Questioning Torque Values

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mark32

Senior Member
Location
Currently in NJ
For those that use torque wrenches on their terminations, do you ever question them?

For example, I swapped out a FP panel today with a 150 amp main breaker Square D Homeline panel. The labeling recommends 250 in.lbs for the main terminals for #4-250mcm. I got up to 150 in.lbs and left it at that. At that point, I felt like the aluminum lug wouldn't take much more, certainly not 100 in.lbs more, before stripping out. I also question the validity of the values because of the wide range of wire sizes, yet they all have the same value? The optimum torque for a #4 conductor is the same as 250mcm? Even the smaller gauges seem off, 14-10 awg is 20 in.lbs for the neutral bars. 20 in.lbs is like nothing for a solid #10. I like doing things the right way, which is why I purchase and use torque wrenches when doing electrical and auto work. I'm sure all of us have, at one time or another, stripped out a bolt hole or snapped off a bolt and once that happens you never really forget that feeling, it's terrible and one that you want to avoid, of course :) This is not the first time I've struggled with trying to abide by the recommended torque values and fearing I'm about to damage some equipment. Anyway, I wanted to hear some thoughts from my colleagues about it.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
I always use a torque wrench when called for in automotive and motorcycle engine work, but almost never in electrical work. I'd rather use my experience, judgement, and feel when making electrical terminations.
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
I'm always a little afraid when torquing because some of those values look too high, but I have learned to trust them. I haven't broken a stud off since I started using the torque wrench/screwdriver
 

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The optimum torque for a #4 conductor is the same as 250mcm? Even the smaller gauges seem off, 14-10 awg is 20 in.lbs for the neutral bars.

For the most part, the torque rating is based on the size and material of the fastener, such as bolt or screw, not the item being fastened.
 

Strathead

Senior Member
Location
Ocala, Florida, USA
Occupation
Electrician/Estimator/Project Manager/Superintendent
I always use a torque wrench when called for in automotive and motorcycle engine work, but almost never in electrical work. I'd rather use my experience, judgement, and feel when making electrical terminations.

Didn't I see something in the 2017 code revisions that is going to require us to use a torque wrench when torque values are provided?
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Didn't I see something in the 2017 code revisions that is going to require us to use a torque wrench when torque values are provided?
Probably, as well as the need to follow manufacturers' instructions, but, since we're still on the '11 NEC in VA, I'm not concerned . . . yet.
 

rambojoe

Senior Member
Location
phoenix az
Occupation
Wireman
i really doubt the 2 values are being mixed up. the metal on these socket heads are junk. the big mistakes i see are...

-uncalibrated tourqe wrenches and nothing kills me more than pulling out a shop tourqe wrench that was put away, still cranked up to 80ftlbs

-using a 3/8's drive for any inchlb rated lug. should only be 1/4"

-and last, not a huge deal but none the less.. having to re-land a conductor after a mistake.

I've stripped the socket with the correct procedure before.. but only on ocd terminals. for bellveus and the like you sorta need a tourqe wrench. some of the shut downs I've had the pleasure (not) to be a part of, with the utility foreman, city inspectors, my boss, and god watching you- you had to use a proper wrench when landing on certain systems. for 120 inchlb's? I could give you that in my sleep... by feel.
 

romex jockey

Senior Member
Location
Vermont
Occupation
electrician
We had one area AHJ make a deal out of wrench calibration , only to find that it's more cost effective to buy a cheap wrench annually.

We had another point out that much 110.3B torque directives mention annual re-torque

methinks it a no-win scenario
:weeping:
~RJ~
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
We had the POCO watching us terminate on the meter can load lugs a couple days ago. The usual response from those that haven’t worked with us before is “Huh? What do you torque them to? We use an impact.”

I have 3/8 torque wrench that includes 120 In lbs in its range. It took me four stops and an hour to find it in a neighboring town that was still 30 minutes from the job site. Why in the world would I continue to look for a 1/4” drive?
 
Ill be hoonest I dont have a lot of faith in torque values. I read a study on it, I dont remember where maybe it was machinery's handbook, and due to differences in thread tolerance, cleanliness, lubrication, material, surface finish, etc, torque values really arent that accurate outside of the lab. Maybe I am wrong, but I am paranoid a lot of these torque values are one of these things that have been around forever (like lock washers - useless) and there isnt a lot of rigorous study behind them from an electrical standpoint. I think there are some good engineered joints, like often you will find in switchgear that employ belleville washers, but as far as a mechanical lug with a range of sizes and materials, hmmmm.....
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2020 NEC
Whats next, tourqe switches and plate screws?

Yes. How do you do, I use a Torque screwdriver.

http://qcode.us/codes/fountainvalley/

Fountain Valley Municipal Code
Title 18 BUILDING CODES AND REGULATIONS
Chapter 18.20 CALIFORNIA ELECTRICAL CODE
18.20.030 Continuous inspection of aluminum wiring.

Article 310.16 is hereby added to read:

Aluminum conductors of No. 6 or smaller used for branch circuits shall require continuous inspection by an independent testing agency approved by the building official for proper torquing of connections at their termination point.
(Ord. 1517 §2, 2016)
 

mark32

Senior Member
Location
Currently in NJ
Hey guys,

Thank you all for the most excellent replies. I really thought most of the responses would say they always torque their terminations to the recommended specs, this is the MH forum after all :) Larry's post (#2) and electrofelon (#12) were especially appealing to me. Larry's because there really is no substitute for experience, let that guide the way in most cases. If something doesn't seem right, it probably isn't. And electrofelon because, from the looks of these values, they could very well have been just kicked around for ages without much if any honest studies done to yield more accurate numbers.

To rlundsrud, surely you jest haha. Like rambojoe said, the two value had not been mixed up. 150 ft.lbs takes quite a bit of effort to hit, at least for me at 130lbs. The lug in question would be toast well before 150 ft.lbs.
 

Adamjamma

Senior Member
Every time I have followed a torque spec it has been lighter than I would have tightened freehand, and not just a little bit lighter.

thats what I have found as well. It is scary sometimes how little they want it tightened but, it works. Just have not found a way to use british electricians bits with a torque wrench.. Wish there was an adapter for a torque wrench to go onto a screw driver...
 
You’ll met this guy named Murphy sooner or later, and you’ll see what he’s capable of.
Thats when you start using lock washers with nyloks and thread lock, and only buy stainless hardware...

Well I'll never use lock washers. They have been shown to actually make the joint more prone to loosening. Nylon locknuts are the thing to use.

Actually stainless hardware is another pet peeve of mine: It's not nearly as strong, expensive, and prone to galling. There are certainly some applications where their use is prudent, but not in general.
 
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