to "make it work." What do you think?
 

pete m.

Senior Member
Location
Ohio
I think it would most likely be a "UL" issue. I'm not positive that you can just arbitrarily tap a buss where it is convienent in a listed piece of gear. I would at least ask for some type of confirmation that this will not void the listing of the equipment.

Pete
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
pete m. said:
I think it would most likely be a "UL" issue. I'm not positive that you can just arbitrarily tap a buss where it is convienent in a listed piece of gear. I would at least ask for some type of confirmation that this will not void the listing of the equipment.

A UL Listing only says that the gear met UL standards when it was shipped from the factory. If provisions for an additional section were not included in the original design then the manufacturer should be contacted for application support.

It is up to the AHJ to approve any field modifications. UL does have procedures to assit the AHJ as well as a field certification process if the customer desires it.
 

statedogg

Member
Thanks for the thoughts. I think I am going recommend that we don't tap the bus, unless provisions for doing so are in place.
 

pete m.

Senior Member
Location
Ohio
jim dungar said:
A UL Listing only says that the gear met UL standards when it was shipped from the factory. If provisions for an additional section were not included in the original design then the manufacturer should be contacted for application support.

It is up to the AHJ to approve any field modifications. UL does have procedures to assit the AHJ as well as a field certification process if the customer desires it.

Well said Jim. Thanks.

Pete
 

benaround

Senior Member
Location
Arizona
statedogg,

Just a thought, would a 400/3 feed-thru panel be worth thinking about?

If one of the other existing 400/3 was lightly loaded , you could feed the new

panel off it's OCPD and refeed the old off the feed-thru lugs. Like I said,just

food for thought.
 
statedogg said:
This could possibly be a UL, Safety, or engineering quetsion but I'll go here.
I couldn't find much using search, my key words: tap, bus, and, bar were too common.

Anyway we have a 12,750 - 277/480 xfmr (not sure of the rating yet) supplying switchgear with a 1200A main, and 6 400/3 switches. 6 switches is all the space the gear has. The facility is requesting an additional service of 400A. The facility electrician has told them we can tap the bus and hang a 400/3 disconnect on the end of the gear. The panel is lightly loaded approx 25% and working clearance would not be an issue. I don't like this idea and feel like its a sub par installation, but I can't find a reason to say we can't do it. I am getting a lot of pressure to "make it work." What do you think?

Find the gear manufacturer's service agent in the area and ask for an engineered solution to meet UL compliance.
 

mdshunk

Senior Member
Location
Right here.
While it's certainly possible to "tap the bus" and "make it work", that's not really the professional approach. There are things to keep in mind, like the rating of the bus itself. It would be more typical to have the switchgear manufacturer, or a 3rd party specializing in such work, make another section for you. This section may be a "tap cabinet", or preferably it will contain one or more overcurrent devices.
 

captaincrab55

Senior Member
Location
Maryland
statedogg said:
This could possibly be a UL, Safety, or engineering quetsion but I'll go here.
I couldn't find much using search, my key words: tap, bus, and, bar were too common.

Anyway we have a 12,750 - 277/480 xfmr (not sure of the rating yet) supplying switchgear with a 1200A main, and 6 400/3 switches. 6 switches is all the space the gear has. The facility is requesting an additional service of 400A. The facility electrician has told them we can tap the bus and hang a 400/3 disconnect on the end of the gear. The panel is lightly loaded approx 25% and working clearance would not be an issue. I don't like this idea and feel like its a sub par installation, but I can't find a reason to say we can't do it. I am getting a lot of pressure to "make it work." What do you think?
I could be wrong and don't have a Code Book handy, but I thought hanging a disconnect on the end of the gear was a no no.... I know it was legal several codes back....
 

MasterDic

Member
Location
SoCal
from my understanding as long as its not being overloaded there should be no problem and from what it sounds like this sounds like something i did almost exactly like this not that long ago.
 

Smart $

Esteemed Member
Location
Ohio
statedogg said:
...we have a 12,750 - 277/480 xfmr (not sure of the rating yet) supplying switchgear with a 1200A main, and 6 400/3 switches. 6 switches is all the space the gear has. The facility is requesting an additional service of 400A...
First priority is to verify the current system can handle the extra load!
 
weressl said:
Find the gear manufacturer's service agent in the area and ask for an engineered solution to meet UL compliance.




As an inspector, I can tell you what I would look for in this type of situation.

1. Follow the above advice. Make sure you get a letter from the manufacturer stating that tapping the bus is permitted, with the gear identified in the letter.

2. Provide a load calculation to substantiate the addition of the 400A disconnect.

3. Provide a drawing to show the intended location of the new disconnect.

After a short review of the document (no longer than 2-3 months :grin: only kidding), we will provide our answer to you.


I can tell you that the manufacturer is probably going to be the "key". I just finished a review of something similar and the manufacturer would not permit tapping of the buss.
I know each situation is different.
 

statedogg

Member
You may find this interesting. The gear is GE, my GE rep was unavailable yesterday, but I was put in contact with a Square D rep who was able to provide some info. He said they could modify the bus and provide what we need. I found it interesting that they would modify GE gear. I will try to attach a picture.
The main is 1200 amps and each switch is 400A.

302690116.jpg
 

benaround

Senior Member
Location
Arizona
statedogg,

I, for one, would like to say Thanks for the follow up on your thread. Too

many times a thread leaves you hanging for the final results, and it really

takes away from the learning expirence.
 
statedogg said:
You may find this interesting. The gear is GE, my GE rep was unavailable yesterday, but I was put in contact with a Square D rep who was able to provide some info. He said they could modify the bus and provide what we need. I found it interesting that they would modify GE gear. I will try to attach a picture.
The main is 1200 amps and each switch is 400A.

302690116.jpg

Aaah, an AKD gear with close coupled, indoor, liquid filled transformer! Had one some years ago. There should be no problem finding a stack on the surpluss/used gear market and just attaching it.
 
Status
Not open for further replies.
Top