PoE+ Camera Rebooting on a Data-Passing Channel
A PoE+ IP camera on an 82 m CAT5e channel works normally during daytime testing but reboots whenever its IR illuminator turns on at night. The cable tester reports wire map pass, length 82 m, insertion loss pass, and NEXT pass. A handheld PoE tester shows the PSE supplying 53 V and the camera receiving about 38 V under a 0.6 A load. DC loop resistance measured through the channel is 32 ohms. The channel uses 5 m 26 AWG patch cords at each end, the horizontal cable is 24 AWG, one jack has visibly corroded contacts, and the cable is bundled with 40 other cables in a ceiling that reaches 45 degrees C. The customer wants to know why a 'data-pass' link cannot power the camera and what to replace first.
1. Why can the link pass data tests and still fail to deliver PoE+ power?
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Data tests are AC/RF tests; they do not measure the DC resistance that PoE uses. The link passes wire map, length, insertion loss, and NEXT, but 32 ohms of loop resistance is high for an 82 m channel. At 0.6 A, 32 ohms drops about 19 V, so a 53 V PSE leaves roughly 34 V at the camera; the measured 38 V is consistent with a severe drop. That is why the camera boots but resets when the IR load switches on. The 26 AWG patch cords, corroded jack, and 45 degrees C ceiling all raise resistance. The 82 m length is not the main problem; it is under the 100 m limit.
2. What should be replaced or corrected first, and how should the repair be verified?
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Replace the 26 AWG patch cords with 24 AWG or 23 AWG cords, and replace the corroded jack. Clean or re-terminate any contaminated contacts and verify the punchdowns. Measure DC loop resistance again; a normal 24 AWG channel should be much lower than 32 ohms. Also check the PoE class and PSE capability, but the measured voltage drop already points to the channel. Retest under the actual IR load, not just at idle. If resistance stays high, replace the horizontal cable or relocate the run out of the hot ceiling area. Do not simply raise the PSE voltage; the fault is excessive channel resistance.
3. What acceptance test should be added for future PoE links?
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Add a DC loop-resistance measurement and a loaded PoE test to acceptance for PoE links. A data-only certification can pass a channel that cannot deliver Class 4 power. Record PSE voltage, PD voltage, and current at the camera, and compare the drop with the loop resistance. Keep patch cords short and of the same or better gauge as the horizontal cable. Avoid bundling in high-temperature spaces without checking the cable's temperature rating and derating. Also verify that the PSE can supply the required class and that the camera's actual current draw is within the design. The fix is to reduce channel resistance, not to assume that a data pass means a power pass.