Black Box QSFP-H40G-CU50CM-BB 40Gbps QSFP+ Direct Attach Copper Cable

Overview

The Black Box QSFP-H40G-CU50CM-BB is a 40Gbps QSFP+ direct attach copper (DAC) passive twinax cable in a 50cm length — built for short-reach, high-density interconnects inside a rack or between top-of-rack switches and aggregation equipment. At half a meter, this cable is purpose-sized for same-rack switch-to-server or switch-to-switch uplinks where a fiber transceiver pair would add unnecessary cost and complexity.

DAC cables at this distance eliminate the optical transceiver budget entirely. There are no SFP lasers to align, no cleaning required, and no per-end insertion loss to manage — the copper twinax assembly handles signal integrity passively at 40G speeds within the reach envelope this cable covers. For network switches and top-of-rack deployments, that simplicity directly reduces both per-port cost and maintenance overhead across high-port-count chassis.

Key Features

• 40Gbps QSFP+ Interface: Matches the native QSFP+ port speed on 40GbE switches and line cards — no speed mismatch, no conversion overhead. One cable replaces four discrete 10G SFP+ links in a breakout configuration, cutting cabling density significantly in aggregation tiers.
• 50cm Direct Attach Copper: The 50cm reach is the correct choice when both endpoints sit within the same rack — longer cables add unnecessary slack management and copper loss. If your switch and server are in adjacent racks, evaluate a 1m or 3m variant instead; at this length, passive DAC remains the lowest-latency, lowest-cost interconnect available.
• Passive Twinax Construction: No active electronics means no power draw from the cable itself, no firmware to update, and no active component failure mode. Passive DAC at 50cm runs cooler and draws less switch port power than active cables or optical modules at equivalent speeds.
• Factory-New Genuine Hardware: Sourced as factory-new product — no refurbished, grey-market, or parallel-import units. For environments where supply chain traceability matters, genuine manufacturer hardware reduces the risk of counterfeit transceivers that can cause intermittent link errors.
• Black Form Factor: Standard black jacket — visually consistent with typical data center cabling schemes and compatible with common cable management color-coding practices.

Integration and Compatibility

The QSFP-H40G-CU50CM-BB (often searched as QSFP H40G CU50CM BB) uses the industry-standard QSFP+ electrical and mechanical interface. Verify compatibility with your specific switch platform before ordering — many switch vendors program their QSFP+ ports to check transceiver vendor ID and may require a compatibility mode or third-party enable setting to accept non-OEM DAC cables. Consult your switch vendor's compatibility matrix or your network cable pre-sales team before deployment in a locked-down platform. For open-standard and whitebox switching environments, QSFP+ DAC cables at 40G are broadly interoperable without additional configuration. Pair this cable with a qualified 40GbE switch and ensure the port is configured for direct attach rather than optical transceiver mode where applicable.

Frequently Asked Questions

Q: What is the reach of the QSFP-H40G-CU50CM-BB?

A: The cable is 50cm (approximately 19.7 inches) in length. It is designed for same-rack interconnects only. If your endpoints are in adjacent or remote racks, you will need a longer DAC or an optical solution.

Q: Is the QSFP-H40G-CU50CM-BB an active or passive cable?

A: Based on the CU (copper direct attach) designation in the model number, this is a passive twinax DAC cable. Passive cables draw no power from the cable assembly itself and have no active electronics to fail or configure.

Q: Will the QSFP-H40G-CU50CM-BB work with my existing 40GbE switch?

A: QSFP+ DAC cables use an industry-standard interface, but some switch platforms enforce vendor ID checks on transceiver ports. Verify your switch vendor's compatibility list or enable third-party transceiver support before deploying. In open/whitebox environments, compatibility is generally broad.

Q: Can I use this cable for 4x10G breakout?

A: A standard QSFP+ DAC cable like the QSFP-H40G-CU50CM-BB connects QSFP+ port to QSFP+ port at 40G. Breakout configurations (4x10G) require a QSFP+ to 4x SFP+ breakout DAC cable, which is a different product. This cable does not support breakout mode.

Q: Is this cable suitable for outdoor or harsh environments?

A: No. Direct attach copper twinax cables are designed for controlled indoor data center environments. They are not rated for outdoor use, high humidity, or extreme temperature ranges beyond standard data center operating conditions.

James Everett

The QSFP-H40G-CU50CM-BB is the cable I reach for when both endpoints are in the same rack and I need 40G without paying for optics. At 50cm, passive copper is the right call — no laser alignment, no cleaning kits, and no transceiver firmware headaches. It is a straightforward interconnect for a straightforward job.

Technical Highlights:

• 40Gbps Throughput: Full 40G QSFP+ line rate — matches the native port speed on current-generation aggregation switches without any speed stepping or conversion layer.
• 50cm Passive Copper: At this distance, passive DAC is the lowest-latency option available at 40G. No serializer-deserializer active electronics means sub-nanosecond cable propagation delay with no active component failure risk.
• Zero Cable Power Draw: Passive construction means the cable itself consumes no switch port power budget beyond what the QSFP+ host logic requires — relevant when you are managing port power across a dense 32- or 64-port 40GbE chassis.

Deployment Considerations:

• Measure your actual port-to-port distance before ordering. 50cm sounds generous but routes tightly inside a 2U or 4U switch — factor in cable management panels and vertical slack requirements before assuming it reaches.
• Vendor ID lock-in is the most common deployment blocker with third-party DAC cables. On Cisco Nexus, Arista EOS, and some Juniper platforms, you may need to issue a service unsupported-transceiver command or equivalent before the port will bring up. Test one cable before deploying a batch.

This cable fits cleanly in high-density top-of-rack designs where a 40GbE switch uplinks directly to a server or storage node in the same rack — hyperconverged infrastructure nodes, all-flash storage arrays, and spine-leaf fabrics with servers co-located in the same cabinet are the natural home for a 50cm 40G DAC.