Introduction

It was only about 10 years ago when telecom distributors had to stock maybe a half a dozen types of long barrel lugs on their shelves. Nowadays, the variations of lugs used on telecommunication sites is mind boggling. The various features include barrel length, material, tongue width, tongue length, brand, wire size, wire type, wire material, color, stud hole size, hole spacing, tongue angle, inspection ports, barrel entrance style, UL listing, coating, and the list goes on! This is a brief attempt to make sense of all these different features so you know exactly what you need when ordering lugs for your next job.

The below information will be specific to lugs used in the telecommunication infrastructure industry. These are typically reserved to uninsulated, tinned copper, compression style terminal lugs. We will not discuss details regarding other lugs like pin lugs, ring lugs, pre-insulated lugs, mechanical screw-type terminals, and C-taps.

Material and Coating

In the telecommunication infrastructure world, almost all lugs used on the sites for the major cell carriers are going to be made of high conductivity copper with a tinned coating. Aluminum lugs and non-tinned lugs are not commonly used in this industry. The main difference between aluminum and copper is that copper will have a higher conductivity to allow for a lower resistance path for ground and/or power current. However, copper has historically been more expensive than aluminum, so aluminum is still used in other industries, especially where current capacity is less of a concern. The copper lugs on telecommunication sites are commonly attached to copper bus bars and crimped onto copper wire, thus creating a like material connection, resulting in a more uniform expansion and contraction with temperature, reducing the risk of loosening connections over time. With both aluminum and copper, another concerning reaction that can happen, especially in outdoor installations is oxidation and corrosion. This is why all of the copper lugs ASK Tower Supply provides are finished with an electro-tin plated coating. Some manufacturers also provide different finishes like silver or nickel plating for various applications.

In indoor installations, a tinned lug will often be installed onto a bare copper bus bar with stainless steel hardware, so there is some concern of dissimilar materials creating galvanic corrosion, however all of these materials have a relatively low galvanic potential, and when used in conjunction with an oxide inhibitor to reduce moisture penetration, oxidation and corrosion are not overly concerning.

Wire, Size, Material, and Type

The most important aspect of a wire terminal or lug is that it will fit onto whatever wire it is being used on! Other terminal types aside, these copper compression lugs are designed to attach securely to the wire to prevent a loose, high electrically resistant connection. So when used with a standard crimping tool, whether it's a hand crimping tool (like this versatile one from Izzy Lugs), hydraulic crimping tool, or powered crimping tool, the inner diameter of the barrel must have a very tight tolerance relative to the outer diameter of the wire conductor to ensure the resulting, crimped connection will not loosen and is a low resistance path for electrical current. The space between the lug's inner diameter of its pre-crimped barrel and the outer diameter of the wire's conductor will vary. This is to allow for some variation between wire manufacturers, wire types, small kinks in wire, and stray strands. But as an example, a common #6 AWG lug from Izzy Lugs like the i62-14, will have a roughly four hundredths of an inch gap (.04 inch) around the wire conductor before it is crimped when used with a #6 AWG, 19 strand conductor. This allows for a tightly fitting connection after they are crimped together.

For a quick primer on the American Wire Gauge (AWG) system, check out this post here. In a nutshell the AWG system provides some consistency for wire manufacturers and end users to measure wire conductor size and diameter.

We at ASK Tower Supply sometimes refer to your standard non-flexible grounding conductors on a telecom site as "code," which can be either stranded or solid conductors, however there are other types of wire and cable commonly used on a cellular site which we often refer to as simply "flex." These "flex" cables are primarily used for power on a typical cellular site, and are called flexible telecom power cables, or brand names like TelcoFlex from Southwire. These cables are technically Class I cables (this nomenclature comes from an ASTM standard B172). For the sake of brevity, we won't dive into too much detail regarding the terminology for wire types and measurements that comes from various electrical standards. Between the way the conductor's strands lay, the amount of strands, the size of the strands and the overall conductor, whether they are tinned, and the copper that is used, all play into what classification and what standard that wire conforms to. For telecommunication sites, what's important to know is that a #2 wire isn't necessarily going to be descriptive enough to determine which lug is compatible with that wire. For example, it could be a #2 solid tinned conductor, or a #2 19 strand with a THHN jacket, or it could be a #2 7 strand with tinned conductors with a THW jacket, or it could be #2 flexible power cable, or it could be a #2 welding wire being used as a gate jumper, which will all have different conductor diameters!

