Correct NEC Reference?

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RSquirrel

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Location
Watsonville, CA, USA
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Mechanical Engineer (retired/consulting)
I have found numerous webpages that make the following identical statement in regard to sizing the main breaker for a load center:

“As per the NEC, divide the total wattage by 230 to get the total amperage.”

However, I find nothing in the NEC that specifically cites this "230" constant. I suspect that it should be replaced by whatever voltage is supplied to the panel (e.g. 208, 240, etc.) but have no evidence that this is the case. Can someone elaborate on 230 being some NEC-specified constant, vs. whether or not my suspicion is correct?
 

kwired

Electron manager
Location
NE Nebraska
NEC load calculations are typically in VA. Which goes one step beyond just watts but also considers power factor of the load.

NEC typically doesn't have any instruction in those calculations to convert to amps for your specific application, rather it is mostly implied, though you will find such conversion in the appendix in the examples. The application can vary on what to use depending on what utilization voltage is.

NEC does consider "nominal voltages" for typically common AC power and lighting systems to be 120, 208, 240, 277, 480, 347 and 600.
 

don_resqcapt19

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Staff member
Location
Illinois
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retired electrician
For Article 220 Calculations, 220.5(A) specifics the voltages to be used, so if you are doing a load calculation, you need to use those voltages.
(A) Voltages.
Unless other voltages are specified, for purposes of calculating branch-circuit and feeder loads, nominal system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.
 

RSquirrel

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Location
Watsonville, CA, USA
Occupation
Mechanical Engineer (retired/consulting)
So even though my question produced no specific/direct answers, I will take the composite responses to mean ". . . it (230) should be replaced by whatever voltage is supplied to the panel (e.g. 208, 240, etc.) . . ." Thanks for confirming my suspicion.
 

kwired

Electron manager
Location
NE Nebraska
So even though my question produced no specific/direct answers, I will take the composite responses to mean ". . . it (230) should be replaced by whatever voltage is supplied to the panel (e.g. 208, 240, etc.) . . ." Thanks for confirming my suspicion.
For NEC purposes of determining conductor sizes, overcurrent devices and such yes.

For more precision activities and/or troubleshooting issues actual operating voltage can be more important.
 

roger

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Fl
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Electrician
So even though my question produced no specific/direct answers, I will take the composite responses to mean ". . . it (230) should be replaced by whatever voltage is supplied to the panel (e.g. 208, 240, etc.) . . ." Thanks for confirming my suspicion.
Post #3 is pretty specific as to what you would use.

Roger
 

RSquirrel

Member
Location
Watsonville, CA, USA
Occupation
Mechanical Engineer (retired/consulting)
Roger,
Good point. In looking back at my post, I should've formulated my questions so as to solicit definite yes or no responses. Bottom line, my questions were answered.
 

Jraef

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Location
San Francisco Bay Area, CA, USA
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Electrical Engineer
I just posted a "Sticky" in this forum to address the voltage ratings issue.
 

Hv&Lv

Senior Member
Location
-
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Engineer/Technician
Well before that, for nominal voltages per ANSI.
I’m thinking the 1984 NEC was when 120/240 voltages for 220.1 was used.
ANSI was before NEC
Maybe someone with an 84 edition and an older one can verify
 
Last edited:

kwired

Electron manager
Location
NE Nebraska
I’m thinking the 1984 NEC was when 120/240 voltages for 220.1 was used.
ANSI was before NEC
Maybe someone with an 84 edition and an older one can verify
For some reason NFPA doesn't have 1984 on the list for free access editions. 1987 maybe worded a little differently but has same voltages we use today in 220-2. I'm not finding any mention of voltages in 1981 in the first portions of art 220. I did see mentioning of 120, 208 and 240 volts in some the sections while browsing around though.

210-8 and GFCI rules mentions 125 volt receptacles.
 
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