Terminal Block Wire Gauge Chart: AWG 30 to AWG 8 Mapped to Pitch, Ampacity and Strip Length for Panel Builders

A panel builder selecting a terminal block for a control panel needs one chart that maps the wire gauge to the pitch, the ampacity, the strip length, and the torque. The chart below is that single reference. It is built around the AWG (American Wire Gauge) system used by UL 1059 and the mm² system used by IEC 60998, with the metric cross-section converted per ASTM B258. The ampacity column follows NEC Table 310.15(B)(16) for 75°C rated conductors in free air, and the strip length and torque columns follow the manufacturer's specification for the corresponding terminal block family.

The terminal block categories covered by the chart are the screw-clamp and feed-through families commonly mounted on 35 mm top-hat DIN rail per EN 50022. The terminal blocks category at NBJGE catalogs the screw-clamp, pluggable, barrier, and feed-through families that share this reference frame. Two product families anchor the chart: the TD20 DIN rail terminal block family for AWG 22-14 control wiring on a 660 V / 20 A rated platform, and the PA12 feed-through terminal block family for pass-through power distribution.

The Master Reference Table — AWG 30 to AWG 8 in One View

The table below is the master reference a panel builder can pin above the wire-prep bench. It maps AWG to metric cross-section, to the common pitch range, to the wire ampacity, to the recommended strip length, and to the torque specification. The three right-most columns are the field-execution variables the panel builder controls during wiring; the three left-most columns are the specification variables the engineer locks at the BOM stage.

Because the ampacity of the wire is typically the lower of the wire rating and the terminal block rating, the wire ampacity is the limiting variable in 80-90% of field applications — a 20 A-rated terminal block used with AWG 18 wire will see the wire limit kick in long before the terminal block rating is reached. The TD20 DIN rail terminal block is rated 20 A at 660 V, with a wire range of 22-14 AWG and a maximum torque of 10 kg·cm (approximately 1.0 N·m), which places it in the AWG 22-14 control wiring class. The PA12 feed-through family shares the same conductor cross-section envelope and is typically used for pass-through distribution within the same AWG class. For AWG 18 control wiring, the practical ampacity is 7-10 A in free air per NEC Table 310.15(B)(16), regardless of the higher terminal block rating.

TD20 sits on the same 35 mm top-hat DIN rail profile used by the other control wiring families in the catalog, sharing the end-stop and partition plate accessories with the AWG 24-18 pluggable and barrier terminal blocks in the terminal blocks category. This shared platform lets a panel builder mix signal, control, and power terminal blocks in the same DIN rail assembly without changing the mounting hardware.

The ampacity values in the right-most data column are taken from NEC Table 310.15(B)(16) for 75°C rated copper conductors in free air at 30°C ambient. Panel builders operating at higher ambient temperatures, in bundled cable runs, or in conduit with more than three current-carrying conductors must apply the derating factors from NEC Table 310.15(B)(2)(a) or the equivalent IEC 60364-5-523 installation method. The Engineering Toolbox copper wire ampacity reference provides the same chart in a quick-reference format for field engineers. The wire cross-section conversion from AWG to mm² follows SAE / ASTM B258, and the metric-conductor cross-section tolerance is specified in IEC 60228.

Why Pitch and Ampacity Set the Panel Layout

Because the pitch is the center-to-center distance between adjacent poles, the pitch is the dimension that decides both the panel width for a given number of poles and the creepage distance between adjacent live parts at a given voltage class. Pitch selection is the panel-layout decision that decides whether the BOM fits the enclosure, whether the panel meets the creepage and clearance of the standard, and whether the wires fit the clamp without splaying.

The de-facto industry pitch progression is 2.54 mm → 3.5 mm → 3.81 mm → 5.0 mm → 5.08 mm → 6.35 mm → 7.62 mm → 10.16 mm → 15.0 mm. Each step doubles or near-doubles the conductor cross-section envelope. A panel builder specifying 5.08 mm pitch for AWG 18 control wiring is following the de-facto industry default set by the major terminal block manufacturers including Phoenix Contact, Wago, and Wago. The 5.0 mm pitch is the metric equivalent used by Degson and Dinkle, with the two pitches being mechanically interchangeable on a 35 mm DIN rail.

