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Discussion Starter · #1 ·
So I am researching solar systems and installations for a friend of mine who wants to install at his appliance store. It looks like he will need available space for a 40amp load (at least that is what we believe to be necessary for an 8.1kW system) at his electrical box to host this system. We have been told that we may have to upgrade his service to 200amps to host this. However this would be way out of budget considering the conduit for the service goes under the driveway, 2 sidewalks and the street (with a median!!). I had an electrician look at the system and he reported to me that it is a 100amp 3 phase 120/208V system (A&B phases=120V, C phase=208V).
After measuring the load to each leg with a clamp ammeter in the middle of a business day with the air conditioner running (it is a pretty old system), he found:
A phase: 115V, 43.5amps (spiking to 75amps)
B phase: 121V, 23.6amps (no noticeable spiking)
C phase: 207V, 22.5amps (no noticeable spiking)

Is a 40amp breaker the right size for an 8.1kW system?
Is there room in this panel to accommodate said system (or do I need to provide more info)?

In addition (or maybe another option), I spoke to a well known solar installer in California that claims that they simply do a "Line Side Tap" to avoid having to conduct a service or panel upgrade. If anyone could offer an explanation for what this is and if it is a potential go-around for my issues with the breaker panel/ electrical service.

Thank you for your time!! Have a great day and wear your rubber boots!!


evil bastard
15,771 Posts
You will need a serice upgradeto comply with this code:

(2) Bus or Conductor Rating.​
The sum of the ampere
ratings of overcurrent devices in circuits supplying power
to a busbar or conductor shall not exceed 120 percent of the
rating of the busbar or conductor. In systems with panelboards
connected in series, the rating of the first overcurrent
device directly connected to the output of a utilityinteractive
inverter(s) shall be used in the calculations for

all busbars and conductors.

With that being said, it's painfully obvious that you're in over your head and should hire a professional. Even the electricain taking load readings was doing it completely wrong. You need to include professionsl in this if you ever want it to operate, even if that means you butting out and minding your own business.
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