Newbie with a question please.

Re: Newbie with a question please.

First, get the normal warning out of the way... Installing Grid Tied inverters without UL/NRTL listings, without building permits, and without utility approval is usually against the law in most places. The utility can disconnect your power and the local town/county could red tag your home. Also, many of the newer utility meters may not turn backwards, and some even will turn forward when you are sending power to the grid (i.e., charge you retail rates for generating power). Also, many new meters can report back to the utility that you are generating power. All as part of revenue protection (people wiring meter backwards, etc.).

The reason for NEC code, NRTL listing services, and licensed electricians/professional engineers/etc. is to reduce the risk of fire/danger in your home.

And the answer, Grid Tied inverters are synchronized with the grid--So, you would keep adding GT inverters in parallel to your dedicated circuit up to the rating of the circuit breaker:

• 15 amp breaker * 120 VAC * 0.80 NEC derating = 1,440 watts maximum input from GT inverters on 15 amp circuit
• 15 amp * 0.80 derating = 12 amps max continuous current on 15 amp branch circuit

Good luck and be safe.

-Bill

PS: Just to add clarification, each GT inverter should have its own array. Usually they will not play together well if you have several GT inverters connected to one solar array. You only parallel their outputs to the home wiring/utility grid (following good design and code requirements).

Re: Newbie with a question please.

Do not parallel the GT inverters on their DC input side.... They actively control the current and voltage from the solar panel/array (Maximum Power Point Tracking). The algorithms from one inverter doing a I*V test of the array will confuse other attached inverters.

Just max out the array for each inverter (single array for a single inverter DC input).

Then simply connect the AC side of the GT inverter to the AC branch circuit (more or less, just like attaching any other loads using L1/L2/Neutral if a 120/240 VAC split phase circuit or just using L1 and Neutral if a 120 VAC branch circuit).

In your case, if using 600 watt GT inverters on 15 amp 120 VAC circuits, then two inverters in parallel on one 120 VAC 15 amp circuit would be the safe limit (assuming GT inverters meet the NEC/NRTL operating requirements).

-Bill

Re: Newbie with a question please.

Yes, but you could wire 2x 600 watt GT inverters to the same breaker as they both would be under the 15 amp current limit when they are both outputting maximum power.

You only need separate breakers when you exceed 80% of the rated branch circuit capacity (at 100% of branch capacity, breakers are supposed to eventually trip--minutes to hours or more). 80% is considered the "design" maximum current of a branch circuit. Or, another way of looking at it, you need to design the branch circuit to be 1/0.8 or 1.25x larger than your maximum sustained current.

-Bill

Re: Newbie with a question please.

Ummm.... First, I assume these are 250 Watt 120 VAC GT Inverters? And you are talking about a 30 Amp 120/240 VAC split phase breaker?

Second, you need to review the specifications of your GT Inverters. They should tell you the maximum sized circuit that they can be connected to. For example they may say 15 amp @ 120 VAC or 20 amp @ 120 VAC, or 20 amp @240 VAC, etc.

I would assume that your GT inverters are 120 VAC units and sized for either a 15 amp or 20 amp maximum branch circuit. In the US, NEC normally requires:

• 15 amp circuit requires 14 awg minimum
• 20 amp circuit requires 12 awg minimum
• 30 amp circuit requires 10 awg minimum

But there are other issues too. Maximum operating temperature, type of insulation, fill factor in conduit, and any local code requirements (the city I grew up in requires 12 AWG wire minimum for all household circuits--an expensive pain in the behind).

Remember that circuit breakers are part of a layered protection scheme... The circuit breaker is to protect all down stream wiring and attached devices from overheating/fire (reduce the chances of harm/failure).

If you have a 30 amp breaker, then you need to run a minimum of 10 awg (properly rated) cable from the breaker to all loads/outlets/attachment points. You should not attach, for example, a 14 awg wire from your 30 amp breaker to a 250 watt GT inverter... Yes, the inverter will not overheat the 14 awg wire, but if there is a fault somewhere (or somebody else adds 10 more 250 watt GT inverters), the 30 amp breaker cannot protect the 14 awg wire and you could get a fire.

Current NEC books/code have sections that list the requirements for Grid Tied Solar PV systems... Also, similar requirements are needed for the DC side of the wiring system too (correctly sized and rated wiring, possibly UV/outdoor rated, and possibly fuses/breakers depending on solar array configuration). There are also DC and AC disconnect requirements (many are locally defined by building departments and utilities).

-Bill