Introduction

The following instructions are recommended by Travis Pattern & Foundry Inc. and should only be used as a guide for the installation of electrical connectors and fittings.  The instructions provided here are intended to provide helpful reference information for three types of installation procedures; bolted, welded, and compression.  Instructions are provided for both copper/bronze and aluminum alloy connectors.

Cleaning and Preparation of Electrical Connections

Although copper/bronze oxidation does not provide as much interference with the flow of electric current as the oxidation produced by aluminum alloys, it is advisable to follow the same procedures for installation of either material.  Aluminum is more critical because aluminum oxide is known to insulate electrical potential and can therefore cause connectors to over heat and eventually fail.  For copper/bronze as well as aluminum alloy applications, a properly cleaned surface with the correct oxide inhibitor applied maximizes conductivity and helps keep outside contaminants from promoting corrosion.  This can cause a reduction of the current carrying capability and life of the connector.  Once oxidation has been removed the use of an oxide inhibitor on all connections can prevent further oxidation from taking place.

All contact areas of a connector, as well as the areas to which they will be connected, should be wire brushed to thoroughly remove any oxidation.  The contact area is the part of a connector, cable, bus, or any other conducting surface that is intended to be joined together for the purpose of conducting electricity.  Each contact surface should be cleaned with a wire brush and a generous portion of oxide inhibitor should be applied.  Excess oxide inhibitor does not need to be removed from connections installed when corona is not an issue.  All excess oxide inhibitor must be removed from connectors installed in EHV applications.  When insulated cable is being connected, only non-petroleum based oxide inhibitor should be used.

After brushing the contact areas clean, immediately apply the correct oxide inhibitor that is designed for that application.  Repeat the wire brushing a second time to work the inhibitor into the clean surface.  The correct oxide inhibitor will depend on the material being connected and the contour of the conductor surfaces being connected.

            Plated surfaces should be cleaned with a mild wire brush or mild abrasive like Scotch Brite being careful to remove as little of the plating as possible.  Chemicals formerly available for cleaning plated surfaces have been found to be hazardous to human health and are no longer available.  The correct oxide inhibitor should be applied in the same manner previously stated as if there were no plating.

           

Selecting the Correct Oxide Inhibitor for Flat to Flat Connections

            Oxide inhibitors containing suspended conductive particles should not be used on flat to flat surfaces, IE:  (ALCOA Filler Compound (AFC)).  As seen in the drawing below, particles prevent the two flat surfaces from coming together in order to maximize their contact area.  They reduce the cross sectional area of the contact points.  Only a non-grit type oxide inhibitor IE:  (ALCOA Electrical Joint Compound #2) should be used for flat and other smooth surface connections such as rigid pipe conductor and terminal pads.

 

 

Oxide Inhibitor (Filler Compound) for Cable Connections

 

The best job anyone can do at wire brushing a cable that is to be electrically connected is to clean only the outer surfaces of the outer strands of that cable.  The inner strands are coated with aluminum oxide and it cannot be removed without unraveling the cable.  Some oxide inhibitors are supplied with suspended conductive particles such as zinc, nickel, or other such hard conductive material.  The function of these particles is to pierce through the aluminum oxidation covering the inner strands of a cable and to make contact with clean aluminum between each strand of the cable.  The particles act as small shunts connecting the inner strands of a cable to each other as well as to its outer strands.  This permits more of the strands to participate in the current carrying function of the cable thus maximizing the efficiency of the connection.

The oxide inhibitor should be worked in-between the strands so that the conductive particles that are suspended in the oxide inhibitor can make contact with each cable strand.  Note that all oxide inhibitors do not contain suspended particles so it is important to select an oxide inhibitor with particles (grit) when making a connection to a cable.  Oxide inhibitors containing particles should be used in all applications involving a cable.  Oxide inhibitors that contain suspended particles should not be used on flat to flat surfaces such as rigid pipe conductor and terminal pads.

