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Author Topic: Overheating CAT cable  (Read 5945 times)

Peter Morris

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Re: Overheating CAT cable
« Reply #20 on: February 08, 2017, 08:26:55 am »

I work on an international open-air touring production, and I came across a problem I hadn't seen before during a recent show in Australia.

At around 3pm, in the peak heat of the day, several of our 90m Proplex CAT-5e lines between FOH and stage stopped working. Upon inspection, it appeared that temperatures in the cable ramp had reached somewhere between 60-70 deg C. Opening the trap and pouring iced water over the cables brought them back to life, and this became a daily ritual every afternoon on show days.

I realise that the operational temperature rating of this cable is -25 to 70 deg C, but I am still surprised to see heat-related failure of a data cable - I had assumed (I guess wrongly) that the upper temperature rating was the point at which the rubber sheath started to break down.

Certainly I have done plenty of shows in the Middle East where temperatures far exceeded what we were seeing in Perth.

Just interested to know if others have experienced this? Is 70 degrees just asking a bit much from this cable, or is this indicative of some other issue? I have suspected for a while now that we may have been delivered a bad batch of cable, as we have had other performance issues in the past with this multi.

http://pub.tmb.com/ProPlex/CAT5e/pdf/ProPlexCAT5e-A4-web.pdf

You have me worried for Saturdays gig ... it was hot today down under :-!
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John Rutirasiri

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Re: Overheating CAT cable
« Reply #21 on: February 08, 2017, 01:30:27 pm »

It boggles my mind that cable companies even produce this stuff in longer runs where it was never intended to see use.
Standard length reels from cable manufacturers are 1000, 2000, 5000ft.  Distributors like Anixter then re-reel it to shorter lengths (e.g. 500ft.)

John R.
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Tim Steer

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Re: Overheating CAT cable
« Reply #22 on: February 08, 2017, 04:01:51 pm »

I think the original implication was that the sun shining down on the black cable ramps the cable was in drove the temp of all the cables up.

Mac

Correct. The loom was laid in yellowjacket, which turned into an oven in the afternoon heat. The IR thermometer was showing 60-70 deg C. Heat generated from other cables was not an issue.

I wouldn't use CAT5 outdoors on the ground at or near the maximum distance spec if the devices I was connection were switches. I'd put the right GBIC in the switch and use fiber. It is more rugged than CAT cable and more reliable.

Mac

Unfortunately the Gigacore 12 doesn't have that option.

It sounds as if, like all the best baffling technical problems, the fault was a result of several problems coming together. Stranded cable, used at or above its recommended operational length, carrying gigabit ethernet, run alongside power and various other signals. Heating the loom to 60 degrees was probably the straw that broke the camel's back, in a system already pushed to the limit.
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Dan Mortensen

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Re: Overheating CAT cable
« Reply #23 on: February 08, 2017, 05:35:49 pm »


It sounds as if, like all the best baffling technical problems, the fault was a result of several problems coming together. Stranded cable, used at or above its recommended operational length, carrying gigabit ethernet, run alongside power...

Could you please elaborate on the bolded part?

What kind of AC cable? Single conductor or twisted wires inside one jacket?

What kind of voltage and especially amperage in use?

How close together were the data and power cables?

For how long a run were they that close together?

Thanks! Like I said, you've given us an interesting problem that crosses some disciplines, maybe.

If you could work Wi-Fi into it you'd cover all the bases.
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Mac Kerr

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Re: Overheating CAT cable
« Reply #24 on: February 08, 2017, 07:47:05 pm »

Unfortunately the Gigacore 12 doesn't have that option.

It would be worth the effort to pop the top on the Gigacore 12 to see if it has fiber ports inside. The only difference between the GP12 and the GP14 is the addition of the SFP ports on the back. They may actually be there on the board inside.

Mac
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Tim Steer

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Re: Overheating CAT cable
« Reply #25 on: February 09, 2017, 07:20:25 am »

Could you please elaborate on the bolded part?

What kind of AC cable? Single conductor or twisted wires inside one jacket?

What kind of voltage and especially amperage in use?

How close together were the data and power cables?

For how long a run were they that close together?

Thanks! Like I said, you've given us an interesting problem that crosses some disciplines, maybe.

If you could work Wi-Fi into it you'd cover all the bases.

Well it's the main cable route between FOH and stage on a fairly involved show. As well as the data lines in question, there is a mixed data/power loom for show comms, a 32A/1ph (TRS) which powers a bunch of stuff at FOH (pulling >16A), various cables relating to a custom-made flame system (low-voltage DC), laser control, E-stop send/return (16A TRS), audio system control and Dante. All running alongside each other for around 60m. Total length is 90m - no extensions used on either end.