The ampacity column drives the terminal block selection in two ways. First, the rated current of the chosen terminal block must be at least equal to the wire ampacity after derating. Second, the panel must contain enough poles of the right pitch to handle the conductor density at the wire entry and exit. The Schneider Electric terminal block catalog and the Wieland Electric terminal block catalog are the cross-references panel builders typically use to verify pitch compatibility with their existing BOM lines.

For the AWG 12-8 power feeder class, the pitch steps up to 10.16 mm or 15.0 mm to accommodate the larger conductor and the higher termination force. The NBJGE catalog offers terminal blocks in the 10.16 mm pitch class for AWG 12-8 power wiring, sharing the same 35 mm DIN rail mounting platform as the control wiring families. The TD35 series, referenced alongside the TD20 in the NBJGE catalog, extends the same platform into the higher-current AWG 12-8 envelope.

The 5 Application Classes — Where Each AWG Pitch Lives in a Real Panel

Because a panel builder sees the same wire gauge used in five distinct functional zones of a control panel, mapping the application class to the AWG and pitch is the engineering exercise that prevents the field-wiring error and the BOM mismatch. The five application classes below are the typical deployment zones for each AWG row in the master chart.

Class 1 — Signal and Instrumentation (AWG 30-26)

Signal-level wiring carries sensor returns, low-voltage analog signals, and communication bus drops. The typical pitch is 2.54 mm or 3.5 mm. The ampacity of these conductors is below the threshold of NEC Table 310.15(B)(16) and is instead limited by voltage drop and signal-integrity considerations. Strip length is 6-7 mm and torque is 0.2-0.25 N·m. The wire entry into the terminal block is typically via a single ferrule or direct insertion for solid wire.

Class 2 — Control Wiring (AWG 24-18)

Control wiring carries relay coils, contactor coils, PLC discrete I/O, and 24 VDC control circuits. The typical pitch is 3.5-3.81 mm for AWG 24-22 and 5.0-5.08 mm for AWG 18. Ampacity for AWG 18 is 7-10 A in free air, but control wiring typically carries well below that limit. Strip length is 7-10 mm and torque is 0.3-0.8 N·m. Anchoring this class, the TD20 DIN rail terminal block fits the AWG 22-14 envelope and serves as the workhorse terminal block for control panels. The PA12 feed-through family is used where pass-through distribution of the same potential is needed.

Class 3 — Branch Circuit (AWG 16-14)

Branch circuit wiring carries lighting loads, small motor loads, and receptacle circuits. The typical pitch is 6.35-7.62 mm. Ampacity is 10-20 A in free air, which matches the typical 15-20 A circuit breaker rating. Strip length is 9-12 mm and torque is 0.8-1.6 N·m. The chosen block must carry at least 20 A to match the wire ampacity, and the panel must follow the NEC branch circuit wiring method and overcurrent protection rules.

Class 4 — Power Feeder (AWG 12-10)

Power feeder wiring carries the supply to motors, subpanels, and high-load equipment. The typical pitch is 10.16 mm. Ampacity is 20-35 A in free air. Strip length is 11-14 mm and torque is 1.6-2.5 N·m. A 30 A or higher rated terminal is the minimum match, and the panel must follow the NEC feeder wiring method and overcurrent protection rules. The pitch increase from 7.62 mm to 10.16 mm accommodates the larger conductor and the higher termination force.

Class 5 — Main Feeder (AWG 8-6)

Main feeder wiring carries the supply from the panel main breaker or disconnect to downstream subpanels or large equipment. The typical pitch is 10.16-15.0 mm. Ampacity is 40-55 A in free air for AWG 8 and 55-65 A for AWG 6. Strip length is 13-15 mm and torque is 2.5-3.0 N·m. For this class, the panel builder selects a 50 A or higher rated terminal block, with the panel wired to the NEC main feeder method and overcurrent protection rules. For currents above 100 A, the panel builder typically moves from terminal blocks to bus bars or power distribution blocks.

