Questions about Sub-Panels
Questions about Wiring Panels
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Roger in Virginia asks:
Is the Wire Size to my Sub Panel Too Small?
I recently installed a sub panel in a storage building located about 150′ from my home. I fed this sub panel with #10 UF cable. From this sub panel, I am feeding 2 – 20 amp circuits with #14 wire. With nothing but the fluorescent lighting on, I pull about 2.7 amps of current with a measured voltage of 125 volts on this feed. When I turn on my shop vac however, I am pulling about 11 amps of current, and my measured voltage on this circuit drops to 118 volts. This causes my fluorescent light bulbs to cycle on and off. Is the voltage drop enough to cause this issue, or am I missing something?
Dave’s Reply:
Wire Length and Voltage Drop
When planning the wire size for a sub panel, or any panel for that matter, it is important to factor in the length of the distance to the panel from the source, and the amperage of the sub panel. The circuit loads placed upon the sub panel will determine the size of the sub panel as well. So basically, everything starts with planning the load that will be placed on the sub panel, and then we calculate the wire size feeding the sub panel based upon the distance. It is also important to factor in any electric motors that may be used due to the starting load which will effect the amperage and the voltage.
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