Wiring Commercial Garages and Preventive Maintenance Software

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

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

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 Electrical Construction and Maintenance Magazine

Electrical Design Considerations for Commercial Garages

By David Herres, Master Electrician

For years, commercial garages have been the source of serious safety hazards, considering their potential for fire and explosion. Service pits, for example, have been the site of workers trapped under burning vehicles, resulting in terrible injuries and/or electrocutions due to concentrations of several flammable liquids and water. Although gasoline is the main culprit, hydrogen is also potentially dangerous -- as a fuel and as a vapor (given off by lead acid batteries during rapid charging). Compressed natural gas and propane (used as alternative fuels) and volatile hydrocarbons (used as solvents in parts cleaners) also present a threat. And don't forget about grease, kerosene, and diesel fuel. Although they are not as easily ignited, these garage staples can contribute a vast amount of heat to the environment, not to mention the presence of oxy-acetylene welding equipment, which adds to the mix.

Based on the underlying danger that exists in these structures, it's fitting that they're deemed Class I Division 1 zones. To mitigate risks, most commercial garages currently under construction are opting for above-slab lifts, while many older buildings have discontinued their pits. Despite this step forward, amid all of this combustible material, there is still extensive use of electricity in lighting, portable power tools, arc welding, and battery-charging equipment, together with large motors. With advances in technology, some companies have employed preventive maintenance software to help with the day to day operation and safety in their garages. Although this does take some of the burden and danger away, it is still important to make sure the original construction was done correctly. All of this means the electrical installation must be impeccable. As an electrician or electrical contractor, the best way to start is by complying with applicable Code mandates in the design stage. Let's take a look at what's involved in wiring commercial garages.

Initial assessment

Examining Art. 511, we see the commercial garage has vertical and horizontal boundaries, and the delineated areas are classified according to the degree of hazard encountered. We also see that the authority having jurisdiction (AHJ) can derate some of these classifications if:

  • The building's use will be restricted to the extent that fuel systems will not be opened. (This would preclude major engine work or fuel system repairs, including replacement of fuel filters and fuel pumps.)

  • Positive air ventilation will be in place at all times (even nights and weekends) as long as vehicles are present.

If you're in the design stage of a commercial garage, it's probably better not to take advantage of either of these options. A better approach is to design the whole building so that a given area is considered Class I Division 2, but wiring is kept out of that zone. Moreover, in the life of the building, the installation and maintenance of an air-venting system means a large amount of energy, parts, and upkeep — just to downgrade a classification. How do you avoid these pitfalls? By proper planning on the front end.

Design considerations

Design work for a commercial garage should address all facets of the proposed construction. The first step is to size out the service. Table 220.12 gives the general lighting load for various occupancies. Commercial garages require ½VA per square foot. This may not sound like much, but remember that unlike dwelling units, the receptacle load is not included in this figure. It has to be added to it, along with all other loads. The ½ ampere-per-square-foot is for lighting only. Thus, the designer has to enumerate all receptacles, motors, and other equipment to calculate the total load (see Table).

If any of the motors will be 5 horsepower or higher — or if there will be heavy arc welding work performed in the building — now is the time to install a 3-phase service. In the early stage of design work, a meeting with the electric utility should take place to agree on type of service, rate structure, and where the service drop or lateral will hit the building. Will a masthead be necessary to achieve minimum ground clearance? If so, you can size out and design the service including metering and ground electrode conductor entry into the concrete.

For a large building, over 100 feet in greatest dimension, you may want one or more feeders and subpanels to minimize voltage drop. All structural metal, water pipe, metal ductwork, gas, air lines, and the like should be solidly bonded back to the service neutral at the main bonding jumper. At that point, the grounded neutral and the equipment-grounding conductor separate — never to rejoin.

Branch circuits higher than 18 inches above the slab (and 18 inches below the ceiling if compressed natural gas will be allowed) should be placed in EMT and MC (or flexible conduit as needed). Under this arrangement, continuous ventilation is never required, and a full range of mechanical work is allowed, including fuel tank changes and major engine overhauls.

Although Art. 511 is only a few pages long, it should be carefully scrutinized. The key is to make sure all wiring is located well outside any horizontal or vertical boundaries.

