# High resistance readings on MI cable



## AllWIRES (Apr 10, 2014)

WronGun said:


> Megging out Mineral Insulated cable runs me getting high resistance on a few circuits.. Aside from a short circuit and damaged cable what else would cause this ? I walked the whole run and it all looks good, factory tested cable.


Sounds like a small leak somewhere. Especially if you're megging out similar runs and your get higher numbers.

If the insulation is squeezed to much somewhere it might not look damaged but it. Other than that I can't help much. I don't have much experience with MI besides looking at installed.


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## Bad Electrician (May 20, 2014)

WronGun said:


> Megging out Mineral Insulated cable runs me getting high resistance on a few circuits.. Aside from a short circuit and damaged cable what else would cause this ? I walked the whole run and it all looks good, factory tested cable.


Are you talking about from the copper jacket to the conductor?

You want high resistance readings.

IF you have low readings, the most likely culprit is moisture absorption close to the exposed ends. You heat the ends up, as I remember it substantially like with a torch for 8"-12" back from the ends Megger it and install it, assuming the readings improve..


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## WronGun (Oct 18, 2013)

Bad Electrician said:


> Are you talking about from the copper jacket to the conductor? You want high resistance readings. IF you have low readings, the most likely culprit is moisture absorption close to the exposed ends. You heat the ends up, as I remember it substantially like with a torch for 8"-12" back from the ends Megger it and install it, assuming the readings improve..


My mistake I will edit that .... Yes getting low readings on a few and OL (infinity) on most. I will be torching tomorrow trying to eliminate possible moisture.


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## Bad Electrician (May 20, 2014)

WronGun said:


> My mistake I will edit that .... Yes getting low readings on a few and OL (infinity) on most. I will be torching tomorrow trying to eliminate possible moisture.


Every case where I had low readings the heat fixed it, I had a commercial heat gun when I did it, but have know electricians that did the torch.


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## bobbarker (Aug 6, 2015)

As has been stated use a blow torch to get condensation out. You will only have to torch about the last 3 feet of the wire and NEVER cut off the taped ends until ready to install and when they are cut off make sure to tape them back up to keep moisture until you are ready to terminate them


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## AllWIRES (Apr 10, 2014)

WronGun said:


> My mistake I will edit that .... Yes getting low readings on a few and OL (infinity) on most. I will be torching tomorrow trying to eliminate possible moisture.


I knew what you meant 👍🏻


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## cagresham85 (Apr 28, 2016)

I have never used the stuff but it is wired to a transformer or motor? Those will throw off megger readings.


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## WronGun (Oct 18, 2013)

cagresham85 said:


> I have never used the stuff but it is wired to a transformer or motor? Those will throw off megger readings.


It's not terminated yet at either end.. After torching all reading came back OL


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## Bad Electrician (May 20, 2014)

cagresham85 said:


> I have never used the stuff but it is wired to a transformer or motor? Those will throw off megger readings.


 With MI Cable you should always Megger it when you unload it off the truck, and reseal the ends, Megger it when installed and reseal the ends, then Megger it at time of installation


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## cabletie (Feb 12, 2011)

Bad Electrician said:


> With MI Cable you should always Megger it when you unload it off the truck, and reseal the ends, Megger it when installed and reseal the ends, then Megger it at time of installation


I was going to say the same thing when I saw someone else say that you should not open up the ends until it is terminated. You have to open the ends to test like Bad electrician stated.

The stuff is horrible to work with as it is. But after a fire, the insulation is supposed to harden, making it impossible to bend. I don't know what temperature that happens at. I would be careful heating it up to much to chase out the moisture if it hasn't been terminated yet.

Pulling long runs in absolutely sucks. If I didn't get fired for pulling one in damaged or damaging it myself, I would probably quit before replacing it!


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## Southeast Power (Jan 18, 2009)

Bad Electrician said:


> With MI Cable you should always Megger it when you unload it off the truck, and reseal the ends, Megger it when installed and reseal the ends, then Megger it at time of installation


Brian,
Do you cut the outer jacket back to meg the conductor or is there a better way to get on it without cutting into it?


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