200 Amp rated busbar with 100 Amp Service Breaker?

[Balake]

Is it NEC compliant or even CEC if I used a 200 amp busbar with a 100 amp service breaker? I am trying to get a solar array installed on my house but I currently have a old 100amp Zinsco panel that flickers my lights so I am in need of replacing it.

Now due to the 120% rule

(Busbar ampacity x 1.2)-main breaker rating=max inverter amps

If I replace it with the same rated busbar and breaker then i can only install a 20amp inverter which limits me to a 3.8kw array. But, if I use a 200amp or even a 150amp busbar with a 100 amp main service breaker then I should be able to use a higher amp breaker for my inverter?

I have searched the NEC about this code but I am terrible at finding that code or maybe it doesnt exist.

TL:DR

Can I install a 200amp busbar with a 100amp service breaker so I can have a higher rated solar array? Where can I find this code in the NEC?

 

[Hedges]

Yes, 200A busbar with 100A main breaker should allow up to 140A of PV, e.g. two 120A backfeed breakers (if those exist) or a 100A and a 125A.
Not that it would necessarily make sense to have PV breaker larger than main; supposed to keep continuous current no higher than 80% of breaker rating.

I haven't seen 100A main breaker for the 200A (actually 225A) panel I use (Square D QO). But there are 150A main breakers for it. 225 x 1.2 - 150 = 90A PV.

Also, `125A panel with 125A, 100A, or 70A main. 125 x 1.2 - 70 = 80A PV. 125 x 1.2 - 100 = 50A PV.

Good thing you noticed the Zinsco while you still had a house.

I prefer panels with copper busbars (QO) rather than aluminum (Homeline).
Some of the new ones are "Plug on Neutral", which lets you install GFCI and AFCI breakers which clip to that neutral, rather than having a pigtail.
(Not sure if that neutral bar is copper or aluminum.)

 

[Balake]

Is there a code for that? I would like to prove that to my contractor that it would be still legal to install that panel.

 

[Hedges]

The 120% rule, main breaker at one end of a panel plus PV breaker at other end of panel, may not exceed busbar rating by more than 20% - that is well known in PV industry.

I don't have a link to NEC itself, but here's one of many web pages quoting and explaining it:

"NEC code mandates that “The sum of the ampere ratings of overcurrent devices in circuits supplying power to a busbar or conductor shall not exceed the rating of the busbar or conductor”. Further, it goes on to allow as much as 120% of a busbar’s rating to be exceeded. This is where the calculation comes in to play.

(Busbar Rating (A) x 1.2) - Main Breaker Rating (A) = Max (PV + Battery) (A)

Let’s start with an example. We have a 200 Amp bus rating for our service panel. In it, we have a 200 Amp main breaker.

200A x 1.2 - 200A = 40A

In this example, the maximum output of our PV system can be 40A. This would satisfy the busbar rating without an issue."

https://www.kumukit.com/pdf/support/System%20Planning%20Series/Home%20Electrical%20Service/National%20Electric%20Code%20(NEC)%20120-Percent%20Rule.pdf?200707

There is actually no technical or engineering reason why each of [Main, PV] breaker couldn't be same as busbar rating. For instance, 100A main breaker at one end of a 100A busbar, and 100A PV breaker at other end. Current flowing in opposite directions doesn't add, rather subtracts, so no portion of busbar would carry more than 100A.

The guys contemplating proposed NEC regulations how to add PV to a breaker panel with main breaker rating same as busbar rating knew this, but were concerned PV breaker might someday get relocated next to main breaker. That would cause currents to add, overloading the busbar. So they threw us a bone and allowed 20% over busbar rating.

 

[newbostonconst]

Flickering lights while connected to the grid most times is from a bad connection.

Could be at:
light
switch
outlet
breaker panel
meter.....

100 amps is more then most use. Does it flicker when something starts up like a well pump or refrigerator? Does your house have a good ground and neutral?

 

[Hedges]

He had me at "Zinsco"

 

[dweick]

The concern with that rule is that you not feed excessive power to that busbar which could come from a combination of the utility (your 100A breaker limits that) plus your PV (limited by your PV breaker). So with a 100A service breaker and a 100A bus bar and non-compliant 50A PV breaker it is possible your house loads could draw 150A and overload the bus bar. So yes, you can upgrade your busbar to allow for a larger PV breaker.

 

[Balake]

Thank you for reply gents, I really appreciate it.

How do you get permits get approved with your city? Do you make your own line sets and drawings and send it to your permitting office? I'd like to make this legit as possible so I wouldnt get in trouble with my city.

 

[Hedges]

Varies by location.
Check their website.

In San Jose, now you request rooftop PV permit on-line. Make your drawings. Nobody looks at anything until inspector visits site, sees finished installation and drawings. (I know for structure drawing, there are specific requirements. Similar size and detail requirements might exist for PV.)

Years ago, I submitted something like a representative drawing from inverter manufacturer, and a simple drawing of panels, inverter, disconnect, breaker panel - a "one-line" drawing, where I marked number of conductors and gauge for each spot.

For ground mount, I sketched something, and for a fee (more than the electrical permit!) it was stamped "no structural permit required"