Copper C connectors—also known as C-tap connectors, C-clamp connectors, or parallel groove (PG) connectors—are one of the most versatile and cost-effective splice and tap connection solutions in the electrical and utility industries. When made from high-purity copper and used with a hydraulic crimp tool, C connectors create permanent, low-resistance electrical connections that meet or exceed the performance of mechanical set-screw fittings at a fraction of the long-term maintenance cost.
What Are Copper C Connectors?
A copper C connector is an extruded or cast fitting shaped like the letter “C” with two channels: one for the main (run) conductor and one for the tap (branch) conductor. The fitting is placed over both conductors and then hydraulically compressed with a matching die to create an intimate metal-to-metal bond across the full contact area. The result is a joint with resistance comparable to the conductor itself, a pull-out strength exceeding the breaking strength of the conductors, and a profile that is acceptable for installation in conduit, cable tray, pull boxes, and direct burial applications.
C Connector vs. Mechanical Connector vs. Split Bolt Connector
Electrical contractors and engineers in the USA frequently compare copper C connectors against set-screw mechanical connectors and split-bolt (parallel-groove) connectors. Each has its place, but for high-reliability, maintenance-free installations, crimped C connectors are often the preferred specification. Set-screw connectors can loosen under thermal cycling and vibration—a failure mode well-documented in utility distribution systems. Split-bolt connectors are reusable and convenient but require periodic re-torquing. Crimped C connectors, by contrast, create a cold-weld-like joint that does not loosen, does not require maintenance, and is unaffected by thermal cycling within the conductor’s normal operating temperature range.
Types of Copper C Connectors for Crimping
Standard Copper C Tap Connectors
The most common type, designed for T-tap or parallel connections where a branch conductor is joined to a main conductor without breaking the main conductor. Used extensively for service drops, street lighting connections, transformer secondary leads, and panel board tap connections in North American utility and commercial installations.
Copper C Splice Connectors (Inline C Connectors)
Designed for inline splicing—joining two conductor ends in series rather than as a T-tap. Used where a conductor must be lengthened or repaired, and where the joint must fit within the constraints of an existing conduit or cable tray raceway.
Insulated Copper C Connectors
Pre-filled with mastic insulation or covered with a pre-attached insulating boot, these are used in medium-voltage overhead distribution, service entrance, and direct-burial applications where post-crimp insulation application is impractical. The insulation sleeve is rated for the application voltage (600V or 15 kV class) and weather-resistance per ASTM standards.
Bare Copper C Connectors for Grounding Applications
Uninsulated copper C connectors are widely used in grounding and bonding applications—for example, connecting bare copper grounding conductors at conductor splices, bonding jumpers, and equipment grounding taps. Because grounding conductors are intentionally uninsulated, no post-crimp covering is required.
Related Products for Conductor Connection Systems
- Copper Compression Lugs – For terminating conductors at equipment, panels, and switchgear
- Copper Compression Splices – Inline butt splices for end-to-end conductor extensions
- Mechanical Copper Lugs (Pressed) – For applications where hydraulic crimping equipment is not available
- Bronze Ground Rod Clamps – For grounding applications requiring conductor-to-rod connections
- Aluminum C Connectors – For all-aluminum or aluminum-to-copper transition service conductors
- Hydraulic Crimping Tools and Dies – Must be matched to the connector manufacturer’s die code for listed performance
Copper Material Grades and International Equivalents
| Property | ETP Copper C11000 | OF Copper C10200 | Phosphorus Deoxidized C12200 | High-Conductivity Copper C10100 |
|---|---|---|---|---|
