Recalculate the load to avoid an upgrade of the service.

C

Charlypt

Member
Location
Florida
Occupation
Electrician
I have a client who wants to add some loads to a heavily loaded 200A, 240V, single-phase panel. It's an office building, 3200 sq ft.

They want to:
- add a washer and dryer (no idea why)
- a photocopier
- eliminate the break room.

Now, the engineer calculated that the panel exceeds the demand and proposes increasing the service to 400A. This would mean a very large expense for the client because it's practically a new service, a new panel, etc. They asked me what could be done to maintain the 200A service.

We proposed:
- first, eliminate the AC heaters; it's in Florida and they are practically unnecessary.
- Then, eliminate everything related to the break room: disposal unit, microwave, dishwasher, etc. Only the refrigerator remains. These loads are unused and can be eliminated.

The engineer provided some values for the lights and outlets, which I don't know where he got them from, but I followed them.

I proceeded to perform a new load calculation:
Lighting - using the given value of 1500 VA at 100%. Table 220.42
Receptacles: - given value 9800 VA at 100% (<10 kVA). Table 220.44
Washer 1200, Dryer 5800, Photocopier 1000, Fridge 1500: 100%
AC condensers (3 units): I used the MCA from the nameplate. Total 21400 VA at 100%. 440.6(A)
Air handlers (3 units): I used the value from the nameplate of the fans, because the heaters would be eliminated. 4600 VA at 100%.

With all this, I got 198 A. I don't understand how that panel could handle that load if the heaters added 40 kVA. Or am I calculating something wrong?

I have some questions about:
- Are AC units calculated at 100% or is only the largest one considered?
- Are AH units treated as motors, all of them or just the largest? If so, would they be calculated at 125%?
- Are the lights and outlets rated excessively and would require an on-site study or a recalculation based on the NEC?
- How could that panel have been approved with those heaters from the beginning?
- Are there any restrictions on using a service, disconnect, and panel at almost their maximum capacity?

Any help would be greatly appreciated. If possible, which NEC 2020 articles would justify this?

Thank you.
 
ptonsparky said:
Use the largest of heating or cooling, not both.
MCA for the AC units already include a 125% value.
Click to expand...
I used the MCA of each CU, but this way 125% is taken for each CU instead of the largest one. Should I take the MCA of the largest (125%) and the RLA of the other two? Then 100% of the AHUs, which are the remaining smaller motors.
I'm eliminating the heaters. I don't know how they could have been connected to that panel.
 
Can you do a 220.87 load calc instead? This uses a year's worth of 15 minute load data from the power company. Many power companies use smart meters now so they have this data, and I would think they have it for most commercial services since those tend to have demand charges.

NEC load calcs tend to be very conservative. My house comes to 145 amps calculated, but the highest 15 minute load data comes to about 55 amps. Even adding the required 125% to this gives me room for much more load.
 
suemarkp said:
Can you do a 220.87 load calc instead? This uses a year's worth of 15 minute load data from the power company. Many power companies use smart meters now so they have this data, and I would think they have it for most commercial services since those tend to have demand charges.

NEC load calcs tend to be very conservative. My house comes to 145 amps calculated, but the highest 15 minute load data comes to about 55 amps. Even adding the required 125% to this gives me room for much more load.
Click to expand...
Interesting. I never would have thought of that.
It means we can determine the true load by analyzing the usage log over a year. I was planning to just do a stress test one day, turn everything on and measure the load, but this is more realistic.

Thanks.
 
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