AC Short? Voltage drop to lamp post


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Old 03-26-21, 08:51 AM
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AC Short? Voltage drop to lamp post

I have a lamp post which for some reason is only showing 67 volts AC. What could cause the voltage drop from 110 - 67? A short?

thanks in advance
 
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Old 03-26-21, 08:57 AM
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How are you measuring the voltage? I doubt a short would do it without tripping a breaker or burning something out but a lot of resistance could do it.
 
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Old 03-26-21, 09:11 AM
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Well we had the breaker trip (a while back) but it hasn't in a year or so. A few weeks ago i noticed the light was barely visible, i opened the top of the lamp post and used my meter to check the voltage on the incoming line and it showed ~67 volts AC.
 
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Old 03-26-21, 12:33 PM
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Here's what I would do. If the first part of any step doesn't agree with what you find, skip that step.

1. Identify which breaker for the pole light and turn it OFF.

2. Inspect the switch(s) controlling the light and check for good connections (backstabs aren't). If a switch is back-stabbed, reterminate using the screws. A failing back-stab could be the cause of your problem.

3. Remove the light fixture from the pole and check for corroded connections. Cap the hot and neutral at the pole with new wire nuts.

4. Turn the breaker ON and identify any other lights or receptacles on that circuit, checking receptacles for reduced voltage as you go.

5. If you find reduced voltage at some receptacles, check those receptacles for back-stabs AND check the next receptacle back toward the panel.

6. If you find reduced voltage everywhere, turn the breaker OFF and check that the neutral for that cable is tight. Next check the wire connection at the breaker. Then pull the breaker and carefully look at the buss bar where that breaker connects. Look at the breaker contacts that connect to the buss bar. Both should be relatively bright with no marked darkening or pitting.

7. If the voltages check OK, try to identify the device that feeds the pole light. This would be a good opportunity do away with back-stabs on any receptacles.

8. Find a way to hold the stripped wires going to the pole together (battery charger clip, jumper cables, locking pliers, etc). At the pole, measure the resistance. You should see about 2 ohms or less. If you find high resistance, you're going to need to replace the cable going to the pole. Use UF cable sized for the breaker. If it's in conduit, use TFWN sized for the breaker.
 
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Old 03-26-21, 12:58 PM
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Most likely you have a faulty connection or a damaged underground cable.
 
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Old 03-26-21, 06:11 PM
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Note: Before measuring resistance or continuity with your meter, be sure the circuit power is turned off.
 
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