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

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  • RShackleford
    replied
    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."
    Last edited by RShackleford; 05-20-2020, 11:50 AM.

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

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  • RShackleford
    replied
    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.


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  • bob-n
    replied
    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

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  • SunEagle
    replied
    Originally posted by RShackleford View Post
    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.

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  • RShackleford
    replied
    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.

    Last edited by RShackleford; 05-17-2020, 02:25 PM.

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  • J.P.M.
    replied
    Originally posted by bob-n View Post
    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.

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  • bob-n
    replied
    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.

    Side story, perhaps with a bit of relevance. My friend's house burned to the ground. He and his wife got out unhurt, but lost everything. The insurance company paid to have the house rebuilt, but not without a hassle. He told me that they traced the cause to a bad power strip. I'm guessing that the MOVs in it absorbed one too many surges. He followed the code. Insurance covered it. But he was horribly inconvenienced for over a year and lost all irreplacable possessions.

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  • brycenesbitt
    replied
    Originally posted by nwdiver View Post
    The whole AC disconnect thing has always amused me. There's a 0.000001% chance it's ever going to be used. The utility isn't going to go around opening AC discos on homes and if there's a fire the fire department is going to pull your meter to turn off the power. No one really has any use for the AC disconnect.
    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 ).

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  • Mike90250
    replied
    The post had been rapidly edited or something, and was locked into spam moderation. It's now out of quarantine.

    And please note his last line:
    Please note that I am not an electrician. This is not professional advice, just me repeating what I've been told. If you have the slightest doubt, hire a qualified electrician. If you are an electrician or if anyone reading this is an electrician, please forgive me if these are ignorant comments.
    YOU are getting information from un-vetted voices on the keyboards of the internet. What matters is the Building Code in your area, and your ability to perform or contract to meet the code. Stray from the code and you will find if there is ever an incident, your insurance company is most likely not going to help you.

    Internet_dog.jpg

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  • bob-n
    replied
    For what it's worth, I used a low-cost air conditioner disconnect, and both town inspector and power company approved.

    Line-side taps have advocates and haters. They work. They are practical. They are relatively easy. They are relatively inexpensive. What's not to like?

    They require making high-current connection to existing high-current cable that is often old aluminum. To me, that seems a bit risky, so before doing mine, I called the application engineer at one of the line-side-tap manufacturers and told him my plans. His response surprised me. He said that he does not recommend using his company's line-side-tap product like this. He said that it will make good connection, but if something does go wrong in that connection, there is nothing between there and the power pole to protect you. The tap is ahead of your main breaker, directly connected to the incoming mains. Between the tap and the power pole, there is no fuse, no circuit breaker. Your only protection is the huge fuse in series with the HV going into the transformer.

    So what did he recommend? He said that you can buy a new meter box that has two connection points on eacn meter pole output. Why is that better? Because those connections are tested and rated for unprotected connection from a load center to the mains. But my power company doesn't allow me to change the meter box. So I went with a new circuit breaker in my load center.

    Many people use line-side taps. I've never heard of one failing. You'll probably be fine. No matter what else, install it extremely carefully. Follow the manufacturer's torque, spacing, and all other instructions to the letter.

    Please note that I am not an electrician. This is not professional advice, just me repeating what I've been told. If you have the slightest doubt, hire a qualified electrician. If you are an electrician or if anyone reading this is an electrician, please forgive me if these are ignorant comments.

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  • RShackleford
    replied
    Originally posted by Ampster View Post

    And you are doing that because of the calculations about your panel buss bar or because you are out of breaker space?
    The latter. Will probably add a critical loads subpanel at some point, which will free up a lot of space, but the line side tap seems more straightforward anyhow. I guess insulation-displacement is kinda kludgy, but its use is widespread around here, and the AHJ cast no shade upon it at all, when he came out to see my conduit trench.
    Last edited by RShackleford; 05-16-2020, 11:42 PM.

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  • Ampster
    replied
    Originally posted by RShackleford View Post
    By installing a *fusible* AC disconnect, one has the option of doing a line-side tap (https://www.zoro.com/buchanan-displa...ctid=123572619) instead of connecting to a double-pole breaker in the main panel. This is what I am doing.
    And you are doing that because of the calculations about your panel buss bar or because you are out of breaker space?

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  • RShackleford
    replied
    Originally posted by nwdiver View Post
    No one really has any use for the AC disconnect.
    By installing a *fusible* AC disconnect, one has the option of doing a line-side tap (https://www.zoro.com/buchanan-displa...ctid=123572619) instead of connecting to a double-pole breaker in the main panel. This is what I am doing.

    Leave a comment:


  • nwdiver
    replied
    The whole AC disconnect thing has always amused me. There's a 0.000001% chance it's ever going to be used. The utility isn't going to go around opening AC discos on homes and if there's a fire the fire department is going to pull your meter to turn off the power. No one really has any use for the AC disconnect.

    Leave a comment:

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