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Backup electrical generator hookup (C) D FriedmanFlickering Lights & Intermittent Electrical Power Loss
Diagnose & fix flickering or dimming lights or lost electricity

  • FLICKERING LIGHT DIAGNOSIS - CONTENTS: what causes lights to dim, appliances to slow, or flickering lights and buzzing electrical noise in buildings? How to diagnose and repair dimming or flickering lights.
  • POST a QUESTION or READ FAQs about building electrical systems, power, wiring, and flickering or dimming lights
  • REFERENCES
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A diagnostic catalog of the causes & cures of of dimming light fixtures or flickering lights & power losses.

How to diagnose the causes of flickering or dimming lights at or in buildings. This article gives simple diagnostic steps that a homeowner can do to determine the type of electrical system problem that is causing flickering or dimming lights or intermittent loss of electrical power. We list the common causes of these problems and suggest what to do about them.

Watch out: flickering or dimming lights often indicates a dangerous condition. Switch off the bad-acting appliance or circuit and ask for help from a licensed electrician.



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Dimming or Flickering Lights Indicate Electrical Hazards in Buildings: What to Do

Six Tips for Diagnosing Dimming or Flickering Lights at Buildings

In diagnosing the cause of flickering or dimming lights at a building the following diagnostic questions can help narrow down the cause of the trouble.

  1. Is the dimming light problem happening in just your building or do neighbors see the same problem at exactly the same time?

    If your neighbors are seeing flickering or dimming lights too, chances are the problem is in the electrical supply network or possibly at local electrical wiring in your neighborhood or its power transformer. If your neighborhood frequently loses electrical power see BACKUP ELECTRICAL GENERATORS
  2. Is the dimming problem showing up in the whole building or just parts of it? If all lights in the house dim then the problem is probably in the electrical panel or at the service entry cabling to your building.

    The electrician will look for a problem in the electrical panel, at the main breaker, at the service entry wiring connections or at the SEC wiring itself, including the two hot wires and the service neutral wire. But see the exception in step 4 below.
  3. Is the dimming or flickering light problem associated with circuits in just half of the electrical panel? Depending on electrical panel layout, damage to one panel bus can cause failures or odd behaviour on electrical circuits connected to that panel bus.
  4. Is the dimming light problem associated with the operation of a single, specific appliance or motor? This is an exception to the case described in step 2 in that all lights may dim when there is a developing failure in a single major appliance such as an air conditioner compressor motor.

    Such motors can draw very high amps (current) for just a brief moment when the motor is starting.

    If the current surge is very brief, no circuit breaker may trip but the load may be sufficient to dim all of the incandescent lights that are on or all of fixtures in just part of the building, depending on how the appliance circuit is wired in the electrical panel. (Fluorescent lights probably won't dim).

    If the problem never occurs when the circuit to that appliance has been turned off you've probably found the trouble.

    If the problem is traced to a specific appliance but is intermittent, other variations in conditions such as temperature, humidity, vibration, or moving around of a loose wire may explain that inconsistency.
  5. Is the dimming or flickering light trouble showing up on just a single circuit? In this case we suspect a faulty circuit breaker or bad connection in the circuit. Some circuit breaker brands are particularly prone to failure such as FPE Stab-Lok and Zinsco-Sylvania. In this case the problem may ultimately show up on additional circuits in the same building, depending on building age and circuit usage levels and other conditions.
  6. Is the dimming or flickering light showing up just at some fixtures or appliances? A likely cause of this problem is a failing appliance or motor that is drawing abnormally high current as we cited in step 3.

    But sometimes the problem may occur only at lights or appliances plugged-in electrically "downstream" from a specific electrical circuit, or at lights operated by a specific switch. In this case we suspect the trouble is not the appliance itself but in connectors within the receptacle or switch or immediately "upstream" (electrically) from it.

    Some receptacle and switch types such as older push-in back-wired devices are more likely to have loose or failing electrical connectors with age and usage.

    Try plugging in the light fixture or appliance at a different location on a different electrical circuit in the home. If the bad behavior continues then the trouble is in the light or appliance itself.

Watch out: for these safety hazards and take the immediate safety measures listed here. Start by turning off any electrical appliance or circuit that is misbehaving. Call for help from a licensed electrician.

List of Causes of Dimming or Flickering Lights at Buildings

Watch out: flickering or dimming lights may, depending on the cause, indicate a dangerous condition. Arcing or overheating at electrical circuits can ultimately lead not only to power loss but to a building fire. That's why we recommend turning off misbehaving electrical equipment while you wait for the electrician.

What Level of Flickering Light Can People See?

