RJ45 Connector: Two Parts, Different Jobs
Quick answer / TL;DR: Short answer: use plugs with a crimp tool for cords, and jacks with a punch-down tool for permanent links. Match the category: Cat6 plugs need staggered contacts, Cat6A needs larger bodies and often shielding. Terminate to T568B consistently, keep untwisted length under 13 mm, and test every link.
Same rack unit, two densities: 48 ports doubles the terminations behind one panel.An RJ45 plug terminates a cable; an RJ45 jack terminates a permanent link. They use the same interface and different termination methods.
Confusing the two is the most common reason a link fails certification.
Plug Against Jack
| Part | Terminates | Tool |
|---|
| Plug | Stranded cord | Crimp |
| Jack | Solid link | Punch-down |
| Keystone | Solid link | Punch-down |
| Field plug | Either | Crimp or tool-less |
The 13 mm untwisted limit exists because crosstalk rises sharply once pairs are opened out.
Category Effects
- Cat6 needs staggered pin rows
- Cat6A needs bigger bodies
- Shielded needs the drain bonded
- Cheap plugs cap the channel
- Test every termination
A single Cat5e plug on a Cat6A link will fail the certification test even when every pair is correct.
Real-World Applications
An office fit-out uses jacks at the wall and plugs on factory cords. A field repair in a warehouse uses a tool-less plug, accepted because the link is short.
Standards and Verification
| Reference | Relevance |
|---|
| IEC 60603-7 | 8-way connectors |
| TIA-568.2-D | Termination practice |
| IEEE 802.3 | Ethernet |
Certification results for a specific termination are not provided in the knowledge base. Test the link.
References
- IEC 60603-7 series, Connectors for electronic equipment
- TIA-568.2-D, Balanced Twisted-Pair Cabling
- IEEE 802.3, Ethernet
Practical Notes
Standardise on one wiring scheme across a site. Mixed A and B terminations create faults that look like cable damage.
Related reading: ethernet cable — blogs/news/ethernet-cable
Related reading: ethernet plug buying — blogs/news/ethernet-plug-buying
Frequently Asked Questions
Plug or jack for walls?
Jack. Plugs are for cords.
Does category matter?
Yes. A lower part caps the link.
A or B wiring?
Either, consistently.
How much untwisted?
Under 13 mm.
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