AC Disconnect: Visible to Firefighter or Visible to Solar Tech? California.

[J.P.M.]

Mike is right. Follow the code.

That said, I also believe that there are better and worse code-compliant ways to implement a system. As proof, simply note that the code is constantly being updated.

While sure not proof, my professional experience has been that changes to codes and standards that have wide use and acceptance most often come about as a result of/reaction to new products and procedures rather than changes found to be necessary/safer/better from experience gathered from long term or wide use.

The former type changes seem/tend to happen quickly and reactively, particularly in response to failures/injury accidents from misuse or ignorance of the limits of an (often) new device.

The latter type changes tend to be more evolutionary and deliberate in nature.

As for better/worse ways to get code conformance, that may be one reason why the Almighty made AHJ's and code inspectors - to protect the great unwashed masses from irresponsible behavior by inconsiderate morons that, while it may improve the gene pool and take out more of the morons if left to their own devices, can cause collateral damage to the rest of society.

[RShackleford]

FWIW, my service entrance cables are copper. And as I said, the AHJ is fine with line-side tap connectors.

I'm not sure I understand the concern that there's "nothing between there and the power pole to protect you". (In my rural case, it's actually a dedicated 7.2kV -> 240Vac transformer). There was nothing there beforehand either. Afterwards, yes, there's still no protection between the main breaker and the transformer. And the only thing that's new is those taps. But, they are connected to fuses in the fusible disconnect between the inverter and the line-side taps. The only danger is at the taps themselves; but the meter will be pulled when I make a connection. I suppose that if there were any shorts in the wires connected to the taps (with each other, or with ground or neutral) that then there would be no protection, same as there was no protection for shorts in the service entry cables before; but I suppose such shorts are more likely, once there are wires connected to the SE cables.

I also frequently read about "your local building code" or "the Building Code in your area". This confuses me. My area is my county, and they simply go by the NEC. Do other localities have local modifications ? What can vary between localities, is which version of the NEC they've adopted; in my case, it's which version the state has adopted, but maybe it's county by county or municipality by municipality in other states. What does vary, of course, is the local AHJ's interpretation of the NEC. Perhaps that's what people really mean.

[SunEagle]

FWIW, my service entrance cables are copper. And as I said, the AHJ is fine with line-side tap connectors.

I'm not sure I understand the concern that there's "nothing between there and the power pole to protect you". (In my rural case, it's actually a dedicated 7.2kV -> 240Vac transformer). There was nothing there beforehand either. Afterwards, yes, there's still no protection between the main breaker and the transformer. And the only thing that's new is those taps. But, they are connected to fuses in the fusible disconnect between the inverter and the line-side taps. The only danger is at the taps themselves; but the meter will be pulled when I make a connection. I suppose that if there were any shorts in the wires connected to the taps (with each other, or with ground or neutral) that then there would be no protection, same as there was no protection for shorts in the service entry cables before; but I suppose such shorts are more likely, once there are wires connected to the SE cables.

I also frequently read about "your local building code" or "the Building Code in your area". This confuses me. My area is my county, and they simply go by the NEC. Do other localities have local modifications ? What can vary between localities, is which version of the NEC they've adopted; in my case, it's which version the state has adopted, but maybe it's county by county or municipality by municipality in other states. What does vary, of course, is the local AHJ's interpretation of the NEC. Perhaps that's what people really mean.

Some towns or counties have their own electric rules that meet some version of the NEC or are stricter. It usually comes down to what the person that does the inspection or as we call them the AHJ that will decide what you need to follow. Sometimes that is more than the NEC.

[bob-n]

I'm not sure I understand the concern that there's "nothing between there and the power pole to protect you". (In my rural case, it's actually a dedicated 7.2kV -> 240Vac transformer). There was nothing there beforehand either.

It wasn't my concern, it was the concern of the engineer at the company selling line-side taps. Silly me, but I didn't ask him to explain in more detail. I only asked what he would recommend, and that's when he mentioned a different meter box.

This is wild speculation, but if the tap itself were defective and became intermittent, it could arc. If the arc bridged the mains, you could get enough energy in one spot to cause a serious fire. Your load center was never engineered for taps and was never tested with taps. Perhaps that's why the engineer at the company didn't recommend them. But I'm just guessing.

I once cut a power cord with wire cutters, while it was powered. It made a big spark, cut two notches in the wire cutters and tripped the breaker, but thankfully, no one was hurt. You can sometimes screw up 120VAC with a 15A breaker and get away with it. It's a much more significant situation with 240VAC and hundreds (thousands?) of amps. Please be careful.

The following a picture is included only for entertainment. I know you won't do this and you know that I'm not recommending this. It came from a discussion on Quora with the subject: "What are signs that electrical work was done by an amateur?"

main-qimg-fa92ac1f4ac70498037d18fd92bb834b.jpg

[RShackleford]

Good ... holy ... I would use my favorite curse here, but not suitable for pubic consumption. Yeah, I guess bad stuff could happen (even without such stupidity). But I'm curious what the engineer (at the tap company) would recommend them for.

