Commercial Electric Upgrade

[SoFloJoe]

Hi All,

I am a professional engineer in FL and do Structural & MEP. Full disclosure I do not usually get into 3 phase electrical these normally sub out to electrical engineers I work with. In this case I am doing a tenant buildout in a commercial space which is a standard single phase 200 amp system which I have done plenty. But it turns out the space does not have 200 amp service, only 100 amp and the main distribution panel is 600 amps 3 phase. Now I need to do an upgrade on a 3 phase and already bid out the project, and due to budget and time constraints I am trying to do this myself if I can make sense of it.

Anyways, this space now needs an upgrade. The existing panel setup is as follows: (see attached for riser layout)
600amp 3 phase panel feeding 6 sub panels for each tenant space.
(4) 200 amp panels
(2) 100 amp panels
This panel is one of the 100 amps that needs to be upgraded to 200 amp.

My questions are as follows:
- Right now this whole system in my opinion needs an upgrade. I usually do using 80% capacity (as a rule of thumb) of the system I should have (5x200)+100 = 1100*0.8 = 880 therefore either 800 or 1000 amp service is require at least. I do not necessarily want to get in doing load calcs for all of these units. If the city requests it then we got to do it, but I do not want to be the one to suggest it. Should I simply call out for a 1000 amp panel and call out the appropriate wire and conduit size and then let the utility figure out the rest? I can handle this.
-OR since this is a 3 phase panel (btw does not look like the 3rd leg is being utilized in any of the sub panels) require a more complicated calculation? Is there a guideline in NEC or others that I should follow in this situation?

Thanks in advance for the assistance!

 

[waross]

I do not necessarily want to get in doing load calcs for all of these units.

Well to get an accurate answer, someone has to do the calcs.
This is getting dangerously close to:
"Do my homework".
But this is Eng-Tips so here are a few tips: (and a little tough love)
Tip #1

I usually do using 80% capacity (as a rule of thumb) of the system I should have (5x200)+100 = 1100*0.8 = 880 therefore either 800 or 1000 amp service is require at least.

This does not have as much basis in reality as you may think and may result in needless expense.
I suggest forgetting this method. The potential for wasted money far outweighs the saving in not doing proper calcs.
Tip #2
Rent some recording meters and, after consultation with the AHJ, measure the actual load on the service for several months.
The AHJ will stipulate how many months he wants to see.
This method is used to justify legally adding to panels and services that are at maximum loading according to the calcs.
Tip #3
In industrial occupancies, the power is billed on a demand meter.
The information is directly available from the power bills.
I have more than once requested from the nice lady in accounting, copies of the power bills going back two years and used the monthly demand charges to justify adding loads to the service.
Tip #4
While many smaller tenancies do not have demand billing, if the utility is using electronic meters the information may be available.
Before renting recording instruments, I would consult with the technical department of the utility as to the availability of either demand or maximum current records on the meters.
If the meters have useful information I would then prepare a letter to be signed by the tenants giving permission to access the records.
If possible this is faster, more accurate and cheaper than renting recording instruments.
Oh, by the way;
A 120/208 Volt, 100 Amp panel has 150% of the capacity of a a 120/208 Volt, 100 Amp single phase panel
If those are single phase panels fed from a 600 Amp 120/208 Volt panel, Your sum of 880 Amps on single phase panels will be approximately 587 Amps on the three phase panel.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[SoFloJoe]

Thank you Waross!

I appreciate your candid response, and this is why I am here to get the tough love!

I agree with you that the calcs should be done, although explaining this to the owner is another issue lol. I would rather have the municipality make us do this. Which I did mention to the owner might be an issue. Also the owner recently purchased the building and has been doing major renovations so there are no current tenants, so no historical utility to go off of and cannot measure the meters.

A 120/208 Volt, 100 Amp panel has 150% of the capacity of a a 120/208 Volt, 100 Amp single phase panel

Did you mean "A 120/208 Volt, 100 Amp panel has 150% of the capacity of a a 120/220 Volt, 100 Amp single phase panel" Just want to make sure its not the other way around.

This might actually help since 100amps would then actually have 150 amps of capacity with this logic, if I am correct. I think 150 amps would work fine within the space. If that is so, then we could put a 150amp panel within the unit?

And that would actually make sense since as you pointed out 880amp/600amp is close to 1.5, therefore my 80% rule holds (just kidding I now know I should not be using that).

Thanks again for your help!

 

[waross]

The standard commercial voltage is 120/208 Volts.
There are some old some 120/240, three phase delta services around, it depends on the occupancy.

Hopefully you have 120/208 Volts.
(220 Volts as a standard voltage went out over 50 years ago, but the terminology lingers)

A 100 Amp, 120/240 Volt single phase panel will have two 100 Amp bus bars.
For comparison, 120 Volts time 100 Amps times 2 bus bars = an ultimate 24,000 Watts.
A 100 Amp, 120/208 Volt three phase panel will have three 100 Amp bus bars.
For comparison, 120 Volts time 100 Amps times 3 bus bars = an ultimate 36,000 Watts.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

but the terminology lingers

Like the smell of something dead..

Keith Cress
kcress -

http://www.flaminsystems.com

 

[SoFloJoe]

Thanks for the clarification. Yes I still see the 240 floating around glad to clear that up.

Yes I do believe it is 208V. Ok So then 36KW should suffice for the space. Thanks again!

 

[itsmoked]

Remember it will also heat the place up at that rate too. If renters are actually going to be using that kind of power the ventilation needs to be able to manage it. You can end up with renters doing all kinds of possibly undesired things to the building while trying to cope with the heat.

Keith Cress
kcress -

http://www.flaminsystems.com