Bus tap method.

J

JP23

Member
Location
California
I have always drilled and tapped bus bars but am wondering if just drilling and bolting
is sufficient for larger loads. Need to keep the power shut-down time to a minimum.
1200 amps with 4-350 MCM's into a quad lug. Any tap
related ideas, tips or methods appreciated. Been using grade 8 bolt sets with thick
washers and conical belleville's.
 
JP23 said:
I have always drilled and tapped bus bars but am wondering if just drilling and bolting
is sufficient for larger loads. Need to keep the power shut-down time to a minimum.
1200 amps with 4-350 MCM's into a quad lug. Any tap
related ideas, tips or methods appreciated. Been using grade 8 bolt sets with thick
washers and conical belleville's.
Click to expand...
I'm a fan of through-bolts, with Belville washers and Nyloks. The use of through-bolts and nuts made from matching materials (Gr.8 bolts & Nyloks) ensure you can develop proper clamping force, and aren't at the mercy of the material strength of the bus bar (copper or aluminum) for the female threads. The Belville washers help keep clamp load even with expansion/contraction from heating and cooling cycles, and the Nyloks make everyone feel better.

That method also eliminates the possibility of a broken tap. You're always one broken tap away from turning a 15min job into an 8hr job.


SceneryDriver
 
SceneryDriver said:
I'm a fan of through-bolts, with Belville washers and Nyloks. The use of through-bolts and nuts made from matching materials (Gr.8 bolts & Nyloks) ensure you can develop proper clamping force, and aren't at the mercy of the material strength of the bus bar (copper or aluminum) for the female threads. The Belville washers help keep clamp load even with expansion/contraction from heating and cooling cycles, and the Nyloks make everyone feel better.

That method also eliminates the possibility of a broken tap. You're always one broken tap away from turning a 15min job into an 8hr job.


SceneryDriver
Click to expand...
I was thinking along the same line thinking what a nightmare if the tap broke which is what prompted this thread. Lugs are commonly just through bolted on all the time but with the larger load I wanted to get some opinions. Using Ilsco PB4-500 lugs. Waiting for Square D to respond with their input and to see if they offer a kit. I thought they would
have the info readily available but they are sending it to their engineering group so it might take a little time. Better safe than sorry! Thanks!
 
I run a lot of mechanical thread shear numbers. Just no question a thru bolt with nut is far superior. A threaded hole will only be for convenience.

In ideal land, we want the bolt in the elastic but deformed zone as it will certainly resist loosening better, and the addition of the belleville is high 9s.
 
I would never consider using a tapped hole in a copper or aluminum bus to hold a lug (unless it's a factory setup), too many possibilities of failure (stripped hole, metal creep, thermal expansion, etc). Go with bolts & belleville washers. And there'll be less downtime when you don't have to run a tap in.
 
retirede said:
I’m too lazy to run the numbers, but I’d think using grade 8 bolts instead of 5s into a tapped bus gains you nothing.
Click to expand...
Grade 2 fasteners have higher yield than bus bar material (copper or aluminum). And cut threads as opposed to rolled make it even worse. Through bolts are definitely better.


ScenreyDriver
 
JP23 said:
I was thinking along the same line thinking what a nightmare if the tap broke which is what prompted this thread. Lugs are commonly just through bolted on all the time but with the larger load I wanted to get some opinions. Using Ilsco PB4-500 lugs. Waiting for Square D to respond with their input and to see if they offer a kit. I thought they would
have the info readily available but they are sending it to their engineering group so it might take a little time. Better safe than sorry! Thanks!
Click to expand...
It is hard to imagine that Schneider is going to provide advice on how to drill / modify the bus in a listed switchboard. Who is doing the field eval after?
 
ron said:
It is hard to imagine that Schneider is going to provide advice on how to drill / modify the bus in a listed switchboard. Who is doing the field eval after?
Click to expand...

ron said:
It is hard to imagine that Schneider is going to provide advice on how to drill / modify the bus in a listed switchboard. Who is doing the field eval after?
Click to expand...
True but I was thinking it can’t hurt to ask.
Just hoping for a bolt kit from them. It’s not a blessing from them for any instance but is what they use in their products. Also, in working all over Ca. many AHJ’s
don’t seem to be interested in looking at anything before the main.
 
Alwayslearningelec said:
Anyone have a pic of a tapped hole in bus bar as opposed to bolts
Click to expand...
Bussed gutters come with preinstalled lugs tapped to the bus so I was under the impression that this
was a preferred method despite common factory through bolted connections.
The input that tapped holes are just for convenience is enlightening. Another question
comes to mind is mixing metal types like stainless and zinc if matched types are not readily available.
I'm reading that that they should match but wondering how big of an issue it is.
 
JP23 said:
Bussed gutters come with preinstalled lugs tapped to the bus so I was under the impression that this
was a preferred method despite common factory through bolted connections.
The input that tapped holes are just for convenience is enlightening. Another question
comes to mind is mixing metal types like stainless and zinc if matched types are not readily available.
I'm reading that that they should match but wondering how big of an issue it is.
Click to expand...
Actually very important! Which is why I would not be randomly reaching for hardware without some EE evaluation. Galvanic reactions and conductivity come to mind, though issues with electrolysis in AC systems is not common, but VERY common in DC. I'm thinking solar there.

Imagine removing plug of good flowing copper to install a stainless bolt. I'm not a huge fan of stainless anyway as it loves to gall up, in which thread treatments are nearly mandatory.

Then you can get all wound up in the world of torque because antiseize will certainly change "torque", but in an ideal world, we are not wanting torsion, we want tension, as in elastic elongation of the bolt. I've been in talks all the way up to engine pylons on commercial aircraft on this. It is always a tricky subject.

It's possible to ignore all of that with the use of a belleville to assist. I probably would run a few numbers before just going with the "guud n tite" method. Remember the potential thermal cycling, in which think of something like engine head bolts. They are usually torqued right to near yield to tap well into that elastic zone.
 
fastline said:
Actually very important! Which is why I would not be randomly reaching for hardware without some EE evaluation. Galvanic reactions and conductivity come to mind, though issues with electrolysis in AC systems is not common, but VERY common in DC. I'm thinking solar there.

Imagine removing plug of good flowing copper to install a stainless bolt. I'm not a huge fan of stainless anyway as it loves to gall up, in which thread treatments are nearly mandatory.

Then you can get all wound up in the world of torque because antiseize will certainly change "torque", but in an ideal world, we are not wanting torsion, we want tension, as in elastic elongation of the bolt. I've been in talks all the way up to engine pylons on commercial aircraft on this. It is always a tricky subject.

It's possible to ignore all of that with the use of a belleville to assist. I probably would run a few numbers before just going with the "guud n tite" method. Remember the potential thermal cycling, in which think of something like engine head bolts. They are usually torqued right to near yield to tap well into that elastic zone.
Click to expand...
Great input! Thank you. From the factory I see 600MCM lugs bolted on with what looks like grade 2 bolts a couple washers, standard lock washer and a nut. Bus splice kits usually have the bellevilles.
 
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