Voltage Drop to Determine Wire Size on a 480/277 Line-to-Neutral Lighting Run?

[kwired]

Right, however notice the thicker primary conductors do not smoke let alone glow red.

Given about 40 seconds of opening time for a 60 amp breaker I'm guesstimating about 150 amps of fault current.

understandable, bet there was still significant heating and maybe even getting to point you wouldn't want to touch it. Temp needed to melt insulation is higher than you want to touch.

Don't know what size of the wire is, maybe 10 or 8 AWG - looking at title maybe 6mm? I think 6mm is between and 4 AWG though, it don't look that big to me.

 

[mbrooke]

understandable, bet there was still significant heating and maybe even getting to point you wouldn't want to touch it. Temp needed to melt insulation is higher than you want to touch.

Don't know what size of the wire is, maybe 10 or 8 AWG - looking at title maybe 6mm? I think 6mm is between and 4 AWG though, it don't look that big to me.

Right, 240.92 (B) lists 150*C for PVC and 250*C for XPLE insulation. 10 AWG is 5.26mm2, so 6mm2 would make this wire slightly larger than 10 AWG. 10 AWG is legal for use as an EGC with a 60 amp OCPD based on Table 250.122

 

[kwired]

Right, 240.92 (B) lists 150*C for PVC and 250*C for XPLE insulation. 10 AWG is 5.26mm2, so 6mm2 would make this wire slightly larger than 10 AWG. 10 AWG is legal for use as an EGC with a 60 amp OCPD based on Table 250.122

But at same time 250.122(B) would require larger EGC if the ungrounded conductors are "upsized" and it looks like those supply conductors are definitely larger than ~6 AWG. Again hard to tell what size the supply is but looks like maybe at least 1 or 1/0 AWG. Off top of head guess the EGC probably needs increased to at least 6 or maybe even 4 AWG to comply with 250.122(B).

 

[mbrooke]

But at same time 250.122(B) would require larger EGC if the ungrounded conductors are "upsized" and it looks like those supply conductors are definitely larger than ~6 AWG. Again hard to tell what size the supply is but looks like maybe at least 1 or 1/0 AWG. Off top of head guess the EGC probably needs increased to at least 6 or maybe even 4 AWG to comply with 250.122(B).

Right, but you don't have to upsize the ungrounded conductors to begin with. Voltage drop is an FPN, in addition to the fact its still possible to have acceptable voltage drop with a light load like a gate opener (or this thread) but still not be able to trip a breaker fast enough.

 

[Jp807]

Kind of overcomplicating it.

Are you really going to specify different size wires along the length of the run? Consider that in the future additional lights may be added to the circuit.

If they are 277V circuits, and you have 900 watts total on a circuit that is 4,000 feet total in length, simply run the voltage drop for the entire length at 900 watts. A #3 wire is needed to limit VD below 3% for the entire length.

Here is a simple voltage drop calculator on southwire's website.

Voltage Drop Calculator

Also, be careful of wiring lights at 480V. There are code implications when doing so based on whether you have a 480V delta system or wye. See NEC 210.6.