single hole or double hole lugs 2

[singapore11singapore]

Hi,
I am seeing more customers asking for double hole lug connectors from cables to busbar connection.
what are the reasons for this? what are the advantages of double over single, and what are the disadvantages.

 

[davidbeach]

More contact surface, better distribution of contact pressure. The higher the current the more of both you need. A lot of what I see are 4 hole pads.

 

[telecomguy]

Also, better resistance to turning the lug and loosening the hardware.

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[jraef]

To that last point, sometimes on large power devices where there can be a lot of fault current potential in the circuit, the issue of the lugs not moving under the extreme mechanical forces during a fault can mean the difference between getting a withstand rating of 25kA or 65kA, and/or having to make the device larger to allow for more separation in case the single hole lugs do rotate under duress. I had that issue come up in an SCCR )Short Circuit Current Rating) test of an 800HP soft starter at 85kA. The testing agency did the connections with single hole lugs (because we didn't specify) and they bent, turned, lowered the separation distance and allowed a flashover. No bueno... We rebuilt it and insisted they use two hole lugs, passed with flying colors. But from that point on, our UL listing REQUIRED that two hole lugs be used for installation.


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[racookpe1978]

Now, once you do specify a double hole (or four hole) bolted connector, YOU have to be able to get enough room AFTER the connector plate for the extra length of wires and cable bends to be routed and pulled and hooked up - which are NOT small for 1 and 2 inch dia copper cables) before interferences: hole in the concrete for example, nearby equipment housings, the other end of the wire or the other end of the equipment housing where the cable penetration is.

So, for the new turbine exciter, we have 4x 2 inch diameter leads that had to come vertically up through a 6 foot thick concrete floor. Then bend in a complex loop to be bolted horizontally to the copper plates on the exciter. The resulting "cable loops" in midair blocked access through the exciter equipment housing on that one side, so they needed an extra door in the housing. It was tight enough that to get room for the lowest of the cable loop, we "rounded off" the drilled holes in the concrete to be able to start the bends a little bit under the floor level.

 

[vikasbly44]

difference between getting a withstand rating of 25kA or 65kA, and to make the device larger to allow for more separation in this case the single hole lugs do rotate under duress.

 

[stevenal]

Received an outdoor breaker equipped with four hole pads that were perpendicular to the bushings. Each pad was attached to the bushing via a single bolt, and came loose during assembly. Fault current forces would easily have loosened the bolts. The manufacturer supplied stud style connections when we pointed this out. Specification now calls for more than one bolt.