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Old 03-10-2009, 02:38 PM   #1
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High resistance in bx...


Well, I had to fix a circuit...original box had too short of wire that broke off on me. I installed a junction box in the attic to extend with romex. Attached romex ground to the box with a grounding screw, used bx connector. Tightened locknut pretty darn tight.

It read 10 ohms from neutral to ground. Neutral connection is solid...so I'm thinking its the bx jacket. There is no box in between this run...so it should be a straight shot to the panel. I checked all the bx connections at the panel, pretty tight. I tightened them for luck...

Another room has the same issue, or at least it "had". It has its own 14/2 bx to the panel. It used to read 40 ohms from neutral to ground! Now it reads 1.5-3 ohms to ground. Maybe the tightening had an effect...but I couldn't even tighten the screws a hair, they were that tight already.

Is it possible that this is just bad bx, like a broken bonding strip? Or do you think there is a junction hidden somewhere?

*maybe the bonding strip was old and cracked when I was up in the attic?


Last edited by rgsgww; 03-10-2009 at 02:40 PM.
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Old 03-10-2009, 03:01 PM   #2
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High resistance in bx...


The DC resistance of the armor jacket should be very low, with or without the bonding strip. How about pulling the cable out of the connector and giving the jacket a good wire brushing. Nice shiny metal should have lower resistance than dull gray old stuff.

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Old 03-10-2009, 03:37 PM   #3
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High resistance in bx...


10A @ 3 ohms = 300w. That connection should get very hot.

BTW, I'd measure resistance this low by passing considerable current (~1A, a 100w bulb) through the connection at considerable voltage (120v).

The contact impedance of corroded metal connections may depend on current and on applied voltage, and rusty connections may actually rectify the AC.

Last edited by Yoyizit; 03-10-2009 at 04:40 PM.
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Old 03-10-2009, 05:15 PM   #4
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High resistance in bx...


Thanks for your replies, I will try to get up there sometime and clean up the connections. I may try a load on the jacket, but since its very close to other bx I may question the accuracy of the results.
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