When installing a cable into a compression connector, the act of completely inserting the cable into a tube that has been properly filled with oxide inhibitor will cause the inhibitor to rise in the tube.  This action will cause the oxide inhibitor to extrude itself into the cable thus filling many of the voids between the strands.  The drawing below demonstrates how the particles fill in between the strands in a cable.  The same method is used for both bolted and compression connections involving a cable.
   
Compression connectors should be properly filled with filler compound so that there is no empty space after the conductor is inserted.  This is especially important if the terminals are to be installed with the barrels in the upright position.  If there are any cavities not filled with filler compound water will eventually find its way into these voids and later freeze and expand making the cavity even larger.  After a number of these cycles the cavity can grow to the point of connector failure.  External contact areas such as the terminal pad need to be cleaned and have non-grit type oxide inhibitor applied as described earlier.

 

 Bolted Connections

The hardware material that is generally supplied with bolted connectors is in keeping with the avoidance of using dissimilar metals.  This is done for protection against electrolysis and other corrosion.  The standard hardware on bronze connectors is silicon bronze and aluminum anodized hardware is standard on aluminum alloy connectors.  Aluminum anodized hardware is sometimes substituted with stainless steel or galvanized steel hardware for use on aluminum alloy connectors.  The primary reason for selecting one hardware material over another should be the environment in which it will be installed and personal experience.  Some harsh environments are more susceptible to corrosion with one material or another.  Examples of this might be when connectors are installed near paper mills, chemical plants, salt water or any other environment that could promote or even accelerate corrosion.  The same selection process can be employed when determining the pad mounting hardware to be used to fasten a connector to equipment or another connector.

Each clamping bolt that goes through the body of the connector and clamps down on the conductor is usually supplied with a nut and lock washer.  The purpose of the lock washer is to prevent loosening due to vibration and to compensate for expansion and contraction of metals.  Pad mounting hardware should also include a nut and a washer that provides some means of compensation for expansion and contraction.  This can either be a lock washer or a Bellville washer.

Bolts used in the connector body as well as those used for pad to pad mounting should be tightened evenly and a torque wrench should be used in accordance with the torque tables below.  PDU connectors are supplied with non-lubricated silicon bronze hardware, stainless steel hardware w/anti-seize and lubricated aluminum hardware.  Using oxide inhibitors, especially those containing particles, as a lubricant can interfere with the tightening of bolts resulting in a poor connection.

Recommended Torque Values in ft/lbs
Bolt Diameter	Silicon Bronze	Stainless Steel (w/anti-seize)	(Lubricated) Aluminum
5/16-18	11	11	N/A
3/8-16	20	20	15
1/2-13	40	40	25
5/8-11	55	55	40

 

 

Selection of Compensating Washers

Whether a washer is being used on a clamping or a pad mounting bolt of an electrical connection, its purpose is to compensate for the expansion and contraction of the materials being connected due to temperature changes, and to protect against loosening due to vibration.  The two most common types of washers used for this purpose are SS 304 lock washers and  SS 304 Bellville washers.  Lock washers are generally provided by the manufacturer for use with the clamping bolts because they are generally smaller in diameter and therefore fit in the connector body more compactly.  Both can provide needed protection.

When selecting a washer there are three major factors to consider.  All washers are not equal and quality can make the difference between a connector operating correctly and one that fails.

