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Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit

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Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit Since its founding in 1924, Milwaukee has focused on a single vision: to produce the best heavy-duty electric power tools and accessories available to professional user. Today, the Milwaukee name stands for the highest quality, durable and reliable professional tools money can buy. This deluxe 17 piece Electricians' Hole Saw Kit has the ultimate range of diameters available. The 12 diameters include: 5/8 inch, 3/4 inch, 7/8 inch, 1 inch, 1-1/8 inch, 1-1/4 inch, 1-3/8 inch, 1-1/2 inch, 1-3/4 inch, 2 inch, 2-1/2 inch, and 3 inch. The kit also includes arbor 49-56-7000 for hole saws up to 1-3/16 inch and arbor 49-56-7140 for hole saws 1-1/4 inch and larger. Additionally the kit has three pilot bits 49-56-8000 and an impact resistant plastic carrying case. The case is also sold separately as 48-55-0784. The hole saws in this kit are of the 6 teeth per inch design. Milwaukee 49-22-4085 17 Piece Deluxe Electricians' Hole Saw Kit Features: • Deluxe assortment of 12 hole saws, two arbors, and three pilot bits • Hole Saws: 5/8 in., 3/4 in., 7/8 in., 1 in., 1-1/8 in., 1-1/4 in., 1-3/8 in., 1-1/2 in., 1-3/4 in., 2 in., 2-1/2 in., 3 in.




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This article originally appeared in Cabling Business Magazine --

The Effect of Twisting Conductor Pairs on Cable Performance


By David Herres


How alien crosstalk and other harmful effects in cable performance can be controlled by twisting conductors--

The past several years have seen a great increase in the speed of data transmission and there is every indication that this trend will continue. Early networks were required to run a Teletype machine at each end or hook up computers to printers, but now we download graphics, music and huge video files so that very high speed connectivity is needed, even in residential applications.

When considered as a complete system, transmitter, medium and receiver, it is obvious that the weakest link is going to set the upper limit on the speed that can be achieved. Accordingly, if we can eliminate that bottleneck, we can achieve higher speed data connectivity. Digital transmission consists of a flow of bits of data. any bit can be in one of two states, variously conceived as true/false, on/off, one/zero, etc. These two states can be expressed as different voltage levels, +5 and 0 volts for example, or +9 and +5 volts. These states, in actual data transmission, do not conform to a traditional sine wave but instead a digital waveform where rise and fall time are almost instantaneous.

The bottleneck in network connectivity has been cabling and this element, also called the "medium," has been the object of a great amount of research and development over the years, and vast improvements have been made. the big problems have been capacitance and inductance, both of which degrade digital information conveyed over copper conductors. Since capacitive reactance and inductive reactance are both frequency dependent, at the newer higher speeds, both have a greater effect, albeit in completely different ways. Capacitive reactance, which is measured in ohms, becomes less at higher frequencies, so that it tends to shunt out the signal. Also, there can be some capacitive coupling to adjacent pairs which results in crosstalk and a reduced signal-to-noise ratio.

Inductance is a different sort of problem. Whenever current flows through a conductor, a magnetic field surrounds that conductor. If the current is non-pulsating DC, the magnetic field is static and invisible to adjacent conductors except at the moment it is switched on or off. If it is alternating current or fluctuating DC, energy is required to move the magnetic field. At low frequencies, the phenomenon is not too pronounced unless the distance is quite long. But as the frequency increases, the magnetic field fluctuates more rapidly and the work required to move the magnetic field diminishes the strength of the signal. This is part of what inductive reactance is all about. Additionally, there is inductive coupling.

Capacitive reactance is a parallel phenomenon that decreases at higher frequencies, tending to short out the signal and also to couple it to neighboring conductors. Inductance is a series phenomenon that increases with frequency, also diminishing the signal and coupling it to neighboring conductors.

One remedy for capacitive coupling is shielding. A grounded metallic barrier is placed between the elements. Installing the cable inside a grounded metal raceway such as EMT (electrical metallic tubing), especially in noisy environments, can be greatly beneficial. Another tactic is to carefully match impedances so that maximum power transfer takes place. Any mismatching will result in harmful reflections, which distort the digital waveform, possibly to the extent that it becomes unreadable. Also, it is necessary to observe maximum distances. For Ethernet transmitted through Category 5e UTP (unshielded twisted pair) cable, the maximum distance is 100 meters, roughly 328 feet, which is sufficient for most indoor work. The characteristic impedance for this cable is 100 ohms, regardless of length. If cable impedance does not match transmitter, receiver and any connectors, harmful reflections will travel back upstream, compromising the signal or making it totally unreadable.

