120% Conductor Rule?

[Sierrasparky]

Silly should be a clue that you're not quite thinking right :slaphead:

Not saying it don't happen... but I am saying rarely.

Base upsizing on the minimum EGC size. 2/0 AL EGC for a 200A OCPD is substantially oversized. The 4/0's would have to be six sizes oversized for the OCP before upsizing the EGC comes into play (in the neighborhood of a 40A OCPD).

It's silly because you need to read 250.112 Nowhere does it indicate a starting point or base on a table. It just says
"shall be increased in size proportionately according to the circular mil area of the ungrounded conductors"

 

[shortcircuit2]

It's silly because you need to read 250.112 Nowhere does it indicate a starting point or base on a table. It just says
"shall be increased in size proportionately according to the circular mil area of the ungrounded conductors"

I thought you guys were going to take this to another thread?

 

[shortcircuit2]

Perhaps it doesn't violate the wording exactly. But feeding an MLO panel from one end with supplies that total more than its rating seems to go against the spirit of it.

Connecting the PV into the 1st panel is allowed by 705.12(D)...we just have to make a change to the feeder CONDUCTOR arrangement to the downstream sub-panel by downsizing the 200amp main to 175amp as Don has suggested or provide overcurrent protection to the feeder to comply with the 705.12(D) (2) Bus or Conductor Rating 120% rule.

 

[Smart $]

It's silly because you need to read 250.112 Nowhere does it indicate a starting point or base on a table. It just says
"shall be increased in size proportionately according to the circular mil area of the ungrounded conductors"

That's where you are in error. The starting point is in 250.122(A) where it says, "Copper, aluminum, or copper-clad aluminum equipment grounding conductors of the wire type shall not be smaller than shown in Table 250.122, ..."

I thought you guys were going to take this to another thread?

Sorry... last post here... honest :angel:

 

[jaggedben]

Connecting the PV into the 1st panel is allowed by 705.12(D)...

If you installing the solar breaker in the second panel, you would be required to do so at the far end of the busbar from the feeder connection. Putting the solar breaker at the same end as the feeder connections would be a violation. Now, if you put the solar breaker in the first panel, that is substantially similar to putting the solar breaker at the same end as the feeder connections. In both cases, the panelboard can be loaded above its rating at one end. Now, does it muster common sense that one is a violation and the other isn't? I would say no, at least on first glance.

Now as far as the wording of the present code, it requires " a connection in a panelboard [to] be positioned at the opposite (load) end from the [line]..." So on the wording itself, I'll grant that this is allowed, simply because the wording cannot be clearly construed to have any bearing on pass-through lugs to another panel. But I have a feeling that future codes may not allow it. What it comes down to is that panelboards are not tested for these types of applications in the listing process, so the CMP has gone quite conservative.