Secondary Connections for Overhead Transformers 1

[nonsinusoidal]

Does anyone know why aluminum underground secondary cables have to be terminated on the secondary terminals of an overhead transformers with a spike connector? On the other hand,Copper underground secondary cables can just be terminated bare on the transformer secondary terminals without any issues. Please advise of the reasons why aluminum underground secondary bare conductors can not be terminated on the secondary terminals of a transformer when exposed to air and rain?

 

[racobb]

I will assume that by the term "spike connectors" you mean a copper lead? Many utilities have the policy not to put aluminum in the transformer lug. Probably an ancient hold over from when the lugs were not designed for aluminum. Also a reasonably sized copper conductor allows for another service to be connected without interruption of the hot service.

Also we all know that copper has a lower rate of expansion when heat cycled which results in fewer loose connections to worry about.

Alan

 

[jmmee97]

To expand on racobb response, the lugs of the transformer are probably tin plated copper or brass. Aluminum wire will eventually become loose due to the differences in expansion. The "spike" connector is used as a transition; the sleeve being aluminum and the spike is probably tinned copper.

 

[waross]

Not sure about transformer terminals but when a copper conductor is tapped to a horizontal aluminum conductor with a compression connector, the copper must be installed below the aluminum conductor. Rain water along with the atmospheric contaminants common everywhere now will react with copper to form salts that cause accelerated corrosion in aluminum. If the copper is above the aluminum you may expect a lot of corrosion. If the copper is below the aluminum it will last years longer.

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

 

[racobb]

Agreed Bill....another thought is a hold over from the past when the line guys thought that "cheasy" aluminum junk would never make it for long. "Old habits are hard to break".

But the big deal is the load/heat cycling as we know. Proper aluminum connections are critical in how they are made.

Thankfully we have come a long way with it and connectors and training are better.

But I still don't understand the term "spike connector".

Alan

 

[waross]

Here's a "Spike". Also called a "Terminal Plug" or an "Aluminum Pin Terminal".

http://portal.fciconnect.com/Comergent//fci/drawing/electrical/yer.pdf

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

 

[racobb]

Oh Yeah, aluminum pin terminal made the light bulb came on!

Thanks

Alan

 

[nonsinusoidal]

It is clear as mud. Do any of you guys know of any other issues which I should considered besides the disimmilar metal issue. How about the water flowing into the terminations of the underground secondary aluminum cables on the transformer lugs? Will water( expand) in the cables and damage the insulation or the stranded aluminum conductors? Please advice

 

[racobb]

Most will form a modified "drip loop" which simply put, has the conductor entering the transformer lug from the top so that the end is extended above the terminal and then turned down to help eliminate water intrusion.

Alan

 

[waross]

At 600V and below, I often form a loop in cables that enter a transformer terminal from the bottom. I cut a notch in the insulation at the lowest point to allow drainage.
I believe that terminal pins are available that shelter or seal the insulation to prevent the ingress of water.

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

 

[racobb]

"At 600V and below, I often form a loop in cables that enter a transformer terminal from the bottom. I cut a notch in the insulation at the lowest point to allow drainage."

Is that one patented or may I use it without fear of recourse?:-D

Alan

 

[waross]

It was old when an old electrician showed it to me a long time ago. It works. I have had water flowing in the cables back into the main switch and the notches cured the problem.

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