250.12 Nonconductive Coatings

[illinial]

I'm teaching JW class on Grounding and Bonding, using Mike's book. I have one question: on 250.12, all nonconductive coatings are to be removed, OR the termination fittings must be designed for proper continuity.
I believe that 2 locknuts properly tightened would meet this requirement. True?

Also, does anyone know where you could get info as to whether a paint used on electrical equipment is conductive? My guess is that Elec. Manuf. use a conductive paint, as I have never had trouble getting a voltage tester to work by simply touching one lead to the paint. Does that sound logical? Went to several equip. vendor sites and got no information about conductivity of their paint.
Thanks. Don't want to pass on bogus info to my students!

 

[iwire]

Re: 250.12 Nonconductive Coatings

I keep a wire wheel in my cordless case to remove paint, if you ever have tried to weld you would notice how much the paint effects the connection.

I have never heard of any manufacturer using conductive paint, unless it said specifically on the equipment I would not count on it.

I probably still would wire wheel it to bare metal for a grounding connection.

The only reference I can give as to a washer that can cut through the paint is from 550.16(4)

The straps shall be fastened with paint-penetrating fittings such as screws and starwashers or equivalent.

[ December 28, 2003, 01:59 PM: Message edited by: iwire ]

 

[ryan_618]

Re: 250.12 Nonconductive Coatings

250.12 is on my top ten red-tag items on a service inspection. I fail about 33% of the jobs I look at for 250.12, in addition to others.

 

[jimwalker]

Re: 250.12 Nonconductive Coatings

Getting red taged once should teach them.I am not above getting taged but i learn from it.Shame on me if you get me twice.

 

[dana1028]

Re: 250.12 Nonconductive Coatings

250.12 "...or be connected by means of fittings designed so as to make such removal [paint, etc.] unnecessary."

Take a look at Soares, 8th ed, Chap 8 - Bonding Enclosures & Equipment.

P. 129-131 covers the testing of conduit fittings (for checking effectiveness under ground-fault conditions..."over 300 conduit fitting assemblies from 10 diff. mfrs.were subjected to a current test to simulate performance under ground-fault conditions.").

From pgs. 130-131: "A visual examination of all the conduit fittings with die-cast zinc locknuts showed there were 3 diff. constructions of the locknuts...flat, ribbed, or serrated...all fittings having die-cast zinc locknuts with serrations completed the current test with acceptable results [flat and ribbed locknuts did not complete the current test with acceptable results]...It appeared as though locknuts with serrations consistently penetrated through the enclosure paint and provided better electrical contact between the fitting and the ...enclosure."

"All of the conduit fittings that were constructed of steel bodies and steel locknuts completed the test with acceptable results. A visual examination of steel locknuts indicated that the nibs on these locknuts...provided for better penetration through the enclosure paint than the nubs on the die-cast zinc locknuts."

It goes on to explain in detail the test, results, findings....bottom line - zinc fittings with serrated locknuts and steel locknuts did just fine in penetrating the paint on an enclosure and providing an effective ground fault path.

[ December 28, 2003, 09:22 PM: Message edited by: dana1028 ]

 

[iwire]

Re: 250.12 Nonconductive Coatings

Dana that is true for fittings, but how about adding a grounding lug to a painted enclosure?

 

[dana1028]

Re: 250.12 Nonconductive Coatings

How are you attaching the grounding lug? I always drill, tap (a threaded hole) and use a screw to attach my lugs....painted surfaces do not become an issue.

 

[iwire]

Re: 250.12 Nonconductive Coatings

Most times a 1/4" nut and bolt for wire sizes below 3 AWG

Above that a 3/8" nut and bolt, most common when installing grounding lugs in transformers.

I personally do not rely on the bolt as the conductor, I prefer the lug to be in contact with the enclosure leaving the bolt as a fastener only.

I think Ryan might red tag you for not removing paint.

 

[ryan_618]

Re: 250.12 Nonconductive Coatings

Originally posted by iwire:

I think Ryan might red tag you for not removing paint.

I think bob knows me pretty well. Non-compliant.

 

[jimwalker]

Re: 250.12 Nonconductive Coatings

What about rust

 

[ryan_618]

Re: 250.12 Nonconductive Coatings

Originally posted by dana1028:
How are you attaching the grounding lug? I always drill, tap (a threaded hole) and use a screw to attach my lugs....painted surfaces do not become an issue.

Dana: For the most part, what you describe is already required by 250.8(???No book here), which discusses sheet metal screws not being used for grounding/bonding. With that in mind, 250.12 would be a moot point if the installation you discuss were compliant.

 

[ryan_618]

Re: 250.12 Nonconductive Coatings

Originally posted by jimwalker:
What about rust

I should hope that a NEMA3R enclosure is used if you are concerned about rust. I've never seen rust inside of a 3R enclosure (But I've not seen alot of things).

 

[dereckbc]

Re: 250.12 Nonconductive Coatings

This may be a little overkill, but I instruct and specify that painted surfaces have paint removed and brought to a shiny finnish, drilled to accept a two-hole compression lug, lightly coated with "NO-OX", bolts, nuts, flat, and lock washers be used.

When done properly they always pass a micro-ohm test (if tested), and I have never seen one fail over time indoors. Just my two cents worth.

[ December 28, 2003, 10:57 PM: Message edited by: dereckbc ]

 

[jimwalker]

Re: 250.12 Nonconductive Coatings

In FL i have seen many rusted out panels outdoors.Where is that picture someone posted that showed a service rusted so bad that nothing was left and the customer upset that poco pulled the meter?

 

[iwire]

Re: 250.12 Nonconductive Coatings

Jim you have to admit that photo is far from average.

Very little of the work I do is exposed to the elements.

You can always hit it with spray paint after the connection is made

Derecks mention of two hole lugs fit right in with some of our job specs.

We could not cad weld our electrode conductors from transformers to building steel on a job due to the smoke, the engineer had us use a standard lug bolted to building steel with two 3/8" bolts after taking a grinder to the steel.