Help with electrical setup for new shop

[TMGT]

I'm hopefully going to be starting on a workshop once the weather breaks in the spring, until then I'm working out details like electrical, I'm friends with electricians but one doesn't have a lot of experience in commercial applications and the others mother just passed so it's not a great time to be bothering him with my questions.

So as for the electric, I plan on bringing in 400a of 480v 3ph, the area I'm getting conflicting information as to what's the best approach for powering my 1ph 240v panel.

The service is 4wire wye configuration at the meter.

I was planning on using a 1ph 480/240-240/120 step down transformer off 2 legs as this is how it was done in a shop I recently had to do a lot of work in and was working with the electrical side quite a bit.

When I researched I found a lot of people saying the max unbalanced load I could do would be 15kva, but I want to have a 150-200a panel for my 240v (still have some welders that run 1ph).

So my question is, would running a higher unbalanced load off the 3ph service cause me any problems other then for the 3ph motors running at the same time not being happy?

What would be a better option?

I have a 1ph 100kva transformer already, I know it's overkill but I should never kill it at my loads, just have a slightly higher static useage.

Thanks.

 

[Tractor Seabee]

You do not provide near enough information:
- Is this service for only a shop or are you supplying a residence also?
- Are there any 480 or 277 volt 3 phase loads? How much of each? 480 provides 277 to ground each phase.
- Consider 277V commercial lighting fixtures if you haven't.
- Your 480 volt to 2-- volt transformer may provide provide 208 single phase not 240 or there may be several tap options. 240 is a single phase voltage provided by the utility to your meter. You still get 120 to ground each phase.
- How big is the shop?
- What are your prospective 120/240-208 single phase loads
- Consider going 3 phase with both 480/277 and 120/204-240 voltages, you can balance the 3 phase better.

Those answers will trigger more questions especially once the electrical experts, both professional and DIY types see this post. My questions are based on many years (30) planning/designing and some actual field work/supervision/inspection of commercial systems.

I used to charge $100/hour for my planning services. I will be in Virginia till 4 Jan (Fairfax Station). Look up my info and call my # if that is close to you. I will not charge you that much as I am now retired from all that stuff.

Ron

 

[TMGT]

This is only for the shop, the house has its own 200a 1ph service but is not practical or adequate to run a sub panel for the shop.

There will be multiple 480 3ph loads, mostly motors, current largest one is 7.5hp but multiple 2-5hp motors, I also have a welder that runs off 480 1ph.
I am planning on using 277 for the lighting and getting 480 3ph welders in the future.

The transformer has multiple taps, here's the info from the tag.

Square D One - Single Phase Transformer
Cat# 100S3H KVA - 100
H.V. 240 x 480
H.V. Amps 416 /208
Hz - 60 % 12-6.5
LV. 120/240
LV. AMPS 832/416
Wt. 705 Class-AA
220 Degree C INS System
150 Degree C Rise Type S

Style # 14551-12212-028
Date Code - 0142 Enclosure - Type 2

The shop is 2000sqft

The current larger 1ph 240 loads are a tig welder requireing a 60A breaker and a plasma requiring a 30A, the other welder is 480 single.
The rest are your typical smaller 120v loads like grinders, power tools, chargers, etc.

The biggest issue is cost, I can have 480 or 208 3ph brought in but not both, the 3ph transformer, even used, is going to cost a bit.

This building is on a budget, I could get by with 208 3ph service but I don't know what the future equipment holds and want to bring in the 480 as it would be cost prohibitive to redo it in the future. Currently it'll cost me pretty much the same to do 208 or 480 from the power company side.

I haven't found a good explanation of why stepping it down with a 3ph transformer then running the single phase panel off that is better for the phase balance other than the transformers static loss, compared to running the single phase transformer off the 2 legs of the 3phase service.