water condensing INSIDE AFCIs?

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dellphinus

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Southern Illinois, USA
Looking for some ideas.

home less than 1 year old
200 amp Siemens panel.
4 20 amp AFCIs in the bottom four spaces in the panel.
Panel mounted 1/2 inch off concrete basement wall.
PVC conduit exits top of panel, LB, through rim joist, LB, into bottom of meter base.

Twice now, during extreme temperature drops (50-60 degree weather to near zero in a day), an AFCI has tripped.
First time, I pulled the AFCI, swapped a known good one in, and it reset and held. Figured it was a failed AFCI and moved on.
Second time, as I pulled the AFCI, it drained a quarter to half ounce of water out of the AFCI. No water outside the box,, some on inside bottom of box, and some of the copper bus bars were wet. Some moisture in between the non AFCI breakers. I originally thought it was warm, moist basement air condensing when coming into contact with cold outside air via the conduit (it was not sealed). But this wouldn't explain more water INSIDE the AFCIs? The only difference I can figure with the AFCIs is the circuit boards inside generating a little heat? Again, doesn't make sense to me- seems counter intuitive- the heat shoudl help prevent condensation?
Looking for some thoughts/experience. Cold conducted thru the feeders (copper) to the bus bars? Cold air into the panel thru the conduit? something else?
 
I guess i'd try sealing the conduit, i'm fairly sure the code updated seal thermal differences recently anyways.....~RJ~
 
hbiss said:
First hunch is that it is dripping from the PVC at the top of the panel. Did you remove the LB covers to see if there was any moisture inside?

-Hal
Click to expand...

Didn't appear so- the feeders were dry, and as best I could see, the inside of the conduit was dry- only place there was visible moisture was on the bus bars, between the breakers, in the AFCIs, and puddled on the bottom of the enclosure.
 
Condensation was likely forming inside the conduit in question then draining into the panel. If this conduit enters center KO it drips right down onto breakers/bus.

The tighter seal you have on the house the more outside air you might pull through that conduit when running exhaust fans, which actually probably helps dry the conduit out. But any time you have a positive pressure in the house then you would force some warmer more humid air into that conduit where it will contact colder surfaces and condense.

A seal to prevent air migration will probably help you a lot here.
 
dellphinus said:
yes- 300.7 covers it. I've sealed the conduit at the LB- we'll see if that fixes it.


Just curious if there really is more condensation occurring inside the AFCIs, or if they are just better containers...
Click to expand...

Well the early variety produced heat w/o a load.

To the extent that my then AHJ asked that i space them vs. stack them in a panel.

But you said the place was new, so i guess that theory doesn't fly


~RJ~
 
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