Wiring Sizes

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gmtt

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Attached is a one-line riser diagram. Could anyone check if the wiring sizes make sense? Please ignore other criteria if not absolutely necessary to determine this. My main concern is: two different sources, 30A from EM Gen and 60A from building panel going to ATS which is connected to a 100A panel. Do ATS equipped with lungs that can take different sizes of wires? (in this case 100A,30A,60A). OR should I size all to 100A (#3AWG) to avoid this concern. Will it be contrary to any code?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
The details seem to ask for a 60 amp breaker in the emergency generator panel (#2), but the wiring is designed for 30 amp and the diagram shows 30.
The lugs will probbaly be designed for your wire range, but it pays to doublecheck.
You might also take a look at 702.5 concerning capacity and ratings.
 

charlie b

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Location
Lockport, IL
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Retired Electrical Engineer
There is no reason that the normal supply to a panel (via an ATS) has to have the same rating as the alternate supply to the same panel (via the same ATS). In such a case, the wires from the ATS to the panel have to be large enough to handle the larger of the two sources (in your case, 60 amps). I would suggest a "value engineering" change (even though I detest that phrase :roll: ) to use a 60 amp panel, with a 60 amp main breaker, instead of the 100 amp panel, if such a thing is available and is less expensive. Someone else would have to find that out.

Please do take issue with the obvious contradiction in the requirements. They are telling you that a run from the third floor to the tenth floor (the "thenth" actually) is no more than 50 feet. Seven floors, including the depth of the ceiling spaces, means the ceiling height of each level is no more than 7 feet. I doubt that is true. If you price it for a 50 foot run, you may have to eat the extra costs of the run.
 

gmtt

Member
Charles, I understand your concerns. I cut and pasted from an actual case so there were some erroneous information in it. But as I mentioned, my only concern is about the coupling the three different amperage. Should I size per amperage of each segment (like as I showed)? or should I wire per highest ratings for all three segments (i.e 100A)? All panels are given, nothing can be changed. Only thing remaining is the connecting the panels thru ATS with right sizes (per code) of wires and with best practice.
 

augie47

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Location
Tennessee
Occupation
State Electrical Inspector (Retired)
The "coupling" should be no problem. The ATS isolates the circuits so that as long as each condutor is properly protected by it's OCP you are fine.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Rack #1 and Rack #2 sounds like it is for IT and computer equipment.

I hope they aren't really using the emergency generator in a 10 story building to run computer or IT equipment that isn't really an emergency load.

Steve
 
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