Sizing Main service after sub panels - any derating possible?

[bryanbdp]

Hi. Continuing on my project to create an electrical plan for our Makerspace.
I have calculated the loads for the subpanels, 5 at 240v 3ph, 6 at 208/120, and 1 at 480v 3ph.

The building has a 500KVA 208/120 utility transformer, that feeds a meter bank in the building with a 1600A main breaker.
A number of meter sockets are available, including 2 at 400a and several at 200a. (208Y120)

The previous design build company seemed to think that was plenty to serve our loads. I planned to use the first 400a 208/120 for general purpose receptacles, LED lighting, and HVAC loads.
Much of the equipment is designed for 240v rather than 208, so I planned to use the second 400a circuit to feed an autotransformer to provide 240 3ph, to serve both single and 3ph loads. Lastly, I only have one machine that needs 480v (waterjet cutter), but planned to run air compressor and dust collection blower on 480 also due to length of circuits.

I have created a spreadsheet that calculate the panel schedules. It adds up the VA on each phase, totals them up, derates the general purpose receptacles over 10kva, adds 125% of largest motor load and lighting load (as calculated at 2VA per foot, not actual loads)

Panel schedule link (dropbox)

if I add up the 5 240v panels, I get a total of 282077 VA or 679A at 240v.
the 480v panel is 101224va or 122a at 480v
the 6 208/120 panels add up to 311398 va or 864a at 208v.

If i divide the volt amps above by 208, I get the amps at the 208 supply voltage: 240>208 783a. 480>208 281a. 208=208 864a.

These figures add up to more than the main breaker for the building (1600a at 208)

If anyone has a chance to glance over the spreadsheets and make sure they seem correct, that would be great.

Is the derating for the general purpose outlets correct for the 2014 NEC? 100% to 10KVA, then 50% of remainder? (light industrial usage)

The big question: having calculated all the subpanels, how do I calculate the main power panels for each voltage?
Do I treat them like a subpanel, and add up all the loads on all the subpanels, derate the GP receptacles, and add 125% for cont. loads and largest motor?
Do you add the subpanel VA or Amps together to get the proper figure?
Or, is there some way to allow for load diversity, or derate a portion of the loads to fit the two 400a and one 200a feeds available?

All my equipment loads are on individual branch circuits.
I have two 240v 50a 1ph welder plugs without dedicated equipment. How do I calculate for these? Full load? 0?

Unlike a manufacturer, it is very unlikely that all the equipment will ever be used at the same time, or even half of it. Usage will be quite variable.
It is a new buildout, I don't have any historical information on power usage.

I know this is a lot of information, I've got a good week or so of work into this. A little direction to bring this to conclusion would be MOST appreciated!

If I've got to bite the bullet and put in a new 480v service, I'd rather know now....

Thank you,
Bryan

 

[iwire]

A number of meter sockets are available, including 2 at 400a and several at 200a. (208Y120)

The previous design build company seemed to think that was plenty to serve our loads. I planned to use the first 400a 208/120 for general purpose receptacles, LED lighting, and HVAC loads.

Your post leads to so many questions not the least of which is why does a GC feel they are qualified and allowed to do this in CT.

But regarding what you said up above, have you spoken to the power company about your plan? Many will not serve the same customer with the same voltage multiple times.

 

[bryanbdp]

Hi. Ultimately, this plan will have to be reviewed and approved by our engineer. However, the more I can rough out the plan, the less it will cost. I also like to understand the tradeoffs in a system, and balance cost with future utility. It also allows me to research pricing and equipment options. For instance, MC cable, even for the feeders is looking like a good choice based on cost and ease of installation for this layout. It also allows for easier reconfiguration of the space as opposed to conduit.
Our space is a non-profit public resource, and we're still raising funds. I do as much work and research as I can to make this project succeed. Any help would be appreciated.

Right now, I really want to know if I have to plan on putting in a new service and utility transformer, which will have considerable cost and effort.
If the 208 service will work, I can look at options for the meter panels and other equipment.

Thanks,
Bryan

 

[kwired]

If you continue to use the meter bank as more less a distribution panel are you bypassing meters and having one meter installed for the entire facility, or do you plan to have multiple electric bills from POCO, one for each meter used?

I would think one customer served, one bill from POCO would be best in most applications for the end user anyway.

If you get to the point where the load is questionable, increasing service voltage to 480 may be well worth it. With any luck you can use existing conductors and have a little over twice the KVA capacity as a 208 system, and you may or may not be able to use existing gear at 480 volts (start getting over 800 amps and often 600 volt gear is used even for 208 appications). The POCO transformer - they may give you some credit for the existing unit and charge you the difference of that and the new unit.