The five-class breakdown aligns with the typical panel layout zones in an industrial control panel: the signal zone at the top of the panel, the relay and contactor zone in the middle, the branch circuit zone at the bottom, and the power feeder and main feeder zone at the side or the bottom of the enclosure. The Designing Buildings Wiki control panel engineering portal covers the typical panel layout zones in greater depth. The Copper Development Association copper wire engineering portal covers the AWG-to-metric conversion and the ampacity derating methodology in the panel context.

The 5 Field-Wiring Decisions a Panel Builder Owns

Because the BOM locks the terminal block family and the pitch at the engineering stage, the field decisions are the strip length, the torque, the ferrule selection, the DIN rail assembly, and the end-of-line testing — five decisions that decide whether the panel passes inspection on the first attempt or requires rework. The five field decisions below are the variables the panel builder controls during the wiring operation, not the variables the engineer controls during the BOM.

Because under-torque produces a high-resistance joint that heats under load, and over-torque strips the screw thread or cracks the insulator, the torque is the field decision with the highest safety consequence — the panel builder must use a calibrated torque screwdriver set to the marked value on the terminal block housing. The marked torque value on the housing reflects the manufacturer's qualification per UL 1059 or IEC 60998, and the field torque must match the marked value within ±10%. A torque audit at the end of the wiring operation is the practical verification method.

Strip length is the second field decision. The strip length must match the manufacturer's specification for the terminal block family. For AWG 22-14 control wiring, the typical strip length is 8-10 mm for the NBJGE terminal block families. For AWG 30-26 signal wiring, the strip length drops to 6-7 mm. A wire-prep bench with calibrated strip-length gauges is the practical method to enforce the specification at the field level.

Ferrule selection is the third field decision. Stranded wire requires a ferrule for reliable termination in a screw-clamp terminal block. The ferrule cross-section must match the wire cross-section, and the ferrule length must match the strip length. The ferrule is crimped with a calibrated crimp tool, and the crimped ferrule is inserted into the terminal block clamp. The Phoenix Contact ferrule engineering portal covers the ferrule selection methodology in detail.

The DIN rail assembly is the fourth field decision. The terminal blocks snap onto the 35 mm top-hat rail per EN 50022 or the 32 mm G-rail per EN 50035. The end stops are placed at both ends of the assembly, and the partition plates are placed between functional groups. The jumpers are placed across adjacent poles where the same potential is distributed. The Wago jumper engineering portal covers the jumper selection and insertion methodology.

End-of-line testing is the fifth field decision. The panel builder tests each terminal block for continuity, isolation, and torque-mark retention. The continuity test confirms the wire is properly clamped, the isolation test confirms no cross-connection between adjacent poles, and the torque-mark retention test confirms the screw was tightened to the marked value. A failed test requires re-work on the specific pole.

The five field decisions above are the practical panel-builder workflow. The BSI Group panel-building engineering portal and the DIN German standards portal cover the underlying standards (EN 61439-1 for low-voltage switchgear and controlgear assemblies, EN 50022 for the 35 mm top-hat rail). The UL panel-building engineering portal covers the equivalent UL 508A standard for industrial control panels in the North American market.

Why Cross-Reference Matters — UL 1059, IEC 60998, and the NEC Table

Because a panel built to UL 508A for the North American market and shipped to a European customer must also meet EN 61439-1 and the IEC 60998 terminal block standard, the cross-reference between standards is the engineering exercise that decides whether the panel can be shipped with one BOM or whether two BOMs are required. The cross-reference methodology is the practice that turns three regional conventions into one engineering specification.

UL 1059 is the North American standard for terminal blocks, covering the pitch, the rated current, the rated voltage, the wire range, and the torque marking. UL 1059 references NEC Table 310.15(B)(16) for wire ampacity and UL 486A-B for wire termination. IEC 60998 is the equivalent international standard, covering the same set of variables with metric units. EN 50022 defines the 35 mm top-hat rail geometry and the terminal block snap-on interface. EN 61439-1 is the low-voltage switchgear and controlgear assembly standard that pulls all the components together into a single panel-level certification.

