Questions tagged [cables]

Questions about cable types, properties, ratings and construction.

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65
votes
4answers
20k views

Securing electrical cables to holes in enclosures?

Suppose I would like to insert data-cables of varying diameters -- e.g., a cable of 5 mm diameter -- into the 6 mm diameter hole of a plastic enclosure. The wires within the cable are terminated via ...
57
votes
2answers
27k views

In a USB cable, is it OK to swap the D+ and D- wires?

I heard that D+ and D- are differential signals, does it matter if I swap them when connecting a USB device to the computer?
53
votes
10answers
42k views

Why is an Ethernet cable not grounded?

There is no dedicated GND in the classical Ethernet 8P8C ("RJ45") pinout.[1] Why does the Ethernet spec not include a ground, unlike many other cable types used for interconnecting devices that may ...
50
votes
11answers
24k views

Why isn't stripping wires by burning with a lighter a more common practice?

I see people suggesting specialized tools, or trying it manually with sharp knife or scalpel, why not just burning the rubber for a second or two with a lighter and just pulling it out a more ...
48
votes
9answers
17k views

Why are copper cables round?

Why are cables only made of round shapes? What is the advantage of it? Why aren't there triangular or quadrilateral or pentagon shapes of cables?
47
votes
7answers
11k views

Why aren't headphone jack shaped plugs used for data?

With Apple's lightning cable, and USB 3.0, reversible cables are taking off, and I personally think this is very convenient. But we have had better than reversible for a long time, in the form of the ...
40
votes
10answers
13k views

Can a premium HDMI cable outperform a standard cable?

Assuming two cables both conform to the same standards (e.g. HDMI2.0, high-speed, ...) is it possible that a premium cable will outperform a standard cable when using an objective benchmark that ...
38
votes
7answers
7k views

Why were coax cables used for networking?

Often, if older standards become obsolete, it's because they are superseded by newer technologies. In the past networking was done using coax, instead of the twisted pair used today. Why did they use ...
33
votes
2answers
4k views

What are those weird wires in the audio cables?

Trying to repair a headset cable, I discovered that it doesn't look at all like the “ordinary” cables I used to repair. I was expecting to see, inside the cable jacket, four wires, each one in a wire ...
26
votes
5answers
104k views

Just chopped a cable, is red power, black ground?

I've just chopped a usb to micro-b usb cable. There are 4 small wires inside Red Black White Green Isn't it universal that Red is power and black is ground?
24
votes
6answers
8k views

Can I use I2C over 2m cables?

In my current project, I need to communicate between a microcontroller and some sensors over I2C. One of them is a temperature sensor, it needs to be placed at approximatively 2 meters far from the ...
24
votes
3answers
3k views

What does "no fit" mean in electronics?

I have found at some places, especially: Raspberry Pi Forums eLinux RPi Hardware page the following wording: S2: DSI interface. 15-pin surface mounted flat flex connector (possibly no-fit) S5: ...
24
votes
8answers
83k views

Is CAT5 cable good enough for RS-485 vs "true" RS-485 cable

I have a serial comms project coming up. A number of boards with RS-485 interfaces need to communicate. Date rate is 57600bps and cable length will be less than a few hundred feet. Will shielded ...
22
votes
5answers
12k views

What's the best cable to transfer audio signal?

Sorry if this is the wrong place but I'm interested in a scientific and electrical explanation and not some HiFi voodoo magic. I guess you all have seen the discussions about expensive audio cables ...
21
votes
3answers
4k views

Pass USB 3.0 connection through D-SUB connector

I need to pass a USB cable through a vacuum chamber wall, for which we have only D-SUB passthrough flanges available. So I cut a USB cable in half and soldered a D-SUB connector to each half. For USB ...
20
votes
8answers
94k views

Why is it dangerous use a coiled extension cord

What aspect using a coiled extension cord makes it more dangerous than using an unrolled power cord. Many fire safety websites reference that an extension cord should not be used while coiled. Is ...
18
votes
4answers
10k views

How is xΩ impedance cable defined?

