Fire Alarm!

[CGabriel]

This is a very good example of why we always recommend that you replace the "cheap commodity" outlets in your wall. A customer sent us this burned up outlet and the power cord that was toasted by the outlet. Fortunately there weren't any curtains or flammable stuff near the outlet or else this fellow's house probably would have burned down.

This particular outlet was an "audiophile grade" outlet. Unfortunately the customer installed aluminum solid core in-wall wiring. The electrical inspector said that the aluminum metal and the contact's metal were "incompatible" and caused contacts to overheat. We were sent the cable and outlet to provide a letter to the insurance agency regarding the possibility of repairing the power cord.

I personally know of two other people were the house was destroyed by fire from an overheated outlet. If you use space heaters or other high current equipment (audio equipment and home theater) do yourself a favor and replace the 59 cent outlet with a good commercial grade outlet. Then don't go too audiophile nuts with the in-wall wiring.

 

[Lee]

Wow, that is very dangerous.

 

[LL21]

Very good to know! Thanks for posting.

 

[CGabriel]

Wow, that is very dangerous.

Most people have no idea how much heat is generated in a simple outlet. But think about all the heat that a space heater can put out or the heat generated by a class A amplifier. All that current is running through the very small contacts in the outlet. Use good quality parts and give some attention to detail in the installation. This type of outlet should not have been used with solid core wire. As you can see the wire will not compress between the contact blades. So the actual contact area between wire and internal contact is quite small. Solid core wire should be wrapped around and under a screw head.

 

[amirm]

Solid aluminum wiring can be very problematic. Its coefficient of expansion is different than steel/metal used on the outlet. So as the connection heats up and cools off, the connection becomes looser. Continued cycles keep making this worse. Eventually the two metals interact and a layer of resistance is built between them which creates even more heat leading to the type of failure above. I am very surprised the customer used aluminum wiring in a new installation.

It is good to once in a while touch the insulated part of the outlet and see if it feels warm to touch.

 

[zztop7]

Green Oxide

View attachment 17887
The electrical inspector said that the aluminum metal and the contact's metal were "incompatible" and caused contacts to overheat.
View attachment 17886

There are other significant issues, but I am not going to contradict the inspector. Inspect the left hand side of the Second/2nd image; see the cut-off aluminum wire coming out of the hole. That is the remains of an inserted wire that is gripped by two extremely thin spring metal pieces - tiny, tiny, tiny contact point -HOT Spot. Notice the charred remains of the hole further down where a wire used to be and burnt through the side. Those insertion holes are wet dreams for electricians & nightmare for your house. Never use the insertion holes.
First Image: Note the male plug, note the copper ground blade [that is the rounded one], note the green corrosion >>> that level of green corrosion [copper oxides] does not happen in a week. Note some green on the flat blade [maybe blades if inspected in person]. Water vapor or water over a period of time is the likely culprit in a house [acid if it was some kind of illicit drug lab, but then the blades would be evenly green - rule this one out]
{ACID from PVC if present might cause the green - any PVC in the male or female?}.
Something was going on here.
First Image again: Note the duplex [female wall outlet], note the explosive outward nature of the burn at the top. Only the top of the male plug is burnt; most likely plugged into the bottom of the duplex.
Was there dampness in the outlet box?
There was and is a lot of bad aluminum wiring, but aluminum wiring did not create that significant green oxide.
???????
zz.

 

[BlueFox]

Was it the outlet, or the aluminum wiring that is the primary suspect here? When I got out of the Navy in 73 I took a job as an electrician's assistant. At that time, in VA Beach they were using aluminum wiring, and I was constantly being told to make sure I was really making a tight, secure connection between the wire and outlet. Even then it appears the fire hazard with aluminum wiring was known.

Is that a Python CX cable? I have two of them with the 20 amp connectors for my HT amps!

Edit: Was I wrong there. The CX cable is wrapped in blue. I don't know why I thought red. I hope getting power cable colors mixed up isn't a warning sign of onset dementia.

 

[CGabriel]

Was it the outlet, or the aluminum wiring that is the primary suspect here? When I got out of the Navy in 73 I took a job as an electrician's assistant. At that time, in VA Beach they were using aluminum wiring, and I was constantly being told to make sure I was really making a tight, secure connection between the wire and outlet. Even then it appears the fire hazard with aluminum wiring was known.

Is that a Python CX cable? I have two of them with the 20 amp connectors for my HT amps!

The electrical inspector is correct in his assessment. The primary culprit is the unfortunate mixture of dissimilar metals. However, there are other complicating factors including the use of solid core wire against two flat contact clamps.

The operative principle is galvanic potential between two dissimilar metals and a consequential result of galvanic corrosion. There is no need for a direct immersion of water. Just the presence of natural moisture in the air and of pollutants, primarily sulfer compounds, is sufficient to cause the chemical reaction. Copper and aluminum are 7 points apart in the galvanic chart and are quite incompatible. Even brass, which is what most electrical contacts are made from, is a copper alloy. In this case, a user unknowingly used what he thought would be a great "audiophile" outlet. This particular outlet has a copper plating over the brass contacts. Perhaps a nice idea but definitely not when used in direct contact with aluminum wire. With low contact area and expansion contraction that Amir mentioned created the ideal situation for disaster. The resulting aluminum oxide, which is an insulator, created the equivalent of a miniature heater inside the outlet.

