Company went out of business. need to check their plans

[Hedges]

How is feeding solar in the bottom going to increase the load in the main breaker? Feed more power in the bottom and less needs to come in through the main.

Yes, Feeding solar in bottom (or anywhere) decreases load on main breaker.

Of course feeding anywhere but the bottom could result in busbar carrying current equal to Main + PV rating.
First thought is that feeding from bottom, ought to be OK regardless of PV breaker size up to 100% of main, a "200%" rule.
Consider 125A main breaker and 40A PV breaker. 125A flows down one busbar, and 40A flows up from other end, able to feed 165A of loads. Yet, no part of busbar carries more than 125A. Should be OK, right?

Now consider the neutral busbar. If inverters are 240V, not feeding current into neutral, the Line1 busbar has 165A of loads, fed 125A from grid and 40A from inverters. Those 165A of circuits return through neutral wires to neutral busbar, which carries 165A. That is way too much for a 125A busbar!

You might avoid this issue if panel has neutral fanned out to busbars on left and right, and you're careful that Line1 circuits have neutral wires distributed across both (same for Line2). However, the neutral wire from utility is also carrying 165A.

So I now consider the 120% rule important, where I previously thought 200% rule ought to be used.

But, the plans call out the main as 100 amp and label it as new in one place and existing in another. Only saw the existing label the first time though. I also didn't see the stacked full panel and overlooked that the main was in the center.

If 100A main breaker, only 80A continuous or could have nuisance trips. It was noted there were quite a few loads, although I don't know what they add up to.

I don't know if the 120% rule works on a center mounted main.

I understood that 100% was the rule for center mounted. But I've heard that rule got waived in a later NEC?

Knowing this additional info, I think the new 200 amp panel is prob the right decision.

Would be nice to do, 200A (or 225A also commonly available), either 200A or 150A breaker. Square-D has those options, other brands may have others.

 

[Ampster]

What exactly are you telling me I am wrong about?

@Hedges calculation was different. I was just pointing that out. Other readers can decide who is right , and the dialogue about that is what is important. There clearly are some workarounds.

 

[Hedges]

Changing main breaker to 100A, in 125A panel, allows more PV.
For a top-fed panel, I would say 50A PV breaker (not just 40A)

If that is a center-fed panel, I thought 100% rule but someone said that was relaxed in later version of NEC.
Ignoring code and just thinking engineering, size of two breakers above 100A main breaker determines how much current busbar would carry.
Is the busbar really 125A? Or closer to 62.5A and counting on loads distributed between top and bottom (therefore busbar not protected by main breaker?) But beware of overloading neutral busbar and utility drop.

Panel is pretty stuffed. Any plans for more circuits? Now would be a good time to put in a 200A 42 slot panel, so no tandem breakers needed, and can use GFCI/AFCI if desired.

His original plans (post # 12) indicate an existing 100 amp main breaker. Originally I didn't notice that they also call the 100 amp main breaker as new. Shoddy work on their part for the plans to conflict on the same page, is it new or existing? Well, initially I only saw the existing tag on the main breaker, so it looked like he was already living fine on the 100 amp main. A top fed 125 amp bus bar is rated for a 100 amp main + 40 amps of solar.


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[Think About It]

If your current panel has 125 amp bus bar and breaker, you could down size the main breaker to 100 amp and be legal.

Not necessarily. I contend if the residence required a 125 Amp service calculated according to the NEC, then downgrading the service to 100 Amp would not meet code.

Also, that load center is a 16 space, 24 circuit. It is already full. No more tandems can be added.

Unfortunately, this is what happens when builders cut costs to the bone. Absolute minimums on everything. Who uses a combination meter socket load center on a residential job? I certainly would never put one in. I hope if the OP does a service upgrade that he doesn't install another combo unit.

 

[Think About It]

Panel is pretty stuffed. Any plans for more circuits? Now would be a good time to put in a 200A 42 slot panel, so no tandem breakers needed, and can use GFCI/AFCI if desired.

Agreed. What sucks is that he'll probably have to trench new underground service entrance cable. I doubt the electrician that put that service in oversized the conduit for future service upgrade.

 

[Hedges]

Might it be good enough for 150A?
You can put a 150A main breaker in a QO series 200A or 225A panel. That allows 90A or 120A PV breakers.

If it was fully stuffed with aluminum, pulling copper would be an (expensive) upgrade.
But it was probably direct burial ...

Ask them to NOT undersize the neutral!

 

[Ampster]

Who uses a combination meter socket load center on a residential job?

It is very common in California and and almost every house I have owned was built that way. The exceptions are townhomes, condos and an apartment buildings. Since the subject of this thread is in Utah, perhaps they follow the typical California custom? I agree with your thoughts and the last two homes I purchased, required panel upgrades to accommodate solar..I still used a combo load center because that was all that was available but I put in sub panels nearby on the inside wall of the garages where the meter was located.