Chapter 2 contains the requirements for wiring and protection. But how can you find the requirements that pertain to what you’re working on without missing something important?

The key lies in understanding how Chapter 2 is organized, and why it’s organized that particular way. There’s logic to the sequence.

In our previous issue, we looked at the requirements for grounded conductors in Article 200. Then begins a sequence: branch circuits, feeders, calculations (for branch circuits, feeders, and services); outside branch circuits, feeders, and services. See the pattern? You’re starting from the load and going toward the source. These articles are in a sequence that matches the electrical design process for a building.

But the next four chapters don’t follow this sequence. Why? Obviously, overcurrent protection (240) applies to branch circuits, feeders, and services. Rather than have a separate article for each level of circuit, there’s just this one. The same is almost true for Article 250, which provides the requirements for grounding and bonding. It’s almost true, because we bond, not ground, feeders and branch circuits.

Surge protective devices (280) could also apply to all levels of circuits. Surge arrestors (285), while typically installed ahead of the service, can also be used anywhere in the system, if the voltage level is high enough. Fermi (Batavia, IL), for example, has surge arrestors installed on high voltage detector circuits.

Though Chapter 2 is long, it need not be confusing or overwhelming.

Source: Mark Lamendola | Mindconnection

Electrical power comes through the service and gets distributed to feeders and then to branch circuits. But when doing a design, installation, or shutdown, you go in the opposite direction, starting with the branch circuits. Why is this?

Design. Before you can properly size your electrical service, you need to know what loads it must support. You start by determining branch circuit loads and working toward the feeders.

Installation. From a project perspective, it seldom makes sense to install a service that has no loads to connect to it. Typically, loads are installed by crews using temporary power (Article 590) for lights and tools,

Shutdown. Flick off a household light switch, and you aren’t interrupting much current. But operate a 1200A breaker under load, and it’s a different story. You want to operate that breaker with little or no load to reduce risk of arc blast and arc flash.

To shut down a facility for maintenance, begin by opening the individual branch breakers. Work toward the supply through the various branch panels, then the feeder panels that supply those branch panels. Then open the main breakers.

In all cases, you’re going from lower energy levels to higher energy levels. Following this practice in all electrical work provides a safety advantage. And that’s why the Chapter 2 load side power distribution sequence begins with branch circuits in Article 210 and ends with services in Article 230

Source: Mark Lamendola | Mindconnection

We see fluorescent lamps everywhere. Many owners upgrade older systems to increase energy efficiency. In new construction, it’s common to specify high-efficiency fluorescents.

Some designers take this to the next level by specifying dimmers. However, installing dimmers can turn out badly if you don’t know what you’re doing.

While dimmers do extend the life of incandescent lamps, dimmers do not extend the lives of fluorescents. A mismatch of dimmer and lamp type can actually decrease lamp life.

With fluorescents, look at the dimmers, ballasts, and lamps as a system. Your electrical distributor can help you correctly match components. When discussing your project, understand that you’re working with several variables. You must control these during all dimming phases, and you can do that only by using a dimmer designed for a particular lamp.

The variables are:

• Cathode voltage. A standard, rapid start ballast has a constant cathode voltage, but a dimming ballast should raise the cathode voltage as it lowers lamp current. This keeps the cathode temperature constant as the lamp cools.
• Lamp current crest factor (LCCF). This is the ratio of peak lamp current to RMS lamp current. You want less than 1.7 LCCF.
• Lamp starting. Dimming ballasts need a rapid start, so they should provide 3V to 4.5V at each cathode.
• Minimum lamp current. Dimming can lower the lamp current from about 200mA to 30mA (some dimming ballasts lower output to 10mA). Over time, the lamp can become unstable at lower currents, as evidenced by swirls or striations.

Source: Mark Lamendola | Mindconnection

Getting torqued up? To know if you’re tightening connections properly, you use a torque wrench. But how do you know your torque wrench is accurate? An inaccurate torque wrench can mean irreversible damage to expensive gear.

Your first line of defense is to use quality torque wrenches. As with your other tools, buy industrial grade only. These will save you money just by lasting longer. They’ll also hold calibration far more reliably than the cheap knockoffs.

What type of torque wrenches should you buy? For field work, we have traditionally used manual torque wrenches because powered ones required compressed air. But that’s changed with the improvements in batteries for power tools. You can now use highly accurate, tendon-saving electric torque wrenches and torque screwdrivers all day long.

These basically put a motor behind the traditional hand-powered, breakaway torque wrench or screwdriver. They can increase productivity and reduce fatigue, but the same principles apply:

• Select the correct range. The torque wrench is a spring-based device. As you go to the extremes of the spring, things become nonlinear. Make sure the desired torque value is between 20% and 80% of the torque wrench’s range.
• Sequence it. Tighten per the recommended pattern.
• Stay relaxed. Set the torque wrench to zero between uses.
• Exercise. Run the torque adjustment well past the desired point, back down to zero, and then to the desired point.
• Calibrate after impact. Dropping a torque wrench can change its calibration. If in doubt, send it out.

Source: Mark Lamendola | Mindconnection

The NEC requires illumination for all working spaces around service equipment, panelboards, or motor control centers [110.26(D)]. This brings up interesting safety considerations beyond merely sticking a lightstick in a corner and “checking off the box” on a compliance checklist.

1. The average electrician is almost 50 today. That has implications for eyesight. Lighting too poor to work by was not the intention of [110.26(D)],      and it certainly won’t improve your safety record.
2. The use of “working spaces” means the lighting must be available when the equipment power is off. It’s generally a good engineering practice to put lights on their own transformer and panel, but it’s also a good safety practice.
3. Think beyond lighting the work area. Think of lighting the job. Lighting on its own transformer helps facilitate this, by allowing you to maintain normal lighting during lockout and tagout of electrical equipment.
4. A good lighting design nearly always includes provisions for task lighting. Provide convenience receptacles for easy use of portable lights. Consider adding overhead hooks for hanging portable lights so that crews aren’t opening switchgear doors for this purpose.

For service panel work, you will need a separate power source to implement the above steps. This often means renting a generator. These two steps will improve safety and efficiency:

1. Pour a cement pad outside, near each service, suitable for the generator.
2. Provide permanent hookups that penetrate, then seal, the building envelope to keep heat in and fumes out. Wire/unwire as needed.

Source: Mark Lamendola | Mindconnection