24 Hour Electrician's blog

"24 hour Electrician is a Georgia licensed and insured contractor. Our licensed electricians can assure you that all work undertaken is carried out to National Electrical Code-NFPA and other safety and construction codes regulations!"

Safety Tips

  • To guard against electrical shocks, install ground fault circuit interrupters (GFCIs) in bathroom electrical outlets and other areas where water and electricity might meet.
  • To guard against fire, install Arc Fault Circuit Interruptes (AFCIs) in electrical panel box.
  • Never set a radio, telephone or any other electrical appliance on the edge of a tub or sink. If you want music in the bathroom, get a battery-operated radio meant for use near water.
  • Don't use an electrical plugged-in appliance, like a hair dryer, when standing on a damp floor or in a wet bathtub or shower.
  • If an electrical plugged-in appliance does fall into water, don't reach in to get it out. Unplug it first by pulling on the electric cord, not the plug. If the electric outlet has a GFCI, it will automatically disconnect the electric circuit in case of an accident like this.
  • If your home has an electrical fuse box or circuit breaker, learn how to replace a blown fuse and reset a tripped breaker. Always keep a supply of extra fuses handy. Never use a penny to override a blown fuse. It can cause serious electrical damage.
  • Check your electrical appliances and electrical tools for the UL (Underwriters' Laboratories) seal, signifying that they've been tested for safety. Be sure to repair or replace any tools that are damaged.
  • Don't overload any electrical outlet or electrical circuit in your home.
  • Make sure you unplug the electric toaster before you pry out the toast.
  • Keep all electrical cords in good condition. Don't run electrical cords under rugs or furniture and never staple or nail electrical cords in place.
  • Remind children not to put anything into an electrical outlet. Use plastic electrical outlet caps if there are young ones at home.
  • If your basement floods, don't enter unless you are sure the water isn't in contact with a source of electricity. Call a qualified electrician to disconnect the electricity before you enter a flooded basement.
  • Keep in mind that electrical utility lines often run underground. Before you dig anywhere, call, CALL BEFORE DIG.
  • If you see a fallen electrical utility line, call your utility power company immediately and warn others to stay away.
  • Remind children that electrical wires, electrical equipment, sub-stations, and transformers are extremely dangerous.

Surge Protective Device:

Introduction,

The popularity of solid-state electronic devices has grown dramatically over the last few decades. In fact, roughly half the electrical power produced worldwide passes through such a device.

It’s easy to see why solid-state electronic devices such as television, DVDs, microwave oven, stereo and computer, are so popular. The devices are small in size, convenience to use, very precise in their function, offering superior performance and exceptionally durable and long lasting.

However these electronic devices have a downside. To provide the precise, dependable function these devices require an equally dependable source of power.Performance could be hampered or even stopped or in the case of a major voltage surge (100V-20KV), these devices could be damaged or even destroyed.

The function of the surge protector is to stop (or at least limit) the effects of less than perfect power quality on electronic devices. Surge protector is a cost-effective solution to prevent downtime and equipment damage.

What is a surge or transient?

An electrical surge or transient is a random, high energy, short duration electrical disturbance which also define as voltage impulse and spike.

Sources of such surges include:

  • Lightening
  • Switching loads
  • Short circuits
  • Variable speed drive operation
  • Imaging equipment operation (photocopier and scanner)
  • Arc welding
  • Lighting dimmer

A surge can travel on electrical, telephone and coaxial cable lines entering a building. It is too fast to stop by circuit breakers or fuses and it can damage solid state devices and corrupt microprocessor data.

The use of surge protector device helps to alleviate some of the problems caused by electrical surges.

What other power quality problems are there in addition to electrical surge?

  1. Short period of undervoltage and overvoltage conditions are called sag and swell in electrical line voltage. They can be caused by one or multiple large loads turning on or off at the same time. The duration of sag and swell is generally between 8.3 millisecond (½ cycle) and one minute. They can cause the computers to shut down or lock up in a program, motors to stall, and contactors and relay to open. The use of voltage regulators and power line conditioners can solve these problems.

