vault backup: 2026-06-03 10:13:33
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---
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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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---
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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,**
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**and your edge case is not covered,**
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**you should seek clarification.**
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%%
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## Wire Material Selection
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[[pdi-estimating]] preference is to use aluminum conductors.
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If [[pdi-bid-estimating|Bid]]'s proposal sells aluminum 100A and larger
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use aluminum for grounds, even if the feeder schedule uses copper.[^1]
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[^1]: [[2026-05-06_14-00-10]]
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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 your [[conest#ConEst Senior Estimator|senior]] 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 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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#### Precast Slab
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Typical of garage construction.
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PVC in-slab may not be utilized for precast slabs.
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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 |
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| ------------:| ----------------------:|
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| 1/2" | 3.0 in |
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| 3/4" | 3.5 in |
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| 1" | 4.0 in |
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| 1-1/4" | 5.0 in |
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| 1-1/2" | 6.0 in |
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| 2" | 7.5 in |
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| 3" | 9.0 in |
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| 2-1/2" | 10.5 in |
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| 3-1/2" | 12.0 in |
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| 4" | 13.5 in |
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| 5" | 17.0 in |
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| 6" | 20.0 in |
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#### Shear Walls
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[[construction-methods#Shear Walls|Shear walls]],
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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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Raceway considerations for
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[[construction-methods#Post-Tensioned Slab|post-tensioned slabs]]
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(namely if PVC may be utilized, and if so, what sizes)
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are contentious.[^2][^3][^4]
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[^2]: > [!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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[^3]: > [!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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[^4]: [[2026-05-12_09-15-34#Post-Tensioned Slab Considerations]]
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#### Pan Deck Slabs
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Raceway considerations for
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[[construction-methods#Pan Deck Slab|pan deck slabs]]
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(namely if PVC may be utilized, and if so, what sizes)
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are contentious.[^5]
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[^5]: > [!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:_
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[MC AP cable](https://www.southwire.com/wire-cable/metal-clad-cable/c/c-mc-mcap)
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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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> [!info]
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> This is not a code requirement,
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> though it is frequently stated to be.
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> It is, however, near universal specification.
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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 pipe and wire for homeruns.[^6]
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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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[^6]: > [!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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Where only set-screw fittings with two screws are permitted
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no change to takeoff is necessary.[^7]
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[^7]: [[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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Where acceptable usually utilized in lieu of EMT.
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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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## Other Considerations
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### Fire Rated Feeders
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Where required see [[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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### Liquidtight Flex
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* [[nfpa-70_356_lfnc|Liquidtight Flexible Nonmetallic Conduit: Type LFNC]] --- "Carflex"[^8]
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* [[nfpa-70_352_lfmc|Liquidtight Flexible Metal Conduit: Type LFMC]] --- "Sealtite"[^9]
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[^8]: From Carflex®, manufactured by Carlon.
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[^9]: From Anaconda Sealtite®, manufactured by ANAMET Electrical.
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