Bolts for Ground lugs

[iwire]

OK Miv, your right, using products as designed means nothing.

I should have just tek screwed the lugs to the cabinets.:roll:

What is the probability that you will have a fault that utilizes the full capacity of all of the EGCs at the same time?

In this particular installation that would not be possible, this is supplied by a generator that is over 600' away. The fault current will not be that high. But my comments where not aimed specifically at the installation I had a picture of.

 

[hillbilly1]

I know you put a bond bushing on that conduit for the grounding electrode.:grin:

 

[iwire]

I know you put a bond bushing on that conduit for the grounding electrode.:grin:

Nope, did not need one on either end.

 

[JohnJ0906]

What is the empty conduit for? (Looks like ?")

 

[iwire]

That is a 1" run for the transformer GEC.

 

[iwire]

I don't know, maybe 3/4" I can't really remember, keep in mind that conductor on the right hand end of the lugs is 600 Kcmil

 

[infinity]

That is a 1" run for the transformer GEC.

Can you put a #3/0 in a 1" or 3/4" LB?

 

[mivey]

OK Miv, your right, using products as designed means nothing.

I should have just tek screwed the lugs to the cabinets.:roll:

Not sure what that response is supposed to mean.:roll: I'm not trying to badger you.:smile: Let me word it a little different:

If you are talking about this installation, then I think Larry is correct that you could use the last lug in the same manner as the others. It would seem pretty obvious that there is plenty of "meat" & remaining capacity available for current flow. Just compare the size conductor you used vs what the lug was rated for. I would call that more than a wild guess. I might even call it an educated guess on his part.

Consider that you have lost about 15% of the pad area. Also, since this pad area is on the edge, I would not think that you have lost 15% of the current capacity of the pad. You should still have plenty of capacity available for another conductor of like kind (in other words, 4 conductors of 85% or less rated lug capacity).

If you are talking about an installation where you have 600s in the three lugs, then I think you have about used up the lug's reduced capacity. While you could say you have used up 3/4 full capacity (or 88.2% of the available), there is probably some room left. This is because there is better contact around the bolt holes (and this would be considered in the rating), so you probably wil not have lost a full 15% of the capacity.

Also, I agree with you and some of the others that you should use a full-sized bolt. Anything less would require a closer look and the current handling requirements. You get more area under the bolt head, higher torque, etc as referenced in Jim's #16 and by the link I posted. Sorry Rob.

[edit: had to fix the % typo. I'm assuming the lugs are rated for 4 600s]

 

[mivey]

BTW, I forgot to deduct for the pad area lost by the bolt-hole:roll: , but the idea is the same.

 

[iwire]

Not sure what that response is supposed to mean.:roll: I'm not trying to badger you.:smile: Let me word it a little different:

If you put all that effort into it then it is no longer a WAG.

Larry said he would just do it with no more then his own judgment. That is what I had a problem with.

I have to say having an engineer throw caution to the wind regarding wire terminations is most unusual.

 

[infinity]

Also, I agree with you and some of the others that you should use a full-sized bolt. Anything less would require a closer look and the current handling requirements. You get more area under the bolt head, higher torque, etc as referenced in Jim's #16 and by the link I posted. Sorry Rob.

IMO your size to torque comparison is incorrect. For the same quality of bolt then I would agree that larger size likely means higher torque. But using a low grade 1/2" bolt in a 1/2" hole in a lug does not mean that the connection will be more mechanically secure than say a 3/8" high torque bolt. Simply using a larger bolt will not automatically ensure a better connection.

 

[iwire]

IMO your size to torque comparison is incorrect. For the same quality of bolt then I would agree that larger size likely means higher torque. But using a low grade 1/2" bolt in a 1/2" hole in a lug does not mean that the connection will be more mechanically secure than say a 3/8" high torque bolt. Simply using a larger bolt will not automatically ensure a better connection.

So what is the limit?

If I had a lug with a 5/8" hole could I use a 10/32?

 

[Pierre C Belarge]

This is a very good thread for several reasons.

