VD Calculation

Alwayslearningelec said:
The load electrical data tells me that?
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Yes. For the case of a 208Y/120 system (the larger number goes first for 3 phase systems), you could have a 2-wire 120V circuit, a 2-wire 208V circuit, a 3-wire 120/208 circuit (this one's a bit tricky, you'd ideally look inside the equipment connected and consider it as a combination of the previous two cases), a 3-wire 208V 3-phase circuit (3 phase voltage drop has a different factor in the formula compared to 2-wire single phase voltage drop), or a 4-wire 208Y/120 circuit (again, you'd ideally look at the loads supplied and consider it as a combination of the other cases).

Cheers, Wayne
 
Alwayslearningelec said:
When you do a vd calc and you have either 120/208 or 277/480 how do you know which voltage to input. e.g. 277/480 which would it be?
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Each state has its own energy code and thats where the code requirements for voltage drop are found.
Some jurisdictions still amend the NEC with a voltage drop and minimum wire sizes like NYC and NM.
Id say as of 2025 the majority adopt the ASHRAE Standard 90.1, I believe NJ does;
ASHRAE Standard 90.1 Section 8.4.1 simply states Feeder conductors and branch circuits combined need to be sized for a maximum of 5% voltage drop in total. Service conductors are exempt.
The starting voltage is the 'Nominal System voltage' from NEC 220.5 or ANSI C-84 Table 1
 
The standard Nominal ones are easy:
120, 208Y/120, 240D/120, 240, 240/480, 277, 480Y/277, 480, 600Y/347, 600, 690Y/400, 690, 2400, 4160Y/2400, 4160.
I used to have a cool chart that had a exhaustive list of standard voltages used in North and South America.
It had the the 'odd' wye 60hz ones 416Y/240, 240Y/139, 220Y/127 and ones various combinations of old 'two phase'.
 
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