Current rating of an RJ45 connection

Both leave you 'stranded'? ;-)

I agree a lot can go wrong when the wiring is installed. I've seen my share of badly crimped connectors, poorly installed wall-outlet and bad punch-down work. But after installation dirt and moisture are the biggest enemy.

I recently designed a board for which the customer and I decided to use a spring loaded terminal block instead of RJ45 because it is much more resistant against poor installation practices and moisture.

My customers are a bit behind the times. Most are currently upgrading to gigabit ethernet (1000baseT). Very little fiber except between servers and switches. Here's a typical horror story. Almost everything in the boxes are defective due to wrong connectors, badly installed connectors, or miserable polishing.

I originally thought the fiber tester was defective because it was rejecting almost everything.

Back in the late 1990's, I did some midnight repairs at distant server farms. Nobody was dumb enough to drive 50-75 miles to reseat a connector except me. That was before multihoming and failover were common. I rarely found a defective connection. What I found was were RJ45 plugs without locking tabs that wiggled out of the jack. Same with common power cords that had little or no retention force. More than once, I found that the CAT5 jumper had simply disappeared. I have seen cases where unplugging the RJ45 and reinserting it solved a connection problem, but that was due to NWAY negotiation failure, not an intermittent connector.

The local university and one company has a policy about non-ratcheting crimpers. If they find anyone using one, the perpetrator gets ejected or thrown down a flight of stairs, whichever is more appropriate.

Agreed, to a point. I once made a big mistake and bought a bag of RJ45 plugs on eBay. Big mistake. Not only was the gold plating insufficient, the dimensional tolerances were well out of acceptable specifications. Thanks to the wonders of Chinese technology, we are now able to successfully produce a genuine intermittent connection at the connector face instead of just at the insulation displacement crimp. Some details and horror stories:

My rough count is that I have about 80 active ethernet ports at my home. My office probably has twice as many.

Traceroute shows 16 hops, each of which has no less than 8 connectors involved for a minimum of 128 connectors. (It's actually more like 50 connectors per hop). However, most of the higher speed connectors are now fiber, not RJ45.

Selective coatings like that can really make things hot. They're sometimes used on thermal solar collectors, or see Dumas' "The Man In The Iron Mask" for a historical example. (Mildy oxidized metal is black in the visible but shiny in the IR, so it gets pretty warm in bright sunlight.)

Cheers

Phil Hobbs

No worries, just saw off a couple of cylinders on the Corolla. There'll be lots of room in the engine compartment, and it'll still be faster than the 2CV. ;)

Cheers

Phil Hobbs

Take the engine out & replace it with a big rubber band and it'll still be faster than the 2CV. :)

Hey, my 2CV could blaze along the autobahns at 55mph. 60-65mph only with a stiff tailwind. But ... 50mpg, and that's with an engine designed in the late 30's.

Just in case you are really interested, the connector is IEC 60603-7-x where x is a speed grade. Straight from my copy of ANSI/TIA-568 C revision part 2.

The IEC spec is 220 US$ if i read the website correctly:

Different optically clear components (as in commercial RJ45) also have different absorption characteristics. But this besides the point, as is the automobile comparison.

"The unit will sit in full sun occasionally and can become as hot as the inside of a car under that condition."

For a start, very few people have any idea what the varying temperatures are in the different areas of their car. They are aware of how hot their seats are, maybe the passenger compartment air, and the dashboard, where their favourite CD just got toasted. This usually involves the IR transmissivity of auto glass and the absorptive capacity of the upholstery or temperature indexes of toasted articles.

Electronic packages that are designed to sit in full insolation need to be packaged appropriately, just as connectors (original topic) need to be selected appropriately for their application.

RL

Put a braided sheath over it. Sheesh.

..

My father painted his stock car's radiator silver one time. From that point on, the engine overheated badly and he could not understand why (I was not old enough at the time to be of any help).

After several weeks of trying to work out the problem he eventually gave up and discarded that radiator and put a different "black" one in. The problem then completely vanished. It wasn't until years later, when I took thermodynamics in high school, that I realized why a black radiator works better for dissipating heat.

But what I don't understand is why air conditioning heat exchangers are all aluminum in color. Why do you not see black A/C heat exchanger coils? Even on your car, your radiator will be black, but the A/C heat exchanger in front of it (which also must dissipate heat) is left an aluminum (no paint) color.

Would the A/C heat exchanger work better if it were also painted a thin layer of black paint? I've never had the guts to try it on my home's central air coils. :)

Warren.

The radiator should not have worked differently because it was silver other than the fact that it was painted and so the spaces between the fins were smaller and the air flow more restricted. Radiators, contrary to their name, don't really do much radiating heat. The heat is conducted to the air flowing over them. That is why they have the thin fins with lots of surface area. If they really radiated the heat, they would just plain be large, likely covering the entire surface of the car.

That explains why the aluminum heat exchanger works just fine, color doesn't matter when you are conducting the heat away.

Rick

I also suspect that the silver paint Warren's dad used was the usual thick and "soupy" type metallic paint. That stuff could add an insulation layer where you really didn't want one.

In my youthful days in the 80's I used that kind of paint for my electronics projects. It looked cool (well, for the 80's it did) and it was so popular that you could always find leftovers or small can on sale.

mainly it was the paint insulating the fins from the air. the black lacquer used on old radiators was to stop them from oxidising,

because copper is too expesive,

I once has a car with an unpainted aluminium rdiator core, this was stock, not a modification.

if it was really thin, like black anodize, maybe .

I suppose you're right.

It could be- it may have been thicker than it should have been (I couldn't tell you now what kind of paint it was).

Copper of course would need some kind of coating to keep the thing from corroding, whereas I suppose the aluminum is prolly not so prone, depending upon the alloy used.

Warren.