Maybe I'll go ahead and install my critical-loads subpanel (thereby freeing up room for a breaker for the GTI). It was in my submitted line drawing (for the solar permit), so if I want to do it later, and have it inspected, I'd have to spring another $100+ for a new electrical permit. Just didn't want to figure that out while I'm trying to complete the solar. But a lot of the work is moving over my essential loads to the subpanel (requiring new home-runs and/or adding boxes, because most of them will not reach the subpanel's location) and I can punt on most of those.

[Ampster]

I am glad it is progressing well and the wood is holding up well.

[RShackleford]

My AHJ seems to be telling me that the connection from the GTI and AC disconnect to the main panel is considered a "service entry" connection. And that therefore it is required to be in metal conduit; I find that a bit odd, since my actual service entry (the honking 2/0 and 1/0 cables from the meter) is in PVC conduit (it's probably Sch80, but still).

EDIT: AHJ provided some reasoning for considering the connection to be "service entry": "Because you're tapping into the service conductors in the main panel on the service side of the disconnect that’s why your only allowed 5 feet inside the structure outlined on the drawing."

[nwdiver]

And just to be clear, when the fire department hits the main, or pulls the meter, the inverter shuts down.

The only need for a "disconnect within reach of the equipment" is for electricians unfamiliar with
circuit breaker lockouts ( e.g. https://www.garvinindustries.com/pan.../one-pole/ubl1 ).

Yep; That's my point. None of the reasons for having an AC disconnect will ever actually be used. The fire department isn't going to go hunting for a disconnect switch when there's a fire. They're going to follow the lines to the meter remove it and carry on to the next task. Removing the meter has the same effect as opening the AC disconnect.

[RShackleford]

My impression was that it's more for if the POCO is having weirdness on the grid and wants to remove the PV from the equation:

"In order to comply with the Final Rule of the Rural Utilities Service regarding the Interconnection of Distributed Resources (IDR) as codified at 7 C.F.R. Part 1730, Subpart C, the Cooperative requires that the Interconnection Facilities shall include a lockable disconnect and visible open EDS that is readily accessible to and operable by authorized Cooperative personnel at all times. The EDS is a manual load break disconnect switch or safety switch with a clear visible indication of switch position between the Cooperative System and the Interconnection Member. The switch must have pad lock provisions for locking in the open position. The switch must be visible to, and accessible to, Cooperative personnel. The switch must be in close proximity to, and on the Interconnection Member’s side of the point of electrical interconnection with, the Cooperative's System. The switch must be labeled "Generator Disconnect Switch.” The switch may isolate the Interconnection Member and its associated load from the Cooperative 's System or disconnect only the Generator from the Cooperative 's System and shall be accessible to the Cooperative at all times. The Cooperative, in its sole discretion, determines if the switch is suitable and necessary."

[nwdiver]

My impression was that it's more for if the POCO is having weirdness on the grid and wants to remove the PV from the equation.

I've never heard that. It's a safety switch to protect line workers and fire fighters. Line workers are protected by the anti-islanding requirement and fire fighters are protected when they pull the meter and the anti-islanding requirement. Xcel has done work on the lines near my house before. I lost power and they never touched my AC Disconnect. I suspect it's they same everywhere. I doubt a utility is going to waste man-hours LOTOing residential AC disconnects then clearing them again when they're done.

[RShackleford]

Well, very little trouble to put in the AC disconnect; they cost $10-15 and are a good way to transition to the metal conduit that AHJ wants to see once going into the house. There is a stud wall perpendicular to the exterior wall of house, and the main panel is recessed into that stud wall, with its edge right up against the exterior wall. So I figure I'll mount the AC disconnect right there, slightly above the top height of the panel, and come out the rear of the disconnect with metal, into the side of the stud wall and down into a knockout in the main panel. Use PVC conduit to get from inverter into bottom of disconnect.

[bob-n]

Newer inverters shut down when the meter is pulled. Older inverters varied. Insisting on a safety disconnect means that they emergency crew (firefighter, etc.) doesn't have to think about the age of the system. Pull disconnect and the line is assuredly cut.

That said, there's still hundreds of volts coming out of the panel string. Let's hope that the installation has the panel string floating so touching one wire and earth doesn't kill you. That has been a requirement for inverters for many years now.

[bcroe]

I do not know how the disconnect question applies to a ground mount array. My boxes are 230 feet from
the array and 270 feet from the house meter. Certainly not visible from the house, but pulling the house
meter will shut all AC down. Bruce Roe

[bob-n]

If you pull the meter, then your array can't feed the grid. But assuming that the rapid shutdown isn't there, can't your array still feed the house? Could a fireman swinging an axe into a wall of the house hit a live wire? Assuming that your array is treated like a backup generator, the output would still be live after the meter is pulled. That's not the way solar works, but that's the way the rules are written.

[nwdiver]

If you pull the meter, then your array can't feed the grid. But assuming that the rapid shutdown isn't there, can't your array still feed the house? Could a fireman swinging an axe into a wall of the house hit a live wire? Assuming that your array is treated like a backup generator, the output would still be live after the meter is pulled. That's not the way solar works, but that's the way the rules are written.

Not under UL1741. If a grid-tie inverter doesn't get AC then it can't make AC, pulling the meter has the same effect as opening the AC disconnect. Even if that were the case the are circumstances where the line from the inverter to the AC disconnect could run a fair distance (with micro inverters for example). IIRC there's no requirement that the AC disconnect be located near the inverter.... just accessible from the exterior of the home.