What about inductance? As mentioned, whenever current flows through a conductor, a magnetic field is established around that conductor, diminishing with distance. If the current varies, the field also moves, and if the field moves, a current is induced, or made to flow, in any nearby conductors to whatever extent they are parallel. This is called "mutual inductance." There is also the phenomenon of self-inductance, which, as the name implies, results in current flow in the original conductor. Since this current is opposite in polarity to the original current, it is subtracted, showing up as impedance. Like resistance, it is measured in ohms and conforms to Ohm's Law, but the big difference is that it is frequency dependent. It is also dependent on the length of the transmission line.

At higher frequencies, capacitive reactance is reduced. Since it is a parallel phenomenon, there is a greater amount of coupling, between members of the same pair, between members of adjacent pairs in the same cable, and between pairs in a different adjacent cable, creating crosstalk. the harmful effects of capacitive coupling can be mitigated by shielding and balanced transmission. In many ways inductance is similar to capacitance, but many of the mathematical relationships are inverted. At higher frequencies inductive reactance is increased. Since inductive reactance is a series phenomenon, greater inductive reactance also diminishes the signal.

The first telephones were hooked to existing telegraph lines or consisted of a single open wire with the earth serving as the return portion of the circuit. High-powered electric motors became common in the late part of the nineteenth century and, especially in cities, introduced an unacceptable amount of noise into these circuits doe to sparking of the brushes, which caused power lines to emit electromagnetic radiation and also due to harmonics resulting from the heavy inductive load. Telephone engineers developed balanced circuits which decreased attenuation and increased range. But within a few years the electrical environment became even noisier. These engineers cam up with a simple yet highly effective remedy, wire transposition. At set intervals, say every third pole, the wires would cross and exchange places. So we wee the birth of twisted pair technology with a twist rate around five turns per mile. this scheme, in conjunction with balanced transmission, reduced noise by canceling interference.

Fast forward to the late twentieth century, we see twisted-pair technology has evolved considerably for telephone and emerging data transmission applications. Shielding and/or screening had been found effective in mitigating electromagnetic and electrostatic interference. Coaxial cable derives its name from the fact that the inner conductor is centered within the outer grounded shield, which is also the signal return conductor. They share a common axis. Coaxial cable was first used in 1936 when AT&T installed an experimental line between New York and Philadelphia.

Coax has been and still is used for antenna transmission, instrumentation, surveillance video and other applications. It was an early Ethernet medium. The only problems with coaxial and other shielded cables are that they are a little pricey and time-consuming to install compared to UTO, such as the widely used Category 5e, which is adequate for many of our telephone and data needs.

UTP depends for its success on balanced signal transmission. As mentioned earlier, this methodology was developed in the nineteenth century in an effort to cope with the emerging noisy electrical environment. Balanced signal transmission means that each of the two conductors carries a different version of the same signal, identical in every way except that they are 180 degrees out of phase. Information is conveyed by the differential amplitude of the signal, which may vary from zero to some predetermined maximum value. If a pair of these conductors were run past a source of interference, such as fluorescent lighting, a motor or an AC power line, one of the conductors, the nearer one, would acquire more unwanted current than the other, resulting in a less than ideal and perhaps unacceptable signal to noise ratio. At the receiver end, the signal could be degraded and even unreadable.

By twisting the members of each pair, it was found that harmful interference could be substantially reduced. This is because first one conductor, then the other, is closer to the source of noise so that each gets an equal dose. And since the balanced signal is differential, the noise is cancelled at the receiver. It must be emphasized that while balanced signal transmission by itself is not totally effective in an electrically noisy environment, it is absolutely necessary for the twisting to work. One problem remained. If two active twisted pairs were run in close proximity for any appreciable distance, there could still be unwanted mutual interference. This is because a member of one pair, white/blue, for example, would always be closer to a member of the other pair, white/orange. Likewise blue and white would always be closer since both pairs twisted at the same rate. Differential noise cancellation would not take place.

A simple remedy, again borrowed from earlier telephone work, has been implemented. the rate of twist (usually measured in turns per meter) could vary for different pairs within the same cable. This scheme is now widely used.

