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Old 03-30-2008, 01:09 PM   #16
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Wire size

Thanks, Marc. I'll write that down as a reference. Very handy when working with metric equipment.

In the above example, a 5.4 anp motor about 600' away, #8's would be my choice as well.



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Old 03-30-2008, 02:13 PM   #17
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Wire size

Originally Posted by idoelectric View Post
#6 copper stranded is good for 30 amps at 120v for a distance of 500 ft.

I'm not sure where the 7 amps came from?

Cmils= 2 x K x I x D / VD
I believe you're mistaken. Use the formula you posted and see what you come up with. Unless you're shooting for 15% VD?

FYI, the 7 amps was calculated using this formula:

I=(CM x VD)/(2 x K x D)
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Old 03-30-2008, 04:45 PM   #18
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Wire size

Originally Posted by elkangorito View Post
I don't know about the USA but calculating the voltage drop for a given cable length & current, is not a simple process in Australia.
I generally use the formula VD = (2KxIxD)/cm

where K is a typical value for the resistivity of copper, 12.9 ohms/cm-ft
I is the current
D is the distance, in feet
and cm is the circular mils of the wire.

I transpose the equation into cm = (2KxIxD)/VD

where VD is 3.6V for 120 V or 7.2 for 240 V.

So if I know the current, this tells me the wire size in circular mills. I can then select from a chart of standard gauges to the nearest size.

Our wire ampacities are selected from a table of based on what conditions the wire is used in. Most typically, it is based on no more than 3 conductors in a conduit of cable, or directly buried in earth. There are other tables for free air and other conditions.



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