Using feed thru lugs to feed a panel?

[jaggedben]

Is my thought in post #37 a viable suggestion?

Sort of. Sort of not.

For one thing, once you add that 2nd breaker you are unlikely to meet any of the 705 rules.

That said, it ought to be safe. I have suggested before that the product standards be expanded so that a panelboard can be used as listed beyond the 705 rules.

 

[tortuga]

Maybe someone will produce a panel with main breakers at both ends.

Then our feed thru lugs would need to be in the middle part of the busbar.
One could put a lug kit in the middle of a load-center.

 

[JetStream]

What if 'Where an overcurrent device is installed at the supply end of the feed-through conductors' is supposed to mean 'Where an overcurrent device is installed at the supply end of the busbar supplying feed-through conductors'. Obviously, that is not what is written but it seems to be logically consistent and even makes good electrical sense. It's basically just back to the Kirchhoff's law idea posted before.

 

[tortuga]

What if 'Where an overcurrent device is installed at the supply end of the feed-through conductors' is supposed to mean 'Where an overcurrent device is installed at the supply end of the busbar supplying feed-through conductors'. Obviously, that is not what is written but it seems to be logically consistent and even makes good electrical sense. It's basically just back to the Kirchhoff's law idea posted before.

I think thats what my AHJ was thinking. The job got installed as per the plans in post #9 and is done, inspected (passed) and paid. The only part of the buss that can be overloaded is shown in post #28, and in this particular panel there were no breakers in there. I was not required to submit 1-line plans for a job like this but I did becasue the code section is so confusing.

 

[jaggedben]

What if 'Where an overcurrent device is installed at the supply end of the feed-through conductors' is supposed to mean 'Where an overcurrent device is installed at the supply end of the busbar supplying feed-through conductors'. Obviously, that is not what is written but it seems to be logically consistent and even makes good electrical sense. It's basically just back to the Kirchhoff's law idea posted before.

That's not what they meant. What they meant was 'where the feed through conductors go straight to an overcurrent device they can be treated like another breaker on the busbar'. It's just badly worded like much of 705.

And what you said does not make good electrical sense. The whole point is that when you have multiple sources connected to a busbar then you need to ensure that they don't overload the feed through conductors.

 

[tortuga]

I just re-read this entire thread and feel more confused than ever.

 

[pv_n00b]

What if 'Where an overcurrent device is installed at the supply end of the feed-through conductors' is supposed to mean 'Where an overcurrent device is installed at the supply end of the busbar supplying feed-through conductors'. Obviously, that is not what is written but it seems to be logically consistent and even makes good electrical sense. It's basically just back to the Kirchhoff's law idea posted before.

When the NEC refers to "conductor" many people think it only means wires, but in the NEC conductors are anything that is intended to conduct electricity in a circuit. So bus, wire, cables, bus duct, etc. are all conductors in the NEC. As far as the NEC is concerned 'Where an overcurrent device is installed at the supply end of the feed-through conductors' means at the supply end of the busbar. Conductors encompass the panel busbar and the conductors on the feedthrough lugs going to a downstream panel. The conductors on the feedthrough lugs are really just a busbar extension. If you look at them like that everything just follows along. Treat it like one long busbar from the main OCPD to wherever it lands at the next OCPD.

 

[petersonra]

When the NEC refers to "conductor" many people think it only means wires, but in the NEC conductors are anything that is intended to conduct electricity in a circuit. So bus, wire, cables, bus duct, etc. are all conductors in the NEC. As far as the NEC is concerned 'Where an overcurrent device is installed at the supply end of the feed-through conductors' means at the supply end of the busbar. Conductors encompass the panel busbar and the conductors on the feedthrough lugs going to a downstream panel. The conductors on the feedthrough lugs are really just a busbar extension. If you look at them like that everything just follows along. Treat it like one long busbar from the main OCPD to wherever it lands at the next OCPD.

Does the code actually say this somewhere?

 

[ggunn]

When the NEC refers to "conductor" many people think it only means wires, but in the NEC conductors are anything that is intended to conduct electricity in a circuit. So bus, wire, cables, bus duct, etc. are all conductors in the NEC. As far as the NEC is concerned 'Where an overcurrent device is installed at the supply end of the feed-through conductors' means at the supply end of the busbar. Conductors encompass the panel busbar and the conductors on the feedthrough lugs going to a downstream panel. The conductors on the feedthrough lugs are really just a busbar extension. If you look at them like that everything just follows along. Treat it like one long busbar from the main OCPD to wherever it lands at the next OCPD.

There are a couple of important distinctions, though. Unless there are taps on the feeder between the feedthrough panel and the subpanel it is feeding and if there is a main breaker on the subpanel, electrically it's no different from the situation where the PV breaker is on the end of the bus in a regular panel and there is another load right across from it. It's also the same as it would be if the PV were on a load side tap on the feeder.

 

[wwhitney]

'Where an overcurrent device is installed at the supply end of the feed-through conductors' means at the supply end of the busbar.

Agree that busbars are conductors. However, where the conductors start to be "feed-through conductors" is not defined. Considering the busbar to be "feed-through conductors" seems unusual to me. The lugs are called feed-through lugs, so absent any clarification, I would take the "feed-through conductors" to start at the feed-through lugs. So they end up being wire-type conductors.

