Fused Disconnect Switch For Supply Side Interconnection

[zemingduan]

I am looking at the solar system drawings below and have two questions:

Q1: Do you need over current protection for the inverter output circuits as per 705.65?

Q2: Which are the line side and load side of this disconnect? Shall we reverse the disconnect switch and fuses? Code reference

 

[don_resqcapt19]

1) you need overcurrent protection because your installation does not comply with the second part of the exception.
2) I would connect the line side to the utility as that is the worst case, and the inverters should shut down when you open that switch.

 

[Carultch]

I am looking at the solar system drawings below and have two questions:

Q1: Do you need over current protection for the inverter output circuits as per 705.65?

Q2: Which are the line side and load side of this disconnect? Shall we reverse the disconnect switch and fuses? Code reference

To elaborate on Q2, the way the drawing shows it it is correct, and the opposite would be incorrect. Make this abundantly clear on drawings, so it doesn't get overlooked, since you don't want another shutdown to correct it. I recommend drawing line terminals on top the way the product appears in reality, and with wire U-turns where needed.

Disconnects are marked line and load, but this has nothing to do with power flow direction. The line/load sensitivity is needed, so fuses and the blade are de-energized when the switch is open. The switch and fuse can handle power flow in both directions, but the permanently energized source needs to be on the line side. The "hinge" of the disconnect blade should point toward the inverter, for both AC and DC.

 

[jaggedben]

The second, non-fused disconnect to the right of the meter is not required by the NEC. It would only be required if the first (fused) disconnect is not accessible for rapid shutdown (but the drawing says it is) or if the inverter is remote from the first disconnect. In fact, the drawing seems to indicate the inverter is remote at the 'Pilot House' so it seems to me the 2nd disconnect belongs there, rather than in the Electrical Room. That said, we've heard on this forum of utilities having a stupid requirement for a disconnect on both sides of a PV meter, so maybe you do need it for that reason.

The solar system cannot output more current that the wiring is rated for so overcurrent protection is really only for the utility. Also when disconnected the inverters will no longer energize the AC wiring. For these reasons, continue to treat the utility as line, like Don said.

 

[Carultch]

That said, we've heard on this forum of utilities having a stupid requirement for a disconnect on both sides of a PV meter, so maybe you do need it for that reason.

Depending on the application of the meter. If the utility is involved in any capacity as the meter user, then utility standards would apply, and possibly require a "sandwich" of disconnects around it (line side fused, inverter side unfused). If it is just a customer-owned meter that doesn't concern the utility, then utility standards wouldn't govern anything about it. Other than to label one that looks similar to a utility meter, so they don't mistake it for their own.

Item E would also be a 200A disconnect in this application. 400A is the next standard size after 200A, and it'd need fuse reducers to host 175A fuses.

 

[jaggedben]

Depending on the application of the meter. If the utility is involved in any capacity as the meter user, then utility standards would apply, and possibly require a "sandwich" of disconnects around it (line side fused, inverter side unfused). If it is just a customer-owned meter that doesn't concern the utility, then utility standards wouldn't govern anything about it. Other than to label one that looks similar to a utility meter, so they don't mistake it for their own.

Item E would also be a 200A disconnect in this application. 400A is the next standard size after 200A, and it'd need fuse reducers to host 175A fuses.

Since the system is shown connected to the line side of the existing meters I'm assuming it's a utility meter. Could be VNEM in Cali or something similar. I hope whoever drew it up knows what they're doing in this respect.

Even if it's a utility requirement it's still a stupid requirement in my opinion.

 

[Joethemechanic]

Since the system is shown connected to the line side of the existing meters I'm assuming it's a utility meter. Could be VNEM in Cali or something similar. I hope whoever drew it up knows what they're doing in this respect.

Even if it's a utility requirement it's still a stupid requirement in my opinion.

If that revenue meter is a utility meter with a disco on the line side, wouldn't that make stealing power really easy?

I'm not wearing my readers, so maybe I'm missing something??

 

[Carultch]

Since the system is shown connected to the line side of the existing meters I'm assuming it's a utility meter.

It looks like a behind-the-meter system to me. There's what appears to be two meters in series, one of which is the utility meter. It's line-side of the service disconnect, but load side of the meter.

At this scale, I'd expect the service to either be transformer-integrated metering, or a CT cabinet style of metering.

If that revenue meter is a utility meter with a disco on the line side, wouldn't that make stealing power really easy?

Hot-sequence is more tamper-resistant, cold-sequence is safer. It's a tradeoff, and utilities standards vary. Generally, the more complicated the equipment, and the higher the voltage, the more likely cold-sequence metering is required.

 

[jaggedben]

It looks like a behind-the-meter system to me. There's what appears to be two meters in series, one of which is the utility meter. It's line-side of the service disconnect, but load side of the meter....

You're right. I was thrown off by the grid being shown at the bottom which is opposite what I normally expect.

 

[ggunn]

I am looking at the solar system drawings below and have two questions:

Q1: Do you need over current protection for the inverter output circuits as per 705.65?

Q2: Which are the line side and load side of this disconnect? Shall we reverse the disconnect switch and fuses? Code reference

View attachment 2567344

If your inverter(s) are not a single SolarEdge inverter with three subunits combined in a single synergy unit, I believe you need to have an OCPD on each one in an AC combiner. The disconnect on the inverter side of the PV meter is not necessary unless the utility requires it (some do in some cases), and even if they do it does not need to be fused. The metering on the customer's side is confusing to me; it looks like two meters in series on a single feed to the MDP. Does one read power in one direction and one in the other? Most modern meters are bidirectional.