Panel Calc Question

[Navypilot15]

Hello! I’m a homeowner working on plans for an addition with my engineer. In the link below are his panel calcs for a 150A meter main combo (panel A, the bottom schedule even though they both say panel B) with a 150A sub-panel (panel B, the top schedule). I have two questions:

1) After taking a closer look, I’ve noticed some discrepancies with the demand in the lower schedule and the totals (highlighted), as well as in the panel A service calcs. Am I missing something or are these actually errors? Is it a big deal?

2) I’m throwing around the idea of changing the meter main combo to 200A instead of 150A. How involved would those calculation differences be? He’s quoting me a boatload to “redo” them.

Any insight from you wise people would be greatly appreciated!

https://imgur.com/a/ZjFyqqF

 

[don_resqcapt19]

I approved this because it is not a DIY how to do type of question. If it becomes such a question, the thread will be closed in accordance with the forum rules.

 

[Navypilot15]

Thank you! Yes, not looking for a DIY, I have an engineer. Just looking for advice and clarification

 

[charlie b]

First, unless your area requires participation of an engineer, I don't know why you hired one. An experienced electrician could do this job.

Secondly, the NEC gives us two main ways to calculate service load: the standard method and the optional method. I usually did both calculations, and selected the one that gives me the lower number. This engineer used the optional method, and I believe he did it mostly right.

Thirdly, I agree that you spotted a minor math error (or more to the point, an error moving data from one location to another). The error is minor and insignificant; it gave a final answer just slightly higher than needed.

Next, why do you think you need a higher rated panel? You have plenty of spare capacity with the existing 150 amp panels.

Next, will the power panels be outdoors? If not, then a NEMA 3R rating is unnecessary expensive.

Next, upgrading to 200 amps will not change the calculation IN ANY WAY!!! The panel schedules would need to have the "150" in the bus and breaker ratings changed to "200." The riser diagram (which you did not post) might need to be revised to show a larger service conductor, but the conductor shown now might be good enough. All in all, I think the revisions should take no more than about 5 minutes of effort by the engineer.

And finally, speaking as a Navy veteran, thank you for your service.

 

[Navypilot15]

First, unless your area requires participation of an engineer, I don't know why you hired one. An experienced electrician could do this job.

Secondly, the NEC gives us two main ways to calculate service load: the standard method and the optional method. I usually did both calculations, and selected the one that gives me the lower number. This engineer used the optional method, and I believe he did it mostly right.

Thirdly, I agree that you spotted a minor math error (or more to the point, an error moving data from one location to another). The error is minor and insignificant; it gave a final answer just slightly higher than needed.

Next, why do you think you need a higher rated panel? You have plenty of spare capacity with the existing 150 amp panels.

Next, will the power panels be outdoors? If not, then a NEMA 3R rating is unnecessary expensive.

Next, upgrading to 200 amps will not change the calculation IN ANY WAY!!! The panel schedules would need to have the "150" in the bus and breaker ratings changed to "200." The riser diagram (which you did not post) might need to be revised to show a larger service conductor, but the conductor shown now might be good enough. All in all, I think the revisions should take no more than about 5 minutes of effort by the engineer.

And finally, speaking as a Navy veteran, thank you for your service.

Charlie,

Thank you so much for your input, and thank you for your service as well.

The engineer did build plans for the entire addition which included mechanical and electrical. I was just taken aback by the quote he just sent me for what I thought would be minor updates to the original plans, so I’m trying to do my due diligence before I get back to him.

I’ve attached the riser diagram below as well- the funny thing is he labeled the meter main combo as 200A on the riser diagram but 150A everywhere else.

It will be an outdoor unit so I need NEMA 3R. I actually already have the 200A meter main combo, and my service is rated for 200A, so I figured I might as well upgrade in the off chance that I get solar or an EV down the road.

Does anyone have insight into adding solar to a 150A panel? Is it doable or is 200A much preferred?

 

[LarryFine]

First, unless your area requires participation of an engineer, I don't know why you hired one. An experienced electrician could do this job.

Next, will the power panels be outdoors? If not, then a NEMA 3R rating is unnecessary expensive.

Next, upgrading to 200 amps will not change the calculation IN ANY WAY!!!

And finally, speaking as a Navy veteran, thank you for your service.

I heartily agree with all of these statements.

I would have chosen a 200a service instead of calculating whether a smaller one would suffice.

The labor is identical, and the materials difference is negligible; 200a panels may even cost less.

 

[LarryFine]

Is it doable or is 200A much preferred?

200a equipment with 225a buses is the cat's pajamas.

 

[Navypilot15]

I heartily agree with all of these statements.

I would have chosen a 200a service instead of calculating whether a smaller one would suffice.

The labor is identical, and the materials difference is negligible; 200a panels may even cost less.

Yes sir, I agree. I currently have 150A for the panel that will become the sub panel. The engineer just recommended to keep the new main 150A as well so I went along with it until I realized it would be a good time to upgrade to 200A but he had already finished and submitted the build plans for permitting. Now he’s requesting a good chunk of $$ to redo the calcs, but it doesn’t seem like a proportional fee to me.

 

[kwired]

200a equipment with 225a buses is the cat's pajamas.

Often 150 - 225 amp panelboards have the same bus in them just a different main breaker.

 

[kwired]

First, unless your area requires participation of an engineer, I don't know why you hired one. An experienced electrician could do this job.

Secondly, the NEC gives us two main ways to calculate service load: the standard method and the optional method. I usually did both calculations, and selected the one that gives me the lower number. This engineer used the optional method, and I believe he did it mostly right.

Thirdly, I agree that you spotted a minor math error (or more to the point, an error moving data from one location to another). The error is minor and insignificant; it gave a final answer just slightly higher than needed.

Next, why do you think you need a higher rated panel? You have plenty of spare capacity with the existing 150 amp panels.

Next, will the power panels be outdoors? If not, then a NEMA 3R rating is unnecessary expensive.

Next, upgrading to 200 amps will not change the calculation IN ANY WAY!!! The panel schedules would need to have the "150" in the bus and breaker ratings changed to "200." The riser diagram (which you did not post) might need to be revised to show a larger service conductor, but the conductor shown now might be good enough. All in all, I think the revisions should take no more than about 5 minutes of effort by the engineer.

And finally, speaking as a Navy veteran, thank you for your service.

Meter main combo may be hard to find that is not a NEMA3R.