6.4 KiB
id, aliases, tags, title, dg-publish
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Wiring Method Selection | true |
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.
Example Wiring Method Selection
Below is an example Wiring Method Selection for a ibc-construction-types#5-Over-1 Construction 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, ibc-construction-types#Type II Non-Combustible 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, like those around stairwells and elevator shafts, may be routed through with special permission.
Post-Tensioned Slabs
construction-methods#Post-Tensioned Slab
[!cite] Joel Jansen 2025-08-15, in reference to 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 (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
[!cite] Joel Jansen 2025-08-15, in reference to 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)
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.
[!info] Edge Case: Vanderbilt Central Neighborhood Residential College
[!cite] Vanderbilt Central Neighborhood Residential College - Project Specifications (pp.) Fittings for Type EMT Duct Raceways:
- Coupling Method: Compression coupling or Setscrew coupling. Setscrew couplings with only single screw per conduit are unacceptable.
[!quote] Joel Jansen via Microsoft Teams @ 2025-10-15 09:33 AM use set screw 🙂
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
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"