Florida Power & Light (FP&L) recently completed a study of proper torque specifications for connections on its transmission and distribution system. Pitting, arcing, burning and eventual connection failures were investigated with component and fastener manufacturers and laboratory tests to determine the correct torque specifications for a variety of bolted connections. Armed with this information, a program was initiated to educate overhead and underground crews about proper tightening procedures. To implement the program, FP&L worked with Wright Tool, a hand tool manufacturer, to develop a versatile torque wrench that solves a specific tightening problem and includes special attachments that enhance its crews' overall torquing capabilities.

No Room Around Connection

Hardened aluminum “multitap” terminal strips have become a boon to line specialists, lead specialists and cable splicers, especially on secondary connections to pad-mounted, pole-mounted and three-phase vault transformers serving high-rise apartments, plants, hotels and other commercial buildings. Before multitaps, crews had to crimp two-hole lug connectors onto each cable and bolt them, using two loose bolts, directly to the transformer spade or bushing. Using the multitaps, they can cut the insulation on the cable, insert it into the multitap and tighten two hex head set screws to the proper torque, depending on the type of cable conductor (aluminum or copper).

However, the multitaps take up much of the space between the spades. With one bolted on each side of the spade, it is difficult to use a conventional square-drive torque wrench with a 5/16-inch hex socket to tighten the set screws, particularly on older transformers. According to Al Arias, underground operations specialist for FP&L, “We shared our problem with Wright Tool rep Mike McGovern and asked him to see about a new torque wrench built to our specification.”

The tool needed to be small enough for the set screw application, yet flexible enough to perform other tasks while still being convenient to use. Wright Tool's McGovern developed several ideas, and an initial prototype for field trial was created. “On the first prototype, we asked them to make the hex drive a little longer, and instead of having to change out the head assembly to handle the square-drive sockets, we asked them to look into using adaptors,” says Terry Liston, FP&L's tool coordinator. The final design was a success. “It has worked out to be just what the crews needed,” Arias says.

Tool Tech

The new tool is a 5/16-inch hex-drive ratchet torque wrench with a head narrow enough to fit between the banks of multitap set screws. In addition, its versatility is increased with a ¾-inch socket for another multitap application that fits the 5/16-inch hex drive. It also includes two square-drive adapters, allowing it to be used with regular ⅜-inch drive and ½-inch drive sockets.

Arias says, “Prior to getting the new tool, we used a ⅜-inch square-drive ratchet torque wrench with a short 5/16-inch male hex socket, and in some cases, it wouldn't fit between the opposing banks of multitap connectors.”

The round ratchet-head, click-type wrench has a 0 to 80 ft-lb torque range, set by pulling down a spring-loaded positive locking ring and turning the handle. A distinct breaking action occurs when the desired torque is reached, and the positive locking feature prevents accidental changes to the torque setting. FP&L also finds the tool equally useful in making connections to “Z” bar multitaps used to simplify connections to low-voltage, one-phase residential transformers.

A Two-Part Solution

FP&L's Liston points out that there is more to making good voltage connections than just having a compact torque wrench. “Before you put a wrench on any threaded connection, you want the mating surfaces clean. Especially with aluminum connectors, you should wire brush them thoroughly and lubricate them with a corrosion inhibitor,” says Liston. With a clean, lubricated connection, the torque reading is a direct indication of the amount of compression resulting from the fastener, not just the difficulty in overcoming the friction of the thread.

“The other thing,” says Liston, “is that if you overtighten, it's just as bad as if you undertighten. When that circuit heat-cycles under load, it draws that aluminum in. Then, when the circuit doesn't have much load on it, you'll have a void there and it will start arcing and burning up.”

Spade Work

When FP&L asked Wright Tool to develop this new wrench to tighten multitap set screws, it also was aware of another important torque requirement. The aluminum multitaps are bolted onto the tinned-copper transformer spades with ½-inch stainless-steel bolts that have ¾-inch hex heads.

“To maintain good contact as the thermal load on the connection changes, we use a stainless-steel bolt setup that includes a Belleville (spring) washer,” says Arias. If the joint is not properly prepared and is undertorqued, corrosion problems and burned-up connections can arise between all these dissimilar metals. If the bolts are overtorqued, the Belleville washer may crack and lose its ability to maintain proper tension and contact.

By designing the ¾-inch 12-point socket that fits the 5/16-inch hex drive on the new torque wrench, this same tool can be used to torque these bolts to the required 40 ft-lb (after the surfaces have been properly cleaned and coated with a corrosion inhibitor).

Elbow Exercise

A third application to benefit from FP&L's torque investigations has been the installation of ETP 600-A elbow terminations (T-bodies) used to connect medium-voltage cables to load-break, dead-front switch cabinets. The elbows fit into cone-shaped bushings, and the manufacturer specifies that they be torqued to 55 ft-lb. If the elbows are inadequately torqued, they can overheat under load, leading to cracking of the bushing and catastrophic failure of expensive switchgear.

This was a particular problem with a previous elbow FP&L was using; it was only torqued to 25 or 30 ft-lb. “Since we stepped up to this new elbow that requires a higher torque, most of our problems have gone away,” reports Arias. He points out that this application is another convenient use for the new Wright Tool torque wrench. With the ½-inch square-drive adaptor in place, it mates to a special tightening tool that is inserted into the elbow.

Spreading the Word

Arias has visited various service centers to discuss the mandatory new torque requirements and other service issues for these new elbows. In the process, he demonstrates proper technique using the new tool and reports a growing number of requisitions for the tool from crews across the state. “Because we are specifying torque on these connections, eventually every crew will have a torque wrench with them,” adds Liston.

Arias and Liston also are spreading the word about the tool at industry gatherings, such as the Southeast Electric Exchange. “We deal with a lot of other utilities around the country. We meet twice a year with them and the word is getting out,” Arias says.