Special concerns

Classified areas within a commercial garage are delineated in 511.3 (B). In the event that flammable fuels will be dispensed into vehicle fuel tanks inside or outside the building, such areas must also conform with Art. 514, Motor Fuel Dispensing Facilities.

If there will be a spray room for automotive painting, it must comply with Art. 516, Spray Application, Dipping and Coating Processes. Here again, rather than design to Class I specifications (rigid or intermediate conduit, Type MI cable, etc.), it's possible to locate all lighting behind indestructible translucent or transparent panels. All wiring should be effectively partitioned from the interior of the spray room, as should any motors and associated equipment that drive ventilation fans. Spray fumes should be vented to a dedicated area outdoors high above grade, and separated from any source of ignition and from any air intake.

If effectively partitioned from the garage service areas, offices, parts rooms, and employee lunchrooms are excluded from the classified zone area. However, the entries to all unclassified areas must have doorsills more than 18 inches above the garage floor. This feature should be addressed early in the design phase so that it's reflected in the foundation plan.

Battery-charging equipment and batteries being charged must be in one of these partitioned rooms. Such an area should be fairly large with a high ceiling to allow hydrogen to dissipate. It should be vented, but not back into the service area. A welding room, with noncombustible wall material, should be partitioned off from the main service area and be provided with receptacles sized to match the arc welding equipment that will be used. These will be hardwired back to the panel with no additional disconnect since the welders have unit switches.

So far, we've considered fire and explosion hazards, but there is another serious danger lurking in the commercial garage work environment: electric shock.

Avoiding underlying danger

Electric shock hazards can be offset by Code compliance. As per the Code, all 125V, single-phase, 15A and 20A receptacles in commercial garages where electrical diagnostic equipment, electrical hand tools, or portable lighting equipment are used must have GFCI protection. This can be achieved by installing either circuit breaker or receptacle-type devices. The least expensive but perfectly compliant and effective way to meet this requirement is by using the feed-through capability of a GFCI receptacle to protect downstream receptacles, which should be identified by affixing the stickers provided. Such GFCI protection is needed for outdoor receptacles as well.

These outdoor devices need in-use (bubble) covers in case vehicles will be left unattended with block heaters plugged in. Article 210, which covers GFCI protection for branch circuits, also requires this technology for all receptacles in non-dwelling bathrooms, kitchens, and rooftops, if equipped for servicing heating and air conditioning.

Fire and explosion hazard resulting from electrical wiring juxtaposed with flammable gas and liquid fuels found in commercial garages is better mitigated by locating wiring outside the classified areas, rather than wiring to Class I standards inside those areas or by encumbering the building with a ventilation system that would have to be maintained in perpetuity or by limiting the scope of work permitted. Careful planning and design work can avert human injury and property loss in the future, making for an efficient and profitable operating environment.



Low-Voltage Accommodations

Increasingly, low-voltage wiring is becoming a part of the electrician's scope of work on commercial garage jobs. For example, telephone and satellite (or cable) Internet, properly grounded, should enter the building at an appropriate place based on outside parameters and be distributed to points of use.

The office, customer service counter, and parts department will need computers connected to the Internet — possibly in a networked configuration. These same areas need telephones every 30 feet within the service area of the garage. Install Cat. 5e or Cat. 6 UTP cable in EMT to all points of use.

Although the Code does not mandate cable fill limitations, four or five cables are the most you can fit in ¾-inch EMT, depending on the geometry of the run. Telephone and Ethernet cables can occupy the same pipe, but not power conductors. You can run 1-inch main lines and ¾-inch drops to the individual points of use. Wall boxes with faceplates incorporating an RJ45 modular Ethernet connector for Internet access, and an RJ25 for telephone will provide excellent service. You can also run coax cable to the office and employee lunchroom if TV is desired. Because the service area can be noisy, there should be public announce capability (audio cabling cannot occupy the same raceway with low-voltage conductors) and an AC-powered telephone ringer.



Lighting the Way

Lighting a commercial garage can also create challenges for the designer. For ceiling heights below 16 feet, low-bay lighting fixtures are the best choice. High-bay fixtures work well where the ceiling height is 20 feet or greater. Ordinary cool white T8 fluorescent fixtures are good over workbenches and other high-use areas.

