We have an ongoing problems with our house lights experiencing "drops" or "dimming".
Our electricity provider has tested all external connections and installed a monitor, with no problems found.

We had multiple electricians inspect the circuit box and all connections, with no problems found.

The problem is that our lights and refrigerator motor will dim and return to normal. The problem exists when the weather changes and then "goes away" until the seasonal change.

It also occurs with and without load on the circuits, meaning if there is only one light on, it will occur.

The problem shows on mutiple circuits, but they all appear to be on the same branch of the circuit box.

Is this something that could be caused by a loose connection on an electrical outlet?

The odd thing is that it is "seasonal" in nature.

To me, "seasonal in nature" indicates that you have a ground problem.

Your neutral supply at the main panel must be securely connected back to the utility neutral. Check your main panel neutral connection. Also, all subpanel neutrals must be securely connected back to the main panel.

Next, have the utility check your meter base connections on the neutral and the transformer neutral connections.

This is especially true if 240V loads are not affected as they do not rely on a neutral.

We have already done all of the above. Utility company replaced the meter head, electrician confirmed all connections in panel.

The utility company also had to tighten a connection in the "pedastal" where the power branches off the main line to each house.

At this point they told us the problem is "not on there side".

Could a bad outlet or loose connection in a box cause this?

The only other thought is an electrical wire underground going to a pond. Not sure if it could be a connection problem or nick in the cable??

If the dimming is visible thruout the house on all branch circuits at once, then I agree with bhayne, the Main Neutral is loose or broken connection, and can be in the Main Panel.

If the dimming is limited to several branch circuits , but not the entire home, the problem can be a defective or pitted contact in the Main Breaker, or a loose connection in a main feeder wire.

If limited to one circuit, then a branch breaker or any splice or connection in the circuit can be bad.

Early on, symptoms like this, can be difficult to find. Look for an electrician that use Infrared cameras , ultrasound detectors, and millivolt testers to find serious hidden connection problems. Can find a local contractor here that uses these tools everyday.

What does seasonal mean? Wet, humid, windy, extreme heat? All of these conditions can affect electrical wiring.

The dimming occurs throughout the house on different circuits, but all on the same phase of the circuit box.

By seasonal, I mean that the problems appears when the seasons change (during winter to spring and summer to fall). Once the change in temperature stabilizes, the problem "goes away" until the next season.

The only thing that has not been tested, tightened, etc. is the main breaker.

The problem can be the contacts inside the breaker, or if the breaker is a plug in can be those contacts the breaker plugs onto. Can even be the bolted connections on the line or load side of a boted breaker.

I doubt this is the problem, but some times the bus bar for one "phase" is split and bolted, something to be sure to check.

If the breaker is only a 100 Amp, do even bother checking, just replace it. If it is a 200 Amp, have an electrician use a milli-volt meter to measure both line and load, if the load side is 100 millivolt or greater difference, the contacts inside can be defective.

Thanks. I will make replacing the breaker my next step, it is a 100 amp.

This is best left to an electrician I presume? Does the meter head need to be pulled to kill the power?

Yes the line to the main breaker is from the meter. You should have an electrician replace the breaker, and he may need to obtain permission from the utility to pull the meter, or they may need to do it, depends on the utilitie's procedure.

This would be a good time to have the connections inside the meter socket checked, if not done already.

Thanks again. I have a call in for an electrician and will post the results.

All of the connection in the meter head have been checked, and the meter head itself was replaced by the utility company because it "did not look right". The problem continued after all of their work and they are firm in their opinion that it is on "my side" of the system.

They installed a recorder and found no oddities in the readings after recording for 2 weeks.

Thanks and fingers crossed since this has been going on for years now.

UPDATE:

Electrician came out, pulled meter head and instantly saw that water was entering the meter box, pooling on the main cable going to ciruit panel. Water was running down inside of cable and dripping directly onto main breaker.

Breaker and contacts were badly corroded and obvious as soon as main breaker was pulled.

Replaced breaker, sealed all openings and inside of meter box, now will wait with fingers crossed until next heavy rain to see if problem is solved.

Ticked that our utility company failed to notice the water issue during the many times they pulled the meter.

Water may continue to enter the meter and main breaker/panel if the weather head and service entrance conductors have not been arranged and treated to prevent water from entering the cable assembly.

The service entrance conductors should be formed to have a drip loop, and the weatherhead may need to be filled with caulk to keep water from entering and following the cable's path.