---
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.**
%%

## Wire Material Selection

[[pdi-estimating]] preference is to use aluminum conductors.

If [[pdi-bid-estimating|Bid]]'s proposal sells aluminum 100A and larger
use aluminum for grounds, even if the feeder schedule uses copper.[^1]

[^1]: [[2026-05-06_14-00-10]]

## 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 your [[conest#ConEst Senior Estimator|senior]] 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.

#### Precast Slab

Typical of garage construction.

PVC in-slab may not be utilized for precast slabs.

#### 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 |
| ------------:| ----------------------:|
|         1/2" |                 3.0 in |
|         3/4" |                 3.5 in |
|           1" |                 4.0 in |
|       1-1/4" |                 5.0 in |
|       1-1/2" |                 6.0 in |
|           2" |                 7.5 in |
|           3" |                 9.0 in |
|       2-1/2" |                10.5 in |
|       3-1/2" |                12.0 in |
|           4" |                13.5 in |
|           5" |                17.0 in |
|           6" |                20.0 in |

#### Shear Walls

[[construction-methods#Shear Walls|Shear walls]],
like those around stairwells and elevator shafts,
may be routed through with special permission.

#### Post-Tensioned Slabs

Raceway considerations for
[[construction-methods#Post-Tensioned Slab|post-tensioned slabs]]
(namely if PVC may be utilized, and if so, what sizes)
are contentious.[^2][^3][^4]

[^2]: > [!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.

[^3]: > [!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.

[^4]: [[2026-05-12_09-15-34#Post-Tensioned Slab Considerations]]

#### Pan Deck Slabs

Raceway considerations for
[[construction-methods#Pan Deck Slab|pan deck slabs]]
(namely if PVC may be utilized, and if so, what sizes)
are contentious.[^5]

[^5]: > [!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 cable](https://www.southwire.com/wire-cable/metal-clad-cable/c/c-mc-mcap)
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]])

> [!info]
> This is not a code requirement,
> though it is frequently stated to be.
> It is, however, near universal specification.

#### Multi-Circuit Homeruns

Different schools of thought exist
on whether to use multi-neutral MC or pipe and wire for homeruns.[^6]
Which is more cost-effective
is apparently subject to transient market conditions.
Seek clarification from your senior on a job by job basis.

[^6]: > [!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.

Where only set-screw fittings with two screws are permitted
no change to takeoff is necessary.[^7]

[^7]: [[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.

Where acceptable usually utilized in lieu of EMT.

## 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
```

## Other Considerations

### Fire Rated Feeders

Where required see [[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.

### Liquidtight Flex



* [[nfpa-70_356_lfnc|Liquidtight Flexible Nonmetallic Conduit: Type LFNC]] --- "Carflex"[^8]
* [[nfpa-70_352_lfmc|Liquidtight Flexible Metal Conduit: Type LFMC]] --- "Sealtite"[^9]

[^8]: From Carflex®, manufactured by Carlon.
[^9]: From Anaconda Sealtite®, manufactured by ANAMET Electrical.
