parallel feeds split unevenly

[canoeman]

I am on a job, where the electrician was given three conduits, to feed three paralell 750MCM aluminum, to a switch gear. the engineer, to save money, switched from two paralell feeds of 500mcm copper to three paralell 750 mcm. At the switch gear, they landed the three sets of three paralell phases in their own ilsco blocks, then to fit breaker, he ran two sets of 500 mcm into double lug breakers, that had max lug size of 500 mcm. Three phase, 480vac.
when the electrician got to the last vault, he put two sets of parallel feeds in one conduit, and one set in another, leaving the third conduit, and a spare empty.
Then when feeding out to sub panels, he ran two sets of paralell feeds in one conduit..
won't this cause heating and power quality problems. The engineer has made many bizarre directions to the electrical contractor, so I know this is already very unusual.
I feel the engineer is way over his head on these issues, this was his first big job.
We have three 600 amp switch gear panels, with thre sets of paralell feeders, and an 800 amp, 4 paralell aluminum 750MCM feeds coming up, with the same set up.

 

[Smart $]

..
when the electrician got to the last vault, he put two sets of parallel feeds in one conduit, and one set in another, leaving the third conduit, and a spare empty.
Then when feeding out to sub panels, he ran two sets of paralell feeds in one conduit...

Running two of three parallel sets in one conduit is a violation [310.10(H)(3)].
Running two of two parallel sets in one conduit is not a violation.

 

[Carultch]

I am on a job, where the electrician was given three conduits, to feed three paralell 750MCM aluminum, to a switch gear. the engineer, to save money, switched from two paralell feeds of 500mcm copper to three paralell 750 mcm. At the switch gear, they landed the three sets of three paralell phases in their own ilsco blocks, then to fit breaker, he ran two sets of 500 mcm into double lug breakers, that had max lug size of 500 mcm. Three phase, 480vac.
when the electrician got to the last vault, he put two sets of parallel feeds in one conduit, and one set in another, leaving the third conduit, and a spare empty.
Then when feeding out to sub panels, he ran two sets of paralell feeds in one conduit..
won't this cause heating and power quality problems. The engineer has made many bizarre directions to the electrical contractor, so I know this is already very unusual.
I feel the engineer is way over his head on these issues, this was his first big job.
We have three 600 amp switch gear panels, with thre sets of paralell feeders, and an 800 amp, 4 paralell aluminum 750MCM feeds coming up, with the same set up.

If you run multiple parallel sets in the same conduit, and simultaneously multiple parallel conduits, then each parallel conduit must contain the same quantity of parallel sets inside.


Given 2 parallel sets, you can put them in the same conduit, or separate conduits.
Given 3 parallel sets, you will most likely put them in 3 separate conduits. Unless somehow you can cram them all in one conduit (unlikely).
Given 4 parallel sets, you can put them in 4 separate conduits. Or 2 conduits with 2 sets in each.
Given 5 parallel sets, you have no choice other than to put them in 5 separate conduits.
Given 6 parallel sets, you can put them in 6 separate conduits. Or you can use 3 conduits, with 2 sets in each. Or, in a rare scenario, 2 conduits with 3 sets in each.


I would like to know, if this still applies for conduits that are 24" and less. Because ordinarily, you can ignore ampacity adjustments in "nipples" that are 24" and less. And ampacity adjustments due to bundling, are the entire reason why we have this rule about how to route your parallel sets of conductors.

 

[Smart $]

...
I would like to know, if this still applies for conduits that are 24" and less. ...

I don't see any exception...

In theory, I don't believe there would be any problem... but so goes theory vs. Code.