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How to Identify Old Home Wiring Problems


By Dave Rongey - Summary:

How to Work with Old Electrical Wiring: Repairing Old Electrical Wiring, Old Electrical Wiring Problems.

Identifying and Repairing Old Electrical Wiring Problems

Electrical Question: I have a 110 year old home that always has odd electrical challenges. Much of the electric has been updated or modified through the years but multiple owners have left a variety of quality to the fixes.

The current issue that has me stumped:

So this has me stumped, and these are my concerns and questions:

  1. How dangerous is it for these lights and receptacles to be sitting as a double positive element?
  2. What could have happened along the line to cause this?

I cant imagine how “out of the blue” this section of electric could end up like this. A break in the neutral, OK- I could see that. But, to end up with both lines as positive. I Need help with that one. Any ideas?

This electrical wiring question came from: Chris, a Handyman from Virginia.

Dave’s Reply:
Thanks for your electrical wiring question Chris.

Application: Repairing Old Electrical Wiring
Skill Level: Intermediate to Advanced – Best performed by a Certified Electrician or Electrical Contractor.
Tools Required: Basic Electricians Pouch Hand Tools and Voltage Tester.
Estimated Time: Depends on personal level experience and ability to work with tools.
Precaution: Identify the circuit, turn it OFF and  Tag it with a Note before working with the wiring.
Important: Burnt or damaged wiring and circuit components should be replaced with new electrical materials of the same voltage and amperage rating.
Notice: Repairs to Home Electrical Wiring should be done according to local and national electrical codes and installing new or replacement electrical parts or equipment may require a permit and inspections.

How to Work with Old Electrical Wiring

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2 Responses to “How to Identify Old Home Wiring Problems”
  1. Dave Rongey says:

    Hi Chris,
    Various tests can be conducted on the circuit, starting with unplugging and disconnecting all of the loads, and then checking the polarity as well as amperage on both the hot and the neutral. If there is a voltage leakage between the two that is not causing a tripped circuit then the test will show, however sometimes the leak will not show unless there is a substantial load. I recently discovered a similar situation where the metal cable clamp of an old metal box was tightened so much that it scored the neutral which arced across but did not trip the circuit. Testing with a megger will be much more accurate for detecting possible faults within the circuit wiring. As you have stated, placing the circuit on an AFCI breaker is a very good safety measure as well.
    I hope this helps,
    Dave

  2. Chris Sahtterly says:

    I had a strange case last month where we had a dead short that melted piece of old BX Cable at the insulated bushing which melted right at the box clamp connector. It tested white neutral to ground downstream,where there was found burned jumpers in two boxes, not directly connected to each other, but the same circuit. I was able to pull the cut-in boxes and get unburned conductors on the existing wiring, and replaced the maxed 8/16 box with 20/40 and put all receptacles on AFCI breakers. AFCI found a mis-wired light with return from another circuit.
    This was originally discovered when the customer had plugged in a space heater, but has always used that plug for a space heater. No visual damage on the wiring to the heater plug, though it is spliced to the same circuit upstream. Could this be cumulative overload on a possible bad anti-short makeup? In the past at one of the burned receptacles they had a plasma TV for awhile, but has since been replaced with an LCD TV. So the overload condition might have occurred up to 3 years ago, and been lighter loaded ever since. Would it be worth testing all the wiring with megger? Do you have to un-wire all junction boxes before doing so, or just unplug all the equipment, TVs lamps dimmers?
    Thanks Chris