- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Usually, humidity in the air which slightly condenses on hot surfaces as they cool.
Panelboard wire strapping code requirements.
- Thread starter Pinnie
- Start date
Plastic wire insulation and parts when they get a little too hot start releasing hydrogen chloride (HCl). Hydrogen chloride is a corrosive gas that when mixed with water vapor forms hydrochloric acid which condenses on and is wicked up by aluminum wire that is not greased with noalox.
there seem to be conflicting ideas in this thread. On one hand it’s no issue when two dissimilar metals touch. On the other when exposed to excessive heat plastic parts release gas which combines with water to make an electrolyte which corrodes the wire. I know we make alloy lugs as well which helps. When did it become a non issue. Was it advances in metallurgy?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
I would say there may be corrosion for different reasons. Not all corrosion is galvanic due to dissimilar metals.
Fred B
Senior Member
- Location
- Upstate, NY
- Occupation
- Electrician
Not sure where the debate is coming from, as whenever AL and CU conductors are used together the means to interconnect must be identified and rated to make such a connection. Seen particularly for one with receptacles and switches, if using AL, the receptacle or switch must be identified for use with AL. 406.3(C), 404.14(C)
Also restrictions for splicing of AL and CU are found in 110.14:
"Because of different characteristics of dissimilar metals, devices such as pressure terminal or pressure splicing connectors and soldering lugs shall be identified for the material of the conductor and shall be properly installed and used. Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors unless the device is identified for the purpose and conditions of use......"
OP original picture would show a loosely spliced AL/CU even though the intent was not likely to make a splice, when the person made a wrap of a copper wire around the bundle of both the copper and the aluminum conductors.
Also restrictions for splicing of AL and CU are found in 110.14:
"Because of different characteristics of dissimilar metals, devices such as pressure terminal or pressure splicing connectors and soldering lugs shall be identified for the material of the conductor and shall be properly installed and used. Conductors of dissimilar metals shall not be intermixed in a terminal or splicing connector where physical contact occurs between dissimilar conductors unless the device is identified for the purpose and conditions of use......"
OP original picture would show a loosely spliced AL/CU even though the intent was not likely to make a splice, when the person made a wrap of a copper wire around the bundle of both the copper and the aluminum conductors.
So is issue the code is addressing how dissimilar metals interact with the terminals/lugs? Or just each other? the danger being fault connection/ failed connection (could be ems equipments on the loads).
- Location
- New Jersey
- Occupation
- Journeyman Electrician
The issue is at the terminals. Bare aluminum conductors are run inside of panel enclosures all of the time where they contact bare cooper conductors and the metal enclosure itself without issue. Bare copper conductors get attached directly to bare metal without issue. With a terminal you want to ensure that the listing of that terminal is for the type of conductor being installed in it so that corrosion does not impede the connection of the conductor to the terminal.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
This is typically done by simply tin plating the aluminum terminal parts. The problem is the non-conductivity of aluminum oxide and the difference in expansion. In general properly terminated equipment lugs have not been problematic since the 70s.
Wiring device terminals are a different matter, but their problem is usually cold flow resulting in a poor connections.
We wired a senior living development with about four planned home/townhome styles, about 24 got a EV pre wire upgrade (50A receptacle). Just over half of them got 6AL cable, the others for whatever reason got #6 copper (NM).
I forget how many but there were enough issues with the chargers and the receptacles our company was worried about a lawsuit, the senior center had sued the roofer and the plumber over other stuff.
All of the problems were with receptacles wired with aluminum cable, we sent the receptacles back to the manufacturer.
About a year later the manufacturer said the issue was with the aluminum terminations, their new heavy duty EV receptacles now have silently dropped support for aluminum cable.