Wire size based on lowest input voltage range? Multi tap devices

gable74

Member
Location
MARYLAND
Here at work the question was brought up of what gauge primary wire should be provided for our LED drivers. The drivers are multi tap:

120v - 277v input / 12vdc output
1.05a @ 120v /.85a @ 208v/ .55a @ 240v / .51a @ 277v
Operating range of 90vac - 285vac
Max load of 1.5a @ 90vdc per driver

The question is, when communicating to the customer what size wire to have their electrician bring to the source, should we tell them the max possible load it could draw @ 90v or the actual load based on the voltage they will be using (usually 277v)? One may require #14 where the other may require #10. What if someone rewires the drivers for 120v at a later date? Now that #14 is too small. Common sense would tell you to use the wire size required for max possible load. In this case 1.5a per driver @ 90v. Would love to know where to find the correct answer in the NEC as well.

​​​​​​​Thanks,
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Electrical Contractor
There is no NEC requirement to provide for possible future changes. Provision for potential future changes is solely a design decision.
And to add to that no electrician needs the manufacturer to tell them what size wire is needed. Why would you want to get involved in that?
 

gable74

Member
Location
MARYLAND
60w @ 12vdc or 5a on the secondary side.

So that was my question, thank you!. We should not make the request based on potential, only what is being installed.

Thanks for the help!
 

gable74

Member
Location
MARYLAND
And to add to that no electrician needs the manufacturer to tell them what size wire is needed. Why would you want to get involved in that?
You are correct, the better way to phrase the question would have been, "Do we tell the electrician the load is 1.5a per driver based on the potential full load of driver, or the actual load based on the voltage being used.

Sorry for the confusion.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
It is wired per the system voltage that it is fed to. No guessing as to what MIGHT happen, the person that makes that change later is responsible for that issue at that time.

I'm thinking you have multiple drivers on the circuit then, because at 0.51A per unit, even 14ga wire on a 15A branch can handle 23 drivers per circuit (12A ON A 15A circuit / .51A).
 
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