Parking Lot lighting design

[lmichael310]

Below is a lighting design problem I am working on. I have worked through most of it but I could use some assistance.

Design a series lighting scheme with 15 luminaries staggered by 100 feet down a right of way, power a trailer and provide lighting for a parking lot. The trailer operates at 1 phase 120/240 V and has a 100 amp breaker panel and it is found that four luminaries are needed to provide the necessary illumination for the parking lot. There is 480 V 1P 3W coming from the substation. Currently my design has the 480 V going to a main panel and from there, feeding two sub panels. The first sub-panel has a 25 kVA step down transformer 120/240 1P 3W to power the trailer and the four 265 VA luminaries at the parking lot. The second subpanel powers the series of 15 luminaries (150 W rating each) at 480 V.

I have designed the main panel as a 225 amp panel, but I am not sure how to size the main breaker for the panel? I did calculate the Individual circuit breaker from the primary of the transformer and a 20 amp breaker for the series lighting load.

 

[beanland]

How many ways to skin a cat?

How many ways to skin a cat?

First: series lighting? We do that on airports but it has not been done on streets for 50 years. I know, I retired them.

Second: let me count the ways to design... There are as many ways, most of them code compilant, to build the electric system you speak.

Third: 480V 1-phase 3-wire?

 

[lmichael310]

First: series lighting? We do that on airports but it has not been done on streets for 50 years. I know, I retired them.

Second: let me count the ways to design... There are as many ways, most of them code compilant, to build the electric system you speak.

Third: 480V 1-phase 3-wire?

Yes the service is 3 wire 480 V phase to phase or 480/240.

 

[beanland]

480/240V

480/240V

Your design seems reasonable. Take service at 480V. Do you need a meter? That is an uncommon service though I have seen a lot ot 480/240V 3-phase 4-wire. You might need a PT and CT.

Then, distribute as 480V to single-phase transformers. Step down to 120/240 at panels. If breakers feeding transformers are sized 125% of transformer, no main breaker is needed in panel, but I would use one and upsize the transformer feeder breaker.

The size of the service and the 480V main breaker should be according to load. I calculate ~28kW of load. That is 59A @ 480V. A 100A 480V service sounds about right to me.

15 luminaires at 150W is only 5A. I would not set a second panel for 5A of load, run one 20A branch circuit with #12. The voltage drop will be almost nothing.