My lights considerably flicker whenever a large load comes on in the house and it has been this way since we renovated five years ago. I am attempting to troubleshoot this now and have already probably waited longer than I should have. I did some reading and ultimately removed the cover of the main panel and tested across the two hot wires at the main panel. All circuits were active. The reading I received was 245 +/- 2V, meaning average of 245V but fluctuated between 243V and 247V. I then had my wife turn our whole-house air conditioning unit on and voltage dropped to 237 +/- 1V while AC was running. Is this a normal voltage drop when a large appliance is turned on or is this indicative of an issue?
Electrical – How to determine why the lights flicker when the A/C is running
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Related Solutions
Flickering is caused by a bad connection somewhere. It could be the bulb or socket that is bad (you did try a new bulb, right?), or it could be a bad connection anywhere along the line: at the fixture, switch, any electrical box along the way or a fault in a cable (staple, screw, etc.). It could be the hot or neutral that is bad. A sign of the neutral being open is other lights getting brighter or dimmer. While the ground not being well connected would not cause the flickering, it might be a sign of other bad connections along the way.
You will need to visually and physically inspect all of the connections with the power turned off. Wiggle wires, look for ones that pull out of connections. Look for nicks or otherwise degrading wires. Check the wire insulation too. Look for heavily oxidizes wires or connections.
You need to get yourself a non-contact voltage tester! You shouldn't be testing live circuits with a screw driver, that's a going to get you killed.
(source: homedepot.com)
Call an electrician if you are unfamiliar with electrical work.
Dimmers have to be compatible with the types of lights in use. The bog standard dimmers that have been in use for years generally work fine for incandescent type bulbs and the halogens that work at direct line voltage.
With the advent of CFLs (compact florescent lamps), low voltage halogens and LED types it talks special types of dimmers for these to be used in a variable brightness mode. Do note that not all items are even dimmable and you can get into serious overheating issues in either the dimmer switch or in the light module if you try to operate with a dimmer. Similar issues can happen when a non-compatible type of dimmer is in use.
My suggestion for you, if you need to keep the mix of light source types, is to convert over to simply using a switched on-off control instead of dimming. If dimming is desired then switch all of the light sources on the circuit to the same type and then select a dimmer that is compatible with that type of lamp. Modern dimmers should show on their box what types of lamps they should work with. In the realm of the light sources themselves you may need to do some additional research to determine if a particular low voltage halogen, CFL or LED lamp assembly is actually dimmable. It may come down to specifically only purchasing items that are marked as dimmable on the box or product information sheet.
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Best Answer
What, if any work was done to the electrical system when you renovated and the problem started? In addition, what, if any work was done on the house in the immediate vicinity of the electrical service entrance?
Do you happen to own a non-contact thermometer (or know someone you could borrow one from?)
If this is a bad connection (and that's my guess), it will be heating itself (more or less depending on how much current loads in the house are drawing) - ie, if your microwave draws 10 amps, it's heating itself with 20 watts (10A X 2V) when you run that - if your AC draws 30 amps it will be heating with roughly 270 Watts (30A x 9V)
Lacking a non-contact themometer you can sometimes find these by touching the grounded exterior of electrical enclosures and feeling for heat. Having one means you can also look at specific parts inside the panel (but the problem may not be there - it may be in the meter box, which you generally can't open yourself anyway.)
Ideally you'd start at some point when nothing much has been using electricity in the house, or you've actually shut off the main for several hours, go around and feel/measure temperatures, then turn on the power and turn on as many loads as possible and feel/look for an area that is getting much warmer than the rest of the wiring/enclosures.
Since you are evidently comfortable in the open service panel, you can also check for voltage differences between the incoming wire and the terminal it connects to, and/or see if the voltage you measure is very different (under load) if measured from terminal to terminal or from incoming wire to incoming wire. That checks that end of the meter-to-service cables - the other end you generally need an electrician or the power company to check.
It is important to find and solve this issue before it gets worse; you're in the early stages of "how electrical fires get started" IMHO.