How To Look At A House
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What causes excessive voltage drop at a wall receptacle outlet?
Monday, July 20, 2020
Higher than normal resistance to current flow in a circuit causes excessive voltage drop. Here’s a few possible culprits:
1) Wiring is smaller than code standard for the amperage rating and/or length of run of circuit.
2) Poor wire splices anywhere in circuit.
3) Loose wire connections at receptacles or switches, especially the backwired push-in type.
4) Corrosion at wire connections or splices.
The National Electrical Code [NEC 210.19(A)(note 4)] specifies the maximum voltage drop at 5% for the farthest receptacle of a nominal 120-volt circuit, which means 114 volts is lowest allowed. Low voltage can cause erratic operation and damage to appliances, wasted energy, and overheating at the inadequate connections or splices causing the voltage drop—which can lead to a house fire.
We test the voltage at a receptacle as part of an inspection, along with resistance to ground. An example of an acceptable reading is shown below.
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