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Overheating Can Kill Optical Thunderbolt 2 Cables, Root Cause is the Mac Itself (Thermal Dumping)

Get Thunderbolt 2 cables and Thunderbolt 3 cables at

See also: Thunderbolt on OS X: Spontaneous Drive Disconnect and 2013 Apple Mac Pro: Cables and Rotating Chassis.

I’ve confirmed this information as correct by a well placed source.

In essence, the embedded lasers in a Corning optical cable can become overheated by thermal dumping from the host computer or from peripherals*, particularly the 2013 Mac Pro.

The Thunderbolt 3 specification prohibits this thermal dumping, so Thunderbolt 3 should be unaffected. All thunderbolt 3 cables conduct power and have a full metal jacket on them.

All Thunderbolt 2 non-optical cables are the same. It’s only the optical Thunderbolt 2 cables at issue, none of which had power with them and specification didn’t have the juice to do power over distance, that have this issue.

* Beware of Thunderbolt2 devices with no metal around the port since plastic is a heat insulator.

This note from reader Ed H captures the issue:

Just wanted to let you know about an experience I’m having with the Corning Optical Thunderbolt cables (10M length). And I believe that Corning OEM’s the optical cables for OWC. In fact, I think Corning might be the only optical thunderbolt cable manufacturer right now. This is a bit long, but have patience and you might be able to give some good info to your readers from my experience.

Optical Thunderbolt 2 Cables from Corning can experience thermal issues leading to decreased operating life when connected to Mac Pros, Mac Mini’s, and possibly other hosts — especially if operating 24x7 and transmitting a lot of data (such as to a RAID array and/or always on display) constantly.

Corning had/has confusing warranty replacement policy and support information, which they are in the process of updating. Optical Thunderbolt 3 Cables *should* not be affected, but time will tell.

Full story—

I have a setup with a Mac Mini (late 2012) is in a rack in a closet, connected with the Corning Optical Thunderbolt 2 Cable (10M) to a sonnet Echo 15 drive dock (populated with two HDDs and BluRay player), then daisy chained to (in various orders that changed with testing when the problem arose) an OWC dual external drive dock, an LG 34” Ultrawide Thunderbolt Monitor, and a Lexar workflow professional HR2 with two SSDs and 2 SD readers.

At first, the cable performed flawlessly, but then the monitor started exhibiting random intermittent signal drops from the Mac Mini. Then the disks in the OWC drive dock and the Echo 15 started disconnecting (though I didn’t realize it yet). Then the monitor problems became more frequent to the point where the setup was unusable. At first, I thought it might be the monitor, or the Mac Mini’s graphics card, or who knows what else… but through step by step testing, I managed to isolate the problem to the optical cable.

Well, on top of this, I had purchased the cable from Safe Harbor Computing through Amazon (who are actually listed as an authorized Corning Optical Cable Dealer), but the Corning website said warranty returns had to be processed through an Authorized dealer rather than Corning Directly.

So I contacted Safe Harbor (and then Amazon themselves, eventually) to inquire about a warranty return. To Safe Harbor’s credit, they went into full research mode because this seemed to be an unusual situation for a warranty return, because industry standard practice is that the MFR usually handles the return. They got at least three or more different answers from their various Corning contacts, most of them unhelpful, but they continued to research and update me. And also let me know that some of their other customers had experienced similar issues.

Finally, I managed to find a phone number for Corning in a very obscure page on a different Corning Optical support page since all the other support info on Corning’s website said to contact the reseller. Eventually after some back and forth with the Corning rep, I received a response from a Sales Development Manager at Corning, who informed me that they’ve had issues with the Thunderbolt 2 version of the Optical cable where the host is thermally dumping excess heat into the connector connected to the host, which has the two 10 gig lasers in it. They’ve seen it with the Mac Pro and also the Mac Mini. This excess heat elevates the internal temperature of the lasers shortening their operating life. Here’s an excerpt from the email:

“The typical damage we see is from the Host computers thermally dumping heat into the Corning Optical cable that has 2 x 10 gig lasers in them. This tends to elevate the internal temperature past the safe operating range of the lasers which reduces the life.

This typically happens more with the Mac Pro, but I have had some customers report your issue with the Mini. There are two or three things you can do to extend the life of the replacement cable being sent to you.

1) If possible, blow some air (doesn’t need to be very high volume) over the interface between the Mac mini and Thunderbolt interface.

2) Plug the Thunderbolt display into a power strip, and at the end of the work day shut the Thunderbolt monitor AC power off. The optical cable plugged into the back of the display will turn off and signal the other end of the optical link (on your Mini) to go into a low power sleep state (much lower internal heating temps!).

3) I have not tested this on the Mac Mini, but running the Mini internal Fan Speed on high on the Mac Pro helps move heat away from the Thunderbolt interface (not sure about its effectiveness on a Mini). Macs Fan control v1.4.2.

Let me know if you have any further questions or concerns. We are currently working on a white paper outlining this potential long term issue and typical lifetime of laser based products in general. The good news is that the Thunderbolt 3 specification will mandate that no thermal dumping into any active assembly is allowed. This requirement was not specified in the initial development of Thunderbolt when only the Macbook (thick version with optical drive) was the only host to test with.”

That makes sense to me with what I’ve seen from other optical transceivers in fiber optic networking cables. I wished that the transceivers on the Optical Thunderbolt Cables were replaceable without having to replace the whole cable, but that would probably discourage the users that the cables are marketed to.

Corning are also switching to handling warranty returns themselves and changing their website to reflect that.

Not related but worth knowing: LEDs can have drastically shortened lifespan if overheated. That’s why the Lupine cycling lights and flashlights and headlamps I use have temperature regulation, cutting output when too hot.

Darren K writes:

Happened to mine, but Corning swapped it out. Kernel panic crashes and the like without any solution messed with me for months. Apple even had the MacPro for 3 weeks to test it. Couldn’t believe it when I got the new cable. Will likely happen again since not much has changed in my setup. Maybe I can run a 10’ TB cable.

MPG: well, doesn’t the Mac look nice and pretty in a photo? I see it as another Apple distraction of form over function—please Apple, spend the time engineering robust operation first and foremost—everything else follows.

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