So when selecting your lug, it's important to ensure that lug will work on your exact type of wire that you're using. Many "flex" lugs will work on a variety of both flexible and rigid wires, and even some "code" lugs can also work with various flex cables. So if you're not sure, it's important to ask your distributor or the lug manufacturer if the lugs and wire you're installing are going to be compatible.

Barrel Length, Entrance Style, and Color

Long barrel lugs are the most commonly used type of lugs on telecommunication sites. However, there are both short and standard barrel lugs as well. Of course, the longer the barrel of the cable lug, the more copper tube is used in the manufacturing process, so the more expensive the lug will be, however these longer barrels allow for the end user to crimp along the barrel of the lug in multiple locations (sometimes 3 crimp locations for long barrels) or to use a larger crimping die allowing for a stronger overall crimp and a better electrical connection. Standard barrel and short barrel lugs are reserved for lighter duty use or in applications where space is a concern and a longer barrel lug will not fit. Along with many other lug characteristics (like tongue width) there is very little industry oversight in place for a lug manufacturer to technically call their lugs long barrel, or standard barrel, or short barrel. Most industry accepted standards will however specify that a minimum pull-out force for lugs, i.e. the minimum amount of force required for a conductor to excessively slip out of a crimped-on terminal lug. So while standards may not directly specifiy barrel lengths, the lug manufacturer must ensure the barrel is long enough to allow for multiple crimps so that the lug and conductor will not slip nor become detached when exposed to whatever specified force is in the standard they are complying with. Typically these minimum pull-out force specifications will vary depending on the size of the conductor and the application of the lug. For example, in IEC 61238-1, a lug used with very small wire in a switch gear environment where the conductors are securely fastened, there is actually no need to perform pull testing. However, if that same conductor and lug combination is being tested to UL 486A-486B standards, there may be a pull test and minimum pull-test force required for compliance. Larger conductors like this 500 MCM lug for "flex" cable will need to withstand substantial pull-out forces, thus the manufacturer needs to ensure the barrel length is long enough so that the user can apply sufficient compression crimps or use a larger crimping tool die. That's a lot of information, that quite honestly, may be irrelevant to the end user, but is important in understanding that a long barrel lug from one manufacturer could have a different barrel length than a long barrel lug from another manufacturer.

Additionally, there can be a secondary machining process applied to the entrance of the barrel. Most lugs used in the telecom industry will have a simple chamfer or beveling applied to the entrance (as shown in the photo below). The primary reason for this is to make it easier for the user to insert the conductor into the barrel of the lug, in addition to removing potentially sharp edges on the copper tube. Although not as common, some lug manufacturers will even apply heavily belled edges to the barrel (also shown in the photo below).

While everyone wants to say the color coding on lugs is standard, there are unfortunately still some variances, mostly when it comes to non-standard classes of lugs like "flex" lugs. Below is a sample color code from Izzy Lugs for a few of their common long barrel lugs. While yes, the color is indicative of the lug size and in many cases the corresponding, compatible crimpe die, it is still important to ensure it will work on your conductor by looking at the spec sheet or asking your distributor or manufacturer. This is especially true if you are using a higher class, more flexible conductor like TelcoFlex, as the outer diameter of these conductors will be slightly larger than their "code" counterparts. Similarly, as previously discussed, conductors will typically have smaller overall diameters if there are fewer strands used in their construction. For example, a single #6 AWG solid conductor will be smaller than a #6 AWG 19 strand conductor, which will be smaller than a #6 TelcoFlex with 65 strands, however all of the lugs used on these conductors may still be finished with a blue color code! Some manufacturers will have variance between other manufacturers with their color coding scheme with flex conductors, so it's important to simply double check the specification sheet or ask your distributor, rather than simply rely on the color of the lug.

Lug Tongue

Tongue, tang, palm, and flat of the lug are all used interchangeably for describing the tongue of the lug (as shown in the photo below). The tongue of the lug can be manufactured in various lengths, widths, with or without holes, and even perforated to allow for the user to snap a portion of it off. Obviously the tongue of the lug will increase in length if the there are two attachment holes needed instead of only one, and even longer if the spacing between those two holes needs to be longer as well. The bottom side of the tongue is the primary contact surface area between the lug and the bus bar or whatever terminal to which the lug is being attached. This is unless the user is stacking lugs on top of each other (not common practice in the telecom industry). As a side note, for those applications where lug stacking is acceptable, manufacturers will make tongues that are further shifted downward from the barrel (as shown in the below photo) so that the user can keep the stacked lugs in line with each other without the barrels colliding with each other. Another way to do this is to use a lug stacking adapter (also shown in the photo below).