Cheers, Wayne

 

[wwhitney]

P.S. The 2023 Second Draft 705.12(B)(5) last sentence is still "Where an overcurrent device is installed at either end of the feed-through conductors, panelboard busbars on either side of the feed-through conductors shall be permitted to be sized in accordance with 705.12(B)(1) through B(3)."

This language seems problematic to me: an OCPD isn't required (physics-wise) for (B)(1) to be reasonable; and for (B)(3), the referenced OCPD should be counted as present in the panel with the subfeed lugs.

Cheers, Wayne

 

[ggunn]

P.S. The 2023 Second Draft 705.12(B)(5) last sentence is still "Where an overcurrent device is installed at either end of the feed-through conductors, panelboard busbars on either side of the feed-through conductors shall be permitted to be sized in accordance with 705.12(B)(1) through B(3)."

This language seems problematic to me: an OCPD isn't required (physics-wise) for (B)(1) to be reasonable; and for (B)(3), the referenced OCPD should be counted as present in the panel with the subfeed lugs.

The language is problematic because I have seen "either end" used to mean "both ends" in some places and "one end or the other" in others.

 

[tortuga]

P.S. The 2023 Second Draft 705.12(B)(5) last sentence is still "Where an overcurrent device is installed at either end of the feed-through conductors, panelboard busbars on either side of the feed-through conductors shall be permitted to be sized in accordance with 705.12(B)(1) through B(3)."

This language seems problematic to me: an OCPD isn't required (physics-wise) for (B)(1) to be reasonable; and for (B)(3), the referenced OCPD should be counted as present in the panel with the subfeed lugs.

Cheers, Wayne

Yeah still seems like poor wording, we should all object to CMP4

 

[jaggedben]

Does the code actually say this somewhere?

No.

Indeed I disagree with pv noob's definition. For example an EGC is a conductor that is not intended to carry electricity in a circuit (at least not during normal operation).

One is left to read the dictionary and use common sense when it comes to 'conductors' in the NEC.

 

[tortuga]

The nec does define a feeder

 

[wwhitney]

The language is problematic because I have seen "either end" used to mean "both ends" in some places and "one end or the other" in others.

In the NEC? An example of "both ends"? In the quote, it clearly means "at one end or the other."

Cheers, Wayne

 

[tortuga]

This is just one of the most spectacularly poorly worded sections of the NEC, it defies logic and NEC definitions (feeder)
I'd say easily 90-99% of the time most of us (Wyane, Peter, Ben, Pv_noob, Larry ) all tend agree in other topics.
Its really strange that this part of the code was just written by CMP4 with no review process.

 

[ggunn]

In the NEC?

Not that I specifically remember, but in normal discourse; what difference does that make? Comprehending the NEC should not require knowledge of special syntax.

Note that I said "should not".

 

[Zee]

A practical note:
Depending on the brand of panel you have, certain lug kits and branch circuit breakers will not be available.
Find out first - because this will eliminate and narrow down your options quick.

Many brands of panels only have maximum 100A, or possibly 125 A, lug kits available.
A few make 200A lug kits.

A 200A branch circuit breaker is also only available for some brands.
These will either be:
a. 4-pole breakers - and hence take up 4 busbar spaces. You will need 4 hot wires (2 blacks, 2 red). Assuming you only have 2 wires now, you would have to run 4 new conductors to the indoor house panel. Also, now you have parallel conductors.*
(*Code requires minimum 1/0 conductors if parallel! So, even though 2 @ #4 parallel should do it for each 100A leg (2 @100A = 200A).....you will need 1/0. See if that even fits in panel. This is just one hair smaller than the 2/0 needed for a 200A circuit)
MURRAY/SIEMENS

b. 2-pole. I think there is one brand of 200A branch breaker that spreads out horizontally across 4 spaces: 2 spaces on left and 2 spaces on right. Only works if you have a panel with 2 columns of breakers. BUT this may be a main breaker. It accepts two wires.
MURRAY /SIEMENS

c. 2-pole. One brand makes a sweet solution that takes only 2 wires (not 4). These two wires land at a right angle to a typical breaker. Vertically not horizontally. The breaker's lugs stick out to the side and are offset to accept two mongo 2/0 wires. Makes all the difference when running 2 @ 2/0 in a narrow wiring channel on the right of breakers in a panel.
SQUARE D HOM

 

[LarryFine]

A 200A branch circuit breaker is also only available for some brands.
These will either be:
a. 4-pole breakers - and hence take up 4 busbar spaces. You will need 4 hot wires (2 blacks, 2 red). Assuming you only have 2 wires now, you would have to run 4 new conductors to the indoor house panel. Also, now you have parallel conductors.

c. 2-pole. One brand makes a sweet solution that takes only 2 wires (not 4). These two wires land at a right angle to a typical breaker. Vertically not horizontally. The breaker's lugs stick out to the side and are offset to accept two mongo 2/0 wires.

As I was reading a., I was planning on 'correcting" you with what you said in c., which is till four spaces wide, AFAIK.

I haven't seen an example of a., except for 4-body main breakers, but couldn't the four terminals be paired into two?