So some potential sources of interference. But nothing out of the ordinary for a live show.

I think a few people have hit the nail on the head in saying that the stranded cable played a bit part. Having seen the cable spec (and max recommended length), I can easily see how adding multiple interference sources + extreme heat into the equation could cause a failure at that sort of length.


It would be worth the effort to pop the top on the Gigacore 12 to see if it has fiber ports inside. The only difference between the GP12 and the GP14 is the addition of the SFP ports on the back. They may actually be there on the board inside.

Mac

Interesting.
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Dan Mortensen

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Re: Overheating CAT cable
« Reply #26 on: February 09, 2017, 03:28:05 pm »

...a 32A/1ph (TRS) which powers a bunch of stuff at FOH (pulling >16A)...

...E-stop send/return (16A TRS)...


This provincial American doesn't know exactly what this Aussie talk means, but assumes that they are both 3 wire cables with a single jacket, so the conductors are spiralling as they travel. If so, then there would be minimal induction onto the shields of nearby data cables.

It would seem like loading them to half capacity would generate a little heat that would only add to the ambient heat combined with that from the black cable covers, made worse by the lack of ventilation in cable covers.

That said, it seems like it's easy to understand why pouring ice water on the jacketed cables would bring the internal cable temperature down so that it's within spec.

Frankly I was hoping you were running single conductor feeder through the cable covers and there was a huge induction.

I mentioned your problem to my AES Committee meeting last night, and someone who knows and lectures about Ethernet cable said that there was undoubtedly some level of voltage drop from one end of your AC cable to the other, and that perhaps the shielded CAT cable saw different ground potentials at each end of the cable and thus created a current down the CAT cable shield.

He also said that when you plug in a CAT cable which is carrying signals using Ethernet protocol (and not something like AES 50) that the devices on each negotiate a connection based on their present conditions. He wondered if you had disconnected the Ethernet cables during your disruption and then plugged them in again, and if the devices would have then negotiated the connection based on the changed conditions. He didn't know how often those devices poll each other and renegotiate, if it is only on initial connection or if they do it periodically.

Sounds like you have it in hand, though. You can tell us what happens when you have the same conditions but solid cable.
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Tim McCulloch

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Re: Overheating CAT cable
« Reply #27 on: February 09, 2017, 03:35:17 pm »

This provincial American doesn't know exactly what this Aussie talk means, but assumes that they are both 3 wire cables with a single jacket, so the conductors are spiralling as they travel. If so, then there would be minimal induction onto the shields of nearby data cables.

It would seem like loading them to half capacity would generate a little heat that would only add to the ambient heat combined with that from the black cable covers, made worse by the lack of ventilation in cable covers.

That said, it seems like it's easy to understand why pouring ice water on the jacketed cables would bring the internal cable temperature down so that it's within spec.

Frankly I was hoping you were running single conductor feeder through the cable covers and there was a huge induction.

I mentioned your problem to my AES Committee meeting last night, and someone who knows and lectures about Ethernet cable said that there was undoubtedly some level of voltage drop from one end of your AC cable to the other, and that perhaps the shielded CAT cable saw different ground potentials at each end of the cable and thus created a current down the CAT cable shield.

He also said that when you plug in a CAT cable which is carrying signals using Ethernet protocol (and not something like AES 50) that the devices on each negotiate a connection based on their present conditions. He wondered if you had disconnected the Ethernet cables during your disruption and then plugged them in again, and if the devices would have then negotiated the connection based on the changed conditions. He didn't know how often those devices poll each other and renegotiate, if it is only on initial connection or if they do it periodically.

Sounds like you have it in hand, though. You can tell us what happens when you have the same conditions but solid cable.

The bolded text is exactly where I was headed.
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Dan Mortensen

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Re: Overheating CAT cable
« Reply #28 on: February 09, 2017, 04:23:28 pm »

The bolded text is exactly where I was headed.

Great minds think alike?

Although you'd have to think that in the absence of a significant problem with too small/overloaded cable, the voltage drop and resultant shield current would have to be pretty minor. And I'm not even sure that would make a difference, since it's the voltage drop over the safety ground wire and not the current-carrying conductors that would affect the ground potential.

Right?

Much more likely cause of significant ground potential difference would be sourcing AC from two different services or transformers, which doesn't sound like happened in this case.

I'm still waiting to see an example of what happens when the digital console CAT cable shield is the only thing connecting two services with significant ground potential difference together. I've never been able to try it.
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Re: Overheating CAT cable
« Reply #28 on: February 09, 2017, 04:23:28 pm »


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