---
tags:
  - occupational
  - type/guide
title: Wiring Method Selection
---
# Wiring Method Selection

Determine where each wiring method can be used.

> [!important]
> This note covers general, system-agnostic selection.
> For certain specific applications,
> It may be necessary to deviate from the general case.

%% TODO
Scripts by others tend to beg questions of edge cases.
It's my intent that if a rule holds in _all_ cases,
even the super special one you're thinking I didn't consider,
that I specifically say so.
If I didn't say so, and your edge case is not covered,
you should seek clarification.
%%

## Example Wiring Method Selection

Below is an example Wiring Method Selection
for a [[ibc-construction-types#^5-over-1|podium]] construction.

> [!example]
> Wire Material:
> * Less than 100A: CU
> * 100A and larger: AL
>
> Outdoors:
> * Above-ground: EMT-Comp
> * Underground: PVC w/ Rigid Elbows
>
> Levels 1-2 (Type IA):
> * Concealed: MC
> * Exposed to Structure:
>     * Up to 2"C: PVC In-Slab
>     * 2-1/2"C and larger: EMT-SS OH
>
> Levels 3-5 (Type IIIA):
> * Concealed: NM/SER
> * Exposed to Structure: PVC OH

%%
This needs reworking.
I know PVC is preferable to MC in the case of feeders, subfeeds, and possibly home runs,
but I think they swap for branch.
%%

## Standard Indoor Wiring Methods

NM/SER < PVC in Slab < MC < EMT-SS < EMT-Comp

### NM/SER Overhead

Nonmetallic-sheathed cables are combustible,
so not permissible in Type [[ibc-construction-types#Type I Fire Resistive Non-Combustible|I]],
[[ibc-construction-types#Type II Non-Combustible|II]] constructions.

#### Concealment

Cable type wiring methods (MC, NM, SE)
may only be used where they will be concealed from view.

### PVC In-Slab

May require rigid stub-ups in certain cases,
which could make EMT more cost-effective.
Consult with the Senior Construction Estimator in this case.

> [!important]
> Be careful of ambiguous terminology in specifications and PDI proposals:
> "underground" and "below grade" are sometimes used inappropriately
> to describe PVC in-slab.
> It may be that rigid stub-ups are only necessary when emerging from grade (dirt),
> but not when emerging from the slab.

#### Garage Slab

_Conventional Slab_: PVC in Slab
_Precast_: EMT

See [[pdi-breakdowns#Garage]] for more info.

#### Slab Thickness

Conduits may only be routed through slabs of thickness
at least 3 times the outer diameter of the conduit.

| Conduit Size | Minimum Slab Thickness (in) |
| ------------:| ---------------------------:|
|         1/2" |                         3.0 |
|         3/4" |                         3.5 |
|           1" |                         4.0 |
|       1-1/4" |                         5.0 |
|       1-1/2" |                         6.0 |
|           2" |                         7.5 |
|           3" |                         9.0 |
|       2-1/2" |                        10.5 |
|       3-1/2" |                        12.0 |
|           4" |                        13.5 |
|           5" |                        17.0 |
|           6" |                        20.0 |

#### Shear Walls

[[construction-methods#Shear Walls|Shear Walls]]

Shear walls, like those around stairwells and elevator shafts,
may be routed through with special permission.

#### Post-Tensioned Slabs

[[construction-methods#Post-Tensioned Slab|Post-Tensioned Slab]]

> [!cite] [[joel-jansen]] 2025-08-15, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
> No affect on takeoff. Routing in slab still possible.

> [!cite] [[joel-jansen]] 2025-08-21, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
> PT slabs do have some affect on takeoff.
> 3in conduit can not be run in an 11in PT slab.

#### Pan Deck Slabs

[[construction-methods#Pan Deck Slab|Pan Deck Slab]]

> [!cite] [[joel-jansen]] 2025-08-15, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
> Do not route in slab.

### MC Cable Overhead

_Market Type = Assisted Living:_ MC-AP may be required.

#### Concealment

Cable type wiring methods (MC, NM, SE)
may only be used where they will be concealed from view.

> [!important] Exception:
> Temporary provisions for unfinished spaces
> (e.g. core and shell [[pdi-building-types#Retail|retail]])

#### Multi-Circuit Homeruns

Different schools of thought exist
on whether to use multi-neutral MC or EMT for homeruns.
Which is more cost-effective
is apparently subject to transient market conditions.
Seek clarification from your senior on a job by job basis.

> [!quote] Art Baldwin (pp.)
> Multi-circuit MC is not cost-effective
> when considering the difficulty of rework.
> Use conduit, even EMT if necessary.

### EMT Overhead

Set-screw fittings are cheaper than compression,
but may not be acceptable.

> [!info]
> EMT has a third coupling type "indenter",
> which are crimped onto the conduit using a special tool.
> These are usually only mentioned in specifications
> to say that they are unacceptable.

[[2025-10-15_09-32-00#Vanderbilt Central Neighborhood Residential College Spec Interpretation]]

## Standard Outdoor Wiring Methods

PVC Underground < EMT-Comp < IMC

### PVC Underground

May require rigid stub-ups.

### EMT Overhead

Use compression fittings.

## Nonstandard Indoor Wiring Methods

### PVC Overhead

Not usually permissible, except in Florida.

## By Specification

> [!info] Example Specs Relevant to Wiring Methods Selection
> * 26XXXX - Raceway And Boxes For Electrical Systems
> * 26XXXX - Conduits For Electrical Systems
> * 26XXXX - Underground Ducts And Raceways For Electrical Systems
>
> * 26XXXX - Low-Voltage Electrical Power Conductors And Cables
>
> * 26XXXX - General Requirements For Electrical
> * 26XXXX - Common Work Results For Electrical

## Flow Chart

```mermaid
flowchart
    A[Construction Type]
    A -- I, II --> B[Can be run in slab?]
    B -- No --> D[Concealed?]
    B -- Yes --> PVC
    D -- No --> EMT
    D -- Yes --> MC
    A -- III, IV, V --> C[Concealed?]
    C -- No --> PVC
    C -- Yes --> NM/SER
```

#### Fire Rated Feeders

[[fire-resistive-wiring-methods-takeoff]]

PDI estimating practice is to run all "emergency" feeds
(life-safety or just standby)
in a 2-hour rated assembly.
This usually requires no change to takeoff for high-rises
since electrical riser rooms are themselves fire-rated.

* RHW-2 insulated conductors in conduit --- "Lifeline Cable"
* 2-hour rated metal clad cable --- "Vitalink"
