Loadbreak elbows are essential components for safely connecting underground power distribution cables to padmount transformers. This article details the installation process for 200 Amp loadbreak elbows, specifically focusing on applications with concentric neutral and copper tape shielded cables. It is crucial to consult the manufacturer’s instructions accompanying the loadbreak elbows for specific guidance, as this document serves as a supplemental guide and does not replace official documentation.
Identifying Bushings and Ensuring Compatibility
The primary side of a padmount transformer features bushing inserts. The number of bushings varies depending on the transformer’s configuration: six bushings are present in loop feed applications, while three bushings are found in radial feed applications. Prior to installation, it is important to understand the difference between radial and loop power distribution systems.
Inspect the selected loadbreak elbows to confirm compatibility with the transformer’s bushing interface. The voltage class of the elbow connector must match the voltage class of the transformer bushings. All bushings should be statically grounded using a #14 AWG bare copper wire, referred to as a drain wire. This wire dissipates static charges between the bushing well and the separable insert. The drain wire should be looped through the grounding tab of the insert and connected to the metal bushing clamp. If a six-bushing primary transformer (loop feed) is installed at the end of a radial lineup, arresters should be installed on the remaining three bushings to protect the transformer from switching and lightning surges.
Cable Preparation: Concentric Neutral and Copper Tape Shielded
The installation process differs slightly depending on the type of cable used: concentric neutral or copper tape shielded. The following steps outline the preparation for both cable types. First, the guide focuses on concentric neutral cable, with a note to skip to step 3b for copper tape shielded cable installation.
To begin, determine the appropriate cable length needed for the elbow termination. Sufficient slack is necessary to facilitate easy installation and removal of the elbow connector using a hot stick. Train the cable in front of the bushing where the elbow will be installed, then use a light marker to indicate the point where the cable crosses the center of the bushing. All cable above this mark will be cut off in a later step. Leaving excess cable above the mark simplifies grounding the concentric neutral wires.
Concentric Neutral Cable Termination
For 15kV concentric neutral cable, the following steps are required. First, determine the proper cable length needed for the elbow termination. Train the cable in front of the bushing where the elbow will be installed. Use a light marker to indicate where the cable crosses the center of the bushing. Everything above your mark will be cut off in a later step. Leaving excess cable above this first mark will make it easier to ground the concentric neutral wires later on.
Apply a layer of mastic tape to the cable. Add another layer of mastic tape over the first to sandwich the ground braid. Next, cover the constant force spring with black electrical tape, ensuring the tape covers both the spring and the mastic. A cold shrink sleeve for the jacket seal should then be slid over the cable for later installation.
Stripping Wire Insulation and Attaching the Connector
Whether using concentric neutral or copper tape shielded cable, the next step involves preparing the termination point of the elbow. An insulation stripping tool should be used to strip back approximately 2 inches of insulation from the tip of the wire, exposing the conductor. The exposed conductor should then be cleaned with a wire brush to remove any oxidation.
A compression connector, appropriate for the conductor’s size and type, should be installed. This connector should include an inhibitor, which must remain inside during installation. Rotate the compression lug to evenly distribute the inhibitor across the conductor’s surface. The hole at the tip of the compression connector determines the orientation of the elbow’s probe; the flat end of the compression lug should face the transformer bushing.
Crimping the Connector and Revealing Cable Insulation
Refer to the manufacturer’s instructions for the specific crimping tool and procedure for the compression fitting being used. Before attaching the connector, verify that the probe fits properly. When crimping, rotate the crimping tool after each crimp to prevent bowing the connector.
After crimping, reveal the cable insulation.
Chamfering, Cleaning, and Applying Silicone
A chamfering tool should be used to create a ¼ inch bevel around the outside edge of the insulation. This bevel facilitates easy sliding of the elbow onto the cable. Thoroughly clean the insulation with a cleaner specified for transformer cables, applying the cleaner to paper towels and wiping down the cable with a clean towel each time.
Apply an even coat of silicone over the insulation. This serves three purposes: filling any tiny voids on the surface, creating a watertight seal, and aiding in the installation of the elbow.
Installing the Elbow and Securing the Connection
Align the elbow and compression connector to ensure the probe can be threaded into the connector properly. Slide the elbow onto the cable and hand-thread the probe into the connector to avoid cross-threading. Exercise caution to avoid damaging or contaminating the white part of the probe during insertion.
Use a wrench to continue twisting the probe after it can no longer be turned by hand. Continue turning until the wrench handle bends 90 degrees from its original position. Proper insertion is confirmed when the wrench deforms at 100-120 inch/lbs of force.
Wrapping the Jacket Seal and Grounding
To prevent moisture ingress, install the jacket seal kit. Place a piece of mastic tape at the edge of the jacket, position the jacket seal over the elbow and cable jacket, and then pull the plastic from the jacket seal to shrink it over the elbow and cable.
Ground the elbow by pulling one of the concentric neutral wires through the ground tab on the elbow, wrapping it around itself a couple of times, and cutting off the excess. Bond the remaining concentric neutral wires to earth ground. Before plugging in the elbow, apply a thin layer of silicone around the bushing. The elbow is properly seated when the yellow ring around the bushing is completely covered by the elbow.
Conclusion
The installation of 200 Amp loadbreak elbows requires careful attention to detail and adherence to manufacturer’s instructions. Proper preparation of the cable, secure connection of the elbow, and effective sealing against moisture are critical for safe and reliable operation. This guide provides a step-by-step overview of the process for both concentric neutral and copper tape shielded cables, emphasizing the importance of compatibility and grounding.