Burnt Polaris tap

[electro7]

Was wondering if anybody had any thoughts on what happened in the photo attached.

This tap was made in a NEMA 3R enclosure mounted on a groundmount array with Enphase microinverters. It was from one phase of a 9 panel circuit. No evidence of any ground fault occurred in the box. They did get high snow levels but there didn't seem to be any water damage in the box.

I am starting to wonder about the polaris taps since I've seen this before with them.

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[rambojoe]

For starters, following the instructions on the correct amount of insulation to remove could have prevented this.
The conductors could have been close enough to be arcing.

 

[electro7]

That wire you see is from the melting that happened. They weren't stripped that far back.

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[wwhitney]

Are you certain the installer torqued the connection properly? Because the above looks like a high resistance connection causing excess heat, and mistorquing the connection would be the most likely way for that to happen.

Cheers, Wayne

 

[electro7]

I was wondering about that. I am almost certain the installer didn't under torque them, but I was wondering about over-torque. Terminations can be over-torqued, correct? If so, what happens if they are over-torqued?

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[Tulsa Electrician]

Maybe an over load. To much heat at the tap.

 

[ptonsparky]

Over torqued would be an issue, especially with a smaller conductor.

 

[wwhitney]

Over torqued would be an issue, especially with a smaller conductor.

Can you explain the failure mode, and whether you could tell by looking at the conductor after removing it from the burnt up Polaris connector?

Thanks,
Wayne

 

[ptonsparky]

You can see where they are compressed to the point of being severed.

 

[electro7]

Overload can't be it with 9 panels, less than16 amps.

I am unable to get the conductor out because the screw head is burnt to a crisp.

Can somebody explain what happens to the current and/or voltage when a termination is over-torqued? I suspect that's what the problem was.

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[ptonsparky]

Reducing the size of the conductor will increase the resistance, which increases the heat. Increased heat increases the resistance, leading to a downward spiral.
VD across the connection would go up.

 

[wwhitney]

Can somebody explain what happens to the current and/or voltage when a termination is over-torqued? I suspect that's what the problem was.

The mechanism in the extreme case is pretty clear: if the screw and lug are harder than the copper, then if you tighten it enough, you will shear all the strands and have no firm connection. Stop a bit earlier, and only some of the strands are sheared, giving you have a connection of reduced area, which Tom expounded on.

The mechanism is a less extreme case is not as clear to me: say you flatten some of the strands and deform them, without any significant change in cross-sectional area. Is that still a problem? Will the copper strands "relax" after being plastically deformed (or possibly after some thermal cycles), so that they may not all be in firm contact with each other and the lug?

Cheers, Wayne

 

[synchro]

If the Polaris connector is made of aluminum with a thin plating, perhaps the whitish material shown could be aluminum hydroxide from corrosion that occurred. Moisture could enable electrolytic corrosion of aluminum in contact with copper. I believe Polaris connectors already have some corrosion inhibitor applied, but in the situation described maybe some extra Noalox could help. If this was the only connector where this occurred, maybe it had little or no corrosion inhibitor when new.

 

[electro7]

Got it. That makes sense. I guess torque wrench for all terminations!

When I was coming up through my apprenticeship in the early 2000s, it was hand tight, then wiggle the stranded wire, and give it a little more tightening. Finding more and more these days, torque is a bigger deal than I was initially trained on.

I can totally see the last post oxidation issue as well. Will keep that in mind.

Thanks, guys!

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[ptonsparky]

Corrosion with those lugs is an issue. Arrange to drain. Make sure they are not the low point.

 

[Tulsa Electrician]

Overload can't be it with 9 panels, less than16 amps.

I am unable to get the conductor out because the screw head is burnt to a crisp.

Can somebody explain what happens to the current and/or voltage when a termination is over-torqued? I suspect that's what the problem was.

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Thanks.

 

[ramsy]

If the Polaris connector is made of aluminum with a thin plating, perhaps the whitish material shown could be aluminum hydroxide from corrosion that occurred. Moisture could enable electrolytic corrosion of aluminum in contact with copper.

In the 1980's I saw lots of aluminum oxide on military aircraft fittings, cable straps & connectors.

At mach speeds the paint flaked off, and aluminum reacted with moisture, disintegrating equipment into a white powder. No power-plant current on bonded parts was necessary, just galvanic-chemical action.

Aerospace time-compliance technical orders (TCTO) were engineered maintenance schedules on the order of 30, 60, & 90 days, which addressed this corrosion. Unlike the comparable NEC 110.12(B), which can be completely ignored after construction, leading to exposure to the elements 20-50yrs without so much as a single oxidation cleaning or maintenance service.

The counterfeit industry of fake NRTL labels, and parts sourced from Amazon.com, may also overwhelm the poorly enforced requirements of NEC 110.3(C). Buyers & installers of Polaris lugs are less likely to recognize required listings, labels, much less a blatant forgery of pot metal, or empty circuit breakers with nothing but springs.

From missing labels to counterfeit parts we live in a world that deals it; along with the Boeing 737Max and CEO's that leverage projected-casualty litigation against unreliable systems for profit, the corporate vale shields against safety & design negligence on the factory floor.

The enforcement of NRTL listing & labeling, much less insurance claims --dependent on inspections & building-codes-- relies upon a significant consumer demand for contractors that avoid permits or undesirable-government leverage.

Ignoramus contractors are not likely to check for fakes, Polaris, breakers, or otherwise, much less recognize it starring them in the face, but that's the reality of demand for business transactions free from regulatory leverage with possible tax assessment.

 

[ppsh]

Are these steel set screws in the connector? Have only seen these burn up in the 14-4 awg sizes.

 

[electro7]

Are these steel set screws in the connector? Have only seen these burn up in the 14-4 awg sizes.

I'm not sure what metal it is, but it does have the set screws

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[electro7]

In the 1980's I saw lots of aluminum oxide on military aircraft fittings, cable straps & connectors.

At mach speeds the paint flaked off, and aluminum reacted with moisture, disintegrating equipment into a white powder. No power-plant current on bonded parts was necessary, just galvanic-chemical action.

Aerospace time-compliance technical orders (TCTO) were engineered maintenance schedules on the order of 30, 60, & 90 days, which addressed this corrosion. Unlike the comparable NEC 110.12(B), which can be completely ignored after construction, leading to exposure to the elements 20-50yrs without so much as a single oxidation cleaning or maintenance service.

The counterfeit industry of fake NRTL labels, and parts sourced from Amazon.com, may also overwhelm the poorly enforced requirements of NEC 110.3(C). Buyers & installers of Polaris lugs are less likely to recognize required listings, labels, much less a blatant forgery of pot metal, or empty circuit breakers with nothing but springs.

From missing labels to counterfeit parts we live in a world that deals it; along with the Boeing 737Max and CEO's that leverage projected-casualty litigation against unreliable systems for profit, the corporate vale shields against safety & design negligence on the factory floor.

The enforcement of NRTL listing & labeling, much less insurance claims --dependent on inspections & building-codes-- relies upon a significant consumer demand for contractors that avoid permits or undesirable-government leverage.

Ignoramus contractors are not likely to check for fakes, Polaris, breakers, or otherwise, much less recognize it starring them in the face, but that's the reality of demand for business transactions free from regulatory leverage with possible tax assessment.

Thanks for the info.

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