Performing "retorque" of bolted electrical bus connections
Performing "retorque" of bolted electrical bus connections
(OP)
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?






RE: Performing "retorque" of bolted electrical bus connections
if below the yield, the work harden should take many passes to occur.
RE: Performing "retorque" of bolted electrical bus connections
Before thermal imaging annual torquing of the bus connections was a common practice. Just make sure they use a torque wrench.
RE: Performing "retorque" of bolted electrical bus connections
I read an article where they said in a paper mill it was found that if loose connections were tightened that only 1 in 5 showed an improvement during infrared scans. If the joint was taken apart and cleaned before putting back together then 92% showed an improvement.
RE: Performing "retorque" of bolted electrical bus connections
If a connection was found to be loose, then contaminants and corrosion can enter. If the connection is not properly prepped, then retorquing would not guarantee a good connection.
TTFN
RE: Performing "retorque" of bolted electrical bus connections
RE: Performing "retorque" of bolted electrical bus connections
In some cases you may want the torque reading to occur during motion as this separates the dynamic friction from the static friction. In that case you may slightly loosen a bolt just enough to allow motion in the tightening direction but only just enough.
First you should just apply force with a torque wrench. If you reach the proper torque before any movement occurs.. just move on to another.
Also if your buss bars are copper the steel bolts are probably operating far, far, below their maximum load levels.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Performing "retorque" of bolted electrical bus connections
RE: Performing "retorque" of bolted electrical bus connections
Whatever happened to bellville washers?
respectfully
RE: Performing "retorque" of bolted electrical bus connections
If you can get your hands on a copy, a book called "Copper For Busbars" by the Copper Development Association deals with bolted busbar joints in terms of joint effiency, joint pressure, torque values, preping the joint etc.
I would go with the manufacturers recommendation with regard to checking bolt torque.
Joint preparation is extremely important, I can recall an incident where I was asked to look at some electrical bushings that were having there threads stripped during assembly with a steel bolt, it turned out that the torque figure quoted for the joint was given dry (ie no lubricant)
however the fitters on the job were coating each conductor as they went along with a electrical conducting grease which in turn inadvertently got onto the threads of the next steel bolt they were using. The result was this reduced the friction between the steel bolt and bushing and for the given torque they were using resulted in twice the expected clamping force and this caused the brass threads in the bushings to fail.
regards
desertfox
RE: Performing "retorque" of bolted electrical bus connections
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Performing "retorque" of bolted electrical bus connections
Eaton offers switchgear with no-retork promise.
Others recommend a periodical disassembly with new paste and burnished contacts, etc.