wire insulation under screw terminal 1

[jamesaustin11]

I was wondering how bad this can be,
It was under fuse block screw terminal, what is the potential hazard? Any information would be much appreciated. I have attached a photo of the wires.

 

[racookpe1978]

Well, it depends.

Total failure: No signal gets through, system burns up.
Total failure: No signal gets through, system never starts.
Total operation. No signal gets through, system never stops.
Total operation. Every signal gets through, system never stops.
Sometimes failure, sometimes operation: Signal/power gets through until plastic melts, then it either never gets through, or never stops.

 

[jamesaustin11]

Even with the length of the exposed wire lying on a metal surface of the fuse block terminal?

 

[waross]

With little or no contact pressure, the exposed wire to terminal connection may overheat. Heat generates copper oxide. Resistance goes up. Eventually a micro arc starts inside the terminal block. From that point it may be a short time until the contactor is destroyed beyond use.

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

 

[jamesaustin11]

Can you point me to where I might find this information, been searching the net and only found this forum?

 

[VEBill]

It's so basic and obvious that it might be difficult to find a formal discussion of the topic. 'How to connect wires to terminals' must be taught in the first hour of the first day of Electrician school.

Maybe track down the actual installation instructions for those exact devices (circuit breakers or whatever they are). If the manufacturer has as many lawyers as average, then there will be a 2-foot square sheet of instructions with every detail described.

 

[jamesaustin11]

Thanks for the information guys, much appreciated!

James

 

[waross]

Somewhere in the instructions there is often a specification for the length of insulation to be stripped off the wires.

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

 

[controlsdude]

I have this problem every time I have to start up equipment. Curse the electricians, tell them to strip the wire to where the insulation is not being torqued by the termination of the screw terminal.

Main reason is during vibration over time. When the screw terminal gets loose, the screw terminal backs off of the wire, but the insulation is still being crimped by the screw terminal. Now if its 3 phase you have a single phase condition. If its other control signals you lose these signals.

I have had this problem on some terminations, to whole cabinets where I had to get who terminated back in to restrip the wire terminations and retighten terminals.

This is my biggest gripe about electricians.

 

[dV8r]

It looks like the OP is looking for information to indict someone for "almost" causing a major problem when this should be used a learning experience for everyone and a lesson not to be repeated. Maybe a lesson even to read instructions and follow them. I would think that the information with the contactors specified how much wire needed to be bared.

 

[bacon4life]

Figure E shows the results have having insulation under the a terminal screw.

http://www.thecircuitdetective.com/melted.htm

 

[zappedagain]

For printed circuit board assemblies, IPC-610-D Section 6.2.2 has a target of 1 wire diameter of length between the a wire's insulation and the solder connecting a wire to a connector (i.e. the clamping point in this case). Acceptable variations are 2 wire diameters, or the wire touching the solder but not interfering with the solder joint. Anything outside of these dimensions can be classified as acceptable, a process indicator, or a defect, depending upon your build classification

For an assembly like this, UL/IEC 60950 or UL/IEC 61010 will define minimum spacing requirements for how close a finger model can get to an exposed conductor. These look applicable to the second wire from the right on the bottom. There are minimum force requirements to pull the wire out. It is required to 'clamp the conductor between metal surfaces', so I'd say clamped insulation violates that one. Other sections say as long as you can bend a similar size wire in any direction without making contact with another conductive part then it is fine.

Again, these are design guidelines. The installer has the ultimate responsibility to do it correctly.

Z

 

[djs]

I once did a start-up on a machine. When power was applied and the start sequence engaged, there was no movement or any sound from the machine. Upon checking I discovered that the power wiring to the motor had not been stripped, but inserted with all insulation intact into the terminal blocks and the terminal blocks tightened. That was a half a day down the drain.

 

[don01]

ah well er um .....
few words can describe that workmanship (that can be printed in public.)
This is why most industrial projects specify crimped terms.
If you are OEM then you are just buying warranty claims ,
If you are client side then YOUR projects are going to be unreliable with intermittent events
that level of inattention to tradesmanship is indicative of a second rate effort by the build team and thier leadership

Ok that's the rant over with
Set up a QA "team" walk through the terms and insist on seeing a tiny bit of daylight between the terminal and the insulation.
Note them, then call the supplier / sub contractor for rectification - (or back charge)
It would be a very easy claim to make against your local standards or even "not done in a tradesman like manner"

don't forget your client (internal or external) will not think well of you if the installation trips /fails / goes wrong
having said all that have a great day and enjoy the ride
Don

 

[wbd]

I would think this would fall under NEC 110.12 which states electrical equipment shall be installed in a neat and workmanlike manner. Further there is ANSI/NECA 1-2006 which is Standard Practices for Good Workmanship in Electrical Contracting.