Since interference and the resultant diminished signal-to-noise ratio, be it electrostatic or magnetic in nature, is frequency dependent, increase in data speeds that we have experienced over the years means that twisting technology has had to advance. This has certainly been the case in cabling and in other areas as well. Printed circuit and solid-state component engineers have battled unwanted capacitive and inductive effects for years and efforts are ongoing. Even the simple RJ-45 connector, long used for Ethernet terminations, has been subject to new design work. RJ-45 was originally AT&T terminology. RJ stands for Registered Jack. To be totally correct, the term is 8-position, 8-contact (8P8C) modular plug and jack. To cope successfully with higher data rates, it is important that the twisted pair conductors be untwisted and separated for termination only enough to permit insertion into the plug, never more than 1/2 inch. The plug itself, invisible at lower data rates, has become a source of crosstalk of lated and engineers are introducing a twist within this piece of hardware. A further innovation has been the introduction of a very small circuit board with capacitors placed inside the jack.

So far UTP cable has kept pace with accelerating data speed increases. While research and development has produced ingenious and successful cable designs which have so far met the high-speed challenge, failure is increasingly possible on the installation level. Unshielded twisted pair cable is fairly easy to run, but a few precautions are necessary to avoid compromising high-speed connectivity.

When fishing this cable through partitions, floors and ceilings, allow extra length at both ends, to be trimmed off before termination. This will eliminate damage that may occur at the ends when pushing the cable through small openings or past obstacles.

As the cable is fed out of the carton, do not allow anyone to step on it or handle it roughly.

Sharp bends, kinks, or excessive pulling force can alter the rate of twist, which can make variations in the characteristic impedance and otherwise limit the intended benefits of a high twist rate.

In securing the cable in place, do not staple it tightly. Leave cable ties a little loose. But at the same time the cable must be adequately secured so that it is not subject to damage in the future.

Do not place UTP in the same raceway, through the same drilled hole, or closer to an AC power line than necessary. An absolute minimum is six inches from 240-volt and eight inches from 480-volt power. Keep data runs away from fluorescent light fixtures, transformers, UPS equipment, motors and other magnetics.

In residential, commercial and industrial work, whether new or retrofit, installer prefer UTP. The more you work with it, running the cable and making terminations, the more you like it.

Optical fiber, which is immune to the frequency dependent problems we have been discussing, will doubtless be the wave of the future, but UTP will probably retain it market share for quite some time, perhaps through several installation generations. For awhile, skyrocketing copper prices seemed to indicate fiber optic would emerge victorious in short order. But the current ongoing economic quagmire, accompanied by a precipitous drop in commodity prices, has given copper-based UTP a new lease on life. No one really knows what the future will bring.

A good strategy for cabling design and installation:

  • Keep on using UTP.
  • Put it in metal raceway so that it can be readily removed and replaced with optical fiber down the road.
  • Get on the optical fiber learning curve now and start working with that medium where appropriate.
--END--


This site is created and conducted By David Herres, NH Master Electrician License #11335M

E-mail: electriciansparadise@hughes.net


Books for electricians --

Here is a selection of the most significant electricians' books available online today, at the best prices around. Clicking on any logo provides access to reviews and ratings by electricians. A good place to start is with the 2008 NEC Handbook, which contains the complete text of the current code plus extensive commentary, diagrams and illustrations. Other books of interest for the electrician are available as well.

Low Voltage, Telecom, Fire Alarm Books --


HOME | Best Web Host | Question of the Week | Archived Questions | More Archived NEC Questions | Still More Archived Questions | Still More Archived Questions-2 | Still More Archived Questions-3 | Articles | Electrical Deficiencies | More Electrical Deficiencies | Electricians Tools | Online computers | Cybercorner | Electrician's License | Electronics Tutorials | Electricians' worksaving ideas | Electronic Theorems | Satellite Dish | Digital Cameras and Equipment | HTML Color Chart | Electronic Acronyms | Electronic Definitions | Electrician's Soldering Tutorial | Photovoltaic Power | Wind Power | Fire Alarm Basics | More Fire Alarm Info | Working with MC and EMT | Electricians' Color Code | Wiring Commercial Garages | Managing Your Emergency Lights | Lighting Design | Industrial Wiring | Wiring Ethernet | Residential Wiring | Low Voltage Wiring | PLC Overview | Electrical Troubleshooting Techniques | Using Loop Impedance Meter | Ten Common Grounding Errors |NEC and Low-Voltage Wiring | Raceway Protection and NEC | Working with Metal Raceway | Inductance and Characteristic Impedance | Understanding Capacitance | History of the Ethernet | Twisting Data Conductors | NEC Article 800, Communications Circuits | NEC Article 810, Radio and Television Equipment | NEC Article 820, Community Antenna and Radio Distribution Equipment | NEC Article 830, Network-Powered Broadband | Troubleshooting Submersible Well Pumps | Wiring Healthcare Facilities | First Edition National Electrical Code 1897 | Books for Electricians | Links


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