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The Controversy Over Accessory Dwelling Units

mark handler said:
Yes and?
Adding a disconnect at the source panel (main house) and at the Subpanel (ADU) gives full "Overcurrent protection."
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If that source panel is inside the main house, then the ADU occupant needs access inside the main house. As stated in post #10.

My understanding is that NEC 240.24(B) is not about having a single accessible OCPD for the supply protecting the occupancy, it is about having access to all the OCPD that could trip and kill power to the occupancy. To avoid the scenario where the occupant loses power due to an OCPD trip and finds they can't access the OCPD to reset it.

Of course, if that is the reasoning behind NEC 240.24(B), then there should be some exception for having properly coordinated OCPDs, where the trip curves are carefully checked and set so that the downstream OCPD always trips first.

Cheers, Wayne
 
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wwhitney said:
If that source panel is inside the main house, then the ADU occupant needs access inside the main house. As stated in post #10.

My understanding is that NEC 240.24(B) is not about having a single accessible OCPD for the supply protecting the occupancy, it is about having access to all the OCPD that could trip and kill power to the occupancy. To avoid the scenario where the occupant loses power due to an OCPD trip and finds they can't access the OCPD to reset it.

Of course, if that is the reasoning behind NEC 240.24(B), then there should be some exception for having properly coordinated OCPDs, where the trip curves are carefully checked and set so that the downstream OCPD always trips first.

Cheers, Wayne
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Which is why you have TWO disconnects, one at the Main and one at the Subpanel.
 
mark handler said:
Which is why you have TWO disconnects, one at the Main and one at the Subpanel.
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Which does not address anything I just said.

If you mean two SERVICE disconnects, that would work, and is allowed by NEC 230.40 Exception 3. You could splice into the service conductors outside the main house (after the meter if the two units are to be jointly metered) and run separate service conductors to the ADU.

Of course, doing that is basically the same as providing a separate electrical service, NEC-wise. The only difference is whether you splice into the service conductors upstream or downstream of the meter. [Along with installing a second meter and setting up an account with the POCO.]

But if the ADU is supplied by a feeder protected by an OCPD inside the main house, then 240.24(B) requires the ADU occupant to have access to that OCPD.

Cheers, Wayne
 
wwhitney said:
Which does not address anything I just said.

If you mean two SERVICE disconnects, that would work, and is allowed by NEC 230.40 Exception 3. You could splice into the service conductors outside the main house (after the meter if the two units are to be jointly metered) and run separate service conductors to the ADU.

Of course, doing that is basically the same as providing a separate electrical service, NEC-wise. The only difference is whether you splice into the service conductors upstream or downstream of the meter. [Along with installing a second meter and setting up an account with the POCO.]

But if the ADU is supplied by a feeder protected by an OCPD inside the main house, then 240.24(B) requires the ADU occupant to have access to that OCPD.

Cheers, Wayne
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Adding a separate electrical service, is not always an option.
Most utility companies will not provide separate services to a property. And it would be cost prohibitive.

CA Codes, by the legislature, forbids cities from requiring separate utilities.
 
mark handler said:
Adding a separate electrical service, is not always an option.
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That and your other comments are all well and good, but the NEC doesn't care how many accounts you have with the POCO, or how many meters there are. And NEC-wise, one service can supply multiple buildings.

My point, and the point in post #10, is that if between the utility transformer, and the loads in the ADU, there's an OCPD inside the main house, then NEC 240.24(B) typically requires access for the ADU occupants to that overcurrent device. If you don't want to provide that access, then make sure there are no such OCPD inside the main house. You can supply the ADU only via conductors that are outside the main house, whether the service disconnect for those conductors is on the outside of the main house, or on the outside of the ADU, or inside the ADU nearest the point of entry for those conductors.

Cheers, Wayne
 
Why do I have the distinct feeling that there are a lot of ADUs where the occupants don't have access to all of the OCPDs to their dwelling.
 
bill1952 said:
Why do I have the distinct feeling that there are a lot of ADUs where the occupants don't have access to all of the OCPDs to their dwelling.
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Happens rarely in California…. So rarely that I don’t recall having ever encountered that… unless perhaps a padlock is added to a panel enclosure after my inspection.
 
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