carbon from flash on emt.

[rong111]

hi all.
sorry i come up with all kinds of strange questions.

i was asked to replace a mains panel that flashed due to improper "handyman" work. of course i will pull all new home-runs where the insulation is burnt. however, i was wondering is there anything that states that emt with dark black carbon around it from the flash must also be replaced?
as long as the butt of the conduit where it makes contact with the collar is cleaned is this ok?
the integrity of the conduit is fine. it is just covered with carbon near the box. pulling new conduit would be a pain. since there are 19 runs and most over 12 feet before they reach a j box or collar that is hidden.


thank you.
ron g.

 

[ryan_618]

Re: carbon from flash on emt.

I think you would have to ask your AHJ that. 250.96 says that metal enclosures and raceways must be connected together so as to make an effective ground fault current path, whether you have an EGC or not. I don't think the charring would disrupt that, but it might. I would reccommend talking with your inspector.

 

[rong111]

Re: carbon from flash on emt.

it is making fine continuity. i will see what the ahj has to say.

thank you,
ron g.

 

[tim]

Re: carbon from flash on emt.

Your questions are not strange.

 

[rong111]

Re: carbon from flash on emt.

thank you tim. some people tell me i ask stupid questions for having been in this industry for a long time. i always like other peoples opinions on things. thats just how i am.

anyways the inspector made me replace this. i think it would depend on who the inspector is if this happens. the nec does not state that simply because the emt is discolored it must be replaced. i do not know if carbon deposits have any degrading effect on metalic tubing. however the stuff wipes right off with citrus cleaner. since i am honest i replaced it like the inspecter asked me to. intrestingly in another jurisdiction an inspector did not make me replace conduit that had lots of surface rust but no perforation. i do know that a certain amount of rust effects the impedance of metal. the stuff on this was the same stuff that you get when your friend holds his lighter on the roof of your van . it wipes right off.


thank you,
ron g.

 

[batch]

Re: carbon from flash on emt.

If it wipes right off and there is nothing wrong with the conduit why would anyone want it replaced?

 

[rhombus65]

Re: carbon from flash on emt.

I have found that sometimes you need to make your own judgement calls based on your own experience.

Time has shown me that when you ask an opion of an AHJ you are almost always going to get the answer you did not want. It is as if the AHJ is saying if you force me to amke a call I am going cover my *^%.

Now I have found that if you just leave the issue alone it goes away.

I can not see how a little bit of carbon on EMT could be a problem. What if the EMT was painted? would you have cahnged it than. Heck I get carbon on my hands all the time, but I don't cut them off.

 

[brian john]

Re: carbon from flash on emt.

We do a fair number of ?BLOW UP? repairs, what we look for is carbon on insulators. These should (MUST) be replaced. But IMO if the carbon is on a conducting surface, and carbon conducts what is the problem. We do try and clean up the mess as best possible. Spray 9 works wonderfully for removing carbon, then if there is metal damage the piece will be replaced.

 

[rong111]

Re: carbon from flash on emt.

he made me replace perfectly good conduit. so i did it. i am not one to challenge an ahj. especially since i rarley work residential and don't even know these people. i however know that the conduit i tore out was just fine. the insulators were not carbonized, they were charred.
so without even asking i pulled all new runs to the mains from their existing termination points. the collars on the conduit above the mains were badly rusted so of course i intended to replace those without asking either. maybe what happened, is he saw what a mess the whole deal was and just made a 'global' judgement call saying it all must be replaced to cover his a$$. anyways the job has been done already. i like sticking to the industrial side. in my experience employees of a factory or industrial plant are less likely to go tampering with the service than homeowners are. maybe because most service in a factory reads something to the affect of: "danger live 480v panel disconnect before servicing"? lol.


ron g.

 

[caosesvida]

Re: carbon from flash on emt.

I had an ac unit the 277 receptacle was tripping the breaker. I removed the cord and still tripped, I ohmed out the wires apart from the receptacle and no short. I noticed the receptacle had carbon on it. I replaced the receptacle and no problem. The arc flash had deposited the carbon on the receptacle and was shorting out from the ungrounded conductor to the grounding conductor. Firt time I had seen this and was very interesting.

 

[rong111]

Re: carbon from flash on emt.

carbon is conductive. it has no problem making a circuit trace from one point to another. caosesvida, now that you mentioned this scenario that may be indeed why they made me replace it. maybe they know more than me after all.

ron g.

 

[brian john]

Re: carbon from flash on emt.

were not carbonized, they were charred.

IMO your inspector was wrong on two accounts.

CHARRED is just as bad as carbon. This is carbon and is conductive additionally damaged insulators are more likely to absorb moisture. Which can be determental over the long term.
Working on 120/208-277/480 VAC (277/480 requires extreme caution) blow ups takes special considerations and care. I have been involved in several cases where electricians were seriously injured and/or killed, by assuming their ohm meter was sufficent for testing for shorts, after a ground fault or phase to phase fault.