Nema 4 hole vs 2 Hole Lugs 1

[majesus]

For North American electrical installations, when it comes to power conductor termination into electrical equipment such as MCCs, starting reactors, VFD, etc, I am always confused on which Nema lug to choose: Nema 2 hole pattern or Nema 4 hole pattern? This is a simple question for someone with the experience. So would someone be so kind to clarify my confusion so that I know in the future what I should specify:

- First of all, is there advantage and disadvantage of choosing a Nema 4 hole pattern lug vs a 2 hole?
- Is there any "rule of thumb" on which pattern to choice depending on equipment type, voltage rating, conductor size, etc...?
- Should I be specifying the lug termination on my electrical equipment? Ie: "Provide Nema 2 hole lug for a #2/0 Conductor." Is it worth the effort to include this detail (and keep track that it is correct)? Or should I omit this, and let the installation contractor determine and supply?


Thanks,
Majesus

 

[rbulsara]

The battle generally is between 2-hole vs. 1-hole lugs and not 4-hole. Unless specified otherwise you would get single hole lugs as they are cheaper to buy and install.

2-hole lugs prevent lugs turning when tightening. Better installations use 2-hole long barrel lugs (vs. 1-hole lugs)

4-holes may be required on the busbars or spade connections.

Rafiq Bulsara

http://www.srengineersct.com

 

[jghrist]

4-hole pads have more contact area and can handle more current. I don't believe that there is a standard answer to when to use 2-hole vs 4-hole. If the termination has 4 holes and you are going to use the full current capacity of the equipment, then use a 4-hole pad.

http://www.hubbellpowersystems.com/catalogs/connectors/ST.pdf

has a table of ampacity ratings of Anderson bolted pad connectors.

 

[majesus]

On the current project I'm working on, it seems everything is either 2 hole or 4 hole lugs. Most vendors are providing us with the 2 hole option. However, for example Toshiba VFDs are coming with the following on their 1300HP VFDs (300MVI): 4 hole on the incoming and 2 hole on the load side. I dunno why that is.


If I have the option, I will specify 2 hole. I see it as the best option in terms of the 1,2 and 4 hole option. 2 hole prevents lugs turning when tightening. The 4 hole option seems to be an overkill and is not necessary. Why make it more complicate in terms of installation and cost if not required.

 

[jraef]

The 4 hole option seems to be an overkill and is not necessary. Why make it more complicate in terms of installation and cost if not required.

I see it exactly the opposite. 4 hole provides better surface area for conduction, less likelihood of termination resistance over time if a bolt loosens between maintenance procedures etc. 4 bolts also distributes out the cable weight over more holes, decreasing the strain on each one. I would say use 4 hole whenever possible, but settle for 2 hole if space does not permit 4 hole.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[waross]

I agree with jraef.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[majesus]

Thanks guys for the reply. I am glad I asked. Ask for 4 hole, and see what the vendor comes back with an answer.