The NEC Table 310.15(B)(16) is the cross-reference for the wire ampacity. The NEC also covers the overcurrent protection (Article 240), the branch circuit (Article 210), the feeder (Article 215), and the panelboard (Article 408). The NFPA NEC portal covers the full text of the standard. For a panel builder shipping globally, the NEC and the IEC 60364 series are the two standards that drive the BOM decisions for the conductor cross-section and the overcurrent protection.

The Engineering Toolbox AWG-to-metric and ampacity cross-reference consolidates the UL 1059 / IEC 60998 / NEC 310.15(B)(16) values into a single reference for panel builders working across both systems. The cross-reference also covers the temperature derating for ambient above 30°C and the bundling derating for more than three current-carrying conductors in a conduit or cable tray.

The 6 Differences Between a Panel-Builder Terminal Block and a Connector

Because a terminal block and a connector both terminate a wire but serve different functions in the assembly, the panel builder must distinguish between a terminal block that lands a wire and a connector that mates with a counterpart — the wrong choice creates a field failure that is difficult to diagnose. The six differences below are the practical distinctions a panel builder sees in the field.

A terminal block lands a wire and provides a permanent connection point on the DIN rail. A connector mates with a counterpart, typically a pluggable header or a socket, and provides a disconnectable connection point. A terminal block is fixed to the panel; a connector is designed to be mated and unmated in the field.

A terminal block is rated per UL 1059 or IEC 60998 for the wire range and the pitch. A connector is rated per UL 1977 or IEC 61984 for the contact rating and the mating cycle. The two standards use different test methods, different marking conventions, and different qualification criteria.

A terminal block typically uses a screw clamp, a spring clamp, a push-in clamp, or an insulation-displacement connection. A connector typically uses a crimp contact, an insulation-displacement contact, or a solder contact. The termination method is matched to the wire type and the field tooling.

A terminal block is mounted on a DIN rail or a PCB. A connector is mounted on a PCB, a panel cutout, or a cable end. The mounting method is matched to the assembly process and the field service requirement.

A terminal block is typically keyed by the pitch and the wire range. A connector is typically keyed by the contact arrangement, the polarization, and the locking mechanism. The keying is matched to the field wiring practice and the field service requirement.

A terminal block is sourced for the panel build per the BOM. A connector is sourced for the cable assembly or the device interface per the BOM. The two sourcing streams are managed separately in most panel-building operations. The Degson terminal block product portal and the Dinkle terminal block product portal cover the terminal block sourcing for global panel builders. The McMaster-Carr industrial supply engineering portal covers the cross-reference for the North American market.

8 Buyer FAQ — Terminal Block Wire Gauge, Pitch, and Strip Length

1. What is the difference between AWG and mm² for terminal block sizing?

AWG (American Wire Gauge) is the North American standard for wire cross-section expressed as a gauge number, while mm² (square millimeters) is the metric and IEC standard. AWG and mm² are inversely related: smaller AWG numbers indicate larger cross-sections. For example, AWG 14 equals approximately 2.08 mm², AWG 18 equals approximately 0.82 mm², and AWG 8 equals approximately 8.37 mm². Panel builders sourcing globally must convert between the two systems because UL 1059 and CSA C22.2 No. 158 use AWG while IEC 60998 and EN 50035 use mm².

2. How is pitch (spacing) selected for a terminal block?

Pitch is the center-to-center distance between adjacent poles. The pitch is selected from three variables: the wire cross-section that will be terminated, the voltage class of the circuit, and the creepage and clearance requirements of the panel standard. Common pitches include 2.54 mm for signal-level AWG 30-26 wiring, 3.5 mm and 3.81 mm for AWG 24-18 control wiring, 5.0 mm and 5.08 mm for AWG 16-12 power distribution, and 7.62 mm and 10.16 mm for AWG 10-8 power feeders. Industrial DIN rail terminal blocks typically follow the 5.08 mm pitch as the de-facto industry default.

