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Old 10-06-2011, 03:23 PM   #1
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Short ciruit with Romex 10/3 cable and cable connectors


I just had an experience today involving shorting of 10/3 romex cable where it passes through the throat of a typical 3/8 NM cable/box connector and would wish to share same with readers for their comments. I'm installing a Siemens 100amp/8 circuit sub-panel but only feeding it with a 30amp double-pole breaker and orange, 10/3 NMD90 cable. For now I'm only adding a few 15amp circuits (120V) only and 30amps is plenty for now. I ran the 10/3 cable to my Stablok main panel, using a 3/8 metal box connector to secure same as seen in photos below. At the sub-panel I used another metal box connector to secure the cable. I double-checked all my connections to ensure all was well before restoring power to main panel. Main breaker on and all is well until I set my new 30amp breaker and then flash! Instant short circuit with a good spark that instantly got my attention. I shut off the main power again to try and figure what the problem was. I soon found the culprit, a short right where the 10/3 cable passes through the throat of the cable connector.


When I initially tightened the connector on the cable I did not crank it down excessively but obviously enough that it compromised the thin outter sheathing and caused a direct short between the black insulated conductor and the connector screw/pad. At this point I removed the cable from the sub-panel also and found signs of sheathing damage there also, as per attached photos. I do not believe I used too much force when securing the wires but obviously the pictures say otherwise. Is 'finger-tight" enough or is there a specfic torque value for these cable connectors?
Attached Thumbnails
Short ciruit with Romex 10/3 cable and cable connectors-06-10-11_0001_edited-1.jpg   Short ciruit with Romex 10/3 cable and cable connectors-copy-06-10-11_0007_edited-1.jpg   Short ciruit with Romex 10/3 cable and cable connectors-copy-copy-06-10-11_0009_edited-1.jpg   Short ciruit with Romex 10/3 cable and cable connectors-06-10-11_0010_edited-1.jpg  

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Old 10-06-2011, 03:28 PM   #2
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Short ciruit with Romex 10/3 cable and cable connectors


I'm not sure those are romex connectors.
They look like ac/mc connectors.
Most romex connectors I use and see are the type with a screw on each side, and I have shorted those before.

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Old 10-06-2011, 03:28 PM   #3
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Short ciruit with Romex 10/3 cable and cable connectors


Finger tight or snug is sufficient. Connector may also have had a burr in the saddle.
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Old 10-06-2011, 03:29 PM   #4
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Short ciruit with Romex 10/3 cable and cable connectors


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Originally Posted by jbfan View Post
I'm not sure those are romex connectors.
They look like ac/mc connectors.
Most romex connectors I use and see are the type with a screw on each side, and I have shorted those before.
I they are listed for NM also.
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Old 10-06-2011, 04:18 PM   #5
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Short ciruit with Romex 10/3 cable and cable connectors


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I they are listed for NM also.
They may be listed but not what I would use for NM.
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Old 10-06-2011, 04:35 PM   #6
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Short ciruit with Romex 10/3 cable and cable connectors


Thanks guys for the quick reply. I'm obviously going to need to pick up some new cable and I'll make sure I'm using the proper connectors. I'll also have to keep tabs on the amount of tightening torque I'll be using. I'll downgrade from "tight" to "snug"!
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Old 10-06-2011, 05:11 PM   #7
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Short ciruit with Romex 10/3 cable and cable connectors


If you use something like the Arlington black button connectors you don't need to worry about screw clamps being too tight.

http://www.aifittings.com/catalog/no...in-connectors/
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Old 10-06-2011, 05:17 PM   #8
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Short ciruit with Romex 10/3 cable and cable connectors


Quote:
Originally Posted by virago View Post
Thanks guys for the quick reply. I'm obviously going to need to pick up some new cable and I'll make sure I'm using the proper connectors. I'll also have to keep tabs on the amount of tightening torque I'll be using. I'll downgrade from "tight" to "snug"!
Somewhat unrelated--Where is the sub-panel located? Do you need to protect the NM cable traveling vertically out of it?

When my basement wiring was done we either used armored cable (10/3 for the dryer) or ran NM but with a 2-3' long piece of PVC electrical conduit secured to a board or plywood strip to protect the cable below the joist level.
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Old 10-06-2011, 05:26 PM   #9
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Short ciruit with Romex 10/3 cable and cable connectors


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I ran the 10/3 cable to my Stablok main panel,



http://ismypanelsafe.com/fpe.aspx
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Old 10-06-2011, 07:52 PM   #10
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Short ciruit with Romex 10/3 cable and cable connectors


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Originally Posted by Code05 View Post
I they are listed for NM also.
I highly doubt it for those. Those are classic AC cable saddle connectors.
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Old 10-06-2011, 07:54 PM   #11
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Short ciruit with Romex 10/3 cable and cable connectors


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I highly doubt it for those. Those are classic AC cable saddle connectors.
Does anyone know of a good site or chart to describe the various type of connectors and what cables they are used for? I see many choices, I know some are better than others... this might be a good thread to post that in...
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Old 10-06-2011, 07:58 PM   #12
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Short ciruit with Romex 10/3 cable and cable connectors


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Does anyone know of a good site or chart to describe the various type of connectors and what cables they are used for? I see many choices, I know some are better than others... this might be a good thread to post that in...
Only the manufacturer's web sites. Most have full catalogs online.
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Old 10-06-2011, 08:28 PM   #13
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Short ciruit with Romex 10/3 cable and cable connectors


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Originally Posted by bubbler View Post
Does anyone know of a good site or chart to describe the various type of connectors and what cables they are used for? I see many choices, I know some are better than others... this might be a good thread to post that in...
Why not just read the printing on the bag or box before you buy?
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Old 10-06-2011, 08:41 PM   #14
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Short ciruit with Romex 10/3 cable and cable connectors


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Why not just read the printing on the bag or box before you buy?
I might not know what I'm looking for... or they might not have what I need and I don't realize it...

Didn't mean to hijack the thread, just seemed like a case where there was a misunderstanding about the type of clamp to use...

For example, I have a double gang switch box with four BX cables entering, they are going into what looks like an old version of an NMSC clamp, but clearly made for only BX (or MC) not NM. These things screw into the middle of the box and either side will clamp down on one cable. So, if I'm taking out one BX and retrofitting an NM replacement, how would I secure both the old BX that is not removed and the new NM that replaced a BX? Would a modern NMSC clamp work?

If retrofitting NM and old metal box with 1/2" KO's, what is the best type of clamp to use?
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Old 10-06-2011, 08:49 PM   #15
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Short ciruit with Romex 10/3 cable and cable connectors


The OP is in Canada. Not sure what the listings are on those connectors up there ....

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