Canada's CCOHS has written some of the most easily-understood description of who sees flickering lights, what people can see or sense, and what health effects may occur when exposed to flickering light. Excerpts are below:

People can see lights flashing on and off up to about 50 flashes per second (50 Hz) - they are most sensitive to time-varying illumination in the 10-25 Hz range. The actual critical flicker frequency increases as the light intensity increases up to a maximum value, after which it starts to decrease.

When a light is flickering at a frequency greater than 50 or so Hertz, most people can no longer distinguish between the individual flickers. At this frequency - the critical flicker frequency or flicker fusion threshold - the flashes appear to fuse into a steady, continuous source of light. This happens because the response to the light stimulus lasts longer than the flash itself.

Most people cannot notice the flicker in fluorescent lights that have a flicker rate of 120 cycles per second (or 120 Hz).

The light flicker may be detected by its stroboscopic effect. When objects move or rotate rapidly, they may be lit at or about the same position during each cycle or rotation.

This makes objects look as if they are moving more slowly than their actual speeds - they may even appear stationary if the object is moving at the same rate as the flicker frequency (or a multiple of it).

This fact is the principle behind a strobe light but it is not the desired effect in general lighting. In fact, it could be a safety hazard if someone mistakenly thought that some equipment was stationary or was moving slowly. - CCOHS, "Lighting Ergonomics - Light Flicker", Canadian Centre for Occupational Health and Safety, CCOHS, retrieved 2015/11/09, original source: http://www.ccohs.ca/oshanswers/ergonomics/lighting_flicker.html

Also, from a different source we see that flickering light can be a source of eye strain and headaches even if it is not related to electrical malfunctions that we listed earlier in this article:

... the use of high frequency electronic ballasts (20,000 Hz or higher) in fluorescent lights resulted in more than a 50% drop in complaints of eye strain and headaches.

There tended to be fewer complaints of headaches among workers on higher floors compared to those closer to ground level; that is, workers exposed to more natural light experienced fewer health effects. - Wilkins, A. J., I. Nimmo-Smith, A. I. Slater, and L. Bedocs. "Fluorescent lighting, headaches and eyestrain." Lighting Research and Technology 21, no. 1 (1989): 11-18.

Reader Question: flickering lights traced to bad utility company neutral wire

(Nov 10, 2015) Phil said:

I've been searching and can't find the answer to my problem. All of a sudden (last couple of months) my lights go dim whenever an appliance cycles on. All of them. Even when the coffee maker cycles on and off you can see it happen.

The lights even flicker to the cadence of the washing machine during the wash cycle. The dryer is the worst as the lights go waaay dim, but only for a second or two. I have no electric heat, a 100 amp service with nothing special in the house requiring anything more than 100 amps. I have a well pump, septic pump and a freezer and all the normal things a house would have requiring intermittent electrical draw.

Nothing special, but why are my lights flickering upon appliance demand all of a sudden? I do have some electrical experience and would like to know some simple troubleshooting I could do before calling in the experts, and the power company etc. Thanks.

Reply: Look for what changed in the electrical system, look for aluminum wiring

Phil,

As you are describing what is a new problem, not one that has been present since original construction, I infer that something has changed. Most likely there is a loose connection or a failing appliance.

The fact that it's "any appliance" is puzzling as I don't expect all appliances to be on the same individual electrical circuit.

Check this for me: take a look at the circuit layout in your electrical panel.

If the flickering only occurs when appliances run, let me know how those appliance circuit breakers are located in your panel. For example if they are all on just one side of the panel that would be diagnostic (and would point to a problem in the panel itself).

While you're there see if you can see any aluminum wiring, and let me know the brand and model of the electrical panel.

Reader follow-up: flickering appliances or lights on more than one electrical circuit

(Nov 11, 2015) Phil said:
None of the appliances are on the same circuit. The washing machine and septic alarm are on one circuit/one breaker, the refer. is on one circuit/one breaker, as is the dishwasher, septic pump, water pump, dryer, and range. I did observe that the range has alum.

wiring which has been treated with a type of grease at the breaker connection. The coffee pot is on my "kitchen receptacle" circuit, but shouldn't be an issue in my opinion. I've checked and re-checked every connection in the panel and all are tight and in good condition.

Washing machine, septic pump and water pump are on the left side of the panel, while the refer, dishwasher, dryer and range are on the right. The panel is Westinghouse and all the breakers are too. The freezer is on the basement receptacle circuit. Hopefully, this doesn't confuse you.

