Engineered Temporary Install Voltage drop

[hjoseph117]

Small city. First time we have been asked to engineer/stamp a temporary install. We are going about 800ft with 240V single phase. We typically design to 2-3% voltage drop to get to the building (less than 5% to end of branch circuit).

For a temporary install, should we try to stick to 5% or could we increase the voltage drop to save some money on the wire soon to be abandoned? Any recommendations on a good percentage (spoke with electricians in field and they would have done 25% voltage drop back before the city required it to be engineered...)?

 

[mayanees]

That's a question that only your engineer could answer since he's the one signing, stamping and dating the document.

 

[LarryFine]

Welcome to the forum.

It would help to know the type of load and its rated load current.

Aluminum still costs less than copper.

 

[hjoseph117]

Temporary, probably a welder, plugs, air compressor, and random 240V items during construction. Guys in field getting a better list at this time. Ran 100a, 0.85 pf, underground in pvc conduit with aluminum scenario thus far.

 

[zbang]

on the wire soon to be abandoned

I hope you're going to pull it out for scrap value.

You're probably fine with 10% in general... what'll get you is starting the motors, like the air comp, or running the comp and welder at the same time, but on a 100a that's probably fine unless it's a comparatively huge compressor.

 

[synchro]

Will there be any lighting powered by this run, and if so what kind lights will be used? Perhaps not if it's only for 240V, but just asking anyway in case lighting needs to be considered. LED and incandescent bulbs will likely flicker when the voltage dips quickly. Larger LED light fixtures often have drivers that are more capable of riding through voltage dips.
If there are lighting loads and the 800ft run is a feeder coming from a panel, then a separate relatively small feeder might be added just for lighting and/or other sensitive loads to avoid any problems.

 

[LarryFine]

If this is something that is needed frequently, perhaps invest in a pair of transformers.

 

[hjoseph117]

If this is something that is needed frequently, perhaps invest in a pair of transformers.

Not a bad idea, thinking 480v primary to 240v near site? Also wondering, if an onsite diesel generator would be cheaper - maybe in future will be doing solar/battery to just be built in to permanent after utility gets there.

Not a cost expert, but I'm thinking it'd be 30k for temporary wiring or $100/day for a genny, solar would be 50k for 10kW with 10kWh battery? Dangerous hand-wavey math here. hopefully someone knows more, want to get better at solar but not many people want it here yet.

 

[hjoseph117]

I hope you're going to pull it out for scrap value.

You're probably fine with 10% in general... what'll get you is starting the motors, like the air comp, or running the comp and welder at the same time, but on a 100a that's probably fine unless it's a comparatively huge compressor.

Also thinking we can just size wire to get above 208V at site (13% V drop). Going back and forth between that and 10% (just a hand-wavey double of 5% of the NEC recommended).

They "shouldn't" be using anything above like a 40a compressor.

 

[hjoseph117]

Will there be any lighting powered by this run, and if so what kind lights will be used? Perhaps not if it's only for 240V, but just asking anyway in case lighting needs to be considered. LED and incandescent bulbs will likely flicker when the voltage dips quickly. Larger LED light fixtures often have drivers that are more capable of riding through voltage dips.
If there are lighting loads and the 800ft run is a feeder coming from a panel, then a separate relatively small feeder might be added just for lighting and/or other sensitive loads to avoid any problems.

No serious lighting loads.