All lighting should be carefully zoned so that the entire building does not have to be lighted at once. Three- and four-way switching should be provided for walk-through lighting, and a small number of T8 fixtures the length of the garage should be unswitched so that the area is never in total darkness. Battery-powered emergency light units, which also drive exit lights, should be tied into the unswitched lighting circuits. Lighting in a commercial garage is considered a continuous load, rated at 125%, since it is expected to operate over 3 hours.

Receptacles should be provided for all bench areas. They can consist of two duplex straps per 4×4 surface-mount box with raised faceplate. The NEC does not require any particular spacing, so it's up to the designer. They should be abundant to minimize the use of extension cords, and, as previously mentioned, all must be GFCI protected. If these are piped in EMT and mounted along the wall 6 inches above the bench, they will be easy to use and well out of the classified area.


END




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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.

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There is every reason for an electrician to become knowledgeable in the vast field of electronics. At one time the emblems of his (almost all electricians were men) trade were the soldering iron and friction tape. Today he or she confronts a vast array of computer controlled equipment and even a hairdryer is likely to contain a printed circuit. For those electricians who have not ventured into the world of electronics, we will be making available starting on this page a series of electronics tutorials which will assume no prior knowledge of the field and progressively address more complex topics.

I. Ohm's Wheel

Georg Simon Ohm first introduced what is now called Ohm's Law in 1827. There is nothing mystical about Ohm's Law Wheel. It is a circular tabulation of formulas, which could also be expressed like this:

E = RxI

E = P/I

E = Square root of PxR

R = E/I

R = E squared / P

R = P/I squared

I = Square root of P/R

I = P/E

I = E/R

P = E squared / R

P = R x I squared

P = E x I


Actually, all these formulas can be derived by knowing just these two:

E = IxR

P = E x I


E is volts. (It actually stands for electromotive force)

R is ohms. (It stands for resistance)

I is current, expressed in amps. It is the most fundamental of these concepts, because one amp has been defined as a certain definite very high number of electrons passing a given point in one second.

E and R are derivative of I. One volt is the amount of electromotive force required to force one amp to flow through one ohm of resistance.


Basic electronic troubleshooting involves primarily taking measurements with a DVOM (digital volt ohm milliammeter). With this instrument Amperage measurements cannot be taken on current over a certain very low level. An ammeter is in series with the current flow and the full amount of current flows through it. An ammeter has very low impedance. A voltmeter has high impedance and is placed across the item being measured. A minute amount of current flows through it.

When you turn on a high impedance voltmeter, you will see a low voltage value displayed, and it will drift in a random fashion. This is called "phantom voltage" and it doesn't mean anything. When you touch the probes to a voltage source the meter will quickly stabilize and the correct voltage will be displayed.

Higher levels of amperage can be measured using a clamp-on ammeter. This instrument is quite accurate and is very useful when repairing all sorts of appliances, motors and other electrical equipment. You just open the jaws of the meter and insert one conductor. If both circuit conductors are inserted as in a jacketed cable, the current flows, since they are going in opposite directions, will cancel and the meter will read zero. To take a reading on a cord and plug connected appliance, make up a short extension cord. Make a six inch slit in the outer jacket and pull out a current-carrying conductor so that a reading may be taken on the current that is flowing through it.

Ohm's Law is applicable in both DC and AC circuits. A resister is a component manufactured to present a definite unchanging resistance in DC or AC circuits. (At high frequencies, the resister will have an unintended capacitive and inductive component, which will alter its opposition to the flow of current. At the 60-Herz frequency that is standard in the United States and the 50-Herz frequency in many other parts of the world, these effects are minimal and do not have to be figured in.)

In the course of ordinary electrical work, many pieces of equipment behave as resistances. Heating elements, light bulbs and long runs of wire are examples.

When two or more resistive loads are in series, the total resistance is found by adding all loads. If the loads are not equal, they will have different voltages across them.

Some of the Ohm's Law derivatives are very important while others are rarely used. Why would you want to find voltage given current and resistance? Generally the voltage supplying a piece of equipment is known at the outset or can be measured easily.

