Noalox on copper to copper connections 2

[bartb102]

We've had trouble with overheating on connections to an 85A contactor. Not sure if lug was improperly tighteded at installation or it just loosened from thermal cycling, or we may be pushing the IEC contactor too far, overheating the contact that then overheated the wire. Burned off the wire & destroyed the contactor.

I know Noalox must be used on any aluminum connection. Can it be used on a copper-copper connection to improve the conductivity? Are there any compounds formulated for copper connections?

Thanks

 

[MacGyverS2000]

How would Noalox prevent loosening of the lug (which appears to be your major problem)?

Dan - Owner

http://www.Hi-TecDesigns.com

 

[bartb102]

It will help only if it results in lower peak temperatures to reduce thermal cycling. This is in a hydro plant, so there is a probabilty of moisture causing corrosion to increase connection resistance. Contactor had been in service for 4 years or so. A few weeks before the failure the load had been increased, but was still withing the 85A motor rating, well be low the thermal rating. Load is a 3phase SCR DC power supply used to furnish field excitation to a synchronous generator.

 

[ScottyUK]

How good is the ventilation? I can think of a few AVR panels which run at fairly high ambient temperatures. A marginally rated contactor in a high ambient is asking for trouble. Check the ambient temperature at which the contactor is rated. If there are other components adjacent to or otherwise impeding free air movement then that will be cause for a de-rate too. Nameplate ratings on some IEC contactors are, in my opinion, the maximum attainable in perfect conditions, which just don't seem to exist in the real world. Some brands are better than others: I usually choose a type from Siemens or ABB, and over-size it by 20% or so. Reliability improves noticeably.

Another thought: is this on the input of the rectifier, or the output? AC-rated contactors on DC duty tend to have a short and tortured life, especially switching a highly inductive load such as a generator field winding. If this is the case then consider one of the bar & shaft contactors for severe DC switching. ABB's R-Line is one of the more reasonably priced ranges, although none are 'cheap'.


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If we learn from our mistakes I'm getting a great education!

 

[jraef]

Describe your conductors and termination methods.

5 will get you 10 that you used DLO or "Welding Cable" or some other sort of extra flexible finely stranded conductor and the standard termination clamps that came with the contactor.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[bartb102]

Thanks for the input. Comments on your suggestions.

Ambient may be part of the problem, but there are 3 4" fans blowing air through the enclosure. However, the external ambient can be quite warm too. I'll put a sensor in one of the units, (there are 10 of them), check it out.

Connections were made with THHN, not motor lead wire. Contactor includes its own clamping terminals.

Contactor is on input to the power supply. Power supply has a quenching diode to absorbe reverse transients.

 

[waross]

I often use No-Alox or Penetrox to both lubricate problem joints on copper and to exclude air. I sometimes use No-Alox on the threads of the connectors. I run the set screw in and out all the way before entering the conductor to spread the compound through the threads. On aluminum alloy connectors I use No-Alox 98% of the time. The exceptions are unexpected repairs a long way from home where No-Alox is not readily available.
Experience and workman-ship may be more important than many realize. An experienced electrician will flex or roll the cable as it is being tightened. If the conductor is entered and the lug tightened on it with-out using a rolling motion, a slight twist will cause the cable strands to untwist and become loose.
I have asked green electricians to tighten a set screw lug as tight as they were physically able on 7 strand #2 AWG cable (Possibly the worst size and stranding.) Then I give the cable a slight twist and it will come loose, often dropping out of the lug by gravity. I have cleaned up the damage from a lot of loose connections over the years. At 85 Amps you are in the sweet spot for possible workmanship issues.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[desertfox]

Hi bartb102

I would just like to ask about the joint that failed? when the lug was tightened was it to a torque and was any lubricant used?
The reason I ask is if the joint was made dry and you now use Noalox, it may cause the joint to be over tightened if the Noalox comes into contact with the bolt threads as it will reduce the friction factor for the same given torque, should this occur the joint might well fail again in the near future.

desertfox

 

[Skogsgurra]

Very good to know, Bill. Albeit somewhat late in my career..

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[bartb102]

Hmm, never thought of the twisting issue. I'll talk to our installers about it.

 

[KF7RCE]

Over my 50 years as an engineer and as a journeyman electrician, I have become so very impressed with the long term stbility of NOOX treated copper and aluminun connections, I will never install a "dry" connection again. Like Waross, I always treat the threads as well.

By the way, I have compared notes with Utility electricians, and they often do not use NOOX, they have their own exclusive yellow "stuff" which looks a lot like vaseline....????

What is it? Is it better than NOOX?

 

[waross]

I understand that No-ox and Penetrox have formulations specific to aluminum and aluminum oxide. I am not sure if the "Yellow stuff" is as good on aluminum as the formulations containing graphite and other aluminum specific ingredients.
BTW Skoggs, Seven strand cable is the worst. Flexible cable with a large number of fine strands is not as susceptible. You may not have an issue with European cable strandings. But if you are working on a machine in NEMA land be aware. Older cables are more likely to have fewer strands and be more problematic.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[stevenal]

Why would you want to use a product formulated for aluminum connections on copper? Yes there are products formulated for copper to copper.

http://www.galco.com/scripts/cgiip.exe/wa/wcat/itemdtl.r?listtype=&pnum=PENE8-BURN

 

[bartb102]

That's what I was looking for. Thanks.
Bart

 

[KF7RCE]

Thanks, Stevenal. The NOOX I use is formulated for both aluminum and copper. See the site

http://www.sanchem.com/aSpecialE.htmlite

 

[Skogsgurra]

Bill, lots of seven strand cables here, too.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[stevenal]

KF7RCE,

I see that. Conductive without metal? Wonder how they do that.
Anyway, Noalux (not NOOX)on copper would put zinc in the joint causing a higher resistance than an untreated connection.

 

[waross]

Why would y....
Because often that is available.
From the Penetrox description:

The specially formulated PENETROX™ compounds are for use with compression and bolted connectors providing an improved service life for both copper and aluminum connections. Additionally, the non?toxic compounds are an excellent lubricant for threaded applications reducing galling and seizing.

If it's Penetrox or nothing I'll use Penetrox every time.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Over here we tend to use a crimped lug on semi-solid cable (i.e. 7-strand), and provide a stud-type or bolt & bar terminal. Based on the products I see arriving from Continental Europe, other countries seem to use un-lugged cable in far larger sizes than we do in the UK.


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If we learn from our mistakes I'm getting a great education!

 

[stevenal]

Bill,

Note the plural "compounds". They are refereing to the line of products, not a single formulation. Penetrox E is the formulation recommended by the manufacturer for this type of connection. See page 74 of

http://ecat.burndy.com/Comergent//fci/documentation/transmission_products_catalog_0710.pdf

The other formulations are for aluminum to aluminum or aluminum to copper.