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I understand from a training session that ProfiBUS is considered intrinsically safe, while ProfiNET is not. Some googling indicates that ProfiNET can never be intrinsically safe, because Ethernet can not be. This surprises me, as Ethernet over fiber seems very unlikely to cause a spark under any imaginable circumstances, and Ethernet over twisted pair shouldn't be much worse in this regard. We're not talking about high voltages or power availability.

So why is Ethernet not considered intrinsically safe, while other low-voltage communication standards like ProfiBUS are?

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    \$\begingroup\$ Define "safe." Safe from what? Based on context, I think you mean arc fault? \$\endgroup\$ – JYelton Sep 11 '14 at 17:13
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    \$\begingroup\$ Power-over-ethernet can carry voltages as high as 56V. \$\endgroup\$ – ACD Sep 11 '14 at 17:30
  • \$\begingroup\$ Intrinsically safe relates to Hazardous Locations ... like those that might have explosive gas in the atmosphere. I believe the voltage on ether net might get above some voltage value and arc...igniting the gas... but that's as far as I know.... \$\endgroup\$ – Spoon Sep 11 '14 at 17:40
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    \$\begingroup\$ @JYelton: "Intrinsically safe" has a precise industrial definition. The specific numbers used vary with the type of equipment in question. \$\endgroup\$ – Dave Tweed Sep 11 '14 at 17:44
  • \$\begingroup\$ Intrinsically safe Ethernet products are available. There's enough energy available in a typical interface (or which can be passed down a fiber) to blow a chemical plant to smithereens, so approvals are a must if IS is required. \$\endgroup\$ – Spehro Pefhany Sep 11 '14 at 18:40
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Profibus is really low speed compared to ethernet and hanging components on the line to convert its energy levels to be compatible with intrinsically safe installations is quite trivial. I'm talking about a thing called a zener barrier - this consists of a fuse, 2 or 3 zeners (hazardous zone dependant) and a resistor.

The fuse protects the zeners, the zeners limit the voltage and the output resistor limits the current.

I can imagine that using such a zener barrier with high speed data systems like ethernet will be a real problem getting them to work. Having said that, such things do exist here: -

enter image description here

I haven't checked what speed it will run at - I'll leave that up to the OP.

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    \$\begingroup\$ Ahhhh. So if the communication cable accidentally shorts to a high-voltage wire, there's no actual explosion, because each individual signal path is protected against overvoltage in an explosion-safe way. \$\endgroup\$ – Stephen Collings Sep 11 '14 at 20:48
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    \$\begingroup\$ Correct - btw I've added a link to an ethernet IS coupler I just found!!! \$\endgroup\$ – Andy aka Sep 11 '14 at 20:49

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