| Copper purity % | 99.90 min | 99.95 min | 99.90 min | 99.99 min |
| Electrical Conductivity %IACS | 101 | 101 | 98 | 101.5 |
| US Standard | ASTM B152 / B187 | ASTM B170 | ASTM B187 | ASTM B170 |
| BS Equivalent | BS 1432 HC Cu | BS EN 1977 Cu-OF | BS 1433 HC Cu | BS EN 1977 Cu-OFE |
| ISO Equivalent | ISO 1337 Cu-ETP | ISO 1337 Cu-OF | ISO 1337 Cu-DHP | ISO 1337 Cu-OFE |
| DIN Equivalent | DIN 1708 E-Cu58 | DIN 1708 OF-Cu | DIN 1708 SW-Cu | DIN 1708 SE-Cu |
| EN Equivalent | EN 1977 CW004A | EN 1977 CW008A | EN 1977 CW024A | EN 1977 CW009A |
| Oxygen Content | 0.04% max | 0.0005% max | 0.04% max | <0.0005% |
| Best Application | General power connectors, C-taps | High-reliability, H2 environments | Welding, brazing environments | Ultra-precision, electronics |
Standards and Listings Governing Copper C Connectors
Copper C connectors for use in US electrical installations must comply with UL 486A (Wire Connectors for Use with Copper Conductors) for 600V applications, and UL 486D for submerged or direct-burial applications. For medium-voltage applications, IEEE C57.12.00 and ANSI/ICEA standards provide guidance. The NEC Articles 110.14 (electrical connections), 300.15 (boxes and conduit bodies), and 230.46 (splices in service entrance conductors) govern application of C connectors in different parts of the distribution system. All connectors should be installed with the manufacturer’s specified die code using a calibrated hydraulic compression tool to achieve the listed performance.
Copper C Connector Size Chart (Common US Sizes)
| Connector Model | Run Conductor Range | Tap Conductor Range | Typical Application |
|---|---|---|---|
| C6-6 | #6 AWG – #6 AWG | #6 AWG – #6 AWG | Residential grounding, small branch taps |
| C4-6 | #4 AWG – #4 AWG | #6 AWG – #4 AWG | Service entrance grounding, panel boards |
| C2-4 | #2 AWG – #2 AWG | #4 AWG – #2 AWG | Commercial service, secondary distribution |
| C1/0-2 | 1/0 AWG – 1/0 AWG | #2 AWG – 1/0 AWG | Large commercial, industrial feeder taps |
| C4/0-2 | 4/0 AWG – 4/0 AWG | #2 AWG – 4/0 AWG | Large commercial, utility secondary |
| C350-3/0 | 350 kcmil | 3/0 AWG – 350 kcmil | Utility secondary, substation connections |
Why Choose Us for Copper C Connectors
We manufacture copper C connectors from electrolytic tough-pitch (ETP) copper per ASTM B152 and B187, providing consistent conductivity, machinability, and crimping performance across all production lots. Our connectors are dimensionally standardized to work with major US hydraulic tool brands and their die sets, eliminating compatibility concerns on the job site. We offer a full size range from #14 AWG through 1000 kcmil in both bare and pre-insulated configurations, with die codes clearly marked on each connector. Custom configurations—non-standard channel combinations, larger conductor combinations, special coatings—are available with engineering consultation. Our quality system includes dimensional inspection, conductivity testing, and pull-out force verification on a sample basis from every production lot.
Frequently Asked Questions About Copper C Connectors
Q1: What is the correct crimp die for a copper C connector?
Each connector model has a specific die code printed on the connector body (e.g., “W”, “D”, or a numeric code). This code corresponds to the die profile required to produce the correct compression geometry. Using the wrong die produces either an under-compressed joint (high resistance, poor pull-out strength) or an over-compressed joint (cracked connector, damaged conductor strands). Always match the die code on the connector to the die code on the compression tool die.
Q2: Can copper C connectors be used with aluminum conductors?
Standard copper C connectors are rated for copper conductors only. For copper-to-aluminum or aluminum-to-aluminum connections, bi-metal (Al/Cu) or aluminum C connectors are required. The connector must be listed for both conductor materials, and anti-oxidant compound approved for aluminum must be applied to the aluminum conductor before insertion. Using a copper-only connector on aluminum risks work-hardening and cracking the aluminum strands during crimping.
Q3: Are copper C connectors waterproof?
