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Joined: Jun 2003
Posts: 1,143
DougW Offline OP
I know we've seen this before (I [b]did[/u] search before I posted this [Linked Image] but I have a customer who's reporting that the bases of his bulbs keep getting corrosion on them.

He, of course, insisted that they must be getting corroded because of a lack of voltage... I explained that the corrosion most likely is causing voltage problems after it appears.

The fixtures are brass outdoor post lights, and yes, there is a drain / vent hole in the bottom (about 1/4") of each, and there was no discernable moisture in the fixtures when I looked.


Joined: Mar 2005
Posts: 1,803
Could this be acid rain?

Wood work but can't!
Joined: Feb 2005
Posts: 693
How about a light coating of Vaseline or anti-sieze compound?

Larry Fine
Fine Electric Co.
Joined: Dec 2004
Posts: 1,064
I would look at the stem at the very top of the fixture. If it is removable, there should be a small round gasket on the threaded stem, to prevent water from dripping in.

I have seen some electricians forget to install this little gasket"probably because they didn't know what it was for", and water drips down on to the bulb.

I don't know if you have such a fixture, but I thought I'd throw that out there.


Joined: Dec 2001
Posts: 300
There used to be a spray that was to prevent bulbs from seizing in the sockets. When I worked for a hotel years ago, the bulb salesman tried to sell me a case. I took a sample to try.

The msds told the secret. It was just silicone spray lubricant.

Maybe this would work for you.

Joined: Nov 2002
Posts: 174
Although most lamps (bulbs) sold today have an aluminum base, brass base lamps are not that hard to find, and would probably solve the corrosion problem.

Joined: May 2003
Posts: 2,876
e57 Offline
I have head the "lose connection" therory too, from an old boss of mine, but I have never bought in to it. I see it as more cause, than effect. The effect is most likely that the wiring to the lamp-holder will be over-heated, but not the cause, IMO.

What type of corrosion is it? Salt crystal type(water/condensate),rust (water), blackend copper type (heat/dis-simualr metal), white Al powder type (all/any of the above)?

Notice any spiders? Some make a fine web/egg sac that looks like corosion, and like to live in fixture bases. Sounds crazy, until you see them in there!

You say it has drain holes. But will it collect condensation before dew point in the morning and be wet?

Warning, avoid flamable or speading oils like WD-40, unless you like fire....

And anything like NoAlOx will dry up into hard clay.

I go for a 2 part solution:
(And a little mechanical abrasion edge of flat head.)

1.)Contact cleaner to get the stuff out.
2.)Then a silicone based spray lube.

I get both cans right next to eachother at the supply house, and often do the prosses in reverse because the cans are from the same company and look the same.

Mark Heller
"Well - I oughta....." -Jackie Gleason
Joined: May 2005
Posts: 167
Silicone dielectric grease. It can take the heat of sparkplugs, it can take the heat of a lightbulb.

Joined: Mar 2005
Posts: 1,803
Look at this problem logically. Practically sealed lamp housing, with a drain hole at bottom. Lamp on: air in enclosed space heats and expands, escapes through the hole.
Lamp off: air inside cools down and shrinks in volume, drawing fresh (damp) air into the enclosure. During the early hours, the air cools further and reaches it's dew point. Condensation forms, starts corroding susceptible parts. A continuous cycle of damp air in /condensation/corrosion, then dry air expelled, damp air drawn in...etc.
The corrosion will be due to the electrolytic action of carbonic-acid (CO2)in the condensation, on dissimilar metals, due to the electochemical series; some common metals in order, (more corroded first);

Magnesium, Aluminum, Chromium, Zinc, Cadmium, Iron, Nickel, Tin, Lead, Copper, Silver, Platinum, Gold.

If the bulb base is aluminum/ or aluminised steel, the aluminum corrodes. Unless the condensation is affecting the contacts or wiring, any overheating must be due to the bulb being overwattage for the fitting, since the cap is only a mechanical fastning device*. Voltage? No, unless it's dc, (which can drive electrochemical reactions the other way). Solution? One of the sprays described above, preventing the electrolyte wetting the metal.
*Bayonet, not the screw fitting type!
Time for a quick name change!
Neddy Seagoon.

[This message has been edited by Alan Belson (edited 06-08-2005).]

Wood work but can't!
Joined: Jun 2003
Posts: 1,143
DougW Offline OP
It's the chalky, AlOx type, from what he's told me.

I'll try the dielectric grase - I've got a tube of it left over from replacing the ignition control module on my old Taurus... twice [Linked Image]

Thanks for the input. I'll let you know what happens.

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