Coring a Post-Tensioned Slab for EV Charger Conduit
No. A post-tensioned deck holds concrete in compression with steel strands stressed near their breaking strength, and those strands can run only inches apart near a beam or opening. Nothing gets cored, drilled or anchored into that deck until tendons are located and an engineer signs off. Surface EMT conduit and suspended cable tray solve most charger routing without it.
Updated 2026-08-25
Can you core drill a post-tensioned garage slab for EV charger conduit?
No, not by default. A post-tensioned deck is concrete held in permanent compression by steel strands stressed to a large share of their breaking strength, and near a beam, column or existing opening those strands can run only a couple of inches apart. Nobody puts a core bit or a hammer drill through that deck until the tendons are located and a structural engineer has said in writing what may be cut, drilled or anchored.
Why a severed tendon is not a small mistake
A post-tensioning strand carries load the day it's stressed and every day after, so cutting one doesn't just leave a gap — it releases stored energy. The Post-Tensioning Institute of Australia's guidance is blunt about the unbonded strand common in U.S. parking decks: a severed, non-grouted strand can fly out of its end anchorage, and that is treated as a safety event on the spot, not a repair scheduled for later.
How tendons are actually located before anyone drills
Two methods are accepted, and guessing from the ceiling below is not one of them. A cover meter or ground-penetrating radar scan maps tendon positions on the deck before a single hole is marked, or — where scanning isn't practical — an engineer directs a pattern of small vertical pilot holes, drilled with a masonry bit rather than a diamond core, to confirm a tendon-free zone before the real penetration is cut.
Workaround one: surface-mounted EMT conduit
Running rigid metal conduit or EMT along walls, columns and beam soffits gets power to the charger without a single core through the slab, and it's the default answer for most garage retrofits. NEC Article 358 permits EMT exposed or concealed in dry locations, and it has to be secured within 3 feet of every box or termination and at intervals of no more than 10 feet along the run.
Workaround two: suspended cable tray
Cable tray hung from the structure above serves the same purpose trenching serves on a surface lot — a route you can add or change circuits in later without opening anything up again — and it can be supported entirely off elements that were never post-tensioned.
What to put in writing before anyone mobilizes
A garage retrofit quote that skips this step is a quote for the easy version of the job, not the real one. Ask for the same three things every time.
Can you core drill a post-tensioned parking garage slab for EV charger conduit?
Not without locating the tendons first and getting a structural engineer's written sign-off. Tendons can run close together near beams, columns and existing openings, and cutting one is a structural event, not a patchable mistake. Most conduit runs for a charger retrofit don't need coring at all — surface-mounted EMT and suspended cable tray solve the same routing problem without it.
Is it safe to drill into a post-tensioned parking garage slab?
Only after the tendons in that specific spot have been located, by ground-penetrating radar, a cover meter, or engineer-directed pilot holes. Drilling blind risks striking a stressed strand, and an unbonded strand severed without warning can whip out of its end anchorage. Every published guidance on this treats locating tendons as the first step, not an optional one.
How do you run EV charger conduit in a parking structure without cutting the slab?
Route it on the surface instead of through the deck. Rigid metal conduit or EMT along walls, columns and beam soffits under NEC Article 358, or cable tray under Article 392 hung from existing structural steel or conventionally reinforced columns, gets power to a charger location without a single full-depth core.
Does a structural engineer have to sign off before coring a parking garage for EV charging?
For anything beyond the smallest fixing holes, yes. Industry guidance on post-tensioned slabs sorts penetrations into classes by size and whether a tendon is cut, and only the smallest class — a fraction-of-an-inch fixing that stops well short of tendon depth — skips a full engineering review. An EV charger conduit run with anchor points and sleeves is squarely in the range that needs one.
What happens if a post-tensioning tendon gets cut by accident?
It stops the job immediately, not just the drilling. A severed unbonded strand can release with enough force to fly out of its anchorage, and a severed bonded tendon still needs a structural repair — commonly a bonded FRP laminate applied by a specialist — before anyone works near it again. Either way, an engineer has to assess the slab before work resumes.
Is a precast parking deck the same risk as a cast-in-place post-tensioned one?
No, and it's worth confirming which one you have before assuming the worst. Precast parking structures use pretensioned strand set in the factory in a known, documented pattern per plank, which is a different situation from a cast-in-place deck stressed on site. Either way, the rule is the same: identify the construction type and get it confirmed before anyone drills.
- Post-Tensioning Institute of Australia — Guidance Note GN06/v.2, Post Cut Holes through Post-Tensioned Slabs (Dec. 2014)
- Post-Tensioning Institute — Repair guidance, naming DC80.2-10 and DC80.3-12 as the U.S. reference documents
- AMSYSCO — MEP Coordination with Unbonded Post-Tensioning Tendons, Part 1
- NFPA 70, National Electrical Code — Article 358 (EMT), Article 392 (cable tray), 300.4 (physical protection)
- Installing EV chargers in a parking structure
- Trenching and conduit for a surface parking lot
- How much electrical capacity do commercial chargers need?
- How many charging ports does a property actually need?
- How long does a commercial charging project take?
- What to look for in a commercial charging contractor
Get a range before you commission a scan
A structural scan and engineer review cost money before a single conduit run is priced, so it helps to know roughly what the charger project is worth first. The estimate takes your port count, mounting situation and distance to the service and returns a modeled range in about a minute.