Anonymous asked in Home & GardenMaintenance & Repairs · 1 decade ago

My lights dim when I turn on a powerful electrical device - vaccuum, TV, CPU, Etc.?

Is this dangerous? Will it lead to my electrical box overheating? Would it be a good idea to upgrade my circuit box? I'm a new homeowner, so alot of this stuff is new to me. How much would I expect to spend if I wanted to upgrade the houses electrical? Its a 1160 sq. ft single story home, with a 2 car detached garage.

11 Answers

  • 1 decade ago
    Best Answer

    You don't necessarily have a problem or need an upgrade. It is also not usually dangerous, more just a nuisance. Truthfully you would never know if your lights didn't dim momentarily.

    Most motors will draw between 4 and 6 times rated current during starting. Most equipment will have some sort of inrush current when first turned on. The TV will degauss its self and the CPU's power supply will have inrush.

    If these are on the same circuit as your lights then you will get a slight dim. This is because the momentary high current will produce a momentary voltage drop on the circuit. After this inrush is over the momentary drop ends and your lights brighten.

    If this is a single circuit you can alleviate the problem by moving the loads off of a circuit that feeds the lights. If this cant be done by just moving to a different closeby receptacle then you may have to rewire to get the lights and receptacles on different circuits. If this is a branch circuit problem like this an upgraded service won't solve the problem because it does not address the cause of the problem.

    If the lights dim continually when the load is on then you just have some voltage drop problems. This is due to long circuit runs and can be mitigated by reducing the load on that circuit or rewiring with larger conductors to reduce the voltage drop. An upgraded service won't solve this problem.

    If this is something that occurs on your whole house then you still may not have a problem and even so whats actually causing it may be totally out of your control.

    Lots of times the starting inrush on a heat pump will dim the whole house. This does not mean the service is inadequate. The major voltage drop thats being experienced is most likely found in the power company conductors between your service and the transformer. The power company follows different rules than an electrician will and the wire between the transformer and the service will usually be smaller than the service entrance conductors of your service. Smaller conductors mean a greater voltage drop and a more noticeable flicker. You can probably talk to the power company enough to get them to change this out.

    This can also be caused by the impedance of the transformer, this is totally out of your control as well and a new service wouldn't help you a bit in this situation. All transformers have an impedance rating. Without getting too technical the transformers impedance is directly related to the transformers voltage regulation. Most power company transformers have a fairly high impedance, meaning that when the load is increased the voltage will droop by a higher amount than a lower impedance transformer.

    You may have a very hard time getting them to change this. They usually won't change one out for relatively minor problems like flicker. It is also a safety concern to have a transformer with a very low impedance. The lower the impedance you have, the higher available fault current you will have. Since equipment is only rated to interrupt a certain fault current you will find that the power company errs greatly on the side of safety when it comes to available fault currents. You don't want them to give you a low impedance transformer just to eliminate flicker and have your breaker box blow up because the fault current rating of the breakers has been exceeded.

    Also I bet you are using incandescent bulbs??

    If so, incandescent bulbs are VERY susceptable to even the slightest variation in voltage. A drop of just a couple volts is noticeable to the human eye. When the drop occurs very quickly due to motor inrush the resulting quick dip in lumens is easily noticed. What you probably dont notice is the difference in light between midnight and the middle of the day. At night your voltage is usually a bit higher because the rest of the world is not using power, however during the day its usually a few volts lower. The intensity of the light bulb will changed during all this, it just happens so slowly that you don't notice.

    Try switching to compact fluorescent lights. They tolerate voltage variation much better than incandescent. You may not notice the flicker at all if you change! You will also be doing yourself a favor and save on your power bill and will do the world a favor because they require less power and therefore less fuel. They generally last a lot longer too.

    The only way I would say you needed to upgrade your service would be if you turned on the TV and the lights in the WHOLE house dimmed and STAYED dim, not just a flicker. Even then the voltage drop concern would likely be solved by larger conductors from the transformer to your service.

    Source(s): I am an Electrical Engineer for a large chemical company and specialize in power distribution. I also have previous education and experience as an Industrial and Residential/Commercial Electrician.
    • elizabeth4 years agoReport

      Don t switch to compact fluorescent light bulbs! They create high EMFs in your home. This is not a good thing. Look up dirty electricity.

