Shielded-cable callouts on U.S. industrial and commercial electrical drawings are governed by NECA 100-2013, the American National Standard for Symbols for Electrical Construction Drawings, which groups shielding into the "Special Cable Types" symbol family [S3].
For the engineer reading a one-line or a floor plan, the shielded callout is the single line of text that says what is inside the jacket, how many conductors, what gauge, and how the shield is terminated. Getting that string wrong is one of the most common causes of rejected submittals and field rework, and it is why the symbol has been codified the same way since the 1999 edition of NECA 100 [S3].
The NECA 100 shield symbol and the S suffix
NECA 100-2013 treats the shield as a dashed-line circle or arc drawn over the conductor line, with a short slash where the shield terminates to a ground point; an ungrounded shield is shown with the same symbol but without the ground slash [S3]. On schematic sheets, the symbol is paired with a text tag that uses an "S" suffix to identify shielded variants of standard cable types, for example "MC-S" for metal-clad with overall shield, "TC-S" for tray cable shielded, or "ITC-S" for instrumentation tray cable with overall foil and braid [S2][S4].
Autodesk AutoCAD Electrical users select the symbol from the Icon Menu under Miscellaneous, Cable Markers, Cable Markers with Shields, and the same block can be mirrored to either end of a run, which is how draftspeople keep left- and right-side callouts consistent across a multi-sheet set [S7]. City of San Antonio and City of Reading standard construction documents both use this same S-suffix convention, listing S, SS, SSSSSS as the abbreviation rows for shielded, single-shield, and multi-shield cable variants on their legend sheets [S1][S2].
Layered callout string format: cable ID, count, gauge, shield, raceway
A typical industrial callout is built as a slash-separated or space-separated string: CABLE TAG / CONDUCTOR COUNT x GAUGE / SHIELD TYPE / RACEWAY [S3]. The shield field is where the engineer tells the installer whether the cable is overall foil (OF), overall foil + braid (OFB), individual and overall shielded pairs (OS + IS), or has a special low-smoke zero-halogen jacket (LSZH) overlay, and the ground-termination letter (G for single-point) rides in the same field [S3][S4].
For an instrumentation loop, the same drawing conventions used in ex shielded cable construction reference documents expand the string to "C-101 / 1PR #16 OS + IS / OVP / 1" EMT", which fixes conductor count, gauge, shield topology, and raceway in one callout, while a power callout collapses to "C-202 / 3C #12 OF / 1" EMT" because the shield requirement is single-line and the conductor count is small [S3][S2].
Comparison of shield callout options by decision criteria
Four shield callout styles dominate U.S. industrial work, and the choice between them turns on four criteria: EMC environment, signal type, raceway space, and termination cost. [S5]
Overall foil only (OF) is the cheapest and most common callout; it is used on 600 V power feeders and on digital I/O where noise is moderate. Overall foil + braid (OFB) is specified for VFD output runs where reflected-wave dV/dt is a concern, since the braid is the only practical path to keep common-mode current off the conduit ground [S3][S2].
Individual + overall shield (IS + OS, also written "OS+IS" or "OSIS") is the instrumentation default, called out on every 4-20 mA and Foundation Fieldbus segment in chemical and refinery work because each pair needs a low-impedance drain to ground and the overall shield then handles bulk plant noise. The last category, LSZH-jacketed overall foil, is a safety-driven callout: it appears in transit, marine, and offshore drawings where the cable must pass IEC 60332-3 flame-spread limits, and the acid-gas emission requirement is covered separately under IEC 60754; it is the one variant where the shield field is paired with a jacket material field rather than a separate LSZH row [S3].
Where shielding callouts appear: one-line, plan, and panel schedule
Shielded-cable callouts appear in three different places on a typical construction set, and the symbol conventions differ slightly in each [S3]. On one-line diagrams, the shielded run is drawn with a single line and the shield is a small dashed arc over the run with the S-suffix in the cable tag. On floor plans, the run is shown as a dashed heavy line weight and the callout is anchored at each end with a leader; for runs longer than 50 ft, the callout is repeated at every panel penetration so the installer can verify the shield termination method without back-tracking [S1][S2].
On panel schedules, the shielded conductors land on terminal blocks labelled "SHLD" or with a ground symbol, and the same S-suffix tag is used in the load column so the panel builder knows which conductors need a drain wire landed. For this reason, most panel schedules in lv electrical reference documents carry a dedicated shield-termination row instead of burying it in the general ground row [S3][S4].
Termination and grounding rules that drive the callout
The shield callout has to be written so it survives into the termination drawing, not just the layout sheet. NECA 100-2013 pairs the shield symbol with a ground slash at one end, and the callout text must say which end: G for source-end single-point, or G2 for both ends [S3].
For a 4-20 mA HART loop, the callout is normally terminated at the field instrument end only, because grounding both ends creates a 60 Hz ground loop that adds 0.5 to 2.0 percent error to the reading, and the same convention applies to most Foundation Fieldbus segments [S3]. For VFD motor leads, the rule flips: both ends of the shield are landed to the drive and motor frame ground lugs, and the callout reads G2 because leaving the motor end floating lets the bearing voltages build until they discharge through the oil film and pitting damage follows within roughly 12 to 24 months of service [S3].
Common callout errors and how the standard fixes them
Three errors show up on roughly one in five submittals reviewed against NECA 100-2013: missing S suffix on the cable tag, ground-termination letter left out of the shield field, and shield symbol drawn without the drain wire [S3]. Each one has a one-line fix: add the S to the cable type, fill the termination field with G or G2, and add the slash to the shield symbol at the grounded end. The same standard also resolves the "where do I put the shield" question for fire alarm and electrical fire monitor reference documents, where the shield is called out as a separate cable from the signal pair rather than as an attribute of it, because the fire alarm run is treated as a circuit survivability element.
For hazardous-area work, the shield callout rides alongside the explosion-proof electrical reference symbols, and the seal-off at each conduit boundary is shown in the same callout string so the inspector can verify the shield is continuous through the seal. On industrial electrical automation panel drawings the callout is usually abbreviated to just the S-suffix and a single ground letter, since the full layered string would clutter the schematic and the detail moves to the panel schedule. The same abbreviation logic is why most electrical measurement reference loops show a 5-character callout on the schematic and a 30-character callout on the loop sheet.
Linking shielded callouts to instrumentation practice
The shielded-cable callout string is the bridge between the drawing and the field, and the right string matches the same shielding rules a servo drive spec checklist applies to encoder feedback wiring: twisted pair, overall shield, single-point ground at the controller, drain wire landed to the terminal block. Engineers who carry that same template into their cable callouts eliminate the most common field errors, and the only place the template changes is for VFD outputs, where both-end grounding is mandatory. [S1]
The next signal worth watching is the 2026 NECA working-group activity on a revision to NECA 100, which is expected to add explicit symbols for Category 6A and single-pair Ethernet shielded cabling; drafts are usually posted to the NECA website in the second half of the revision cycle.