Contents

What it means
Why isolation matters
Brainboxes devices have power isolation
What does the circuitry look like
See it in action
References

Power isolation is a critical requirement when choosing a PoE Ethernet Switch. There are many different types of Industrial Power over Ethernet (PoE) Switches on the market. PoE Switches while all having the same name can have vastly different performance, functionality and critically safety.

Over the years Brainboxes has looked at many PoE Switches and found dubious compromises made by a small number of other manufacturers, often for cost reasons. One such compromise being some brands DO NOT isolate the power between the PoE lines and the rest of the device.

What it means

Without power isolation a Power over Ethernet device:

doesn’t follow the PoE specification
- IEEE 802.3af/at
- the IEEE spec mandates that the PoE power should be isolated for the other power domains
  so technically it’s not a PoE device
doesn’t meet UL standards
- specifically IEC 62368-1 IEEE 802.3 Clause 33.4.1
- so shouldn’t have UL certification, however we do see some devices with UL accreditation which don’t really meet the spec
- by UL we are using a short-hand for Nationally Recognised Test Lab (NRTL) as recognised in America or IEC – the International Standards Body – as recognised world-wide

Why isolation matters

Power over Ethernet Switches without Power Isolation are not safe

they are susceptible to electrically interference through both the ethernet cables (which could travel up to 100m outdoors) and the power supply
and susceptible to ground loops
therefore there’s a higher likelihood, particularly in industrial environments, of equipment damage; to the switch itself and potentially to other powered equipment

Brainboxes devices have power isolation

All brainboxes PoE ethernet switches have galvanic isolation between the PoE and the other power domains of 2kV

we follow the PoE standards IEEE 802.3af/at
we have UL accreditation (through MetLabs an NRTL) including conforming to IEC 62368-1 IEEE 802.3 Clause 33.4.1
to do this takes more components, and costs more money, but it makes our customers’ investment safe

What does the circuitry look like

Looking at brainboxes SW-135

We can split the image up into different power domains:
power isolation in the brainboxes SW-135 PoE ethernet switch

Its the job of the PoE Isolation Transformer to ensure the power available to the PoE lines completely isolated from the power in the rest of the device. These 2 power domains marked in red (PoE power domain) and blue (protected digital 3v3 power domain) are kept separate from each other through the isolation barrier created by the transformer. This barrier is the same strength as the isolation barrier within the ethernet magnetics 2000 Volts.

Look for a PoE Isolation Transformer on your PoE Ethernet Switch.

In addition any equipment also connected to the same power supply as the device is protected from electromagnetic interference (EMI) and ground loops thanks to the isolation.