Reply: check the incoming service entry wires

As you're seeing flickering across multiple circuits I suspect the problem is

1. in the panel, a bad connection at the incoming service wire, neutral or hot, or bad connections of breakers to bus - since I don't know of defective breaker/bus issues specific to Westinghouse (and haven't seen many of those) I'd look with care (watch out you can be killed touching anything in the panel) at the connection of the mains and neutral to the main lugs in the panel - a job for an electrician.

An example of that problem is at
inspectapedia.com/electric/Electrical_Neutral_Lost.php

The SEC wires coming into the panel are secured in (in some brands) an aluminum lug with a steel screw or set-screw. The screw can feel tight because it's binding in the lug but it might not actually be tight on the wire.

If all of the bad-actors happen to be fed from breakers that pick up one of the two 120V sides of the panel that'd point to the culprit.

If the bad actors are on both sides of the panel the problem can also be outside: e.g. a buried (UF) service entry cable that's damaged or other damage to the utility company's SEC wires or overhead wires or even a pole transformer

Reader follow-up: hiring an electrician to check the panel for cause of flickering lights

Nov 12, 2015) Phil said:
Ok, I'm gonna hire an electrician to troubleshoot the panel, although it appears to be ok it my estimation. I have to start digging somewhere. I will let you know the outcome.

(Nov 16, 2015) Phil said:
My estimation was right. The panel is sound, very clean in the electrician's opinion. Took off every breaker and inspected them, all ok, very tight connections to the bus bars. Measured the power coming in and it was 120v on both legs. I'm miffed.

Reply: check the service neutral

Phil:

If the panel seems OK I'd expect the electrician to start working outwards from the main lugs that connect the service entry wiring to the panel and onwards;

I've found, for example, that the service neutral was disconnected and the panel was "working" through its local ground path - a dangerous condition.

Reader follow-up:

(Nov 19, 2015) Phil said:
Everything in the panel is satisfactory. There are no problems with the service neutral. Panel is 100% good.

As I sit here around 5:00 AM the only things running are my pellet stove (about a 200 watt draw), and 2 lights, and they continue to flicker with each cycling of the coffee pot going on and off. Oh, the refer. is going on and off too causing much flickering.

Reply: check the panel again or look outside the panel

Phil

As flickering lights are occurring on two different circuits I'd want to trace back those circuits to their origin, either in a shared junction box or in the panel.

I would look for a loose connection, aluminum wiring, or a problem in the panel that was not at first so obvious such as a poor connection of the panel neutral to the bus.

It would help to know the panel and breaker brands, and also to know if any aluminum wiring is present.

OR the problem is outside the electrical panel as suggested earlier.

Reader follow-up:

(Nov 20, 2015) Phil said:
I'll attempt to trace back the circuits. Could take a while.....No aluminum, other than the SEC. The panel is Westinghouse and all the breakers are too.

Reply: check the SEC (service entry conductors) wiring

(Nov 21, 2015) (mod) said:
Phil the SEC could be the problem: particularly if the binding-head screws in the panel lugs are not really making sound contact with the SEC wires.

In some electrical panel, tightening the screw binds in the lug and you think it's tight on the wire when in fact the wire is loose. An electrician, who knows how to do this without being killed, might pull the meter, then remove and re-make teh SEC connections.

Reader follow-up: flickering light problem found: bad neutral wire from the utility company

Had the local power company here yesterday. They installed a device in the meter socket that simulates a 1500 watt draw, and then measured the voltage on both legs. One side was 135v and the other 108v. That prompted him to check the transformer at the pole.

Transformer was fine, but found that the aluminum ground wire on the cable assembly from the pole to the house was 99.9% severed, with only one strand of aluminum left holding on.

They replaced the cable and VOILA, no more issues. My question now is
: What would have happened if it was 100% severed?

Reply: effects of a lost neutral at the SEC

Thanks for this important feedback, Phil. I've come across this issue before and have described it at InspectApedia.com in an article LOST NEUTRAL Shocks Homeowner - found at inspectapedia.com/electric/Electrical_Neutral_Lost.php

What happens is this: if you lose the electric utility's neutral AND if your panel is properly installed, you still have a local connection to earth - to ground - at your building. IN the panel where neutral and local ground are tied together, all of the neutral wires in all of your circuits continue to work but all of their return current is flowing out on the local ground.

Watch out: a lost neutral or bad electrical grounding are both very dangerous. Once the neutral has been lost the ground system will be doing work it's not designed to perform.

If there is anything marginal about the local ground - which is common - you can have flickering lights or even overheating and burn-ups on individual ground wires or circuits in the home.
Ultimately the result is very dangerous as loss of safe grounding can result in someone being electrocuted.

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