Sparks and flames from low voltage conduit through a concrete floor

Location
Tavares Florida
Occupation
Facilities maintenance
We have a one inch EMT, with data lines, through a concrete floor that is creating sparks and flames. I have pictures of the conduit I would like to attach.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
Funny story..
At least to me anyway..
We had a bad primary cable some years back, and couldn’t thump it because the neutral was corroded too bad. I told a guy to go get the backhoe, let’s fix the neutral and thump the cable..
I left for a few minutes..
The line super came up and said to plug it in, see if they could hear it.
they did, and they did...
They plugged it in and they heard it come out of the telephone pedestal right next to them.
14,000 volts doesn’t play well with phone lines..

point is.. I agree with the others. There’s a fault somewhere that’s tracking on your data cables.
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
The problem started when a crew of workers spilled floor wax down the hole where the conduit penetrates the floor to the room below.
Oh crap! There’s a fire on the floor below. The wax went into the conduit into the panel...
😂
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Yeah, we need pictures and good ones too. Don't show us something that looks like Big Foot.
We need pictures of the conduit where it goes down through the floor as well as what's below.

-Hal
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
Don't see anything unusual. Where are the sparks and flames coming from? Looks to be some blackening around the hole through the slab from the underside.

-Hal
 
Location
Tavares Florida
Occupation
Facilities maintenance
Don't see anything unusual. Where are the sparks and flames coming from? Looks to be some blackening around the hole through the slab from the underside.

-Hal
The sparks and flames have been seen where you indicated in your question, right around the conduit where it comes out of the floor.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
The sparks and flames have been seen where you indicated in your question, right around the conduit where it comes out of the floor.
I don't doubt that this slab is a fire rated assembly. Where is the fire stop around the conduit? It should also probably be sleeved with schedule 40 pipe as well to 4" above the floor. There are UL listed assemblies that are also water resistant. Probably liquid wax resistant, for that matter. I don't see how data lines, in and of themselves, could be causing any fireworks, especially on the outside of the conduit.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Either the conduit has been energized or it's touching something that is energized.

From the OP, I expected sparking between an exposed cable and a conduit sleeve.
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
The first thing I would check is that data cable to see that it isn't damaged where it goes through the hole. There absolutely should not be any kind of voltage on that cable that would cause sparks and flame but you never know what somebody might have done.

The other thing (more likely) is that the conduit is contacting the rebar or reinforcing wire in the slab on the inside of the hole. Both the conduit and the rebar or reinforcing wire should be bonded to ground but It's been my experience that there still can be a considerable potential between the two. So, make sure the conduit is bonded back to ground but I'm open to suggestions on how to bond the reinforcing in this situation, short of breaking up the slab to expose it.

I don't think this had anyhing to do with the cleaning people spilling cleaner down the hole other than in trying to stop it from running down and cleaning it up they may have stuffed a rag down the hole which moved the conduit. So really, you should thank them for exposing what might be a serious situation.

-Hal
 

Jerramundi

Senior Member
Location
Chicago
Occupation
Licensed Residential Electrician
...they may have stuffed a rag down the hole...
A bit out of my league, but I was about to say... wouldn't there have to be something actually flammable in the hole, such as rag (good catch Hal)??

Is the OP certain there were actually flames? Or just sparks? You're also dealing with subjectivity here. Someone could have seen a single spark and dramatically described it as bursting into flames.

It would seem to me that all of the situations described above would create arcing / sparks... but for there to be ACTUAL FLAMES, there would have to be something flammable in the hole. The only thing I can think of, aside from unknowns, is either the jacket on the low voltage cable melting (which I don't believe it should) or the floor cleaner was flammable to a degree (which I don't believe it should be).

Either way, something is causing ignition which is a serious problem in and of itself... but for there to be actual flames, well... there has to be something flammable in there.
 
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