  2. Noise distortion takes the form of unwanted electrical signals present on the steady-state voltage waveform in the shape of low voltage high frequency signal. Radio Frequency Interface (RFI) produced mainly by communication system components, can contribute to system noise. Have you ever experienced static on your TV caused by a hair dryer or a nearby CB radio? These are example of RFI.

    Another form of similar noise is brought about by poor grounding systems. Our audiophile customers should be familiar with this interface.

What is a lightning surge?

The most destructive power disturbance of all is lightning. First, let’s consider a few statistics from the National Lightning Safety Institute (NLSI):

  • At any giving time, over 1,000 thunderstorms are in progress worldwide.
  • Lightning strikes the ground somewhere on our planet over 100 times every second.
  • Tall structures, such as audio towers and office high-rises are struck by lightning 5 to 10 times a year. Smaller buildings can expect to be struck once per year.
  • Lightning strike in the United States cost over $2 billion in annual economy losses. Mainly through computer damage and data loss. This figure climbing rapidly as microchip-driven devices continue to gain popularity.

Lightning is a more serious problem than most people think. In fact, NLSI states that lightning is an under-rated hazard.

If a building is hit directly, an impulse current measured in thousand of amperes can find its way into the facility’s electrical power, data, and telephone lines.

How many types of surge are there?

There are two types of surge: The combination wave and the ring wave

The combination wave waveform is a unipolar pulse, similar to a lighting strike.  The rise time of this current wave is 8 microsecond.

The ring waveform is an oscillating waveform that most often occurs inside a premise.

How do we categorize surges based on its amplitude and location?

The amplitude and available energy of the standard waveforms are dependent upon the location within the house. For this reason, the standard classifies the location in three categories:

  1. Category C: outside electrical service up to the electrical panel
  2. Category B: electrical panel, short distance branch circuit, feeders to heavy appliances with short connection to service entrance.
  3. Category A: outlets and long branch circuits; all outlet that are more than 30 feet from category B and more than 60 feet from category C

Category

Voltage(V)

Current (A)

 

 

Ring Wave

 

0.5 nS- 100KHz

Combination Wave

(Impulse)

8-20 nS

A3

6,000

200

N/A

B3

6,000

500

3,000

C3

20,000

N/A

10,000

What do surge protectors do?

The design goal of a surge protective device is to divert as much of a transient power disturbance away from the load as possible. To accomplish this, a Surge Protective Device redirects the surge and transient voltage to ground.

How important is grounding system in operation of Surge Protecting Devise (SPD)?

The system ground provides path for the surge to follow to the earth grounding connection, preventing damage to the electrical equipments. If the ground is not solid, the surge will go through alternative paths for example electronic equipment, leading to equipment damage. Roughly 80% of power quality issues are tied to grounding problem.

Why a surge strip is not enough?

If a surge strip (a grouping of few receptacles connected to an extension cord, with an integrated surge protective device) is all that stands between your expensive electronics (stereo, TV, computer , etc.) and a lightning strike, your investment is not as safe as you think.

Surge strips alone can’t provide sufficient protection. The typical surge strip provides a current rating of 2,000 to 6,000 amps. The maximum lightening surge is defined as 20,000 volt and 10,000 amps. When the lightning strike overwhelms that surge strip, you can guess where the rest of that surge goes.

So what is the solution then?

IEEE recommends that SPDs be coordinated in a staged or cascaded approach. The First SPD which we call whole house surge protector should be placed at main electrical panel (service entrance) to reduce the voltage surge to the acceptable level for any downstream devices including surge strips. To deal with any residual voltage, a second SPD in the form of surge strip should be installed just ahead of critical loads, such as computers, sound systems, TV, etc. This will reduce a 20 KV lightning surge to well under 330 volts peak.

What is let-through voltage?

Let-Through voltage or clamping voltage is the amount of voltage that is not suppressed by the surge protective device and passes through to the load. Lower Let-Through voltage offers better protection for downstream load.

What should we consider when choosing a Surge Protective Device (SPD)?

Surge current per phase: For houses 120 KA or more per phase for panel boards or other location. Surge current capacity is an indication of a SPDs life expectancy. The higher SPDs surge current capacity rating, the greater its life expectancy. We will look at this shortly.

