The Circuit Detective    -  Solving a Shock

You should be able to walk under a tree or touch a lamp without the surprise of a branch in the face or a shock
The Circuit Detective's Diagnostic Tree

What Is the Source of a Shock at Home?


Caution: Please do not continue using your body to judge whether stray voltage is still there. I recommend a neon tester to check metal for hotness (a non-contact voltage checker may be too sensitive).

For this sort of ground-fault-ready-to-happen, two strategies are possible: either leave the ungrounded fault in place and locate it first (and ground things better later), or else provide a good ground to the thing that delivered the shock (thereby probably creating a breaker-tripping short) and then deal with it as you would any short. Though it feels less safe and I have to be more careful about myself, I find it more efficient as a professional to use the first strategy for going after shocks. You should only attempt what is safe in your judgment, according to your knowledge. I once had to hunt for a ground-fault which had energized all the metal-sheathed cables, all the pipes, and all the ductwork throughout a house and its basement. Walk softly (rubber shoes) and carry a big non-conductive stick for probing!

OK, if you have decided to leave the hot things hot, first see which circuit, when turned off, eliminates the hotness. Get well acquainted with what is part of that circuit and then turn it back on. See if any other things of that circuit show hotness, including the grounding hole of receptacles. ... (If the home was built after the 1960s, hotness is more likely to be limited to one thing or to the fraction of the circuit from which a ground wire has gotten disconnected; if the home was built before the 1960s it is more likely to spread hotness to various metal things if there is metal-sheathed cable that has lost its connection to ground.) ... If nothing else shows hotness, then (with circuit off) disconnect the hot (black) wire from the one item in question; if hotness has gone away (when you turn the circuit back on), then that item has a faulting wire or part within it. If hotness persists (from the ground wire being hot, for instance) then on this circuit unplug everything and turn all on/off switches off and turn only one switch in each 3-/4-way system the other way. Did one of these actions eliminate the hotness? Which one? Also look for any broken receptacles, like where a too-long silver cover-screw may have broken apart the receptacle's own plastic (we don't care about its cover). Also, take all covers off receptacles and switches and look for a ground wire curled up next to the hot terminals.

If the shock -- the hotness -- is not always there, might there be some automatic appliance or light that is responsible when it turns on? Or if the shock is only around at certain times of the day, consider what faulty appliance or light might be running at those times.

Beyond all this, pick a place midway along the circuit and (with circuit off) undo its hot wires there; if the shock-location hotness has disappeared when power is put back on, then the fault was coming from somewhere electrically between this midpoint and there. If the shocker is still hot, the fault is electrically back toward the panel from both of these places. You can reconnect the hots and repeat this divide-and-conquer procedure at other points to narrow the fault location down (keep a written record as you go). If nothing leads you to the fault itself, you can give a good ground to the shocking thing, so that a short is created and trips the breaker; then troubleshoot it as a Short.

© 2005-2012 Larry Dimock

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