1. this topic is a good topic, something we all perform, but maybe do not think enough about what we are really doing..."installing by habit"

2. the pictures really help support the questions/answers

3. There is good conversation about the bus-bolt-surface area ratio in regards to current carrying ability.


I have installed 1000s of these types of terminations, from small to very large in my career. Most of the time it has been engineered, especially the larger terminations, hence little thought as to it performing properly on my part.

The discussion in this thread has been mostly towards "experience" and not towards engineering.
I agree that in some instances we can draw on our past experiences to gather enough information to make a sound judgement as to whether or not a termination will work for the installation at hand.

What I have learned over the last few years is to "pass the responsibility" to those who know more than I.


I have grounded/bonded large transformers in the past. There have been many instances where we did not use a busbar that large. Based solely on my past experience, I will say that install will be sufficient for its task, especially as Bob mentioned the source is quite the distance from the transformer.

On the other hand, if there is some concern, utililize the expertice of an engineer.


One other thing. Also based on my experience, I would venture to say that the open lug on the overhanging bus would be sufficient for termination.
What I would like to see is a response from an engineer who could say, "yeah or neah" to my response.


P.S.
Take a good look at the 2 pictures Bob posted of the transformer installation. There are many good 'aspects' of an install in those pictures.

 

[Pierre C Belarge]

IMO your size to torque comparison is incorrect. For the same quality of bolt then I would agree that larger size likely means higher torque. But using a low grade 1/2" bolt in a 1/2" hole in a lug does not mean that the connection will be more mechanically secure than say a 3/8" high torque bolt. Simply using a larger bolt will not automatically ensure a better connection.

Here is where I would depend on the Engineer to provide me with the answers. Pass the responsibility. :wink:

 

[mivey]

I have to say having an engineer throw caution to the wind regarding wire terminations is most unusual.

Caution to the wind? :roll: I might do it with your terminations, but not mine.:grin:

Watch those fingers at 3:57/5:51
http://www.youtube.com/watch?v=gxFfB3z6Szs

 

[mivey]

IMO your size to torque comparison is incorrect. For the same quality of bolt then I would agree that larger size likely means higher torque. But using a low grade 1/2" bolt in a 1/2" hole in a lug does not mean that the connection will be more mechanically secure than say a 3/8" high torque bolt. Simply using a larger bolt will not automatically ensure a better connection.

If you can get the required torque using a tiny bolt made of spider silk, then great, but you have lost the current-carrying capacity of the bolt. It would only make sense to add more "meat" to the connection.

I would also think having a larger bolt head would aide in the force dispersion and decrease deformation.

 

[infinity]

If you can get the required torque using a tiny bolt made of spider silk, then great, but you have lost the current-carrying capacity of the bolt. It would only make sense to add more "meat" to the connection.

I would also think having a larger bolt head would aide in the force dispersion and decrease deformation.

But are we relying on the bolt for current carrying or the surface contact between the lug and surface it's attached to?

 

[mivey]

But are we relying on the bolt for current carrying or the surface contact between the lug and surface it's attached to?

I think the surface contact, but I see no reason to throw out the added current carrying capacity of the bolt or the force dispersion advantage. Some may even include it as a factor, but I would have to investigate.

We had an issue once with some pads in a substation and the discussion was centered around current through the pad and the quality of the surface contact. I don't recall any bolt current specifically being discussed. And yes, the bolts matched the holes.

 

[jim dungar]

I think the surface contact, but I see no reason to throw out the added current carrying capacity of the bolt or the force dispersion advantage. Some may even include it as a factor, but I would have to investigate.

We had an issue once with some pads in a substation and the discussion was centered around current through the pad and the quality of the surface contact. I don't recall any bolt current specifically being discussed. And yes, the bolts matched the holes.

The bolt should never be considered in the capacity calculations. It is the surface area of contact that counts. Some lugs are built larger than they need to be to handle the number of conductors, in theses cases all of the lug does not need to be in contact with the mounting surface.

 

[nakulak]

I like the idea of using spider silk to install lugs. I'm going to look into that. If I can train the spiders to pull wire when they are not bolting in lugs, so much the better. I can only hope that the spiders I employ will have all the necessary paperwork to avoid any tax issues.