Panelboard Bussing

[vpower1989]

Hello All,


I am a fairly young Electrical Engineer whose currently working with a client to update/ clean up some of their site construction specifications.

I am currently working on their Panelboard section. One requirement that they have in the specification is a current density of 1000A/sq-in for bus bars. I think this is a bit of a "legacy" requirement as my counterparts on the client side don't know why it is required. I have looked at UL67 and NEMA PB1 and all I see is a requirement for bus bars to pass temperature rise testing. My gut is telling me that this requirement can be removed from the specification, and as long as future Panelboards have buses that are sized per UL67, we should be good.

Does anyone have any experience or insight as to why such a requirement could be in this specification?

 

[jim dungar]

Current density is a left over spec from more than 40 years ago.

UL tests to heat rise, but custom shops may use density (especially in switchboards and switchgear). So if your require UL Standards you would not need anything else.

 

[Jraef]

1000A/sq-in is still the standard in UL891 for SWITCHBOARDS, but it's not there for PANELBOARDS under UL67 and I don't think it ever was. That doesn't stop some entities from adding it though. I'm pretty sure for instance that the City of Los Angeles, who have their own standards in addition to the NEC, requires that. I've also heard that Chicago does too, but I've never done projects there.

It also used to be an internal standard at Boeing facilities, which led to their panelboards having to all be custom built instead of COTS stuff. I had an acquaintance who worked for WESCO in Seattle, but couldn't sell Westinghouse panelboards to them, so he cut a deal with a custom builder named IEM to build panelboards to Boeing's specs, making him the sole supplier. Every year he would hit his sales goals in around September, then quit working the rest of the year in order to avoid going too far over.

 

[vpower1989]

1000A/sq-in is still the standard in UL891 for SWITCHBOARDS, but it's not there for PANELBOARDS under UL67 and I don't think it ever was. That doesn't stop some entities from adding it though. I'm pretty sure for instance that the City of Los Angeles, who have their own standards in addition to the NEC, requires that. I've also heard that Chicago does too, but I've never done projects there.

It also used to be an internal standard at Boeing facilities, which led to their panelboards having to all be custom built instead of COTS stuff. I had an acquaintance who worked for WESCO in Seattle, but couldn't sell Westinghouse panelboards to them, so he cut a deal with a custom builder named IEM to build panelboards to Boeing's specs, making him the sole supplier. Every year he would hit his sales goals in around September, then quit working the rest of the year in order to avoid going too far over.

Ok. Thanks for the information. Part of what this client wants to do is move to more standard equipment and reduce "gold plating" where possible. In my mind, panels that meet UL67 will suffice.

 

[vpower1989]

Current density is a left over spec from more than 40 years ago.

UL tests to heat rise, but custom shops may use density (especially in switchboards and switchgear). So if your require UL Standards you would not need anything else.

Thanks for the information.