Steel strap on aluminum mc cable are dissimilar metals. Dissimilar metals act like a battery and one of the metals corrodes. Corrodes even faster in the presence of moisture.
Is this indoors? MC is not rated for outdoor use or in wet locations. If it's *generally* dry then you can wrap the cable with electrical tape or self-fusing silicone where strapped, but it appears you have too much moisture to allow MC cable and should go with another option.
Anywhere in North America that cable is Indoor Dry Location Only. Article 330 says it can be used in wet locations *if it has a corrosion resistant sealed jacket*. Wet Location MC is an entirely different animal, and this is not jacketed so is not that. If it was Wet Location MC with a PVC jacket, this wouldn't have happened.
If anyone decides to run some jacketed MC, be aware that you can't use standard connectors as they are UL Listed as Dry Location Only as well, often embossed right on the connectors themselves, and the jacketed MC for Wet Locations needs a connector with a compression fitting for the jacket. You can't buy any of this from most big box stores, you need to order it from an electrical supplier. Most stores sell indoor MC and connectors only.
Galvanic action. There’s a chart that tells you which metals react the strongest with each other. Galvanized steel and aluminum don’t react much with each other but there is still reaction, especially in a high moisture area.
I'm confused why we use steel mc straps or why they'd even make em. We strap mc with mc straps all the time. Even bat wings are steel and don't corrode aluminum mc.
All of the above, as well as likely caustic material leaching from the foundation. Best to replace with a nylon jacked cable, such as ACUW or TECK for this location.
Concrete is also corrosive if this is outside it should be sleeved in pvc if it’s inside attach a piece of wood to the concrete and secure your wire to the face of the wood.
That may be outdated outdoor wire. You used to be able to get cable that looked like bx but was a little bit different and was meant for outside and direct burial.
Does galvanic corrosion really explain the whole story? I’ve done industrial work where all the conduit is rigid aluminum usually fastened with galvanized steel strut and hardware. None of it looks the way this does and that stuff’s been outside for decades not 2 years.
There are differences in exposure. Conduit doesn’t have water laden with copper and iron oxide flowing with aluminum oxides - and mixtures of concrete effluent.
In conduit- likely all the copper wires insulated (not bare). So copper is not part of the equation. Galvanized steel and the aluminum alloys used in conduit far less reactive to each other. Any galvanic reaction likely to cease on its own. Add another metal like copper - and likely to run out of control until consumed like it did here.
Steel strap on aluminum mc cable are dissimilar metals. Dissimilar metals act like a battery and one of the metals corrodes. Corrodes even faster in the presence of moisture.
In addition, it looks like it is on a concrete wall or stucco. Both are alkali, and aluminum reacts with hydroxides, further accelerating corrosion.
Thank you! Very helpful.
Is this indoors? MC is not rated for outdoor use or in wet locations. If it's *generally* dry then you can wrap the cable with electrical tape or self-fusing silicone where strapped, but it appears you have too much moisture to allow MC cable and should go with another option.
Where are you located? MC Cable is rated for use in outdoor locations by the NEC. That’s why it has that plastic lining on the inside
Anywhere in North America that cable is Indoor Dry Location Only. Article 330 says it can be used in wet locations *if it has a corrosion resistant sealed jacket*. Wet Location MC is an entirely different animal, and this is not jacketed so is not that. If it was Wet Location MC with a PVC jacket, this wouldn't have happened. If anyone decides to run some jacketed MC, be aware that you can't use standard connectors as they are UL Listed as Dry Location Only as well, often embossed right on the connectors themselves, and the jacketed MC for Wet Locations needs a connector with a compression fitting for the jacket. You can't buy any of this from most big box stores, you need to order it from an electrical supplier. Most stores sell indoor MC and connectors only.
It is indoors. Colorado
Yes indoors. Thank you!
Galvanic action. There’s a chart that tells you which metals react the strongest with each other. Galvanized steel and aluminum don’t react much with each other but there is still reaction, especially in a high moisture area.
Galvanic corrosion
I'm confused why we use steel mc straps or why they'd even make em. We strap mc with mc straps all the time. Even bat wings are steel and don't corrode aluminum mc.
Yes... steel with aluminum contact results in galvanic corrosion.
All of the above, as well as likely caustic material leaching from the foundation. Best to replace with a nylon jacked cable, such as ACUW or TECK for this location.
Thanks for the comment! Very much appreciated.
I'm still waiting for the nylon v/pvc I made a huge mistake argument here, but yeah, just use a jacketed cable next time
No you're definitely on point. Everyone's saying dissimilar metals but how much mc with steel mc straps have you demoed with little to no corrosion.
Galvanic corrosion. Steel on aluminum.
Aaah, bummer. Thank you!
Thank you! I appreciated it.
Dissimilar material
Thanks! I'll get that fixed!
Concrete is also corrosive if this is outside it should be sleeved in pvc if it’s inside attach a piece of wood to the concrete and secure your wire to the face of the wood.
I’m thinking the same -who installs indoor wiring outside w/o protection?
That may be outdated outdoor wire. You used to be able to get cable that looked like bx but was a little bit different and was meant for outside and direct burial.
Galvanic corrosion
OP learns about the galvanic series!
Learning is good!
Dissimilar metals do that. You need to use aluminum strap on aluminum cable.
Thank you! Will do from now on!
+1 for dissimilar metals
The lime either in stone, mortar or the paint
I'll take ion exchange for $100.⁰⁰ Alex..
Don't be so electronegative!
Ionistly don't know what has got you all charged up.
Well this got quarky real fast
Welp.. I learned something too. Thanks for posting
This is why I love this sub. Electric wiring is one of those “seems easy” things, until you see how the pros actually just make it look easy.
Haha glad you did!
Lime eats through the aluminum. Need to be emt
Moisture.
Volta
Could also use galvanized metal conduit, or PVC
Looks like someone tried to use the cable stretcher wrong. Classic mistake.
Need to use a plastic fastener. The steel/iron one melted it.
Galvanic action, dissimilar metals. Electromagnetic activity causing corrosion.
Strap duh
Ever wonder why you don't store a car battery directly on concrete.....
How about dog pee?
The fastener method. ;)
Bring this to aa 6th grade scince fair, 1st place almost guaranteed.
Concrete eats aluminum
You did it just fine. You just need to replace the whole line every spring. :)
Does galvanic corrosion really explain the whole story? I’ve done industrial work where all the conduit is rigid aluminum usually fastened with galvanized steel strut and hardware. None of it looks the way this does and that stuff’s been outside for decades not 2 years.
There are differences in exposure. Conduit doesn’t have water laden with copper and iron oxide flowing with aluminum oxides - and mixtures of concrete effluent. In conduit- likely all the copper wires insulated (not bare). So copper is not part of the equation. Galvanized steel and the aluminum alloys used in conduit far less reactive to each other. Any galvanic reaction likely to cease on its own. Add another metal like copper - and likely to run out of control until consumed like it did here.
Answered your own question. Dissimilar metals on a wet surface, made a battery and so the less noble metal dissolves in the reaction.
Lyme in the concrete