Exposed Copper on Power Wires

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cooltc2004

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I'm writing a company wide specification / procedure on building control cabinets, and I want to put a limit / rule for exposed copper on power wires traveling from the main breaker all the way to the terminal blocks (with components in between). Does NEC call out a maximum exposed copper when making these connections? Is any allowed or should the clamp (on a contactor for example) make contact with the insulation? Any help would be appreciated, as I've searched through the NEC without luck (doesn't mean its not there, just maybe looking in the wrong section)
 
jumper

jumper

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cooltc2004 said:
Yes. Once the wire is fully inserted into the component, what is an acceptable amount of exposed copper on the wire?
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I am guessing you want a more techinal answer than "a tad".:)

There is a chart somewhere in the NEC that would define the distance between live conductors and ground and each other but a strip length is not defined.
 
qcroanoke

qcroanoke

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jumper said:
I am guessing you want a more techinal answer than "a tad".:)

There is a chart somewhere in the NEC that would define the distance between live conductors and ground and each other but a strip length is not defined.
Click to expand...

We comply with MIL-I-45208A, MILITARY SPECIFICATION: INSPECTION SYSTEM REQUIREMENTS
Which is probably way yonder more than you want to know. But it's in there.
 
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cooltc2004

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I can open that up to any information that would help.

We use to leave "a tad" and got complaints from the field. Without my knowledge, the guys on the floor were told by management to have "no exposed copper", which resulted in not enough insulation being removed for an adequate connection.

I'd like to go back to having a minimal amount of exposed copper so that there are no problems in the future, I just want to have good ammunition to fire back with if the customer questions our logic. The reason I specified NEC is because when you mention that spec to most people dealing with electrical components (electricians or not) they tend to respect it.
 
qcroanoke

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
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jumper said:
Yes and I deal with job specs, but OP specificaly asked about the NEC.
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Understood and you told him its not there in the NEC, I told him a place where he would find it.
Granted that spec is not the NEC.....
 
hbiss

hbiss

EC, Westchester, New York NEC: 2014
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EC
Nothing in the NEC that I can think of. It really falls under workmanship. I'm trying to decide whether to call this too picky or not. I could see the point if the termination is insulated, there should not be any exposed copper (the simplest example would be an insulated crimp-on or even a wire nut). But if the termination is not insulated what difference does it make? Anything within reason (a tad) should be acceptable, other than that you are costing additional labor. It would be nice to look at a panel installation and see that every conductor is stripped back exactly 1/16" from the breaker lugs but that's up to the installer as to whether he wants to be an artist or get the job done.

That said, control panels are a different story. They are usually built under controlled conditions so uniformity and neatness should be required and easily maintained. So decide on the stripping requirements and see to it that they are followed.

-Hal
 
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jaggedben

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Some, but not all, circuit breakers come with a guide on how much wire to strip.

I would probably write something like:

"Where a component is supplied with any instruction or guide on the minimum and/or maximum length of insulation to strip from a connected conductor, those instructions or guides shall be followed. In all other cases, exposed copper on conductors for less than 600V shall be no more than 1/8" from the terminal lug or housing and no less than 1/8" from other exposed conductors."

1/8" is close enough to 'a tad' for me, under 600V. Pick slightly different numbers if it pleases you, depending on the components you use and the voltages.
 
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jim dungar

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cooltc2004 said:
I'm writing a company wide specification / procedure on building control cabinets, and I want to put a limit / rule for exposed copper on power wires traveling from the main breaker all the way to the terminal blocks (with components in between). Does NEC call out a maximum exposed copper when making these connections? Is any allowed or should the clamp (on a contactor for example) make contact with the insulation? Any help would be appreciated, as I've searched through the NEC without luck (doesn't mean its not there, just maybe looking in the wrong section)
Click to expand...

Is your equipment built to UL508A standards? Have you looked into using NFPA 79 as a reference for your panels?
The NEC is 'intended' for premises wiring.

