Surface Oxidation Increases Electrical Fire Risks

[Stratoflyer]

ENSURE TECHNICAL UNDERSTANDING/QUALIFICATION AND REMOVAL OF POWER AT CIRCUIT BREAKER PRIOR TO DOING ANY ELECTRICAL DEVICE INSPECTION OR REPLACEMENT.

I recently encountered a potential electrical fire risk associated with my home clothes dryer. This incident could manifest with most any higher current devices such as electric dryers and electric stoves/ranges that utilize 220 volts alternating current (Vac). Even lower voltage high current devices may be subject to this type of failure mode. Gas ranges may be susceptible to this risk for those that use 220 Vac to heat the oven. Without going into all the details, in a previous life I had occasion to wear the hat of that of a Mishap & Accident Investigator, so I had to scratch the itch nagging at me to understand the root cause. From my cursory examination, user manuals and electrical codes either fail to mention this or adequately throw caution to conditions that can pose these kinds of risk.

Namely, Surface Oxidation can lead to increased contact resistance that in turn creates hot spots produced by localized off-nominal power dissipation.
P watts=(I^2 amps)(R ohms).

One evening while running the electric dryer, an odor not unlike that of burning plastic became noticeable and upon turning off the dryer, that odor soon dissipated. The odor was that of melting plastic. Upon further investigation, the below photos show what I discovered.

Initial examination of the dryer plug showed one leg of the 220 circuit plug contact (nearest in photo) having oxidation over entire surface and scorched arcing burns about the tip. Removal of the wall receptacle revealed melting of the plastic housing most pronounced about the 220 contact associated with the oxidized/burned dryer plug.

You might be saying, ” That can’t be! My dryer only pulls 26 amps and the plug and the receptacle are rated for 30 amps!” True, but keep in mind whatever assurances this gives is only good for nominal operating conditions.

Quick back-of-the-envelope estimate of what I encountered after measuring plug-receptacle contact resistance of 15 ohms was around
19,140 watts. Wow...that’s hot. Granted, the actual thermal initiator most likely occurred when the contacts went into an arcing phase as set up by the oxidation. And the initial onset of oxidation likely led to more rapid cascading by the heating of the entire set of contacts, but I haven't tried to replicate that. Good subject to explore for an enterprising STEM student.

Cause and Solution? I live on the Chesapeake Bay in Virginia. House is 70 feet back off the water. Lots of wind...lots of salt laden air that
everything is exposed to, which no doubt accelerates oxidation faster compared to more benign environments. Older installations should also be examined for oxidation, no matter their location. My installation was less than ten years old but was exposed to a lot of salt air.

Replacement of plug and receptacle with every exposed contact getting a thin layer of Ox Gard will hopefully mitigate future occurrences

To further scratch my curiosity as to fires attributed to electrical sources, I ran across the following U.S. statistics. *Fire departments responded to an estimated average of 46,700 home fires involving electrical failure or malfunction each year in
2015–2019.

• These fires caused an estimated average of 390 civilian​

deaths and 1,330 civilian injuries each year in 2015–2019, as​

well as an estimated $1.5 billion in direct property damage a​

year.​

• Electrical failures or malfunctions were the second leading​

cause of electrical home fires in 2015–2019 accounting for​

13% of home structure fires.​

• Three in ten fires (30%) involving electrical failure or​

malfunction occurred in the cold weather months from​

November through February.​

• Arcing served as the heat source in over three in five fires​

(63%) of home fires involving an electrical failure or​

malfunction in 2015–2019.​

​

*https://www.nfpa.org/education-and-research/research/nfpa-research/fire-statisticalreports/​

electrical-fires​

 

[ponytug]

I'm glad that turned out well for you! Was your wiring ok? I've had one "plastic smell" that we couldn't locate, and cut the power, but it was too late and the fire broke out at 2am. Lots of damage despite the fire department being literally around the corner. We had one that we did locate the issue in time at a different place.

Have you considered dielectric filled wire nuts as well? Personally, I also check the circuit breakers and main panels bus for corrosion, and I assume external corrosion on a breaker means internal corrosion and out it goes...I believe that some, but not all, service panels allow approved dielectric compounds on the contacts.

When I was responsible for maintenance on a house that close to salt air, the receptacles and switches were on a regular replacement schedule, and unused outlets got baby proofing covers. These days, I'd probably buy the tamper proof outlets to keep things sealed. I also used the foam air tight seals on the cover plates to try and reduce salt infiltration.

Much as I like being near the ocean, that experience gave me an appreciation of wear items in homes that close to the ocean, rather like living on a boat, but without the stainless, and NEMA4X wiring.

All the best,

Peter

 

[Stratoflyer]

I'm glad that turned out well for you! Was your wiring ok? I've had one "plastic smell" that we couldn't locate, and cut the power, but it was too late and the fire broke out at 2am. Lots of damage despite the fire department being literally around the corner. We had one that we did locate the issue in time at a different place.

Have you considered dielectric filled wire nuts as well? Personally, I also check the circuit breakers and main panels bus for corrosion, and I assume external corrosion on a breaker means internal corrosion and out it goes...I believe that some, but not all, service panels allow approved dielectric compounds on the contacts.

When I was responsible for maintenance on a house that close to salt air, the receptacles and switches were on a regular replacement schedule, and unused outlets got baby proofing covers. These days, I'd probably buy the tamper proof outlets to keep things sealed. I also used the foam air tight seals on the cover plates to try and reduce salt infiltration.

Much as I like being near the ocean, that experience gave me an appreciation of wear items in homes that close to the ocean, rather like living on a boat, but without the stainless, and NEMA4X wiring.

All the best,

Peter

Thanks for the additional info Peter. I've had no problems since. You're spot on about paying attention to breakers...anything handling higher current loads. I lived in the midwest most of my life and yes I love the Saltlife. But it brings with it unique aspects that require attention that those further inland may not have to worry as much about. I put this online here for those who don't normally think about such things. Those conveniences mounted in the wall that we don't normally see...out of sight, out of mind. Hopefully more folks will become aware of these hidden risks and become more proactive with mitigating the risks. Originally this was a writeup I did for family and friends (oldest son lives in Deerpark, TX southeast of Houston, a few feet from the bay). All your insight and suggested options are great! Best...David