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SFP modules convert electrical data from the equipment to optical signals. There is no incoming power surging from an optical port to damage the equipment according to my undarstanding of fibre optics. SFP draws voltage/power from the equipment itself. So can wrong or incompatible SFP modules or cable damage the equipment itself, such as switchs or network adapters or is the possible damage exetent is from the SFP module to the SFP modules and the network equipment is safe from harm ?

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No, not normally.

By design, all SFP/SFP+/SFP28/... modules are electrically compatible. The maximum power-supply current defined by the SFF standards is 500 mA.

All signal contacts are well defined as well, so there's no reason for any damage as long as the standards are observed.

However, there are some devices that don't obey the standards. Generally, it's advisable to check the vendor's compatibility list. Even if fitting an incompatible module is no risk it doesn't accomplish anything.

And of course, damaged hardware may also damage other hardware that it is electrically or mechanically connected to.

You can read up on all SFF standards on snia.org: https://www.snia.org/technology-communities/sff/specifications

Cables are mostly interchangeable - there's no damage if you mix single-mode and multi-mode fiber, the link just might not work or perform poorly.

However, you must not mix APC (usually green) with PC/SPC/UPC fiber connectors/ports (grey or blue): fitting an angled endface connector into a flat port or vice versa may cause damage to either.

Also, using an extended-range SMF transceiver (for 40+ km) with a short link may permanently damage the receiver optics on the far side. Use an attenuator to avoid blinding.

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  • Just to cover all the bases, there are also SFP transceivers that are for use with RJ45 copper cabling connections which are obvious electrical just like a normal copper Ethernet network interface. So electrical surge on one of those might impart damage to the SFP cage and host device. Jul 6, 2023 at 18:42
  • @FrameHowitzer You'd need a lot of juice to do damage - electrical transceivers (magnetics) isolate the medium from the device. By standard, they withstand up to 1500 VAC or 2250 VDC. See IEEE 802.3 Annex J for details.
    – Zac67
    Jul 7, 2023 at 7:48
  • Yes, I'm basically thinking of experiences I have had with electrical 'transients' AKA lightning damage. ;) Jul 7, 2023 at 14:56
  • @FrameHowitzer Agreed, exceeding those voltage limits is easily possible during a nearby lightning strike - unless you've got decent surge protection (coarse at distribution, fine near the outlet).
    – Zac67
    Jul 7, 2023 at 15:17
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So can wrong or incompatible SFP modules or cable damage the equipment itself,

I've had that happen to me, but the problem was more mechanical than electrical.

On a series of refurbished Cisco N3K-C3164PQ-40GE, some QSFP caused damage to the contact pins back in the QSFP socket. The effect of which was that only some of the 4 lanes would work, even useable when the port was in 4x10G breakout mode, but of course the port was unuseable as a 40G port.

Quite the experience, that was: check/test 64 ports x 4 lanes on a series of like 24 switches...

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