--- 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.