"Nobody torques a breaker"

[sfav8r]

I was recently installing a new service at a residential project where other work was going on. One of the other electricians noticed I was torquing the main lugs (it's hard not to notice those cementex handles) and inquired as to why I was torquing them.

To make a long story short, he made a comment that made me wonder. He said "I bet you can't site a single example since records have been kept, where over tightening a circuit breaker has caused any problem."

I torque primarily because there are torque specs and I don't see any valid argument not to. But I confess I don't really know what problem would be caused by overtightening (assuming it wasn't a ridiculous amount).

Any info?

Thanks

Rod

 

[George Stolz]

Re: "Nobody torques a breaker"

Well, I've had experience where a big guy at our shop tightened lugs too tight, and although the lug didn't snap while he was standing there, it failed about four months later.

Under-torguing = arcing.
Over-torquing = broken lugs arcing.

If it had been a neutral, we could have had a pretty justifiable bill from the tenants.

 

[bphgravity]

Re: "Nobody torques a breaker"

The fact of the matter is that the terminations of conductors are just one of many points that could lead to failure at some point down the road. In most cases, improperly torqued connections will not lead to an immediate failure however could result in a loss of system life over time.

So, the other worker was probably correct. There is no real way to prove that a breaker / connection / conductor / insulation / etc... has failed directly due to an improperly torqued connection. However, it can be shown that improper torqued connection will lead to failure of these items over time.

There are many requirements of the code that are intended to provide protection of things that "might" happen and not necessarily "will" happen, but that doesn't make them less important in many cases.

 

[pierre]

Re: "Nobody torques a breaker"

Over torqueing may destroy the strands in a conductor, or mishap the lug itself causing failure - sometimes the failure may be years, sometimes it may be days. I have seen both.

Manufacturers test and retest for torqueing and install the instructions to CYA for themselves.

I read somewhere that failures in terminations is one of the largest percentage of failures in our industry. Failure of terminations can almost always be found to be the installers fault.

 

[charlie tuna]

Re: "Nobody torques a breaker"

having been doing infrared testing since 1989, i can tell you that undertorquing is the bigger of the two choices. but as an example a particular office building might have had one "big armed" guy terminating certain equipment--say elevator disconnects. and he overtorques the connections--well the actual terminal remains operational --but while overtorquing, he has bent the blade area of the disconnect, so the blade has lost surface contact and is causing a problem in it's operation. remember, a termination that operates at 40 per cent load can withstand a poorly terminated connection for it's lifespan. while the same terminal operating at 80 per cent load will fail--it takes the combination "load-torque"!
and i have seen damage to breaker terminals from "overtorquers". the proper way is to hold the terminal stationary with a wrench while applying proper torque -- then allow it to set and then re-torque it.

 

[brian john]

Re: "Nobody torques a breaker"

Over torquing can and is a problem, maybe not as big as a loose connection but still a problem.

One advantage of torquing is most electricians mark all that was torqued and are less likely to miss a connection.

I was on a load test of a UPS battery system, immediately after applying load during the battery discharge test the inter cell connector blew off several batteries. We stopped the load test and summoned the electrician and asked him if HE FOLLOWED INSTRUCTIONS for installing the inter cell connectors as we had recommended. Prior to installation we met with the contractor to instruct his people on installing batteries. The electrician informed us he had torqued the batteries as instructed. We asked to see his torque wrench he purchased for the job. He bought a foot pound wrench NOT A inch pound wrench and had torqued the 1/4 bolts to 115 FT LBs NOT 115 inch LBS.

Also did a follow on a separate job where we were required to check all connections prior to the owner taking control of the building, several of the bolts snapped as we attempted to torque them to the re-torque value specified. The electrician
told us he was aware of the importance of proper torque and used as breaker bar inside a 3 foot piece of pipe to torque all bolts a tight as possible.

I believe most connections that are tight are most likely over torqued. Torque for a branch circuit breaker is 20 inch lb. (from Memory it may be a bit higher) watch any electrician tightening a connection he/she puts all he /she has into it.

Over torque of connections may result in those connections failing with a downstream fault, due to magnetizing forces and the stresses placed on the cables, bus and connectors during the fault.

[ April 30, 2005, 03:58 PM: Message edited by: brian john ]

 

[joebell]

Re: "Nobody torques a breaker"

I don't understand , If you are properly using the torque wrench to tighten the lugs to the manufacturers listed specifications how could you over tighten? :confused

 

[brian john]

Re: "Nobody torques a breaker"

Joe:

Not sure if your post is addressing my post, but if so please reread my post.

 

[celtic]

Re: "Nobody torques a breaker"

Originally posted by joebell:
If you are properly using the torque wrench to tighten the lugs to the manufacturers listed specifications how could you over tighten?

The key is "properly torqued to manufac. specs". I see nothing confusing about that.

 

[joebell]

Re: "Nobody torques a breaker"

no Brian my post is a comment to the original but after rereading your example shows how this might happen. I am surprised that the 1/4-20 took that much force and didn't snap in the wrench.

 

[brian john]

Re: "Nobody torques a breaker"

Joe we were surprised also.
And you should have seen the folks leaving the room through the two doors and me holding an IR camera

 

[bigjohn67]

Re: "Nobody torques a breaker"

The torque rating has nothing to do with the "connection". Rather how much stress the "lug" can safely be tightened before breaking.

How many times have yall overtightened a "copper Kearney" and it "Pop" on you. (stripped)
At that point, throw it away and get another one.

 

[templdl]

Re: "Nobody torques a breaker"

NEC Art 110.3(B) Installation and Use?? Listed or labeled equipment SHALL BE INSTALLED and used in accordance with any instructions included in the listing and labeling.

Or is it situational ethics where the code is followed where we choose to do so, i.e.to torque in accordance to the manufacturer's listing and instuctions or to ignor them.

 

[charlie]

Re: "Nobody torques a breaker"

IMO all connections should be torqued . . . period. I know that the testing laboratories torque all the connections. Since most termination failures are because of improper torquing, why not take the time to do it right?

 

[brian john]

Re: "Nobody torques a breaker"

The torque rating has nothing to do with the "connection". Rather how much stress the "lug" can safely be tightened before breaking.

BigJohn:

I disagree with this statement, otherwise torquing a connection would stress the bolt and the bolt could fail under further stress like a downstream bolted fault. And if you use a torque wrench and the connector fails then you have a defective product.

http://www.surebolt.com/Bolt-Tutorial-BS.htm

And Charlie I agree with you, CRAFTSMANSHIP, I do believe,

[ May 09, 2005, 02:55 PM: Message edited by: brian john ]