This is probably a really simple question, but I can't seem to find a definite answer anywhere. I'm guessing 50Ω cable means 50Ω per unit length. What unit length is this? If this is not how its ...
18
votes
2answers
32k views

Maximum cable length for 3.3V UART signals

I would like to avoid using RS-232 converters between two microcontrollers on two different boards. For various reasons, only UARTs are supported, e.g. no SPI or I2C, and I will be using CAT5E cable ...
17
votes
2answers
3k views

Is there a minimum length for SATA cables?

Today I stumbled across a piece of information that surprised me. Apparently there is a minimum cable length for SATA. From Seagate, a reputable manufacturer of SATA devices: Serial ATA (SATA) data ...
15
votes
6answers
4k views

Is there a low-cost alternative to RJ45 cables for large number of signals?

We are designing two interface (printed) boards and need to connect them by cables (0.5-1.5m). So we're thinking about which connectors to use. We'd like to use twisted-pairs like in a RJ45 cable. ...
15
votes
5answers
1k views

Why do we still use cable for a lot of forms of data transmission?

Like many people I'm often annoyed by ugly cable clutter, especially when it's long distance. In my opinion it would be ideal if cables could be eliminated altogether, so that you'd just have two ...
15
votes
6answers
61k views

Max Serial Cable Length?

What is the maximum length of serial cable I can use, to connection work properly? Is length of serial cable in connection with baud rate? I am using about 5 meter cable at speed 38400 bauds and RS232 ...
15
votes
3answers
363 views

Communication among briefcase halves

I'm building a small laptop-ish device in a briefcase. Imagine the green wires aren't there. The LCD half lies somewhat deeper in its case than the keyboard part. For now, testing and programming, I'...
15
votes
2answers
17k views

Twisted Pair Twist Rates

What are the mathematics behind twisted pair cabling? I know that the twists are there to help eliminate cross talk and interference, but I want to know about the math of how they find the specific ...
15
votes
2answers
2k views

Terminating shielded/screened twisted pair correctly

Theoretically, I can't see a problem if the twisted pair has an end of cable termination that is: - A single resistor (R) that matches the characteristic impedance of the cable placed across the two ...
14
votes
4answers
4k views

Are there any advantages to using rigid RF coaxial cables?

While watching this Signal Path video, I came across this shot: I saw few rigid coaxial cables there and so I started wondering what might their advantages be. I could only find disadvantages: They'...
14
votes
6answers
3k views

Piezoelectric effect in cables?

I am using a very sensitive transimpedance amplifier on a 3m long cable to a photodiode. Signal levels are about 70 nA - 700 nA. Bumping into the cable causes a large voltage spike on the output of ...
14
votes
2answers
3k views

What are these teardrop-shaped loops in power lines for?

I just happened to notice this along a road near where I live: So these were in a pair, oppositely facing, "tip" to "tip" of the teardrop. At first glance, this doesn't seem to be ...
14
votes
0answers
792 views

Why is there a textile thread in some cables [duplicate]

Here is a photo: I have seen many cables with a single textile thread in them and I always wondered why it is there. Does anyone know?
13
votes
12answers
37k views

Avoiding DC voltage drop over long distances

I am trying to power my IP camera over a long distance from the power socket (about 10m). The included power adapter, rated for 5V 2A is about 1.5m long. I cut the cable and extended it using a ...
13
votes
8answers
7k views

Apple power supply: thick AC cable, thin DC cable - why?

Apple power supply consists of a very thick, inflexible AC cable (wall outlet to converter) and a very thin, flexible DC cable (converter to computer): Why? The currents through the cables should be ...
13
votes
4answers
3k views

Heat-shrink tubing available as a roll like adhesive tape?

Many people who have used heat-shrink tubing have probably experienced this: you forgot to insert heat-shrink tubing before soldering, and now it's too late! Indeed, once the soldering is done: you ...
13
votes
3answers
74k views

Why do thunderstorms knock out power?

It isn't like lightning strikes the wires. And surely the whole apparatus is designed to be water-proof. So what is it that causes power outages during thunderstorms?
13
votes
2answers
10k views

Why is current rating for multicore cable lower than single core with the same cross section?