  • Janet
    Lv 4
    4 years ago

    Energy can neither be created or destroyed (outside of fission and fusion) it is merely converted from one kind to another normally all energy ends up as heat (When you consider machines that vent fluids, here the system should be defined to consider the other room.) A TV set will heat up a room,as will a PC as will the radiant or fan heater. The heater is just better at doing it. Heaters are more efficient and quicker. For the fan heater a small amount of electrical energy is used to transport the hot air directly onto the person creating a thermal gradient and heating the person up faster, for the fan electrical energy is changed into kinetic energy, which in term is converted into heat. While in a TV the electrical energy will mainly be converted to heat, some will be converted to light, when the light hits a wall and is absorbed it will be converted to heat, some will be converted to sound and then to heat. The TV will vent the heat out of the back protecting the workings but not heating any people efficiently. As the heating is not directed much more energy is lost to the environment so the perceived heating effect is much less. So two TV sets will warm up a room but your perception would be that the heater would do it much faster, and as less heat would be lost so higher temperature would be reached.

  • Berke
    Lv 4
    4 years ago

    lights dim turn powerful electrical device vaccuum tv cpu

  • 1 decade ago

    If you have a fuse panel.It would be a good Idea to up-grade to a breaker panel. If you have less than a 200 amp service,

    while I was doing the Change-out I would also up-grade to,

    200 amp service. At any rate I would get a Licensed Electrician to make an evaluation of your home.

    As far as price is concerned it would depend on what has to be done. Get the evaluation ask for an Estimate.

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  • 1 decade ago

    You can have a soft start breaker installed to avoid this problem. The start up amps on any motor can be significantly high than the operating amps and by using a soft start you will prevent having a tripped breaker which can be disastrous with your PC!

  • Anonymous
    1 decade ago

    Nick, a couple of other thoughts here. How long do the lights dim? If this is momentary ( less than 2 seconds), for a large demand item that isnt too bad. Take a look at your service panel ( the circuit breaker box) and the very top switch has a rating on it. This is your master switch and it tells you what you are rated for coming in at that box. If you have a 100 amp or less, I would definetely consider upgrading. The other thing you can look at is how many different items do you have plugged in on the same line? If you have your fridge, a microwave and a toaster all on the same circuit, you would really be pushing the amp limit for that line. If in doubt, call a professional to come in and assess what you have and what your demand loads are. Make it clear that you want a FREE estimate over the phone. No surprises that way and get at least 3 appraisals. I hope this helps and good luck.

  • 1 decade ago

    You definitely need an upgrade. Sounds like you have a sub standard set-up. Look at the top breaker in the panel box to see what the amperage is listed at. It should be at least a 150 amp breaker. If it's any less I would certainly have it upgraded to at least that or 200 would be even better. With all the electric and electronic gadgets now available and coming soon, 200 amps will soon be a minimum for new homes. Cost to upgrade, by a licensed electrician, which is certainly recommended, as it will most likely have to be inspected when it's finished, will probably cost in the neighborhood of $500 - $700, but your lights won't dim and you'll be safe, when it's done.

  • M M M
    Lv 5
    1 decade ago

    It could be a problem and yes it could be dangerous. It sounds like you have an overloaded circuit. The fix could be simple or a major repair. It all depends on the age and condition of the wiring and the electrical panel. Try to spread out the number of items plugged in to other outlets and consider having an electrician take a look. The cost to upgrade the entire electrical service can get quite expensive but the cost of not taking care of it could be fatal.

  • Ellen
    Lv 4
    1 decade ago

    Every house does this. There's no way to prevent this. Any time you turn on a 10amp vacuum cleaner, the lights will dim when the motor starts. It doesn't stay this way as the lights go back to normal brightness. It's just that you see this when an appliance is first turned on.

    No it's not dangerous, but maybe to your computer if it's on and the voltage drops below 92volts. You should get a battery backup to protect your computer.

  • 1 decade ago

    i would recommend an upgrade if you can afford it.

    A vacuum motor upon start up temporarily draw a little 1 or 1 1/2 more amps more than the rated amps on the sticker.

    All electrical devices power consumption can be added up mathematically to avoid tripping or blowing individual fuses on a single circuit try that first its cheaper.

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