Let Through Voltage: Performance should be specified based on three standard IEEE test wave form (category C3 and B3 Combination waves, and B3 Ringtone). Lower let-through voltage provides better protection.

Effective filter: Noise attenuation at 100 KHz should exceed 50 dB (L-N modes)

Why shouldn’t Joule rating be used to compare SPD?

IEEE,IEC and NEMA do not recommend using Joule ratings when specifying or comparing surge suppressors because they can provide misleading and conflicting information. For example on a 120 volt system, a 150 volt or 175 Volt MOV could be used. Even though 175 Volt MOV Has a higher joule rating, the 150 Volt has a much lower let through voltage. Joule rating is a function of let-through voltage, surge current, and surge duration. Each manufacturer may use a different standard surge wave when publishing surge Joule rating.

What is different between surge current per phase and per mode?

Industry standard publish surge current per-phase, by summing surge current per modes: Line-Neutral mode and Line-Ground mode in a wye system, or Line-Line mode and Line-Ground mode in a Delta system. Surge current capacity should be stated on a per-phase and per-mode basis when specifying an SPD for a given application.

If the maximum surge is 10 KA, why they suggest installing a device that can handle up to 250 KA per Phase?

Based on available research, the maximum amplitude of a lighting-related surge on a facility’s service entrance is a 20 KV, 10 KA combination wave. Above this amount, the voltage will exceed basic insulation rating, causing arcing in the conductors and/or the distribution system.

But the answer is life expectancy. A service entrance SPD will experience thousand of various magnitudes. Based on statistical data, a properly constructed SPD with a 250 KA per phase surge current rating will have a life expectancy of 25 years in a high exposure location. A 400 KA/phase SPD has 500-year life expectancy.

How reliable is a surge protective device (SPD)?

The failure rate of an SPD is 0.1%, very low! Should a SPD fail, it is likely the result of excessive overvoltage (swell, i.e. the nominal 120 VAC line exceed 180 VAC for many cycles) duo to a fault on the utility power line. Should this rare event occur, call the utility to investigate the problem.

What is MOV?

Metal Oxide Varistor is a reliable and proven technology available for reducing a transient voltage. In AC power applications, over 99% of SPDs incorporate MOV technology. Under normal operating conditions, the MOV is a high impedance component which has a small leakage current passing through it. But, when subjected to a voltage surge of, Say, 125% system nominal voltage, the MOV reacts in nanoseconds, becoming a low impedance path to divert the surge away from the load.

Why is independent testing (as UL) important?

Manufacturers are not required to have their units independently tested to their published surge current capacity rating. Most published ratings are theoretical. They are calculated by summing the individual MOV capabilities. For example, a manufacturer may claim a rating of 100 KA, but due to the poor construction integrity, the unit may be unable to share current equally to each MOV. Without equal current sharing, the expected life expectancy cannot be met.

How does the installation effect on SPD performance?

Installation is the most important factor in determining the effectiveness of a particular SPD. Installation wire length reduces the performance of any surge suppressor. As a rule of thumb, each inch of installation wire length adds between 15 to 25 volts to the let-through voltage. Because surge occur at high frequency (about 100 KHz), the wire from the bus bar to the suppression element creates impedance in the surge path.

Published let-through voltage ratings cover the device or module only. These ratings do not include installation wire length, which is dependent on the electrician installing the unit.

For example, consider an SPD with a 500 Volt rating. This is the true rating only if the SPD is integrated into the panelboard it is protected. If it is connected to a panelboard with 14 inches of #14 wire, it allows approximately 300 Volts to be added to the let through voltage. The true let through voltage at the bus bar is 800 Volts.

Other considerations;

Surges also enter a home through antenna cable, coaxial cable and phone line. Surge Protective Devices (SPDs) should be installed at the service entrance on all cable conductors.

If you have any special case or need further information please contact us at 24 Hour Electrician.

Definitions:

Ballast Factor

. IESNA Definition: the fractional flux of a fluorescent lamp operated on a ballast compared to the flux when operated on the standard (reference) ballast specified for rating lamp lumens. Ballast factor (BF) is the measured ability of a particular ballast to produce light from the lamp(s) it powers.