Sometimes our audiophile desire for performance needs to be tempered with solid metallurgical and materials science knowledge. In any case, even if there was not the use of aluminum wire, I still recommend you get a good outlet. Copper oxide and carbon is not a particularly good conductor either. And these are quite common in cheap outlets with push to connect contacts and contact areas that are like the edges of a razor.

 

[GaryProtein]

That outlet could have properly been used with solid wire. The wire was placed incorrectly in this case.

The wires should just have been placed on the other side of the plate, wrapped around the screw under the screw head.

 

[FrantzM]

Justa question : if an outlet get to be warm or hot isn't it the sign of something wrong ?

 

[CGabriel]

That outlet could have properly been used with solid wire. The wire was placed incorrectly in this case.

The wires should just have been placed on the other side of the plate, wrapped around the screw under the screw head.

I already mentioned that but that does not make aluminum wire safe with copper junctions which is a well known fact in the electrical trade.

 

[CGabriel]

I would say so, to a point. Warm is an indication of not enough metal to metal contact, but it shows resistance of course, which we are trying to minimize, as noted above in winding the wire around the screw to increase contact area and reduce resistance. Very good point. I have some dimmers that get warm, but its due to the electronics in them, not the wire contact.

All wire and electrical contacts (connectors) heat up when there is current flow. The issue is how much current can a certain size conductor carry before the heat melts the insulation. In the USA the NEC defines the size of wire and insulation types that can be used for specific applications. The primary reason the code was created was to decrease the possibility of fire. Even with good local electrical building codes and practices, one of the most common causes of home fire are electrical faults. Think about it - the power grid supplies almost unlimited levels of current which is entirely dependent upon the draw of the load device. In a short circuit condition the contacts and wire can be vaporized. This is the purpose of the circuit breakers to limit maximum current draw to a safe level.

I like the Hubbell 5362 outlet because it has much larger contacts and the method of clamping the wire is superior. Also the body of the connector is larger with more internal airflow to cool the contacts. Even with large gauge wire and good outlets, there is significant heating of the wire and outlet contacts in a typical circuit powering a home entertainment system that is pulling 10-15 amps of current.

 

[amirm]

In a short circuit condition the contacts and wire can be vaporized. This is the purpose of the circuit breakers to limit maximum current draw to a safe level.

Indeed. I was putting in a number of light fixtures in my workshop garage. I hooked one up and figured I test it. So I flip the circuit break and happily see the fixture light up. It was end of the day and I was tired and forgot to flip the breaker off! I go and cut the rest of the romex wire with my linesman electrical plier and of course there was a massive spark. I looked and the cutting jaws of the pliers had simply vaporized! We are talking thick metal plates and big chunk of the steel gone. The breaker simply could not respond fast enough or else it did not require more current to vaporize the metal than the breaker.

When we built our new house, I put in a rule for the electrician to put in 20 amp commercial rated outlets and 12 gauge wire in the entire house. He was surprised as the norm is 15 amp/14 gauge. My answer was simple. The cost differential was negligible in grand scheme of things so why not have proper amount of power available. Fast forward to a few weeks ago when I had two 1,000 watt electric dehydrators running out of the same outlet concurrently. I touched the outlet and it was nice and cool. The thin wire from the dehydrators were pretty warm but not the outlet.

The electrician said his guys didn't like 12 gauge wire because it is stiffer to pull than 14. Hence the reason they opt for that.

At our primary house built to building specs, our kitchen outlet can get quite warm powering just the rice cooker. I looked at its contacts once and boy had it suffered. Reminds me to go and replace it soon .

 

[Don Hills]

That outlet could have properly been used with solid wire. The wire was placed incorrectly in this case.

The wires should just have been placed on the other side of the plate, wrapped around the screw under the screw head.

This is incorrect. Aluminium wire must never be connected to a Cu-only outlet. Even putting it under the screw head will eventually fail, because aluminium cold flows over time and the connection will loosen(*). Various outlet designs for aluminium wire have been produced over the years but none have proved satisfactory in the long term. The current best practice (short of rewiring the building) is to terminate each aluminium wire with a copper pigtail, using a COPALUM or Alumiconn connector.

(*) For the same reason, never tin (solder) wires to be terminated in screw terminals. The solder cold flows and the connection loosens.

 

[Kal Rubinson]

That outlet could have properly been used with solid wire. The wire was placed incorrectly in this case.

The wires should just have been placed on the other side of the plate, wrapped around the screw under the screw head.

Amen. My electrician is amused by the "fancy" wires I have given him for various purposes but he insisted that solid wires need a solid wrap around the screw for proper contact. Compression connections are OK for stranded wire.

 

[Revel Salon 2]