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Ground Wire Size Question
Hello,
I'm not an electrician but I have done some wiring in my time. Where I am currently working we are installing a machine that required three phase 480 we ran three 1 AWG conductors and one 8 Awg conductor as the ground wire, the lenght is appox 150 ft. I question the ground wire size as any engineers I have worked with in the past ran a ground wire of equal size. When I questioned the person in charge about the size, he showed me in an old book he used that 8 Awg was a minimum for a ground when ruinning 1 Awg wire. I'd like to here what the truth is. Thank You Geezer |
The equipment ground is sized according to the overcurrent device protecting the circuit.
For a 100A circuit a #8 ground is appropriate and typical. NEC Table T250.122 I have to say, any electrician who sizes the equipment ground equal to the circuit conductors (on larger than 30A circuits) is wasting money. |
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OK, I'll have to pay closer attention to detail. That 100 amp example sucked me right in to a panel :wallbash:
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Speedy, you have failed to consider that the #1 conductors have been upsized from a #3, for a 100 Amp circuit.
Normally, a #8 is allowable for a 100 Amp circuit, per table 250.122. But if you consider the requirement of 250.122(B), you will have to upsize the EGC by a proportional amount. A #1 conductor is 59% larger than a #3. A #8 conductor is 16510 circular mils. 59% of that is 9741 circular mils. The total of those numbers is 26251 circular mils. A #6 conductor is 26240 circular mils, close enough for me, but a real stickler (are you paying attention, electures?) might require one to upsize again to a #4. |
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Maybe not, but my response was directed to Speedy, who used 100 Amp in his example.
IF the OP is dealing with a circuit that exceeds 100 Amp, then a #6 EGC would be the minimum size required, adding more if upsizing was involved. |
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90.1 Purpose. (A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. (B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use. Before we travel down that road lets find out more about the machine and wiring. Don't want to get the "experts" excited yet. :no: |
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If there are 60 deg terminations somewhere #2 or #1 would be required, yet only a #8 ground. |
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