Sub Panel Voltage doesn’t add up

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Old 09-18-19, 07:09 PM
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Sub Panel Voltage doesn’t add up

Hi all. 60 amp sub panel, detached bldg. 75 feet #6 four-wire underground. Two-rod ground at building. On startup i measured 116v on each hot to neutral but hot to hot only reads 201v. volts at outlet is 116v. Any thoughts on this? This is the first sub panel I’ve done.

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Last edited by pcboss; 09-18-19 at 08:10 PM.
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Old 09-18-19, 08:12 PM
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Your voltage from hot is neutral is well within the normal range. Were there any loads in use when you measured hot to hot?
 
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Old 09-18-19, 09:46 PM
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No there weren’t. I checked connections; all seems to be good and I have a good multimeter. What would cause a discrepancy like that?
 
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Old 09-19-19, 01:52 AM
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201V / 116V = 1.73 = sqrt (3) which is just what you would get if the two hot lines are each phases from a "wye" type three phase system. The nominal hot-to-hot would be 208V and the hot-to-neutral 120V. Your voltages are 3.4% low but that's considered acceptable.
 
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Old 09-19-19, 09:44 AM
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Very interesting. I just read a bunch of articles on single vs three phase, delta and wye. The main panel i ran from has three big wires from transformer plus neutral and ground. Not sure type transformer but it seems the numbers are right for this setup, as you said. Thank you for the heads-up.
 
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Old 09-20-19, 09:17 AM
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The main panel i ran from has three big wires from transformer plus neutral and ground.

That would be 3-phase 4-wire, most likely 120/208 volt.
 
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Old 09-21-19, 12:45 AM
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The comment about the 3 phase (3 hots) is right on. Depending on where you live and the age of the system you MIGHT have 120/240 volt system. This is a delta transformer configuration with 180-190 volts to ground on the wild leg. Connecting any 120 volt load to the wild leg is the best way to destroy the device.
Suggest you go to the main panel and check voltages on all hots to ground, hots to neutral, and hot to hot. This way you will know what you have to start with.
 
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Old 09-21-19, 11:41 AM
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This is not likely a 120/240 volt 3-phase when considering the OP's first post.

On startup i measured 116v on each hot to neutral but hot to hot only reads 201v.
 
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