Manhole Conduit Layout – Spacing & NEC Compliance Concerns

[aelkhatib]

Hello everyone,

I’m working on a manhole conduit layout where I need to add 12 three-inch conduits and 4 two-and-a-half-inch conduits into an existing manhole that already has six 6-inch conduits.

The issue is that all conduits must enter from one side of the manhole, and I need to ensure proper spacing, staggering, NEC compliance, and constructability—all while working within a very limited space.

Manhole Details (Smallest Assumed Size):

• Manhole Size: 4’ x 4’ x 6’ deep (assumed I don't have any details on the dimension)
• Existing Conduits: Six (6) 6-inch conduits (already installed at the upper elevation).
• New Conduits to be Added:
  • Twelve (12) 3-inch conduits (to be staggered in two rows).
  • Four (4) 2.5-inch conduits (placed at the lower elevation).

Spacing & NEC Considerations Applied:

• 6-inch conduits are placed at ~51 inches above the manhole floor
• 3-inch conduits need to be staggered in two rows:
  • First row at ~25.5 inches above the floor.
  • Second row at ~22.5 inches above the floor (to create staggered spacing).
• 2.5-inch conduits should enter at ~20.25 inches above the floor, with at least 6 inches vertical clearance from the 3-inch conduits.
• Horizontal spacing between conduits is set at 2-3 inches, Challenges & Questions:

1. Will this many conduits fit within a 4-foot-wide manhole wall without structural issues? it seems very tight.
2. Does this arrangement allow enough room for future maintenance inside the manhole? Is there a better way to arrange these conduits while still keeping them in a single entry wall?
3. Would too many core drill penetrations into the wall weaken the manhole structure?
4. Are there any additional considerations for cable pulling?

Given the small size of this manhole, I’d really appreciate insights from those with field experience on the best way to handle conduit congestion like this while staying NEC-compliant.

Thanks in advance for any guidance!