Bus Bracing for Low Voltage Switchgear 1

[Barry1952]

Please advise if there are any specific guidelines for bracing/supports for 480V 50kA Switchgear. There seams to be a table/chart available from UL891 Supplement B for Switchboards but haven't come across anything for Switchgear.
Also, have not been able to actually "find" the Supplement B that many refer to, even when searching on the UL web site. They only list Supplement A???

 

[VTer]

Thats because Switchgear is designed, assembled, and tested in compliance with ANSI/IEEE standards in US. Try IEEE C37.20.1.

"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla

 

[rbulsara]

Also check UL 1558, which applies to LV switchgear. UL891 is for switchboards.

Rafiq Bulsara

http://www.srengineersct.com

 

[Barry1952]

Thank you both for your responses.
Yes, 891 is for Switchboards and 1558 is for Switchgear Assemblies.
It appears that UL provide charts (in Supplement B that I can't find on the UL web site)for mfgr's to build switchboards but to build swgr, one has to follow testing guidelines to prove it can withstand the levels it maybe subjected to. Therefore, there are no charts for swgr bus supports and bracing. If someone has a different information on this, please advise.
I know that there are companies out there that will modify existing bus systems for a higher IC rating and I wonder what they use for guidelines/calculations to warrant what they do.

 

[asco1]

Re UL 891: There is no more Suppliment B.
See Annex G (at the very end of the 891 file). Annex G covers 4000A maximum & up to 100,000 RMS.

1558 Switchgear: Supports & bracing must be per individual testing. Once that testing has been done, we can design per the spacings in our UL File.

 

[jraef]

Powell Switchgear used to publish a set of technical papers, one of which described this issue and why there is no "standard". I had to wave that in the face of an over zealous nspector once. He still rejected it and siad I had to bring UL out to the jobsite to inspect it, assuming it would fail. I had to pay for a UL field inspection, during which the UL inspector came out and told him "It's fine, they tested it. THAT'S the standard." I was vindicated, I still had to pay the bill...

"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
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[ScottyUK]

Is that typical in the US - inspectors whose authority is out of balance with their knowledge, not adequately knowing the standards they are supposed to enforce and landing the customer with a bill because of their error? I'm surprised there isn't any recourse in such a case.


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If we learn from our mistakes I'm getting a great education!

 

[wcarter]

Yes Scotty, it is VERY normal. I work for a manufacturer and you'd be surprised at how many of our customers get conflicting data. One you might love. Requirements for ground fault testing on initial installation of service entrances. It IS required in many cases, though easily over half of the inspectors are unfamiliar with this rule.

Barry, the company I work for utilizes a arc-flash study along with a design program. The placement is dependant upon final kA rating.

 

[jraef]

An extension of old axiom popular in such situations:

"Those who can't do, teach But those who can't teach, inspect!"

Inspectors here are referred to as an "AHJ", Authority Having Jurisdiction. It means the are the demigod of their own little world. There is an appeal process, but you are loathe to use it if you are not prepared to be challenged on everything. Most inspectors are retired (or failed) contractors, not engineers. This one was a retired engineer, but he was not an EE, I think he was an ME, maybe even a CE.