Frequently Asked Question
Industrial Managed Ethernet Switches with PoE
Last Updated 5 years ago
IEEE802.3af/at comes with some "Gotchas." While PDs must support BOTH Mode A and Mode B to be compliant with the 802.3af/at standard, there is no such requirement for PSEs. There are a few different ways this can lead to mistakes.
1) Default configuration settings of managed CTC Union PoE switches have PoE DISABLED by default. The port must be specifically ENABLED for AF (15W) or AT (30W) in management.
2) A PoE (Power over Ethernet) port that is 802.1af/at compliant will NOT provide any power unless and until there has been proper negotiation with a standard 802.3af/at PD device.
3) You might assume your device is 802.3af compliant because it is listed as PoE-capable, but this is not always the case. A recent customer had a PoE-capable Ethernet/IP WiFi router, but closer datasheet inspection revealed it was not 802.3af compliant. As it turned out, this was an 8-wire device, utilizing power from pins 4,5,7,8 and therefore incompatible with Mode A PSE. CTC Union's PSE switches and converters are all Mode A. Our injectors are Mode B. We often refer to these Power Devices (PD) as 'Passive'. They require Mode B to be turned on, WITHOUT negotiation. PD that do normal negotiation are referred by us as 'active' PD. They negotiate with our switch and then power is supplied to the PD.
4) In addition to no requirement for PSEs to perform BOTH Mode A and Mode B, many vendors' documentation don't state which mode their device utilizes. This makes it challenging to locate the proper equipment for scenarios like the one above. Our user guides all make clear which pins provide power and data. In our product line it is pretty much universal, all PoE switches use Mode A, while our injectors all use Mode B.
5) You must confirm specific model numbers and operation. We came across one vendor's "PoE" wireless transmitter which was not IEEE802.3af/at compliant and instead required an injector that had Mode B power always on (no negotiation). This was a completely non-standard, proprietary "POE" device. We were able to modify our injector to be non-standard and always supply power for this special transmitter, although it would then be very dangerous to connect other Ethernet devices to this injector, after it is modified in passive mode (always providing power).
1) Default configuration settings of managed CTC Union PoE switches have PoE DISABLED by default. The port must be specifically ENABLED for AF (15W) or AT (30W) in management.
2) A PoE (Power over Ethernet) port that is 802.1af/at compliant will NOT provide any power unless and until there has been proper negotiation with a standard 802.3af/at PD device.
3) You might assume your device is 802.3af compliant because it is listed as PoE-capable, but this is not always the case. A recent customer had a PoE-capable Ethernet/IP WiFi router, but closer datasheet inspection revealed it was not 802.3af compliant. As it turned out, this was an 8-wire device, utilizing power from pins 4,5,7,8 and therefore incompatible with Mode A PSE. CTC Union's PSE switches and converters are all Mode A. Our injectors are Mode B. We often refer to these Power Devices (PD) as 'Passive'. They require Mode B to be turned on, WITHOUT negotiation. PD that do normal negotiation are referred by us as 'active' PD. They negotiate with our switch and then power is supplied to the PD.
4) In addition to no requirement for PSEs to perform BOTH Mode A and Mode B, many vendors' documentation don't state which mode their device utilizes. This makes it challenging to locate the proper equipment for scenarios like the one above. Our user guides all make clear which pins provide power and data. In our product line it is pretty much universal, all PoE switches use Mode A, while our injectors all use Mode B.
5) You must confirm specific model numbers and operation. We came across one vendor's "PoE" wireless transmitter which was not IEEE802.3af/at compliant and instead required an injector that had Mode B power always on (no negotiation). This was a completely non-standard, proprietary "POE" device. We were able to modify our injector to be non-standard and always supply power for this special transmitter, although it would then be very dangerous to connect other Ethernet devices to this injector, after it is modified in passive mode (always providing power).