Repairs with Bellevilles

In the previous issue, we ended this section with the question, "For feeder bus 06E, which Belleville washers do we use?"

The most common bolted connection consists of a bolt, spring-type lockwasher, and nut. This method concentrates the clamping power on one point of the connection hardware. The uneven clamping, normally not a problem, is a problem for current-conducting bus bar.

The solution is the Belleville washer, which spreads clamping force along a continuous arc for more even pressure at the joint. However, this solution is good only if the washer is used correctly, which it’s often not.

As with any electrical joint, those being secured with Bellevilles must be properly prepped. There are two differences with Bellevilles, however:

1. Select the proper design for the application. Bellevilles come in various configurations designed for specific applications.
2. Select the proper size. This may seem obvious, but sizing a Belleville requires looking at multiple parameters — not just the bolt size. The diameter is particularly important.

Furthermore, when selecting a Belleville, you must look at the torque spec and match it to the bolt torque. With Bellevilles, the cup deforms as you approach the specified torque during assembly. If the bolt reaches the desired elasticity point at one torque and the Belleville reaches the desired deformation at another, the joint will never hold properly.