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Identifying The Cause Of a Dimming Light Circuit

By Dave Rongey - Summary:

How to Identify and Fix the Cause of Dim Lights: Dimming Lights may be a Indication of an Electrical Problem, How to Check Circuit Wiring.

Dimming Lights and Electrical Problems

Electrical Question: There is one circuit in my home that dims than regains power several times in a row.

  • It’s not a flicker and at times everything seems normal, plus it doesn’t matter if one rooms’ electricity is being used or several.
  • I have replaced the circuit breaker for that line, but still the problem exist.
  • There has not been any reconstruction on this 55 year old house for over ten years and any new upgrades utilize their own separate circuit.
  • I have considered there may be a bad rheostat (dimmer) switch in the line, but I’m not sure how to make an accurate meter check.
  • Aside from the frustration, I am concerned that there may be a short or bad wiring that could cause a fire.

Please reply ASAP.

Thank you
Background: Greg, from Massapequa, New York.

Electrical Question #2: I would like to know why everything gets dim in my house when the microwave is turned on, or the dryer is started.

  • I have replaced the main breaker as per power company recommendation, and they replaced and repaired all on their end.
  • I also noticed the ground post was hot and steaming in the rain, why?
  • What can be causing these issues?

This electrical wiring question came from Ken in Irwin, Pennsylvania.

Dave’s Reply:

Thanks for your electrical questions Ken and Greg.

Dimming Lights may be a Indication of an Electrical Problem

Application: Troubleshooting and Repairing Circuit Problems.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrician.
Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester or Volt Ohm Meter or plug-in circuit analyzer.
Estimated Time: Depends on the age of the home and the condition of the electrical wiring and access to the circuit wiring to be inspected, evaluated and repaired.
Precaution: Identify the outlet circuit at the electric panel, turn it OFF and then Tag it with a Note before performing any wiring inspections or electrical repairs. If an outlet or the electrical wiring is found to be damaged then repairs and replacement parts should be obtained with the same voltage and amperage rating. Working in an electric panel is dangerous due to arc flash hazards and the possibility of electric shock.
Notice: Burnt or damaged electrical wiring and circuit components should be replaced with new electrical materials of the same voltage and amperage rating.

How to Identify and Fix the Cause of Dim Lights

  • Dimming lights may in fact be a sign of a bad electrical connection or a malfunctioning electrical device.
  • You mention that this happens with one circuit only, so that will be our focus. The possibility of a bad dimmer switch can be easily tested by simply replacing the dimmer switch with another dimmer or a standard light switch just to see if the problem still exists.
  • If a dimmer switch is not the problem then electrical junction boxes will need to be opened so that the wiring splices may be inspected. This is done by starting with electrical junction or device boxes that are up-stream or close to the incoming power source.
  • This is a process of elimination which will eventually reveal the problem. Typically a bad splice is found which is identified by discolored or burnt insulation on the wiring and or the splice connection itself.
  • Upon discovery the affected wiring must be repaired in such a way to ensure that the new splice and affected wiring are re-spliced properly to prevent a repeat occurrence.
  • Understand that the problem with this circuit may be with the hot or the neutral, in fact often it is a neutral connection that is faulty.
    • How to Check Circuit Wiring at the Panel

      • At the electrical panel identify the affected circuit neutral wire and follow it to the position on the neutral terminal block.
      • Check that the screw is firmly holding the neutral wire in place. Often a loose neutral wire can produce a similar problem.
      • If this is the case, the neutral wire may be discolored due to a loose connection.

Yes, this could be a fire hazard so I would encourage you to have this taken care of asap.

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8 Responses to “Identifying The Cause Of a Dimming Light Circuit”
  1. George Grussi says:

    This morning my bedroom lights went dim. The cable box was on but my TV was not coming on. The bathroom fan and lights seem to be losing power, and everything in the bedroom looks like if t was not getting enough power.

    • Dave Rongey says:

      Hi George,
      This sounds like the electrical system is experiencing a feedback due to a lost connection within one of the circuits, or a problem at the electrical panel, or a problem with the electrical service to the home. The situation should be evaluated by a Certified or Licensed Electrician who is experience with electrical troubleshooting. Until the problem is identified and repaired the circuit to the items and devices you have described should be turned off, and the devices should be disconnected or unplugged to avoid possible damage.
      Be Safe,

  2. Bill says:

    I work in a commercial building. The lights on one circuit are dim in the morning, but by late afternoon they are bright again. I had an electrician come in and he tightened all the connections but this fix only lasted a month.

    • Dave Rongey says:

      Hi Bill,
      Consider having a series of voltage readings made to see if there is a difference between the morning and the afternoon. The voltage readings may be made by your local electrical service provider, and I’m sure they would be interested if there is a problem on their end.
      I hope this helps,

  3. Scott culp says:

    Here in the past few days when my dryer comes on it dims the light or even trips the breaker. I check the volts at the arc fault breaker and it shows 104. I have a 200 amp service. I check the phases and one reads 106 the other 141 what is the problem.

    • Dave Rongey says:

      Hi Scott,
      This condition of a low voltage reading on the 240 volt dryer circuit is due to loosing one conductor of the 240 volt circuit. The electric dryer circuit wiring and connections should be inspected and tested starting at the panel and throughout to the dryer outlet. This is best repaired by a qualified electrician who is experienced with circuit failures and the safety precautions involved during inspecting the circuit components.

  4. Brenda says:

    Every time I turn on the switch for the garbage disposal the lights above my sink flash. I had an electrician check it and he said that is normal and nothing to worry about. Is that true?

    • Dave Rongey says:

      Hi Brenda,
      When lights dim when a motor driven appliance is turned ON, in this case the disposal, this may indicate that the circuit for the disposal is shared with other devices such as the sink light. Typically the disposal is on a 20 amp circuit that is shared only by the dishwasher. Dim lights may also indicate that the main electrical service may be too small, especially with older homes that have older electrical systems. This condition could also caused because the disposal is old and is not performing optimally, which can be checked by taking an amperage measurement and comparing the readings to the electrical specifications found on the label of the disposal.


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