Bare copper C connectors are not waterproof unless sealed with mastic tape, heat-shrink, or other approved insulating and sealing material post-crimp. Pre-insulated C connectors with factory-applied mastic fill provide a degree of moisture sealing and are listed for underground or direct-burial use per UL 486D when properly specified. For underwater applications (flooded vaults, manholes), use only connectors specifically listed for submerged service.
Q4: How many crimps should be applied to a copper C connector?
The number of crimps depends on the connector design. Single-indent connectors require one crimp per channel. Two-indent connectors require two crimps per channel, typically at specific locations marked on the connector. Always follow the manufacturer’s installation instructions—applying fewer crimps than specified leaves the joint under-compressed; applying more than specified can distort the connector body and create re-entrant shapes that concentrate electrical stress.
Q5: What is the temperature rating of a copper C connector crimp joint?
UL 486A-listed copper C connectors are tested for compatibility with conductors rated at 75°C and 90°C. The connector itself does not limit the temperature rating—the rating is determined by the insulation system applied post-crimp. For high-temperature applications (above 90°C continuous), specify connectors tested with high-temperature insulation materials or use bare connectors in dry, ventilated environments.
Q6: Can I reuse a copper C connector?
No. Crimped copper C connectors are one-time-use only. The crimping process permanently deforms both the connector and the conductor strands to create the joint. Attempting to reuse a crimped connector by spreading it back to its original shape will cause stress fractures in the copper, resulting in a mechanically weak joint that may carry current adequately initially but fail under vibration or thermal stress. Always use a new connector for each crimp connection.
Q7: Are copper C connectors code-approved for use in panelboards?
UL 486A-listed copper C connectors are acceptable for use in panelboards, load centers, and other equipment enclosures under NEC Article 110.14, provided they are installed per the manufacturer’s instructions and are accessible for inspection. For conductors connected directly to panelboard terminal lugs, the equipment manufacturer’s connection requirements supersede—some equipment manufacturers specify only the use of ring lugs or compression lugs at their terminals.
Q8: What AWG sizes are most commonly used for service entrance C connectors?
For residential service entrance conductors, the most common service drop tap connector sizes are 4/0 AWG through 350 kcmil (for service drops to 200A and 400A residential and light commercial panels). Commercial service entrance feeder taps range from 250 kcmil through 750 kcmil. These sizes represent the bulk of US utility secondary distribution and service connection work.
Q9: How do I inspect a completed crimp on a copper C connector?
Visual inspection should confirm that the connector is fully seated, the conductor is fully inserted to the bottom of each channel, the crimp indents are centered in the connector body, and there are no cracks, splits, or sharp deformations in the connector body. A continuity and resistance check using a digital micro-ohm meter should confirm resistance below the manufacturer’s specification (typically < 50 µΩ for a conductor-rated joint). Pull-out testing at a sample level during QA is also recommended for large utility projects.
Q10: Are there minimum bend radius requirements for conductors entering C connectors?
Conductors entering C connectors should not be sharply bent at the connector entrance—maintain at least the minimum bend radius specified in NEC Table 300.34 for the specific conductor and insulation type. Sharp bends at the connector entrance can damage conductor strands and insulation, concentrate mechanical stress at the point where the crimped (rigid) and uncrimped (flexible) sections meet, and accelerate fatigue cracking under vibration.
Q11: What is the difference between a copper C connector and a copper H connector?
A C connector has two channels in a C-shape, allowing a tap or splice where one conductor lies alongside another. An H connector (or H-tap) has an H-shaped cross-section that accepts conductors from opposite sides in a symmetrical arrangement. H connectors are commonly used for symmetric T-taps in overhead distribution where both legs of the tap are similar in size. The selection between C and H is partly based on conductor geometry, partly on crimp tool die availability, and partly on project specification.
Q12: Can copper C connectors be installed in concrete or direct burial applications?
Bare copper C connectors may be directly buried or encased in concrete where the application involves bare copper grounding conductors. For insulated conductors, a UL 486D-listed (underground rated) insulated C connector, or a bare connector with approved direct-burial insulating wrap, must be used. In all direct-burial applications, use appropriate anti-oxidant compound and verify that any insulation sealing is complete before backfilling.
