There seems to be two camps of thought on performing "retorque" of bolted electrical bus connections. One promotes regular retorquing of bolted connections while the other calls for repairs made to connections based only on the results of a thorough thermographic survey. I have also been led to understand that regular retorque can max out the elasticity of the fasteners and cause the joint to loose its clamping force. Who's more correct and what are the details?
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Performing "retorque" of bolted electrical bus connections
- Thread starter meengrn
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Geoff says:
Every 2-6 years retorque all bus duct terminations, bus duct taps (usually fused disconnects), and assembly hardware according to manufacturer specifications. This must be performed only by a competent electrical contractor working under manufacturer direction, with the power off.
Some bus duct manufacturers do not recommend retorquing due to visual indicators/fasteners such as compressed convex “Belleville” washers at each joint. However, even with such hardware, whenever a bus duct system is de-energized for service or alteration, random sections should be checked for proper torque. If the sample sections demonstrate the need for retorquing, the entire system, as well as other similar systems should be scheduled for retorquing. Never over-torque Belleville washers beyond their rating, as damage to the washer can occur.
Before Retorquing - Perform an infrared scan prior to retorquing to identify areas of concern that can be studied while the bus duct is de-energized.
After Retorquing - After bus duct is restored to normal service with significant loads, perform an infrared scan on entire assembly or at least sections of bus duct that required abnormal adjustment or service.
When performing de-energized service to bus duct, after isolating all loads by opening all means of disconnect, be sure to document the resistance readings (megger) before and after service
Every 2-6 years retorque all bus duct terminations, bus duct taps (usually fused disconnects), and assembly hardware according to manufacturer specifications. This must be performed only by a competent electrical contractor working under manufacturer direction, with the power off.
Some bus duct manufacturers do not recommend retorquing due to visual indicators/fasteners such as compressed convex “Belleville” washers at each joint. However, even with such hardware, whenever a bus duct system is de-energized for service or alteration, random sections should be checked for proper torque. If the sample sections demonstrate the need for retorquing, the entire system, as well as other similar systems should be scheduled for retorquing. Never over-torque Belleville washers beyond their rating, as damage to the washer can occur.
Before Retorquing - Perform an infrared scan prior to retorquing to identify areas of concern that can be studied while the bus duct is de-energized.
After Retorquing - After bus duct is restored to normal service with significant loads, perform an infrared scan on entire assembly or at least sections of bus duct that required abnormal adjustment or service.
When performing de-energized service to bus duct, after isolating all loads by opening all means of disconnect, be sure to document the resistance readings (megger) before and after service
electricpete
Electrical
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