Even if you are not an electrician, but are involved in another related role on a building project, such as IT installation, you should still understand how to check an electrical outlet to ensure it is wired correctly. The haste at which some projects are built sometimes leads to oversights, and a seemingly-innocuous mistake such as a miswired outlet can have bad consequences down the line. The good news is that you don't need to be an electrician to know how to perform a basic outlet test. Below is how you can check outlets with a minimal amount of equipment and time:
Tools and materials needed
Digital multimeter with test leads
1. Electrical current can kill, even at relatively low amps and volts. Be sure to only attempt to test outlets with a maximum of 240 volts output; anything higher than this, and you may expose yourself to electrical arcing and potentially deadly burns and shocks. Consult a qualified electrician if you find a need to check an electrical supply that exceeds this level. Wear protective eyewear whenever testing in case of shorting that causes debris to pop out of the outlet. Finally, keep your hands and fingers clear of any exposed metal on leads or inside uncovered outlets.
2. Set your multimeter to read voltages at the zero-to-500 volt range or the closest range available on your particular device. Most multimeters use a dial that allows you to pinpoint volt ranges for increased accuracy. Be careful not to dial the range too low, or it may cause the device's fuse to blow or damage the multimeter itself. If your multimeter has an autoranging feature, place it on that setting and allow the device to locate the most appropriate range.
Next, insert the black test lead plug into the common jack, represented as "COM" on most meters, and the red test lead plug should be inserted into the 10 AMP jack. Be sure the leads are plugged into the jacks completely to prevent faulty readings or electrical shock.
3. Begin by inserting the black-colored common lead into the outlet's "hot" slot, which is the shorter of the two vertical slots on the outlet. Push the lead all the way into the outlet slot until it can't be easily inserted further.
Once you insert the common lead, fully insert the red-colored 10 amp lead into the neutral slot on the outlet, which is the taller of the two slots. Once again, be sure it is fully inserted into the slot.
4. With the multimeter on, the voltage reading should be within a volt or two of the nominal current output of the selected outlet. In most situations, expect to see readings close to positive 120 volts or 240 volts; these readings indicate the "hot" and neutral wires are appropriately placed. A negative reading of 120 or 240 volts indicates a reversed pair of wires, and this will require repair of the outlet. If your facility has outlets with unusual voltage outputs, consult with an electrician to determine the nominal readings to expect.
5. After taking a look at the polarity and voltage reading, you will need to take a look at the grounding of the outlet to be sure it is in place. To do so, leave the black common lead inside the "hot" slot, but remove the red 10 amp lead from the neutral slot.
6. Next, insert the red lead into the outlet's grounding slot; this is a small, round hole located either above or below the two vertical slots. Check the multimeter's reading; if the display indicates a voltage that is identical to the nominal voltage measured in step 5, then your outlet is properly grounded. However, a voltage that is less than the earlier measured voltage output is indicative of a miswired grounded connection. This means that devices plugged into the outlet will not be provided with proper ground connection. It is important to locate the flaw in the outlet so that potential equipment damage can be averted. Again, consult with an electrician, such as Albarell Electric Inc, to address the problem and have them correct the mistake.