1. Material – All washer materials do not provide the same ability to spring back to their original position.  The best grade of stainless steel washer may not be the best selection for a particular application.  A washer that has very high resistance to corrosion may also be very low in its ability to retain its spring.
2. Curing – Some type of heat treating, pre-stressing, or curing is needed in order to provide necessary resilience in any washer, by the manufacturer.  All washers are not necessarily prepared in the same fashion and the results can be different.
3. Corrosion resistance – A balance must be found that provides both corrosion resistance for the particular application, and still be able to provide necessary spring ability.  When considering corrosion resistance of hardware, there are two issues to evaluate.  The first issue is to make sure that electrolysis is minimized by not introducing dissimilar metal hardware that will promote electrolysis.  (See also “SELECTION OF MOUNTING HARDWARE”)  The second issue to be aware of is the environment in which the connector will be installed.
4. Length of travel – The amount of necessary travel must be considered to ensure that compensation for expansion and contraction are both considered.  Although some washer manufacturers recommend installing washers close to or at the flattened position, consideration must be given to how the connection will perform when heat is applied and expansion takes place.  Cold flow may result because the aluminum body of the connector is not allowed to expand and may also lead to a loose connection.
5. Pressure – The amount of torque that is applied to a mounting bolt will determine how much pressure will be developed on the connecting surfaces.  High pressure decreases electrical resistance, but this pressure must be maintained as temperature increases and decreases.  If a washer is installed too tight initially the resistance may decrease. Then the temperature will increase and cold flow will begin to occur.

 

Simply selecting a lock washer over a Bellville or the other way around is not enough.  Either washer can do the job if it is made correctly.  Once a washer has been selected, it must be installed in a way that will maximize its efficiency.  A flat washer should always be used between the spring washer and the body of the connector.  This is especially important on aluminum because it is a soft metal and the washer can dig into the part being fastened.

Nuts should be tightened evenly with a torque wrench.  Torque tables for the specific hardware material should be followed closely.  Excessive torque can reduce the washer’s ability to compensate for expansion of the material being fastened.  Cold flow can occur as the connected material tries to increase in volume due to changes in temperature, but is restricted from increasing because a washer has lost its ability to expand and contract.  The result is the washer material being fastened appears to be imbedded into the connector, but in fact it is the material being fastened that has escaped from under the washer, thus reducing its thickness and possibly loosening.

When using a Bellville washer it is the manufacturer’s recommendation that it be installed at no less than 80-90% of its being flattened.  If the required travel is greater than the washer can offer, more that one washer may be needed.  If this is the case, sets of two washers should be installed with the concave surfaces facing each other in that set.  It should be understood that as a Bellville washer approaches the flattened position, it begins to lose its ability to fully return to the original position.

Consideration should be given to the material being fastened.  Aluminum compression connectors are made of pure aluminum, so they are softer than a similar bolted or welded connector.  Excessive tightening only displaces more material and does not necessarily make a better connection.

 

Connecting Dissimilar Metals

Although it is best to avoid making connections using different metals like copper and aluminum there are times when this cannot be avoided.  There are a few steps that can be taken to minimize potential problems.

A.  Electrolysis (see section on Electrolysis)

This is the most commonly known problem that occurs when two different metals are forced to cohabitate together in a potentially corrosive environment.  This is called galvanic corrosion. It is the action of one material giving off molecules (anode) to another material (cathode).  The result can cause a failed connection.

Possible prevention

1. Tin plating the aluminum or the copper/bronze component of the connection can help reduce the effects of electrolysis.  It can also help slow down corrosion caused in some environments.
2. A transition plate is a plate that electronically bonds aluminum to copper in the form of a washer-like plate.  This plate is usually supplied in the same size as the terminal being connected and can be drilled for either two or four hole applications.  It is then positioned between the two dissimilar metals like a washer would be.

 

Electrolysis

Electrolysis is sometimes also described as galvanic corrosion, both are the same.  This is the same phenomenon through which a battery can exist.  By placing two dissimilar metals in a corrosive environment a difference in electrical potential is created.  The most common example of this may be the high school science experiment where zinc and copper strips are placed in a beaker containing sulfuric acid.  Using a voltmeter a voltage can be measured across the two strips.

In a controlled environment this energy can be harnessed and put to good use.  Electrolysis does not always occur in a controlled environment and its effects are not always desirable.  There are conditions and situations when an electrical circuit design may require the use of either a copper or aluminum conductor.  Both have benefits that may be desirable under certain conditions.  There are also times however, when these two dissimilar metals must be connected together.  The result is similar to the creation of a battery in an uncontrolled environment.