3. How is ampacity read for a terminal block?

Ampacity is the maximum continuous current the terminal block can carry at its rated temperature without exceeding the wire insulation limit. The rated current of the terminal block is the upper limit, but the wire ampacity from NEC Table 310.15(B)(16) or IEC 60364-5-523 is typically the lower of the two and dictates the practical limit. A terminal block with a 20 A rated current used with AWG 18 wire is limited to the wire ampacity, not the terminal block rating. Derating for ambient temperature, bundling, and conduit fill must also be applied.

4. What strip length does a panel builder prepare for an AWG range?

Strip length is the length of insulation removed from the conductor end before insertion into the terminal clamp. Strip length is determined by the terminal block's clamp depth and the manufacturer's specification, typically 6-7 mm for AWG 30-26 signal wiring, 8-10 mm for AWG 24-14 control wiring, and 10-15 mm for AWG 12-8 power wiring. Under-stripping leaves insulation inside the clamp and creates a high-resistance joint; over-stripping exposes bare conductor beyond the clamp and creates a shock and short-circuit hazard.

5. What torque should be applied to the terminal screw?

Torque is the tightening force applied to the screw clamp, specified by the terminal block datasheet in units of N·m, kg·cm, or in·lb. Under-torque produces a high-resistance joint that heats under load and may cause a fire; over-torque strips the screw thread or cracks the insulator. UL 1059 and IEC 60998 specify torque markings on the terminal block housing for field verification. Typical values are 0.2-0.4 N·m for AWG 30-22 signal clamps, 0.5-1.2 N·m for AWG 18-14 control clamps, and 2.0-3.0 N·m for AWG 12-8 power clamps.

6. Can stranded wire be used in any terminal block?

Stranded wire requires either a ferrule (bootlace crimp) or a terminal block designed for stranded wire. Solid wire can be terminated directly in a screw-clamp terminal block, but stranded wire without a ferrule will splay under screw pressure and create a high-resistance contact. Many modern terminal blocks (including the TD20 DIN rail screw-clamp family from NBJGE) accept ferruled stranded wire directly. Spring-clamp and push-in terminal blocks are inherently friendly to ferruled stranded wire and offer reduced wiring time.

7. How is a 35 mm DIN rail selected for a terminal block assembly?

The 35 mm DIN rail is the global standard for industrial control-panel terminal block mounting, defined by EN 50022 (top-hat rail) and the symmetric 32 mm G-rail (EN 50035). The TD20 DIN rail terminal block series from NBJGE snaps onto both rail profiles and accommodates a wide AWG range (22-14 AWG per the TD20 specification). For panel builders, the rail length is calculated as the sum of all terminal block widths plus 10-20 mm end-clamp allowance, with end stops, partition plates, and jumpers planned into the assembly.

8. When is a feed-through terminal block the right choice?

A feed-through terminal block is the right choice when the panel builder needs to land a wire from an external source and route the same potential through the panel to a downstream device. The PA12 feed-through terminal block family from NBJGE accepts a wire range matching the connector's rated cross-section and uses a zinc-alloy copper conductor for low contact resistance. Feed-through blocks are distinct from disconnect blocks, fuse blocks, or ground blocks, which add a function beyond simple pass-through.

Get the Wire Gauge Chart for Your Panel BOM

Because a terminal block that meets the wire range but misses the pitch-versus-panel-width fit, the ampacity-versus-circuit-breaker match, or the torque-versus-strip-length calibration becomes a field-rework event at the wire-prep bench, the right specification at the BOM stage is the engineering decision that decides whether the panel passes inspection on the first attempt. The wire gauge, pitch, ampacity, strip length, and torque are specification variables, not afterthoughts.

Send the wire AWG, the metric cross-section, the circuit class, the panel layout drawing, and the destination country with the applicable standard (UL 508A for North America, EN 61439-1 for Europe) to the NBJGE engineering team through the contact us page. The team will return a quotation with the matching terminal block family, the pitch, the rated current, the strip length, the torque specification, and the lead time for the destination country. Cross-reference the full terminal blocks catalog against your BOM, and review the TD20 DIN rail terminal block product page for the AWG 22-14 control wiring class and the PA12 feed-through terminal block page for pass-through distribution.