As per this resource, a single core 10 AWG (5.3 mm2) copper cable is rated for up to 52 amps, while the same cross section cable of 43 cores and more is only allowed to carry up to 15 amps. Why is ...
13
votes
3answers
12k views

How does "bidirectional" transmission on gigabit ethernet work?

I was reading about the various twisted pair protocols, being distracted by the marvels of Wikipedia when I went to look up the way to wire a connector. And I'm wondering how it can transmit in both ...
13
votes
1answer
2k views

Why must USB low-speed devices use a captive cable?

The USB 2.0 spec says: "A low-speed device is required to have a captive cable." However, I can't find a good explanation for why this is the case. I have seen hints towards two possible ...
12
votes
6answers
8k views

What makes a high speed USB cable high speed?

I was shopping around for USB 2.0 cables. Some manufacturers claim their cables are "high speed". My understanding is that the electronics on the device determine the speed, not the cable. I ...
12
votes
2answers
40k views

How does a ferrite core wire terminator work to reduce EMC?

The following question was asked on superuser: What is that cylinder on cables? How does that cylinder work? As far as I can tell, even if you put one on either end of the cable, any HF signal should ...
12
votes
3answers
6k views

Software for creating cable schematics

I'm looking for free software to create drawings of communication cables eg. DE-9, RJ-45, Ribbon Cables, and Molex. I can't seem to find any software that comes with images of the connectors that can ...
11
votes
6answers
8k views

Is it necessary to separate DC power cables and data cables?

I have had this discussion with my colleague earlier. A DC power supply is non-alternating, so the magnetic field a DC power wire generates is constant (is it?). Now, I know the rule is to separate ...
11
votes
4answers
3k views

When wiring a European (Schuko) plug, what thing should I focus on not to mess up?

I know this might be a dumb question, as wiring a plug isn't some rocket science, but I am wondering if there is something not so obvious that can go wrong, or any tip at all for me to care when doing ...
11
votes
2answers
6k views

What is this 3.5mm plug designed for?

Here is a technical drawing for a 3.5mm stereo audio plug, taken from a product datasheet (http://www.tensility.com/pdffiles/50-00396.pdf): The right-hand end is a standard 3.5mm audio plug. The left-...
11
votes
5answers
32k views

Bring 5V DC 20 meters away

Sorry if my question is stupid but I'm an electronic passionate only during the weekend. I had a talk with a friend, we want to bring the power supply to a box containing a microcontroller inside a ...
11
votes
7answers
2k views

Is there any difference between transferring DC over one 36 mm² wire or six 6 mm² wires?

I am designing an off-grid DIY solar power site where the distance between the solar panels and inverter is going to be several dozen meters, so I would prefer to put a thicker wire to minimize losses....
11
votes
4answers
3k views

Why do cables have multiple grounds?

Many cables have multiple grounds. Why? For example, according to Wikipedia: The SATA standard defines a data cable with seven conductors (3 grounds and 4 active data lines in two pairs) and 8 mm ...
11
votes
3answers
2k views

Crimping tool basics

When I design a printed circuit board, I often put 100mil male header anywhere. Sometimes I think it would be better to place some connectors for more reliability. Anyone here knows which connector/...
11
votes
3answers
2k views

USB vs Ethernet cable length

I was talking to a colleague about the limitations of USB cable length and as far as I could remember it was limited by the tight window the host requires the device to respond in (mentioned here). ...
11
votes
3answers
16k views

How do network devices detect whether an ethernet cable is connected?

I have a bit of kit with an FPGA on it which includes an ethernet adapter. I'm trying to diagnose why it's not working and while I do that I've noticed that with an ethernet cable connected to my ...
11
votes
4answers
1k views

What are these coaxial connectors called?

I know these are coaxial and probably SMB, however, I'd like to know how each particular type of connector is called. Moreover, I was wondering if these colors mean anything in particular (i.e. if ...
11
votes
2answers
9k views

Noise (capacitance-related?) in serial signal

The "executive summary" pictures: I want to decode the serial signal coming out of my tablet's headphone jack. This is a somewhat weird "hack" that exists in a few phones and tablets: basically, if ...

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