Our company manufactures and distributes equipment racks, frames and enclosures for telecommunications and data equipment. Our customers conform to Telcordia standards, and as such, we are required to provide product which will also conform to these standards. One of the standards per Telcordia is that equipment racks and frames in excess of 84" SHALL BE top supported.
Today, I get a request from one of our customers (whom must conform to Telcordia standards) to provide them with a frame to support 48RU of equipment in a 7' environment. For those who don't know, 1RU = 1.75". I checked... twice... 48 X 1.75" = 84".
Our typical 84" frames support 44RU and have top and bottom members to 1) secure the mounting rails at a set distance and 2) to allow for anchoring to the floor and cabling from the top. These members are approximately 3" high. Thus, 84" - 6" = 78". Using simple math, 44RU or 1.75 x 44 = 77". This allows half an inch at the top and bottom to allow for installation clearance and such.
I responded to the customer's request, citing the Telcordia standards relating to the overall height. They did not want to exceed 84" and thus require a expensive and cumbersome top support system (read: seismic rated stanchions, auxiliary framing, etc). I was asked, "Well, how are we supposed to fit four 12RU chassis into a 44RU frame?"
"Buy two frames."
We received a purchase order for two frames within the hour.
Reminds me of a customer I had many years ago where my invoice was approximately $1000 LESS than the Purchase Order. They would not pay because the invoice did not match the PO.
Solution - I invoiced for the full amount of the PO per their instructions. Got paid quickly...