RJ45 Cable Tester UK: Wiremap, PoE and TDR Explained
An RJ45 cable tester checks that all eight wires in an Ethernet connector reach the correct pins at the far end. This guide explains wiremap testing, PoE verification and TDR fault location — the three features UK installers ask about most — and shows when each one matters on real jobs.
Why RJ45 Testing Matters More Than Link Lights
Ethernet link lights lie. A cable with a crossed pair or high-resistance crimp can negotiate a link at reduced speed — or show solid green while passing zero usable data. UK home-network forums are full of posts describing exactly this: "Wi-Fi works fine but the wired port is dead" turns out to be a mis-wired faceplate, not a faulty switch.
An RJ45 cable tester eliminates the guesswork by testing each of the eight conductors individually and reporting the result as a wiremap: pin 1 to pin 1, pin 2 to pin 2, and so on through the T568A or T568B standard you used when crimping.
Understanding RJ45 Wiremap Results
When you run a wiremap test, the tester sends a signal down each wire and checks what comes back at the remote end. The display shows one of these outcomes for each pair:
- OK: Wire connects pin-to-pin correctly.
- Open: A wire is broken or not connected at one end — common after a bad crimp or a pulled-back conductor.
- Short: Two wires touch each other — often caused by nicked insulation during stripping.
- Cross: Wires are swapped — e.g. pin 1 connects to pin 3. Link lights may still appear because some pairs negotiate.
- Split: A pair is divided across non-standard pins — harder to spot without a proper tester.
Budget blink-light testers show green or red per pair. A 5-in-1 unit like the Mcbazel 5-in-1 network tester displays the full wiremap on an LCD screen, names the exact fault type and stores results for client handover.
PoE Detection on RJ45 Testers
Power over Ethernet delivers DC voltage through unused pairs (or shared pairs on Gigabit links) to power IP cameras, VoIP phones and wireless access points. A continuity test alone cannot confirm PoE — the cable may be wired correctly but the switch port may not be configured for PoE, or voltage may drop below the device threshold over a long run.
PoE detection on an RJ45 tester connects to a live switch port and reports the voltage present. This is the feature CCTV installers request most: mount the camera, connect the cable, verify PoE at the device end, then fix any issues before drilling fixings. The Mcbazel 5-in-1 PoE network tester and the 5-in-1 network cable tester PoE checker both include PoE voltage detection alongside standard wiremap and TDR functions at £76.27 with free UK next-day delivery.
TDR Fault Location: Finding Breaks Without Re-Pulling
Time Domain Reflectometry sends a pulse down the cable and measures how long the reflection takes to return. The tester converts this to distance, showing how many metres from your position the fault sits. This matters when:
- A cable run passes through a loft and you need to know whether the break is near the socket or mid-span.
- You are fault-finding on a pre-installed link where the far end is inaccessible.
- A client reports intermittent connectivity and you suspect a damaged section rather than a connector.
TDR is the feature that separates a £15 continuity box from a professional install tool. On the Mcbazel 5-in-1 range, TDR works on Cat5e, Cat6 and Cat6a cable from a single end — no remote unit required for length and fault-distance readings.
How to Test an RJ45 Cable: Step-by-Step
- Visual check: Inspect both RJ45 connectors for untrimmed wires, uneven pin height and correct clip engagement.
- Wiremap test: Connect the main unit to one end and the remote to the other. Run the wiremap. All pairs should show OK.
- Fix and retest: If a pair shows cross or open, re-crimp the affected end and retest before installing.
- TDR (installed cable): Connect to one end only. Read total length and fault distance. Compare against the known run length.
- PoE check (live link): Connect to the switch port. Verify voltage is within the device spec before powering the endpoint.
- Document: Note results for client records or warranty claims.
Choosing the Right RJ45 Cable Tester for UK Work
| Feature | Budget Tester | Mcbazel 5-in-1 |
|---|---|---|
| Wiremap (8-pin) | LED indicators | LCD with fault type |
| TDR length/fault | No | Yes |
| PoE detection | No | Yes |
| Wire tracing | No | Yes (tone + probe) |
| Cat6a support | Sometimes | Yes |
| UK price | £10–£25 | £76.27 |
| Warranty | Varies | 2 years |
Common RJ45 Wiring Mistakes in the UK
Most faults we see in field testing fall into predictable categories:
- Mixing T568A and T568A/B: Both standards work if used consistently end-to-end, but mixing them creates crossed pairs.
- Untwisted pairs at the connector: Exposing more than 13 mm of untwisted wire degrades signal quality even if the wiremap passes.
- Wrong gauge for PoE: Thin CCA (copper-clad aluminium) cable may pass continuity but overheat under PoE load.
- Keystone mis-punch: The wiremap looks fine at the patch panel but the faceplate keystone has a loose punch-down.
A proper RJ45 cable tester catches the first three before you close the wall. For keystone issues, test at the faceplate with a short known-good patch lead to isolate the fault segment.
Frequently Asked Questions
Do I need different testers for Cat5e and Cat6?
No. RJ45 pinouts are identical across Cat5e, Cat6 and Cat6a. A tester that supports all three categories handles wiremap, TDR and PoE on any standard Ethernet cable.
Can an RJ45 tester check fibre optic cable?
No. Fibre requires an optical power meter or OTDR. Mcbazel testers are designed for copper twisted-pair Ethernet (RJ45/RJ11).
How long should a good RJ45 cable tester last?
Professional units like the Mcbazel 5-in-1 range are built for daily trade use and include a 2-year warranty. Budget units often fail within 12 months of regular site use due to fragile remotes and poor connectors.
Need a reliable RJ45 cable tester? The Mcbazel 5-in-1 PoE network tester covers wiremap, TDR, PoE detection and wire tracing — £76.27, free UK next-day delivery, 2-year warranty.