electrical designer

[elect-rick]

I need to energize a marquee sign that needs two seperate 120v circuits. 1 for fluorescents and 1 for (2) LED panels. Available voltages are 480v 1 phase or 208v 1 phase. No neutral is present. (parking lot lights are source) Load is under 9 amps (2 or 3 kva xfmr) Can I provide primary protection at 1.67% of load for primary protection only and feed both loads with no secondary protection?

 

[John Paul]

Table 450.3(B) says yes you can. Why do you ask?

I've been out of the design buisness for a long time now and miss working with AutoCAD to produce a set of construction documents.

 

[augie47]

My first answer, looking at it from a 450 and 240.24(C) standpoint, woulkd be that you could do so if the condcutirs were sized accordingly.( If you uses a 480/120 volt transformer with 2 wire secondary you meet the requirements of 450 and PART of the requirements of 240.21(C). You would need to watch the 2nd part of 240.21(C) in regard to the ratio.
Assume a 3 kva transformer (with a 10 amp OCP)..the 480/120 ratio would reqiure a #8 secondary)
That said, the fact that you are feeding a sign would require compliance with 600.5 which requires a 20 amp overcurrent device on the branch circuit. It would be an arguable point if the transformer primary would satisfy that requirement.

 

[elect-rick]

I thought 600.5 was just for the tenant sign requirement. A 20 amp circuit must be designated for the provision of a sign above a door exposed to pedestrian traffic, like in a strip mall. I was considering specifying a SQ D type tf xfmr with factory wired fuse blocks to clean up the installation. (no safety switch) just a 600v two-pole, single throw switch in front of the xfmr for sign disc. requirements. Good tip on the wire size my wiring schematic did not specify wire sizes, but it will now. Thank to all.