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Manipulating Load Calculations

jar546

jar546

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This is a SFR undergoing a level 2 renovation with an existing 150A service.
This is what it looks like when the architect tries to manipulate the numbers to make it appear as though the load calculation works when, in fact, it is not even close. This includes bogus numbers for the range, incorrect numbers and circuits for the tankless electric water heater, manipulated numbers for kitchen circuits, laundry, etc. Also, take note of how he labels the 240V as AMPS. The electrician would have done a much better job.
Screen Shot 2019-10-31 at 07.31.10.png
 
I'd like to see the plan connected to this. We don't ask for electrical plans if dwelling falls under the IRC (that's left up to field inspections only), but if this is a condo, we would review. It's been a little while since I've done these, but this looks messed up all around. Based on some of the numbers provided for what could be assumed as the general lighting loads, this could be a 4500 sq.ft. dwelling. Is it? And where did the demand factor of 60% come from for the HVAC, and how did that number arrive at 14,001 VA? Looks like he's mixed demand factors from 220.44 (non-dwelling at first 10 kVa at 100%) and the balance (40%) from 220.83. The sad thing is, it is possible, if the calculation were done correctly, that the 150A would still be sufficient.

Observation: post indicates this is an existing 150A service. Panel schedule says new M.L.O. panel, assuming that disconnecting means and OCP is somewhere near the service provider meter?
 
rgrace said:
I'd like to see the plan connected to this. We don't ask for electrical plans if dwelling falls under the IRC (that's left up to field inspections only), but if this is a condo, we would review. It's been a little while since I've done these, but this looks messed up all around. Based on some of the numbers provided for what could be assumed as the general lighting loads, this could be a 4500 sq.ft. dwelling. Is it? And where did the demand factor of 60% come from for the HVAC, and how did that number arrive at 14,001 VA? Looks like he's mixed demand factors from 220.44 (non-dwelling at first 10 kVa at 100%) and the balance (40%) from 220.83. The sad thing is, it is possible, if the calculation were done correctly, that the 150A would still be sufficient.

Observation: post indicates this is an existing 150A service. Panel schedule says new M.L.O. panel, assuming that disconnecting means and OCP is somewhere near the service provider meter?
Click to expand...

There is an existing 150A service. They are replacing the exterior service disconnect and interior main panel. The tankless numbers alone with throw this load calc way off as I have yet to see a tankless that does not require less than two 40A 240V circuits that is capable of providing adequate water flow. Most I see in condos are three 40A 240 or 208 circuits.
 
jar546 said:
There is an existing 150A service. They are replacing the exterior service disconnect and interior main panel. The tankless numbers alone with throw this load calc way off as I have yet to see a tankless that does not require less than two 40A 240V circuits that is capable of providing adequate water flow. Most I see in condos are three 40A 240 or 208 circuits.
Click to expand...

Daaang ! (public forum etiquette) I had no idea an electric tankless used so much power. I suppose that's why I see gas-fired tankless more than electric. In fact, I can't say that I've actually seen an electric one, but of course that's not saying much since my primary work function focuses on mechanical/plumbing, and only occasionally, electrical. Gonna have to look into this more. My water heater will have to be replaced at some point (going on 30 yr old) and I don't have gas at my house. I do have 400 AMPS worth of service for my cozy little 1,500 sq.ft. home :cool: and could consider tankless as an option.
 
Yup, so the first one I looked up has this to say:

Prior to purchase & installation, please verify that this model is the right size for your hot water needs and electrical requirements. Electrical requirements: 27 kW, 240 volts, (3) 40 required breakers, 112.5 maximum power (AMP), (3) 8 required wire. Amperage Draw:113 A

AMPERAGE DRAW: 113 AMPS !!!!! Yea, that's gonna overburden a 150A panel.
 
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