And as someone else mentioned, there are usually 'strip lengths' provided with the equipment
 
Jraef

Jraef

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cooltc2004 said:
I'm writing a company wide specification / procedure on building control cabinets, and I want to put a limit / rule for exposed copper on power wires traveling from the main breaker all the way to the terminal blocks (with components in between). Does NEC call out a maximum exposed copper when making these connections? Is any allowed or should the clamp (on a contactor for example) make contact with the insulation? Any help would be appreciated, as I've searched through the NEC without luck (doesn't mean its not there, just maybe looking in the wrong section)
Click to expand...
Control cabinets for industrial machinery would fall under NFPA79.

Section 12.2.1.3 would apply to general circuits:
12.2.1.3 Exposed, nonarcing, bare, live parts operating at
50 volts ac (rms value) or 60 volts dc or more within an enclosure
or compartment shall have an air space of not less than
13 mm (1⁄2 in.) between them and the uninsulated walls of the
enclosure or compartment, including conduit fittings. The air
space for uninsulated doors of the enclosure shall be not less
than 25 mm (1 in.). Where barriers between metal enclosures
or compartments and arcing parts are required, they shall be
of flame-retardant, noncarbonizing insulating materials. ...
Click to expand...
This is what (conceptually) Jumper was referring to.

But technically, the code(s) don't absolutely require that your conductors be insulated at all, think bus bars. It's just that if not insulated, they are mounted in a manner that is safe. Insulation makes that a whole lot easier though. :roll:

Then still:
3.3.41 Exposed (as applied to live parts). Capable of being
inadvertently touched or approached nearer than a safe distance
by a person. It is applied to parts not suitably guarded,
isolated, or insulated. [70:100]
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The end of that is a reference indicating it is the definition used in NFPA70 (the "NEC") section 100 as well.

"Suitably" is one of those nebulous terms that gets people in trouble. If someone gets hurt, your idea a "suitably" can be shown, by a good lawyer, as being incorrect, evidenced by the injury in question. So in that context, the answer would be zero exposed cable, right? It's not practical of course, but it's also not spelled out as an absolute distance either. I'd say use common sense. But since you are tasked with writing a spec, I think it's going to come down to you picking a number and being willing to stand by it. 1/8" sounds like a workable value to me, others might say 1/4". the use of "finger safe" IEC components would be something to think about too. Although not in any NFPA documents, that concept, IEC-60529, says that "finger-safe" as defined by IP-2X, is if a 12.5 mm (1/2 inch) metal sphere probe 80 mm in length (the size of an average little finger) is unable to make contact with any potentially energized circuit component within the assembly. I've seen that standard used.
 
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Besoeker

Besoeker

Senior Member
Location
UK
jumper said:
I am guessing you want a more techinal answer than "a tad".:)

There is a chart somewhere in the NEC that would define the distance between live conductors and ground and each other but a strip length is not defined.
Click to expand...
And who would measure each conductor anyway..............
 
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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
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Consulting Electrical Engineer - Photovoltaic Systems
If there is enough space to get your finger onto the metal of the conductor between the lug and the insulation, it's probably too much, but I don't recommend checking it that way. :D
 
Jraef

Jraef

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ggunn said:
If there is enough space to get your finger onto the metal of the conductor between the lug and the insulation, it's probably too much, but I don't recommend checking it that way. :D
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Why not? That's how I check for rotation. 2 fingers on the phase conductors, if my hand jerks to the right, it's ABC, if it jerks to the left, it's CBA.:thumbsup::thumbsup::jawdrop:

Just kidding... do NOT try this and home!

Comes from a fun moment in my life with my now deceased business partner Gene. We were working on cranes at Boeing with overhead duct-o-bar power rails and one of the young electricians we had hired to pull wire etc., who had zero exposure to industrial work to that point, asked how we knew which phase was which. My partner, who was 6'8" with a long reach, immediately put his fingers up to the bus bars and touched two of them, then jerked his hand with a twist, then told him that jerk left/right story. He of course knew for sure I had locked off the disconnect, it was part of our daily safety routine. But that kid didn't know and freaked out. :eek: Gene was going to leave it at that, I made him tell the kid the joke because I was afraid he would take it seriously. :slaphead: I'll never forget the look on that kid's face or how hard we all laughed up on those catwalks.
 
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