Cycling circuit breaker closure for maintenance?

Many years ago, I gained the knowledge that turning circuit breakers on and off a few times would help reduce contact resistance by wiping away resistive films at the contact surfaces. But now, I do not remember how I found that out. A brief Google search failed to find any such wisdom.

We have been having a significant amount of rain and the ocean is not all that far away. The circuit panel is accessible from outside. There is a breaker box with a cover and then another cover. That is, two covers have to be opened to get access to the breaker handles.

I began to notice fluctuations in the lamp brightness. My computer's UPS started to click in and out in synchronism with the dips in brightness. I measured the voltage at my microwave oven with a DVM. When the microwave turned on, it dipped as low as 75V. There was no microwave heating, but I was surprised that it timed out normally.

A few open close cycles on the breakers seemed to help, but this morning I got some light dimming again.

So here are my questions:

  1. Is off-on cycling of the breakers a good maintenance technique?

  1. How may cycles should be used? Put another way, how do you know if you have cycled a sufficient number of times?

  2. What kind of resistance or voltage drop is reasonable for breaker contacts?

Bill

-- Ferme le Bush

Reply to
Salmon Egg
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While "anythings possible", I doubt that it is breaker contact resistance causing your problems. Hard to troubleshoot over the internet, but it

*does* sound like some high-resistance connections. If you're near salt-water, corrosion is quite possible. But not in the breaker contacts, in the screw connections hold the wiring. Or the power coming in from the 'pole'.

Aluminum wire is often used for service entrance wiring and it really, really, hates salt-water. Corrodes pretty easy if it gets wet often. If you're comfortable/competent, you could check inside your service panel for lose connections and signs of corrosion. Otherwise, best to call a pro. If the voltage dips that much right at the service panel (not at the microwave outlet), then you'll need to call the utility as well.

daestrom

Reply to
daestrom

Its possible the buildup is also on the contacts where the breakers attach to the bus-bars.

If you're up to it, you could remove the panel cover and unseat/reseat all the breakers. You should be able to do this without disconnecting any wires.

A prudent approach would be to shut off the main breaker before doing this. If you like to live risky, kill each indiv breaker before you unseat it.

If this temp. fixes the problem, you'll know what the issue is, but you should prob. get an electrician in there with some dielectric grease.

Dave

Reply to
spamTHISbrp

What is a good reason for the voltage to go back up to normal and stay there under load after cycling the breaker?

The oven is working fine now. The one or two slight voltage dips may have come from the usual garbage seen on power lines.

So far, the trouble seems to be gone.

Bill

-- Ferme le Bush

Reply to
Salmon Egg

Rain is not the problem. Salt water is. I spent every year for 5 years at a plant in San Diego next to the ocean. Working on large frame breakers, it would take a two man team 2 days to go through clean, check and relube 16 breakers. The bolted pressure switches were by far the worst to keep working. We ended up working on the same equipment year after year. So we knew that they worked fine when we left. We had expensive equipment that would allow us to measure the time it took for the breaker to close.

As a maintence technique absolutely not. To see if they are working correctly one or twice a year sure. Most circuit breakers are not switch rated, unless stated on the breaker.

Each manufacture publishes data on this subject by breaker

Do you have a DLRO? If not then you will never be able to measure the resistance in the contacts. If you do, then back to the manufactures book on the breaker type. Lower numbers are better.

FYI the above suggested proccedure is good on 100 amp FRAME and larger breakers. If your dealing with molded case, then check out what daestrom said.

Reply to
SQLit

One way of checking your switch or breaker is to put a decent load on it and then put a volt meter across the input and output of it looking for a voltage drop. In my experience, anything above about a1/4 volt drop is causing some heating, depending on system voltage and load of course. Put one meter probe on the same leg that feeds the pole you're checking, then compare other breakers of the same size and similar load in that panel to see if there is a common range, and any out of that range by an appreciable amount. On a multi-pole breaker, check for the same, or nearly the same drop across the poles while under load. I have never seen a breaker with weak contacts improve with cycling.

Reply to
Long Ranger

After cycling, I seem to have no apparent problem. My UPS is not cutting in. My microwave oven is working. It is a bit difficult to put a voltmeter across the breaker contacts to check out contact drop.

-- Ferme le Bush

Reply to
Salmon Egg

Why would that be difficult?

Reply to
Long Ranger

I am an EE not an electrician. My experience with real panel boxes is limited.

Bill

-- Ferme le Bush

Reply to
Salmon Egg

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