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Joined: Oct 2000
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i see the problem, yet am fuzzy on a fix for it.
would a definition help?
meanwhile, it would be ashame to have brighter students balk at a loaded Q here.
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Joined: Aug 2002
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Joined: Jul 2001
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Power systems are rated for nominal voltages such as: 120, 208, 240, 480, and 600V. These voltages are specified by ANSI and have been the "correct" voltages to use since the early 1950's.
110.4 says in part "...nominal voltage of a circuit..."
220.2 says "Unless other voltages are specified, for purposes of computing... nominal voltages ... shall be used."
Motors are rated for utilization voltages (they allow for voltage drop from nominal) of: 115, 200, 230, 460, and 575V. These are the nameplate voltages referred to in Articles 430 and 440.
In my opinion, the question was intended to test the knowledge of the formula (va = volts x amps). Art 220.2 gives the writer the authority to specify the voltage (yes it appears to be a trick question).
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Joined: Jun 2002
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Isn’t the whole point of 220.2(A) to make us use nominal voltages for computations?
Wouldn’t the “Unless other voltages are specified” refer to other voltage systems not listed at the end of this section? (not any arbitrary voltage by any entity)
[This message has been edited by engy (edited 08-07-2003).]
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Joined: Oct 2000
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When we figure what the VA is per outlet (strap), the result is less than 180 VA. Section 220.3(B)(9) indicates that the minimum per strap is 180VA.
20 x 115 = 2300 VA 2300VA/13 = 176.9 or 177 VA per outlet, less than the required 180VA
Joe Tedesco, NEC Consultant
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Joined: Nov 2000
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Joe,
I did my calculation at 180 va per strap. I just chose to do the calculation in a manner where the code clearly permits rounding. Even if I do it like this, I still get a 20 amp "code" load.
13 x 180va = 2340 va 2340va/115v = 20.348 amps. The code permits me to drop the .348 amps giving me a "code" load of 20 amps which is permitted on a 20 amp circuit.
As I told Roger, we'll have to agree to disagree on this one. I will insist that 13 are permitted until someone can show me a code rule that says 2340 va is not permitted by the code on a 115 volt, 20 amp circuit.
Don
Don(resqcapt19)
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It may be worth noting that for receptacle branch circuits, utilization equipment is of two types. Loads can be constant-resistance or constant kVA—corresponding to heating/incandescent-lighting and inductive/motor loads. The point is—within limits—resistive-load current increases with increasing line voltage, and inductive-load current decreases with increasing voltage. Equipment nameplates usually list 115V, nominal system voltage is 120V, [and the wiring-device rating is 125V.]
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