Mechanical Room Fire Wall Electrical Penetrations

[kwired]

On this single story building the cost difference does become closer, but you likely still can install underground faster. A big box store means running 20-30 feet up, following framing, more bending and fitting, and more trips up and down the scaffold or lift. Under the floor, unless you have rock hard base to dig through, can be run as the crow flies for the most part is quick and simple to cement raceways together Vs having to tighten fittings with wrenches or screwdrivers and the length of runs will be significantly shorter than for a building with high ceilings. One of the biggest challenges is going to be ensuring that you do emerge from the floor in the correct spot.

 

[growler]

The original building was done with all of branch circuits fed under the concrete.

Is it?

Given the choice we go under with as much as we can.

PVC is cheap, installs easily, you can run it 'as the crow flies' saving wire.

But yes of course you can penetrate fire walls if you use the correct methods ... which add costs and time.

I think the OP is asking as an engineer.

You can go underground or overhead but the EC will probably prefer going underground unless it's speced to be overhead. If overhead is speced then he will have to figure in the extra cost in his bid.

If the EC is qualified to do this work he will have no problem going underground.

 

[growler]

I prefer it for the following reasons: (1) It eliminates the risk of missing a wall. (2) If I miss a wall, then there is a lot of extra work that I really don't want to deal with.

If the crew doing the PVC knows how to do slab work they are not going to be missing any walls.

If any walls move that is a change order.

 

[ghorwood]

Slab vs overhead

Slab vs overhead

I would highly recommend running conduit in the slab. Sit with the A pages and work on layouts for your crew. Pay attention to the details.String column lines or control lines from which they can measure. It takes a little time on your part, but try to make your layout simple for them to understand. It helps to be good buddies with the plumbers. Buy them beer. They have no choice but to know exactly where the walls are, and can help you out. I also highly recommend upsizing your conduits, especially if they are over 100', and remember to use GRC 90s.
Even if you miss a wall or two, the cost of chipping up a pipe or two is still less than running overhead. For your overhead, you'll need ladders/lifts/scaffolds which increase the chance of injury. You will need straps, screws, mettalic conduit or MC cable, connectors, couplings, perhaps a trapeeze to mount all of your conduit/MC cables. If your feeders are overhead too, now you are running larger fittings, straps, supports, etc. Plus you'll need a Hilti book to identify the assemblies you will need to penetrate fire walls. Man! I would avoid running overhead like the plague.
Don't be afraid, you can do it.