What is this substance in an old motor lead tape job?

[alblock]

Took a 40hp motor off today and inside the tape, surrounding the copper compression lugs, was a white substance. It is hard, dry, and turns to powder when pressed.


Thanks

 

[Little Bill]

Looks like they used what they thought would be an anti-oxident that went in reverse!

 

[sameguy]

Mastic tape? Plymouth, 3m, being very old it oiled be asbestos containing so be careful.

 

[Craigv]

Mastic tape? Plymouth, 3m, being very old it oiled be asbestos containing so be careful.

Agreed, that looks to me like asbestos tape wrapped with vinyl tape. Mask up, don't tear it apart...the safest thing would be to cut off the leads with the tape intact. Bag it and dispose.

 

[gadfly56]

You appear to have MI cable there. It's likely magnesium oxide. It looks like they tried to Rube Goldberg the terminations instead of using the proper termination kit(s).

 

[GoldDigger]

You appear to have MI cable there. It's likely magnesium oxide. It looks like they tried to Rube Goldberg the terminations instead of using the proper termination kit(s).

And dangerous as all get out electrically, even though not toxic.

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[alblock]

Could the white substance be asbestos?

 

[gadfly56]

Could the white substance be asbestos?

It could be feta cheese for all we know. You can't tell without testing, which involves an industrial hygienist checking it under a microscope. Because it is chemically inert, there are no chemical tests for asbestos. If the material is magnesium oxide it will be soluble in ammonia. Asbestos is a silicate mineral characterized by long crystals composed of much small "hairs". It's toxicity is related strictly to its morphology, with the fibers physically irritating the lung tissue and leading to scaring which reduces lung function. It is also linked to mesothelioma which can be cancerous or non-cancerous, The cancerous form is very aggressive and almost uniformly fatal.

 

[Tony S]

If it’s MI I would have expected it to have gone bang after loosing that amount of insulation.

 

[FionaZuppa]

looks like sacrificial corrosion between the copper and something. is that area always damp?

 

[Besoeker]

It could be feta cheese for all we know. You can't tell without testing, which involves an industrial hygienist checking it under a microscope. Because it is chemically inert, there are no chemical tests for asbestos. If the material is magnesium oxide it will be soluble in ammonia. Asbestos is a silicate mineral characterized by long crystals composed of much small "hairs". It's toxicity is related strictly to its morphology, with the fibers physically irritating the lung tissue and leading to scaring which reduces lung function. It is also linked to mesothelioma which can be cancerous or non-cancerous, The cancerous form is very aggressive and almost uniformly fatal.

I wouldn't touch it with a 10 foot barge pole.

 

[alblock]

looks like sacrificial corrosion between the copper and something. is that area always damp?

Yes, the whole motor terminal box was rusted bad.

I wouldn't touch it with a 10 foot barge pole.

Too late now, at least i know to be more cautious in the future. I've read up on asbestos, what products may contain it, and the health effects from exposure.

 

[Jraef]

You appear to have MI cable there. It's likely magnesium oxide. It looks like they tried to Rube Goldberg the terminations instead of using the proper termination kit(s).

I agree, that’s MI cable and the terminations were done incorrectly; the magnesium oxide was not sealed to prevent moisture and it has reacted to it, making it extremely risky to continue using like that. Terminating MI wire is a complicated process to do it right, taking up to 30 minutes per termination. Someone paid extra money to use MI cable, often that is only done for things that must resist heat and fire, like fire pumps, or for nuclear applications. I’d think that given the lack of attention and/or knowledge about the special termination/sealing process, this reasoning no longer exists. But with that wire has been contaminated, you can’t re-use it now unless you cut it all the way back to good solid MgO filler and depending on how long it has been exposed to moisture it may be as much as 15 ft.

By the way, here is the MSDS in MgO, it’s not that bad really.
http://www.inchem.org/documents/icsc/icsc/eics0504.htm

 

[Cow]

The only time I see that white chalk, is when aluminum has corroded, generally in direct buried wire that has went bad.

Are you sure there wasn't aluminum inside those taped splices?

 

[Jraef]

This is what Mineral Insulated cable looks like new (although the one in this photo has a stainless steel outer sheath over the copper for corrosion resistance). The white substance in the core is the magnesium oxide.


Termination process:

 

[winnie]

IMHO that is not MI cable. The insulation color looks sort of copper-ish, so it _might_ be MI cable, but it seems to me in the photo that you can sort of see the stranded wire through the translucent insulation.

This is motor lead wire, so I am guessing that it is some sort of nickel coated copper cable with a silicone insulation.

The OP can tell us if the outside of the wire was copper or some sort of polymer.

-Jon

 

[GoldDigger]

Looking at the photo of the end of the cable and looking at the untaped conductors I also have doubts about MI. First, the center conductor does appear to be stranded. Second, the bends appear far too tight to be a metal sheath.
Maybe copper oxide corrosion? Copper sulfate would be blue.

If is really is MI, I have three comments:
1. If the tape job was not a hermetic seal or if you left the ends untaped for too long, the insulation resistance of a length between several feet and the entire cable has been compromised. As long as the sheath was grounded and there was no GF detection on the circuit, that might never cause symptoms.
2. Far more important, since the powder is all that was keeping the conductor centered and insulated from the sheath, you are far too close to causing a ground fault/short circuit if you try to do anything with the existing ends. Too much powder has been lost.
3. Find out why MI was used in the first place (fire pump motor?) and either replace with new MI or with another wiring method.

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[gadfly56]

Looking at the photo of the end of the cable and looking at the untaped conductors I also have doubts about MI. First, the center conductor does appear to be stranded. Second, the bends appear far too tight to be a metal sheath.
Maybe copper oxide corrosion? Copper sulfate would be blue.

If is really is MI, I have three comments:
1. If the tape job was not a hermetic seal or if you left the ends untaped for too long, the insulation resistance of a length between several feet and the entire cable has been compromised. As long as the sheath was grounded and there was no GF detection on the circuit, that might never cause symptoms.
2. Far more important, since the powder is all that was keeping the conductor centered and insulated from the sheath, you are far too close to causing a ground fault/short circuit if you try to do anything with the existing ends. Too much powder has been lost.
3. Find out why MI was used in the first place (fire pump motor?) and either replace with new MI or with another wiring method.

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I agree that there seems to be an anomaly with regard to the stranded center conductor. I don't know if MI was ever made with stranded conductors. The outer sheath very definitely appears to be copper. Is there another cable type out there with a copper outer sheath?

 

[GoldDigger]

Now that several suggestions have been made, the OP should be able to quickly resolve our doubts.

 

[alblock]

The only time I see that white chalk, is when aluminum has corroded, generally in direct buried wire that has went bad.

Are you sure there wasn't aluminum inside those taped splices?

Yes i remember thinking that powder may DE-OX but all connectors were copper.

This is what Mineral Insulated cable looks like new (although the one in this photo has a stainless steel outer sheath over the copper for corrosion resistance). The white substance in the core is the magnesium oxide.
View attachment 21086

Termination process:

Watching the video this cable doesn't appear to flex easily, the motor leads were very flexible.

IMHO that is not MI cable. The insulation color looks sort of copper-ish, so it _might_ be MI cable, but it seems to me in the photo that you can sort of see the stranded wire through the translucent insulation.

This is motor lead wire, so I am guessing that it is some sort of nickel coated copper cable with a silicone insulation.

The OP can tell us if the outside of the wire was copper or some sort of polymer.

-Jon

It was was copper. The insulation had a very translucent appearance to it. I think the copper color was from the rust.