Home > Articles > Certification > CompTIA

CompTIA A+ Exam Cram: Understanding and Testing Power Devices and Supplies

This chapter explains what you need to know to install, test, and troubleshoot power supplies and test power that comes from the wall outlet. The skills learned will be tested in the A+ 220-701 and 220-702 exams.
This chapter is from the book

Everything relies on power. Clean, well-planned power is imperative in a computer system. It's so important, that I almost made this the first chapter of the book. I can't tell you how many power-related issues I have troubleshot in the past. Many of the issues that you see concerning power are due to lack of protection and improper planning, and as such you will see several questions (if not more) on the A+ exams regarding this subject.

Imagine a scenario in which you work for a technical services division of a company. You are required to install a new, more powerful power supply in a computer that contains many devices and requires a lot of electricity. You need to install the computer in a new area of the company's building. This requires you to plug the computer into an AC receptacle that has never been used or tested.

What kind of power supply should you select? How can you verify that the AC outlet is properly wired? And how can you protect the computer? This chapter answers all those questions and furnishes you with the knowledge you need to install, test, and troubleshoot power supplies and test power that comes from the wall outlet.

Understanding and Testing Power

The power for your computer is derived from electricity, which is basically the flow of electric charge. Electricity is defined and measured in several ways, most commonly

  • Voltage, a representation of potential energy; sometimes it's more simply referred to as pressure; its unit of measurement is volts (V).
  • Wattage or electric power, the rate of electric energy in a circuit, measured in watts (W).
  • Amperage or electric current, the movement of electric charge, measured in amperes or amps (A).
  • Impedance, the amount of resistance to electricity, measured in ohms (W).

Each of these is covered in this chapter, but by far the most common of these that you will be testing is voltage. Here are two examples of voltages you are probably familiar with:

  • 120 Volts AC (the voltage associated with many U.S. homes)
  • 5 Volts DC (the voltage associated with some of the internal power connections in your PC)

The difference in these two examples (aside from the amount of volts) is that a house's outlets use alternating current (AC), in which the flow of electrons alternate, and your computer, again internally, uses direct current (DC), in which the flow of electrons is one way.

Back to our scenario; because you can't control who wired the AC outlet that you will be connecting the computer to, or how clean the power is that comes from your municipality, you should test the outlet prior to plugging the computer in. Two good tools to use when testing are a receptacle tester and a multimeter.

Testing an AC Outlet with a Receptacle Tester

Type B AC outlets are the most common, and might also be referred to as wall sockets, electric receptacles, or power points. It is type B that you need to be concerned with for the A+ exam. If any of the hot, neutral, or ground wires are connected improperly, the computer connected to the outlet is a sitting duck, just waiting for irreparable damage. To ensure that the AC outlet is wired properly, you can use a receptacle tester, like the one shown in Figure 5.1. These are inexpensive and are available at most home improvement stores and electrical supply shops. When you plug in the receptacle tester, it tells you if the receptacle is wired properly or indicates which wires are incorrect.

Figure 5.1

Figure 5.1 A common receptacle tester and labeled receptacle

In Figure 5.1 the test has passed. With this particular tester, two yellow lights tell you that the outlet is wired correctly. Any other combination of lights tells you that there is a wiring error. The different combinations are usually labeled on the tester itself; for example, an open ground error is displayed by one single, yellow light on this tester. Important: If you receive any erroneous readings or if there are no lights at all, do not use the outlet and contact your supervisor and/or building management so that they can bring in a licensed electrician to fix the problem.

Testing an AC Outlet with a Multimeter

Every PC technician should own a multimeter, and we use one throughout this chapter. A multimeter is a hand-held device that, among other things, can be used to measure amps and impedance, and to test voltage inside a computer and from AC outlets. It has two leads, a black and a red. Whenever using the multimeter, try to hold both of the multimeter leads with one hand, and hold them by the plastic handles; don't touch the metal ends. It will be like holding chopsticks but is a safer method, reducing the severity of electric shock in the uncommon chance that one occurs. To test an AC outlet with a multimeter, run through the following steps:

  1. Place the multimeter's black lead in the outlet's ground. (The parts of the outlet are labeled in Figure 5.1.)
  2. Place the red lead in the hot opening
  3. Turn on the multimeter to test for volts AC (sometimes labeled as VAC). Hold the leads steady and check for readings. Optimally, the reading will hover around 115 volts or 120 volts depending on where you are in the United States. Watch the readings for a minute or so. Remember the reading or range of readings that display. A common reading is shown in Figure 5.2.
    Figure 5.2

    Figure 5.2 A receptacle tested with a multimeter

  4. Turn off the multimeter.
  5. Remove the red lead.
  6. Remove the black lead.

What was your reading? A steady reading closest to 120 volts is desirable. It might be less in some areas, but the key is that it's steady at one voltage; this is also known as clean power. If the reading fluctuates a lot, say between 113 volts and 121 volts, for example, you have one of the varieties of dirty power. This could be because too many devices use the same circuit or because power coming from electrical panel or from the municipal grid fluctuates, maybe because the panel or the entire grid is under/overloaded. A quick call to your company's electrician can result in an answer and possibly a long-term fix. However, we are concerned with an immediate solution, which in this case will be to install an uninterruptible power supply (UPS) or other line-conditioning device between the computer and the AC outlet. This can regulate the output of AC to the computer.

You can also test the neutral and ground wires in this manner. You should be especially concerned with whether the ground wire is connected properly. Previously we showed how to test this with the receptacle tester, but to test this with the multimeter, connect the black lead to ground and the red lead to neutral. This should result in a reading of 0 volts. Any other reading means that the outlet is not grounded properly, which can result in damage to a computer that connects to it. You can also use a voltage detector, which is a pen-shaped device that beeps when it comes into contact with voltage. On a properly grounded outlet, the only part that should give audible beeps is the hot. Everything else including the screw and outlet plate should not register any sounds. If sounds do register by simply touching the outlet plate with the voltage detector, the outlet is not grounded properly. If this is the case, or if you got any other reading besides 0 volts on the multimeter, contact an electrician right away.

Cram Quiz

Cram QuizAnswer these questions. The answers follow the last question. If you cannot answer these questions correctly, consider reading this section again until you can.

  1. What tool would you use to test the amount of voltage that is coming from an AC outlet?

    circle-shade.jpg

    A. Multimeter

    circle-shade.jpg

    B. Voltage detector

    circle-shade.jpg

    C. Receptacle tester

    circle-shade.jpg

    B. Impedance tester

  2. Which of the following is a representation of potential energy?

    circle-shade.jpg

    A. Wattage

    circle-shade.jpg

    B. Voltage

    circle-shade.jpg

    C. Impedance

    circle-shade.jpg

    D. Amperage

  3. Which wire when tested should display zero volts on a multimeter?

    circle-shade.jpg

    A. Neutral

    circle-shade.jpg

    B. Hot

    circle-shade.jpg

    C. Ground

    circle-shade.jpg

    D. Red

Cram Quiz Answers

  1. A. The multimeter is the only testing tool that can display voltage numerically.

  2. B. Voltage is a representation of potential energy; an analogy for voltage would be water pressure in a pipe.

  3. C. When testing the ground wire with a multimeter, it should display a reading of zero volts.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020