Voltage itself is not the primary concern. The physical effects of electrolysis are when a condition causing electrolysis exists, one of the two dissimilar metals becomes the anode and the other becomes the cathode.  To determine which metal will become the anode and which will become the cathode refer to the Galvanic Series table in this section.  The metal listed with the most relatively positive voltage is the cathode and the metal with the relatively more negative voltage is the anode.  When electrolysis is taking place the anode gives off some of its molecules to the cathode.  After the period of time that this action has taken place the anode eventually has no more molecules to give off.  This is sometimes called galvanic corrosion.  When this occurs with an electrical connector, failure eventually results.

By understanding how various factors can influence electrolysis on electrical connections made with dissimilar metals, its corrosive effects can be minimized.

Electrolysis Factors

1.   Voltage

The higher the relative voltage difference of the two different metals the faster the anode will deteriorate or corrode.  By keeping the relative voltage between the two metals on the Galvanic Series table to a minimum, corrosion of the anode slows down.  Using the Galvanic Series table for example we find that copper has a relative voltage of -0.20 volts.  On the same table aluminum has a relative voltage of -0.80.  Therefore the relative voltage between the two metals is the difference between copper and aluminum, or about -0.60 volts (difference between -0.20 and -0.80).  Notice that tin-plate has a relative voltage of -0.50 volts.  By plating one of the metals the relative voltage can be reduced to -0.30 volts.

2.   Anode size Relative physical size of the anode to that of the cathode in an electrical connection can contribute to the life expectancy of the connection.  Since the anode will be giving off molecules to the cathode it stands to reason that when the mass of the anode is significantly greater than that of the cathode its life expectancy of the connection is improved.

3.  Environment In the previous high school experiment, sulfuric acid was used for the environment of the zinc and copper strips.  The Galvanic Series table uses salt water.  A change in the environment that the two metals used in making the electrical connection can also change the effects of galvanic corrosion.

 

Galvanic Series
Metallurgical Category	EMF
Gold, solid and plated; gold-platinum alloys;	+0.15	Cathode
wrought platinum
Rhodium plated or silver-plated copper	+0.05
Silver, solid or plated; high alloys	0
Nickel, solid or plated; Monel metal, high	-0.15
nickel-copper alloys
Copper, solid or plated; low brasses or	-0.20
bronzes; silver solder; German silver; high
copper-nickel alloys; nickel-chromium alloys;
austenitic corrosion-resistant steels
Commercial yellow brasses and bronzes	-0.25
High brasses and bronzes; naval brass;	-0.30
Muntz metal
18 % chromium type corrosion-resistant steels	-0.35
Chromium, plated; tin plated; 12% chromium	-0.45
type corrosion-resistant steels
Tin plated terneplate; tin-lead solder	-0.50
Lead, solder plated; high lead alloys	-0.55
Aluminum wrought alloys of the duralumin type	-0.60
Iron,  wrought, gray, or malleable; plain, carbon	-0.70
and low alloy steels, armco iron
Aluminum, wrought alloys other than duralumin	-0.75
type; aluminum case alloys of the silicon type
Aluminum, cast alloys other than silicon type;	-0.80
cadmium, plated and chromated
Hot-dip-zinc plate; galvanized steel	-1.05
Zinc, wrought; zinc based die-casting alloys;	-1.10
zinc plated
Magnesium and magnesium-base alloys, cast	1.60
or wrought		Anode

 

Corrosion

No metal is totally immune from corrosion from any chemical.  Corrosion can lead to the deterioration of the mass of a connector or conductor which eventually leads to failure of the electrical connection.

Possible preventions

• Always be aware of the environment in which a connection is being made as well as its compatibility with that environment.  For example, will this connection be made near salt water, a paper mill, a chemical plant or any other toxic environment?  Through the use of corrosion tables and personal experience, one material can be found that will work better than another.

• When connecting aluminum to copper, always make sure that the aluminum is physically above the copper.  Copper salts can accelerate corrosion of aluminum.

 

 

 

 

 

Substation Connectors