2.5 Termination Blocks and RJ45 Connectors

Insulation-Displacement Contacts (IDC)

Modern copper termination is built on insulation-displacement contacts. An IDC is a V-shaped metal contact that the Technician presses the insulated conductor into with a punch-down tool. The contact's sharp edges slice through the insulation and cold-weld to the copper conductor without stripping. The result is a gas-tight connection that resists oxidation for the life of the install.

Three rules apply to every IDC termination:

1. Use the correct punch-down tool for the block type (110, 66, Krone, BIX). The tool's blade geometry matches the contact's slot.
2. Press the conductor straight into the slot — never loop or wrap. The IDC relies on the conductor entering at the correct angle.
3. Do not strip the insulation. Stripped conductors oxidize and produce intermittent high-resistance connections.

110-Blocks

The 110-block is the standard cross-connect block for data cabling from Cat 5 onward. It consists of a 110 wiring block (a plastic base with rows of index strips) and 110 connector blocks (4- or 5-pair blocks that snap onto the base and provide IDC contacts on one side and a secondary termination field on the other). The block supports Cat 5e, Cat 6, and Cat 6A when used with the appropriate category-rated connector blocks.

110-blocks come in several densities — 100-pair, 200-pair, 300-pair base blocks are common. The Technician routes the horizontal cable onto one side of the 110 connector block and either cross-connect wire or a connector on the other side. Cross-connects between two 110-blocks use interconnect blocks with bridging clips.

110 termination is preferred over 66 for data because:

• Denser (more pairs in less wall space)
• Lower crosstalk design
• Category-rated up to Cat 6A
• Compatible with the patch panel form factor commonly used in telecom rooms

66-Blocks

The 66-block is an older M-shaped punch-down block originally used for voice cross-connects. Each row has 4 clips (M-block, type 66M1-50); the inner two clips are electrically common, the outer two are separate. The block uses a different punch tool than 110 and has higher crosstalk at data frequencies.

66-blocks are not category-rated for Cat 5e and above in the data channel. They remain acceptable for voice, analog telephone, and very low-speed data. A common retrofit mistake is to terminate new data runs on an existing 66-block — the channel may pass wiremap and length but fails NEXT at the block.

For the Technician exam, the rule is simple: 66-blocks are for voice, 110-blocks are for data. Where a 66-block is encountered on a data run being certified, recommend re-terminating on a 110-block or category-rated patch panel.

Krone and BIX Blocks

Krone blocks are a proprietary IDC design (Krone GmbH, now TE Connectivity) using a slotted L-shaped contact. They are common in Europe, Australia, and some legacy US government sites. Krone blocks use a specific punch tool and provide a high-reliability IDC; for data, only Krone blocks specifically category-rated for the target category should be used.

BIX blocks are a Nortel/Avaya proprietary system used in some Canadian and legacy enterprise installs. They use a different contact geometry and a BIX-specific tool. Like Krone, BIX blocks are not interchangeable with 110 blocks or tools.

The Technician working internationally or in legacy enterprise sites should recognize all three block types and use the correct tool. The exam typically tests the 110-vs-66 distinction rather than Krone/BIX specifics.

RJ45 Modular Plugs and Jacks

The RJ45 (more precisely, the 8P8C modular connector) is the standard end-connector for horizontal patch cords and equipment cords. The jack (female, on keystone wall plates and patch panels) is field-terminated to the cable with IDC contacts; the plug (male, on patch cord ends) is crimped onto a stranded conductor cord.

Two critical rules:

1. Use category-rated plugs and jacks. A Cat 6A cable terminated with a Cat 5e plug is a Cat 5e channel. The plug's internal pair geometry and load bar must maintain pair separation and twist at the contact.
2. Match plug construction to conductor type. Solid-conductor plugs are designed for solid horizontal cable; stranded-conductor plugs are designed for stranded patch cord wire. Using the wrong plug on stranded wire produces intermittent opens after flexing.

Field-terminated RJ45 plugs are a frequent certification failure point because the plug's pair geometry cannot match a factory-molded plug at high frequency. BICSI's general guidance is to use factory-made patch cords and field-terminate only the keystone jack end. Where field-terminated plugs are required (long cord runs, unusual lengths), use category-rated plugs with load bars and certify carefully.

Termination Tools

A good punch-down tool has a spring-loaded impact mechanism that seats the conductor and trims the excess in one motion. Cheap, non-impact punch tools leave untrimmed tails and inconsistent seating — a source of intermittent failures.

Pair-Untwist Limits

Preserving pair twist to the IDC point is the single most important mechanical skill in copper termination. The TIA-568 limit for Cat 5e/Cat 6 is 13 mm (0.5 in) of untwist at the termination; Cat 6A is more restrictive and some manufacturers specify 6 mm. Exceeding this limit is the most common cause of NEXT failures at the connector.

The Technician's mechanical process:

1. Strip jacket only as far as needed (typically 25–50 mm) — never strip a long section and coil the pairs.
2. Untwist each pair only as far as needed to seat the conductor in the IDC slot.
3. Cut the conductor flush with the punch-down tool's trimmer — no tails.
4. Verify with a wiremap tester before closing the faceplate.

Hands-On Exam Tasks

The 12-task hands-on exam includes copper termination tasks. The candidate is expected to terminate a 110-block or keystone jack cleanly, with proper pair order, pair twist preserved, jacket stripped the correct length, and no conductor tails. The evaluator inspects visually and then runs wiremap and certification. A termination that passes wiremap but fails NEXT because of pair untwist scores poorly.