Voltage drop with more than one conductor per phase
- Thread starter tmautn1
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- Chapel Hill, NC
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- Retired Electrical Contractor
Why would that be too simple. CM is what you would use so I would think you would double the cir mil when you parallel. You could find the equivalent cm of the two conductors and check it with this on line calculator-- http://www.elec-toolbox.com/calculators/voltdrop.htmtmautn1 said:What is the formula for calculating the voltage drop when more than one conductor is used per phase(Parallel)? Do you simply multiply the CM by the number of conductors per phase? That would be too simple. Please help. Thanks
winnie
Senior Member
- Location
- Springfield, MA, USA
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- Electric motor research
tmautn1 said:
"Too simple" requires an evaluation of just how accurate you need the answer to be. Essentially all of the equations used in engineering are approximations, and an equation is "too simple" if it does not give results which model reality well enough for the job at hand.
Simply multiplying the CM per conductor by the number of conductors would be a good approximation, and probably accurate enough for practical work.
Because AC circuits are subject to inductive effects from both the other conductors in the circuit and any surrounding conduit, it is almost certain to be the case that multiple smaller conductors will behave _slightly_ differently than a single large conductor.
If you run your voltage drop calculation using only conductor size, conductor length, and calculated load, then other errors in the result will be larger than the error caused by conductor geometry. If you need more accurate results, then you would need to consider factors such as ambient temperature (because conductors change resistance with temperature), load power factor, conduit type, transformer regulation, etc.
-Jon
Every engineer is anal about something. For me its understanding how electricty really works, Neher-McGrath and voltage drop.
"If you run your voltage drop calculation using only conductor size, conductor length, and calculated load, then other errors in the result will be larger than the error caused by conductor geometry. If you need more accurate results, then you would need to consider factors such as ambient temperature (because conductors change resistance with temperature), load power factor, conduit type, transformer regulation, etc."
Right on Winnie!!!!! You're absolutely right on!!! It is so refreshing to see someone correctly state VD conditions.
Thank you.
"If you run your voltage drop calculation using only conductor size, conductor length, and calculated load, then other errors in the result will be larger than the error caused by conductor geometry. If you need more accurate results, then you would need to consider factors such as ambient temperature (because conductors change resistance with temperature), load power factor, conduit type, transformer regulation, etc."
Right on Winnie!!!!! You're absolutely right on!!! It is so refreshing to see someone correctly state VD conditions.
Thank you.
wcollinge2000
Member
there are lots of factors that can be concidered to put the min amount of size to what ever equip or what ever your hooking up but there is this the nec is the min required nothing says you cant be higher a higher standard.cost is the only thing keeping it minimum. art 90.1(b) keeping that in mind you can add all the factors and get the real answer. like winnie or snorks stated. use all physical aspects and enviromental. there are lots of undersized wiring out there . I won't be one of them doing it.
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