One of the commonly used formulas is P = R X I squared. It gives the loss in heat dissipation of a resistive load.

Another important and often used formula is I = P/E. In order to size out a circuit in accordance with the National Electric Code, you have to know amps. Amperage is the unknown which you have to solve for when you are given the wattage and of course voltage of a piece of equipment. In the denominator go any other mitigating factors such as efficiency, power factor and 1.73 for a three-phase circuit.

An important fact to understand is the difference between cold resistance and hot resistance. A resistive load will become lighter (that is it will have a higher resistance) once it gets to an elevated operating temperature. A lightbulb will read artificially lower resistance measured with a meter than in actual operation. Sometimes lights on a circuit will be seen to dim momentarily when an additional bulb is switched on. Much equipment draws more current while it is moving from a lower (or zero) energy state to a higher one. This is particularly true of a motor as it gains speed under load.


We have considered resistive loads in series -- to find the total resistance, just add them. What about resisters in parallel? The calculation is a bit more complex. If you think of a resistance as opposition to current flow, it is easy to see that two or more resistive loads in parallel will be less of a bottleneck than just one of these. In fact, the total resistance is given by this formula:

1/total resistance = 1/R#1 + 1/R#2 + 1/R#3 . . .

This formula works when the resisters are not all the same value. It also works when they are all the same value, but in that case a simpler formula is possible:

Total resistance = (R#1 X R#2)/ (R#1 + R#2)


Combination circuits made up of series and parallel elements are not difficult to figure if you take a methodical approach. There are two basic forms, with more complex variations.

The first scenario is series resisters in parallel.

The second scenario is parallel resisters in series.

In the first case, figure the series elements and then treat the subtotals as single resistances and solve for two parallel resistive loads.

In the second instance, figure the parallel elements and then treat the subtotals as single resistances and solve for two series resistive loads.

For information on analyzing more complex DC networks, please refer to Electronic Theorems.

II. Understanding AC Circuits

When America was first powered up, a great controversy erupted over what type of electricity was to be used, AC (alternating current) or DC (direct current). Engaged in this debate were Thomas Edison and George Westinghouse, who was allied with the highly eccentric but brilliant innovator Nikola Tesla. In the end, the Westinghouse-Tesla team won, and today it is AC that is primarily used in the United States.

Direct current (DC), while simpler and more fundamental than alternating current (AC), is in someways less useful. DC is the flow of electricity in one direction, generally at a fixed rate. Early researchers were mistaken about the direction of flow and incorrectly labelled positive and negative poles. When the true state of affairs was ascertained, rather than switching terminology with regard to poles, electrons were arbitrarily declared to carry a negative charge and an electrode that had a shortage of electrons was considered positive.

From their experience with dry cells in flashlights and toys, many children at an early age become familiar with simple DC circuits. They observe that both poles have to be connected for current to flow and that the flow of electricity is in some ways like the flow of water in a pipe in that there has to be a complete circuit for a load to become energized.

AC is a little more complex, but the fundamental mechanics is the same with the additional concept of frequency or periodicity added to the pictures.

In the case of AC, the poles reverse, usually aat a fixed rate. This is largely due to the nature of the source, a rotary electromechanical generator.

Both systems have their advantages. AC can be changed (rectified) to DC easily by placing a diode in series with the voltage source and load. DC can be less easily converted to AC by means of a rotary inverter or solid state circuitry. DC is needed to charge batteries and to power most solid state equipment such as found in amplifiers, computers and the like. All of these have power supplies which incorporate diode rectification, which produces pulsating DC, and filtering capacitors which smooth out the ripples to produce more or less pure DC like what is available at the terminals of a battery.

Unrectified AC cannot be used to charge a battery -- for every half cycle that would charge the battery, the other half cycle would discharge it. So it is more difficult to store AC than DC. Another advantage in DC is for arc welding. It produces a better weld. DC welders, powered with utility AC, incorporate large rectifiers.

But AC has one decisive advantage, it can be stepped up or down to any voltage with not too much loss. Just feed the available voltage into a transformer and another voltage is available at the output terminals, that voltage dependent upon the windings ratio. Later, when we get to the topic of inductance, we shall see how a transformer works.

To be continued . . .


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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