I have an application where I'm using a pre-cast manhole as a pull box (angle pull). When calculating the minimum required size of the manhole (per NEC 314.28), do I care about inside dimensions or the outside dimensions (see attached picture for reference)?
The way I read the code it's the outside dimension, but wanted to confirm.
Thanks in advance!
There are Engineering Firms that specialize in manhole designs including underground vaults for transformers.
Most aspects of manhole design and vaults etc are pretty much custom sized like the type and size of wires to be pulled through and voltage.
For generic designs however-- some are prefabricated and they can be purchased outright and delivered in place.
Depending on whether the project is subject to vehicular traffic—they maybe precast iron.
Some covers are just precast concrete for pedestrian traffic.
I spent a good portion of my engineering life in military installations and underground utilities are second nature.
The location of manholes and topographic maps are very important.
If for example a manhole is to be located at a sloping grade, the manhole has to have a small sump pit for water build up that allows water to sip into ground or sucked out. In some cases the bottom is covered only with loose gravel.
If the area is subject to flooding--this of course would be a different story.
Some manholes are deep that will require climbing ladders for access and eye bolt for pulling wires.
They may come with porcelain/hardware for
cleats (wire holder)
Too many things to consider that may fall outside the realm of this website.
I suggest consulting Mr Google (lol) for an engineering firm that offer this service. I cannot endorse any engineering services, sorry
Call me
over zealous or paranoid --but better safe than sorry.
After all--isn’t this what engineering is all about?
BTW:
Is this “application” a completed , sealed and signed and accompanied with working drawings and details that your are referencing to for a cost analysis?.
Or
Are you designing from scratch?
Thanks.