 

[augie47]

I have some concern with the auto-transformer for your 240 1 ph and 3 ph loads. Do any of those loads have a neutral load associated ?
Being the type facility it is, I see no reason you can take load diversity into account.

 

[bryanbdp]

The 208 v meter system serves other floors of the building. So i won't be able to reuse transformer pad, underground conduit, etc, but will have to add another transformer, pad, conduit, metering and other gear to the building.

The electricians who have look at the building seem to think that the POCO could combine multiple meters into one bill.
If the 208 volt system does prove to be inadequate, the code does seem to allow for multiple services if a facility requires different voltages or is too large for a single service.
So if I install a 480 volt system, I'd hope to also be able to use some of the 208 service to reduce the size of the new service needed, rather than putting in a larger 480v service. If not, I could probably run all the equipment on either 480 or 240 volt, plus 120 for outlets.

augie47

I have some concern with the auto-transformer for your 240 1 ph and 3 ph loads. Do any of those loads have a neutral load associated ?
Being the type facility it is, I see no reason you can take load diversity into account.​

The autotransformers do not need a neutral as proposed, they would serve line to line 240v single phase loads and L-L-L 3 phase loads.
All 480 volt loads are 3 ph.
I don't think the equipment is particularly noisy, so I don't think lack of isolation should be a problem.

So Augie47, you're saying that basically all the loads have to be accounted for at 100% in this type of usage? More or less what I've done so far?
That seems to be what I was thinking, I haven't been able to find anything that would allow otherwise.

Can anyone advise on how to calculate the main power panels in this scenario? Do I do a panel schedule for the mains with ALL the same loads as the subpanels (pretending they aren't there)? Or is there a different method?

I really appreciate the help, I've been asking multiple electricians these questions, but they typically let the engineers handle this type of stuff. I did go to school for engineering, just not electrical! This is an amazing project, and formulating the best plan will save money and help insure success.

Lastly, is there any "penalty" in KW, PF or otherwise for using transformers to "upconvert" from 208 rather than "downconvert" from 480? Other than feeder conductor size...


Thank you,
Bryan

 

[iwire]

I would think one customer served, one bill from POCO would be best in most applications for the end user anyway.

This is what I was getting at, some power companies will not allow more than one meter at the same address to the same customer for the same voltage / phases etc.

I would not spend much time on the design until I spoke with the power company.

 

[bryanbdp]

I am planning to talk to the poco again, but i was hoping to determine if a new service was needed first...

 

[kwired]

I am planning to talk to the poco again, but i was hoping to determine if a new service was needed first...

You do need to talk to them to see what options they even will allow and/or how much they may charge to provide each different option.

You also need to know what your expected load will be like, maybe even some expected demand figures, such information may make a difference in what they will offer for options or what cost of those options may be. If you have a large load but little demand, they will be less willing to eat any cost on equipment that won't pay back compared to same load that sees a lot of run time. Then you also have peak demand charges that can come up as well.

 

[bryanbdp]

FWIW

FWIW

I think I may have answered my question. The NEC doesn't really allow sizing of the service by including demand factors and diversity (other than those clearly listed in the code), but a PROFESSIONAL ENGINEER with the proper background and expertise should be able to design a facility taking these factors and others into consideration before signing and stamping the plans for submittal.

I am used to this in building issues, i.e. you need a beam that isn't listed in the code book, so you hire an engineer to design a beam, and submit a stamped drawing which the building inspectors will accept. I do believe it is the same for electrical.

Comments?

 

[iwire]

I think I may have answered my question. The NEC doesn't really allow sizing of the service by including demand factors and diversity (other than those clearly listed in the code), but a PROFESSIONAL ENGINEER with the proper background and expertise should be able to design a facility taking these factors and others into consideration before signing and stamping the plans for submittal.

I am used to this in building issues, i.e. you need a beam that isn't listed in the code book, so you hire an engineer to design a beam, and submit a stamped drawing which the building inspectors will accept. I do believe it is the same for electrical.

Comments?

An engineer cannot add their own demand factors.

The only changes an engineer can make to standard NEC requirenents have to do with conductor ampacity.

 

[Ingenieur]

What type of hvac units?
heating: gas or electric?
total square footage?

honestly
it sounds like you've inherited someone elses mess
hire an engineer or electrical contractor
may save you a lot of grief in the long run

don't want to mess with drop box so haven't seen the schedules

as others have said
too many unknowns
too many variables