Other unique lug tongues would be double tongue, or split tongue lugs like this one here.

For lugs used in tight spaces, there are additional options where the tongue is bent at an angle (anywhere between 15 degrees and 90 degrees).

This allows the user to install the lug in a tight space where there is not enough room for the conductor to come off of the terminal at a zero degree angle.

Additionally, some terminals are very close to neighboring terminals, often with insulators between them, also taking up more space. In this case, a narrow tongue lug (like this one here) might be needed so that the lug can properly land in it's appropriate slot. Similar to the nomenclature for barrel length, standard tongue width and narrow tongue width is not necessarily prescribed in any standard. The manufacturer must ensure that even with the narrower tongue, the lug is still compliant with all electrical and mechanical performance criteria.

With lug tongue widths, it's important to check that when they are used with attachment hardware, that the washers will not interfere with neighboring washers of lugs. Similarly with narrow tongue lugs, flat washers can collide with insulators on the sides of the lug landing, and in some cases can collide with neighboring lugs and their hardware, which is very problematic if that lug and conductor is being used for power, causing a short in the system's circuit. Ask your distributor for narrower lug washers (like these) to accommodate for these types of applications.

Bolt Hole Size and Spacing

The holes in the tongue of the lug can be referred to as stud holes or bolt holes. These hole configurations can come in a variety of sizes and spacing depending on the application. In the telecom industry, lugs are commonly used with #10, 1/4 in., 3/8 in., and 1/2 in. hardware and each lug is commonly attached with two bolts or studs and the spacing between those can be 5/8 in. or 3/4 in. or 1 in. or even longer for power and battery installations. Some lugs will come with a slotted hole as show in the below photo to allow the user to use it on a landing with either 3/4 in. or 1 in. spacing.

Burndy manufacturers a lug with a perforated line between the bolt holes to allow the user to snap the end of the tongue off if they are using it with only one attaching bolt, sometimes referred to as a break-away lug.

Of course the variations in bolt hole size and spacing is also endless, so much so, that some manufacturers have lugs with blank tongues so that the user can drill their own bolt or stud holes on site.

Inspection Windows

On the lug, where the base of the barrel meets the tongue, the manufacturer can include an inspection port or inspection window, so that the user can ensure the stripped conductor is buried all the way into the barrel of the lug.

In the telecommunication industry, there has been some confusion between various carriers when an where lugs with inspection ports can be used. A common practice is to use windowed lugs when being installed inside of a shelter or non-windowed lugs when being installed outdoors. The logic with this practice is that the windowless lugs will prevent water intrusion, thus also preventing additional corrosion and oxidation at the lug to conductor connection. It is important to double check with your authority having jurisdiction and your carrier specifications whether or not lugs with port holes can be used on your site.

Brands and Manufacturers

At ASK Tower Supply, we only sell UL listed, copper lugs that come from reputable manufacturers like Izzy Lugs, Burndy, Panduit, and many others. As discussed above, each manufacturer may have slight variances between lug sizes, colors, and even part numbering schemes, so it's important to ask your ASK representative if one lug is an exact equivalent for another, and if not, what those differences are.

Ratings

In the North American telecommunication market, at the very least it is important to ensure the lugs you are using are UL listed. Most lugs will comply with all of the performance and testing requirements of UL 468A-468B. As with any electrical product the verbiage associated with standards can get very confusing with words like listed, rated, compliant, conforms, approved, recognized, etc. If you're ever unsure of a rating, ask your ASK representative for the appropriate certificate, control number, or letter confirming whatever compliance is necessary. Other standards that may be associated with electrical lug connections are ASTM, TIA, ETL, CSA, IEC, and even some carrier specific standards or best practices. In fact, if you are working on an AT&T site, we are a stocking distributor for Izzy Lugs, which has AT&T assigned CEQ part numbers assigned to most of their lugs. Even for Verizon, T-Mobile, and now Dish, the user should still check with their regional manager regarding any concerns around what variants of lugs can be used on your site.

Conclusion

In conclusion, even in niche industries where only a small subset of conductors are used, like telecommunication infrastructure, the variants of lugs are still endless! Depending on what carrier you're working for, the application, and even what part of the country you're working in, ask your ASK team member what copper lug is right for your job.