Wall Outlets Feel Warm?

September 17, 2011

According to the United States Fire Association (USFA) Electrical fires in our homes claim the lives of 485 Americans each year and injure 2,305 more. Some of these fires are caused by electrical system failures and appliance defects, but many more are caused by the misuse and poor maintenance of electrical appliances, incorrectly installed wiring, and overloaded circuits and extension cords.

A day doesn’t go by that I don’t get a comment on the webpage about warm or hot electrical outlets.  Before we get into the guts of the issue, lets define what most (residential) electrical branch circuits are designed to provide.

NEC 210-23  15 and 20 Amp branch circuits: …The rating of any one cord- and -plug connected utilization equipment shall not exceed 80% of the branch circuit rating. Furthermore… the total rating of equipment fastened in place shall not exceed 50% of the branch-circuit. In short, no one plug should exceed more than 80% of the circuit rating and that any stationary equipment (i.e. dishwashers, waste disposers) that constantly draws power should not exceed 50% of the rated circuit. Typical residential branch circuits (outlets, wall switches and fixtures) may be rated at 15 or 20 Amps.  Typically things like window air conditioners, washing machines and refrigerators are on their own circuit.

NOTE: This is a very basic description of this code requirement and how it is applied to typical residential branch circuits. There are numerous differences when applying the code to specific uses. Greater detail can be found in sections 210 and 220 of the NEC. 

 The National Electric Code (NEC) was originally developed in 1897. As the housing market continues to respond to new demands and changes in the industry, the Code is continually updated. However, as with most houses, the electrical system installed in the house was designed based on the code of the era and unless the house has had the electrical system upgraded, either all or part of the system is still based on the original design.  The most noticeable change to the average homeowner is that older homes have fewer outlets per room, and for this reason, it can be common to find excessive extension cords and power strips. All of these item place greater strain on a system that may have been designed and built 50 years ago. 

Why is the electrical outlet warm?

  1. What’s plugged in: Things  like  cell phone chargers, computer printers, lawn sprinkler controllers, DLS Modem, video cameras, MP3 players, cordless drills and some small appliance. All these products use a “transformer” (aka: wall wart). Based on what they do (change the voltage input to a different voltage output) will cause them to be warm. Unplug it, wait about an hour and check the outlet again. The outlet should be normal ambient temperature. It is not uncommon to find these wall warts as much as 20 degrees warmer than ambient. However if you find one that is too hot to touch, it should be replaced.
  2. Excessive Demand At An Outlet: As stated above, no one device plugged in to a single outlet (receptacle) should exceed 80% of the rated circuit.  To get perspective, residential grade appliances that are designed to plug directly into a standard (15A) wall plug will normally not exceed 1500W; such as a blow dryer (1500W/110V)/.95=14.35A  ((Watts/Voltage)/PowerFactor =Amps).  With two blow dryers in the same outlet or on the same circuit the circuit breaker should trip (e.g. turn off).  Add in the fact that in many older homes it is very common to find extension cords, outlet multipliers, outlet extenders or un-fused power strips. All of these items can increase the opportunity to overload an outlet.
  3. yellowstone-0111Excessive Demand on the Circuit: Most standard residential electrical circuits are wired in a series where the circuit wires loop through the electrical box, terminate on the outlet, then continue on to the next outlet.  In other words, the electrical current being used by one outlet (on the same circuit) may pass through terminations of another receptacle. If the current is excessive, the outlet may be warm without anything attached at the receptacle.  As part of an electrical design, it is normal  to have at least one outlet in the same room to be on a different circuit.  This allows you to share the load requirement from one room into multiple electrical circuits.  
  4. Poor Electrical Terminations: If electrical terminations (at the receptacle) are loose, or the wires are damaged, this too can cause excessive heat at both the point of use as well as in the circuit described in #2. Additionally, outlets terminated using the spring-loaded  stab-lock on the rear vs. the screw-down attachment can cause excessive heat.
  5. Oversized fuse or breaker:  Typically these values can be compromised in older homes as there are fewer outlets per room, and the circuits are not designed to support all the electronic gear we find in the modern home. Assuming the circuit was installed correctly, the circuit breaker should be the lowest rated item in the circuit and the wire in the wall should be the highest. For obvious reasons, if there was a fault or failure, you want the circuit breaker to fail first. If a breaker was replaced with a higher ampacity breaker, the circuit has been compromised potentially creating a fire risk by allowing higher current levels to pass through the circuit that was designed at a lower level. In this case finding a warm outlet is a warning that the wiring may be operating above its rating.
  6. Physical Deterioration of Plug: Outlet that appear worn, broken, cracked or chipped are all conditions that can compromise the function its function and can create heat at the outlet.

In urban areas, faulty wiring accounts for 33% of residential electrical fires.

What to Do?  Analyze the problem within your capabilities. Some of these suggestions may be beyond your comfort (experience) level, so you may want to contact an electrician at this point.

  1. Identify all the receptacles associated with the warm outlet.  After turning off the circuit breaker use an outlet tester to find all the outlets. Identify the circuit breaker rating found on the paddle of the switch. TIP: Inspect the entire house, both outlets and light fixtures. With the circuit breaker off you will be looking for dead outlets.
  2. Do any of the outlets have extension cords, power strips or outlet multipliers? Ensure the extension cord is rated  for its use.  Replace all unfused power strips or outlet multipliers with a fused power strip  as these devices include a circuit breaker to add further protection. Do not daisy chain multiple power strips or extension cords. Try to de load the outlet by re-associating the plugs to different circuits.
  3. Follow the testing methods as found in Electrical Switches and Outlets. These testing methods will identify any wiring issues that should be resolved as well.
  4. By now, you may have found the problems associated with an outlet, fixture or receptacle. If you still have problems, the outlets may be internally bad, the connections may have deteriorated or may be loose. With the electricity off, inspect the wiring of all suspect outlets. Check for tightness of the screw terminations, crimped or cut wires. You can also perform this test by using a digital thermometer gun with a laser site. Scan the electrical outlet, specifically the wiring terminations,  without disturbing the wiring. The probe should identify the problem by indicating a noticeably higher temperature.
  5. Replace suspect receptacles with higher quality equivalent receptacles using the screw down connection point.
  6. If you still have problems, review the tests found in the Electrical Service Panel post. Perform the tests that apply to the condition.
  7. If you still have problems, the circuit may have been compromised by enlarging the breaker, you may consider hiring an electrician to validate the condition and to correct the problem.

Additional Items to Consider

With over 15% of all electrical fires originating in the bedroom, municipalities have adopted local electrical code requirements that include arc fault circuit interruption (AFCI) circuit breakers to be installed in new construction. These breakers have the ability to recognize an arc usually due to a defective cord appliance or wiring.

One of the newest concern with electrical fires is the fact that many extension cords, plug adapters, power strips, appliances and etc. are coming from overseas areas that use counterfeit certifications. Here in the U.S., agencies such as UL, ETL, CSA are recognized as certified testers of electrical products. Unfortunately, many items are filtering in with fake labeling.  Always purchase name brand products from reputable stores and inspect the product for the safety agency’s certification.

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