234 lines
6.3 KiB
Markdown
234 lines
6.3 KiB
Markdown
---
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id:
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aliases: []
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tags:
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- occupational
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- type/guide
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title: Wiring Method Selection
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dg-publish: true
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---
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# Wiring Method Selection
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Determine where each wiring method can be used.
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> [!important]
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> This note covers general, system-agnostic selection.
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> For certain specific applications,
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> It may be necessary to deviate from the general case.
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%% TODO
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Scripts by others tend to beg questions of edge cases.
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It's my intent that if a rule holds in _all_ cases,
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even the super special one you're thinking I didn't consider,
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that I specifically say so.
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If I didn't say so, and your edge case is not covered,
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you should seek clarification.
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%%
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## Example Wiring Method Selection
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Below is an example Wiring Method Selection
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for a [[ibc-construction-types#^5-over-1|podium]] construction.
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> [!example]
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> Wire Material:
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> * Less than 100A: CU
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> * 100A and larger: AL
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>
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> Outdoors:
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> * Above-ground: EMT-Comp
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> * Underground: PVC w/ Rigid Elbows
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>
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> Levels 1-2 (Type IA):
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> * Concealed: MC
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> * Exposed to Structure:
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> * Up to 2"C: PVC In-Slab
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> * 2-1/2"C and larger: EMT-SS OH
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>
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> Levels 3-5 (Type IIIA):
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> * Concealed: NM/SER
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> * Exposed to Structure: PVC OH
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%%
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This needs reworking.
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I know PVC is preferable to MC in the case of feeders, subfeeds, and possibly home runs,
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but I think they swap for branch.
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%%
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## Standard Indoor Wiring Methods
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NM/SER < PVC in Slab < MC < EMT-SS < EMT-Comp
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### NM/SER Overhead
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Nonmetallic-sheathed cables are combustible,
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so not permissible in Type [[ibc-construction-types#Type I Fire Resistive Non-Combustible|I]],
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[[ibc-construction-types#Type II Non-Combustible|II]] constructions.
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#### Concealment
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Cable type wiring methods (MC, NM, SE)
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may only be used where they will be concealed from view.
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### PVC In-Slab
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May require rigid stub-ups in certain cases,
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which could make EMT more cost-effective.
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Consult with the Senior Construction Estimator in this case.
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> [!important]
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> Be careful of ambiguous terminology in specifications and PDI proposals:
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> "underground" and "below grade" are sometimes used inappropriately
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> to describe PVC in-slab.
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> It may be that rigid stub-ups are only necessary when emerging from grade (dirt),
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> but not when emerging from the slab.
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#### Garage Slab
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_Conventional Slab_: PVC in Slab
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_Precast_: EMT
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See [[pdi-breakdowns#Garage]] for more info.
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#### Slab Thickness
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Conduits may only be routed through slabs of thickness
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at least 3 times the outer diameter of the conduit.
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| Conduit Size | Minimum Slab Thickness (in) |
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| ------------:| ---------------------------:|
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| 1/2" | 3.0 |
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| 3/4" | 3.5 |
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| 1" | 4.0 |
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| 1-1/4" | 5.0 |
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| 1-1/2" | 6.0 |
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| 2" | 7.5 |
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| 3" | 9.0 |
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| 2-1/2" | 10.5 |
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| 3-1/2" | 12.0 |
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| 4" | 13.5 |
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| 5" | 17.0 |
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| 6" | 20.0 |
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#### Shear Walls
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[[construction-methods#Shear Walls|Shear Walls]]
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Shear walls, like those around stairwells and elevator shafts,
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may be routed through with special permission.
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#### Post-Tensioned Slabs
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[[construction-methods#Post-Tensioned Slab|Post-Tensioned Slab]]
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> [!cite] [[joel-jansen]] 2025-08-15, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
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> No affect on takeoff. Routing in slab still possible.
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> [!cite] [[joel-jansen]] 2025-08-21, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
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> PT slabs do have some affect on takeoff.
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> 3in conduit can not be run in an 11in PT slab.
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#### Pan Deck Slabs
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[[construction-methods#Pan Deck Slab|Pan Deck Slab]]
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> [!cite] [[joel-jansen]] 2025-08-15, in reference to [[belle-meade-plaza|Belle Meade Plaza]] (pp.)
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> Do not route in slab.
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### MC Cable Overhead
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_Market Type = Assisted Living:_ MC-AP may be required.
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#### Concealment
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Cable type wiring methods (MC, NM, SE)
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may only be used where they will be concealed from view.
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> [!important] Exception:
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> Temporary provisions for unfinished spaces
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> (e.g. core and shell [[pdi-building-types#Retail|retail]])
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#### Multi-Circuit Homeruns
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Different schools of thought exist
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on whether to use multi-neutral MC or EMT for homeruns.
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Which is more cost-effective
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is apparently subject to transient market conditions.
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Seek clarification from your senior on a job by job basis.
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> [!quote] Art Baldwin (pp.)
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> Multi-circuit MC is not cost-effective
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> when considering the difficulty of rework.
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> Use conduit, even EMT if necessary.
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### EMT Overhead
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Set-screw fittings are cheaper than compression,
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but may not be acceptable.
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> [!info]
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> EMT has a third coupling type "indenter",
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> which are crimped onto the conduit using a special tool.
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> These are usually only mentioned in specifications
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> to say that they are unacceptable.
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[[2025-10-15_09-32-00#Vanderbilt Central Neighborhood Residential College Spec Interpretation]]
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## Standard Outdoor Wiring Methods
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PVC Underground < EMT-Comp < IMC
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### PVC Underground
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May require rigid stub-ups.
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### EMT Overhead
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Use compression fittings.
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## Nonstandard Indoor Wiring Methods
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### PVC Overhead
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Not usually permissible, except in Florida.
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## By Specification
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> [!info] Example Specs Relevant to Wiring Methods Selection
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> * 26XXXX - Raceway And Boxes For Electrical Systems
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> * 26XXXX - Conduits For Electrical Systems
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> * 26XXXX - Underground Ducts And Raceways For Electrical Systems
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>
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> * 26XXXX - Low-Voltage Electrical Power Conductors And Cables
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>
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> * 26XXXX - General Requirements For Electrical
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> * 26XXXX - Common Work Results For Electrical
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## Flow Chart
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```mermaid
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flowchart
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A[Construction Type]
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A -- I, II --> B[Can be run in slab?]
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B -- No --> D[Concealed?]
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B -- Yes --> PVC
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D -- No --> EMT
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D -- Yes --> MC
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A -- III, IV, V --> C[Concealed?]
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C -- No --> PVC
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C -- Yes --> NM/SER
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```
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#### Fire Rated Feeders
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[[fire-resistive-wiring-methods-takeoff]]
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PDI estimating practice is to run all "emergency" feeds
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(life-safety or just standby)
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in a 2-hour rated assembly.
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This usually requires no change to takeoff for high-rises
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since electrical riser rooms are themselves fire-rated.
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* RHW-2 insulated conductors in conduit --- "Lifeline Cable"
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* 2-hour rated metal clad cable --- "Vitalink"
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