Feeder "taps" not actually "tapped"?

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wwhitney said:
Per the diagram posted earlier, the 125A breaker would be in lieu of the plug-on lugs, not in addition.

Cheers, Wayne
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No, it wouldn't, because the 125A panel fed by the backup interface is 'new' and the OP confirmed that. The 200A feeder on the plug-on lugs would stay in place.
 
jaggedben said:
The 200A feeder on the plug-on lugs would stay in place.
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I reviewed the OP's posts starting at the diagram in post #24 and I don't believe that is correct. The diagram does not show that. And post #35 with the picture says "the straight feeders lugged off the main will be pulled out of that panel and landed in panel "C" on the 2p breaker that has a note saying "Existing Feeder....."

So I don't believe there will be both feed-thru lugs and a 125A breaker on the bus in picture #34.

Cheers, Wayne
 
wwhitney said:
I reviewed the OP's posts starting at the diagram in post #24 and I don't believe that is correct. The diagram does not show that. And post #35 with the picture says "the straight feeders lugged off the main will be pulled out of that panel and landed in panel "C" on the 2p breaker that has a note saying "Existing Feeder....."

So I don't believe there will be both feed-thru lugs and a 125A breaker on the bus in picture #34.

Cheers, Wayne
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I see now where the 'Existing Feeder ...' language is cut off at the edge of the drawing.

But this makes no sense and is almost certainly being done wrong.
They have an existing 200A feeder and they are proposing to repower it through a 125A feeder while also adding new additional load on a 100A breaker (apparently? It's partially cut off). ??? They have conveniently left out of the drawing the breaker rating for the existing feeder to hide the fact that they are downgrading it. ;-)

The entire fee to the BU interface should just be rated 200A if they are backing up the existing 200A feeder for the whole house. That's almost certainly the right way to do this. Maybe a load calc will show it can be 150A or something, but still.

The OP will have to clarify if this can possibly make any sense.
 
BTW I'll just add that if you swapped the apartment to the lower busbar and put the backup interface on an appropriately size breaker and feeder connected at the top service disconnect position in the MSP, it would really be better in several ways. In particular you'd no longer have to worry about how to qualify the lower busbar section for backfeed, or whether anyone would come along later and mess up that qualification. It would also make more sense to the homeowner or anyone else not qualified to open the panel to figure it out.
 
Ok, a few points to everyone's input. 1st, I attached the entire drawing, redrawn from original per the below ideas from this discussion. I originally cropped the image just to make it easier to see the area of concern - my bad. So the total PV is 80A with 2 7600 inverters @ 125% output. As for 705.12 bus rules, options a and b are not possible and assuming I don't swap the apartment and house as Jaggedben suggests (which is a very interesting idea btw but still limits me to 125A max) then that leaves option "c". And Wayne is correct, the feeder wires on the feeder lugs are getting relocated to the BU subpanel so it won't violate 705.12 taps rule, which only leaves the PV breaker and welder breaker on the 200A MSP lower bus. This is a great idea unless I'm forgetting something (highly possible)!

The welder's OCP is over what is needed and can be dropped to 25A easily if not more which would allow a 175A PV breaker in the MSP: 175 + 25 = 200A total bus rating for option "c". 175A is more than enough for the loads on the 200A subpanel in the house. It's a doublewide trailer btw at about 2K sf with standard electric appliances. Load calcs derated are less than 120A.

So am I missing something?


DannyRonald - Modifiedsmaller.jpg
 
Those (2) 175 amp branch breakers should be interesting to find. :)

JAP>
 
That diagram works if the Backup Loads panel has a 225A bus rating, which I don't see specified. Then its bus qualifies under the 120% rule: 175 + 125% * 32 + 125% * 32 < 120% * 225.

The 100A (could be 80A) breaker is required in either Backup Loads panel or the Combiner Panel, but not both. However, if it's in the combiner panel only, then the feeder from the Backup Loads panel to the Combiner Panel has to comply with the tap rules, which I'm not sure is possible with the production meter in there. So better/easier to put it in the Backup Loads panel, or both.

Cheers, Wayne
 
P.S. You can avoid any 175A breakers and the need for a 225A bus in the backup loads panel by using the feeder interconnection rules. You'd need to:

A) Lose the welder breaker from the service panel's house side. I.e. move it to the panel with all the other house loads. Or if the service panel with 200A/125A main disconnects supports 200A/200A main disconnects, you could put a 125A distribution breaker in the distribution section with the welder, use that 125A breaker to supply the apartment, and then use the 200A service breaker only to supply the Solaredge Backup Interface.

B) Put in a 200A feeder with 3 segments to a common point (e.g. Polaris 3-way connectors; or if the Backup Interface panel has double lugs that would work): one from the Backup Interface backup panel lugs ; one from the backup panel (which needs to have a 200A main breaker); and one to the production meter and then combiner panel.

C) The feeder segment to the combiner panel would either need a 200A rating; or to meet the tap rules based on the 280A of power sources connected to it.

Cheers, Wayne
 
wwhitney said:
That diagram works if the Backup Loads panel has a 225A bus rating, which I don't see specified. Then its bus qualifies under the 120% rule: 175 + 125% * 32 + 125% * 32 < 120% * 225.

The 100A (could be 80A) breaker is required in either Backup Loads panel or the Combiner Panel, but not both. However, if it's in the combiner panel only, then the feeder from the Backup Loads panel to the Combiner Panel has to comply with the tap rules, which I'm not sure is possible with the production meter in there. So better/easier to put it in the Backup Loads panel, or both.

Cheers, Wayne
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Agreed. The bus rules problem gets solved in the MSP but then sort of moves to the subpanel. I'm getting closer though. Dropping the solar breaker in the subpanel from 100A to 80A doesn't seem to help me with the bus rules since it's 125% of the inverter output current that gets added to the bus protection not 125% of the breaker rating. I believe the 690.9 OC rules for PV only apply to the DC side so technically I can do that as you suggested. Regardless, I'm still 15A over the 240A total (120% rule) - 175 + 80 = 255. And bus rule "c" that's helping me out in the MSP is definitely out in the subpanel.

So either I install a 200A subpanel with a 225A bus rating (which are definitely available) or I drop the 175A breakers in all locations to 150A and I'm good. 150A is still plenty for the main house loads.
 
hitehm said:
So either I install a 200A subpanel with a 225A bus rating (which are definitely available) or I drop the 175A breakers in all locations to 150A and I'm good. 150A is still plenty for the main house loads.
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Yes. Or you go with my feeder interconnection suggestion, which is arguably better. Tesla makes their Backup Gateway with double lugs on the load side for this purpose, not familiar with the Solaredge Backup Interface.

Cheers, Wayne
 
hitehm said:
...assuming I don't swap the apartment and house as Jaggedben suggests (which is a very interesting idea btw but still limits me to 125A max) ...
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You can put a 200 or 175A breaker in the top slot. So you're not limited to 125A. This is still the cleanest approach.
 
jaggedben said:
You can put a 200 or 175A breaker in the top slot. So you're not limited to 125A. This is still the cleanest approach.
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No, I can't actually. If you look at the panel label I attached on post #37, it clearly shows the max for the upper slot is 100A. Whoever installed the 125A feeder for the apartment is already 25A over. Technically I should've said I'm limited to 100A.
 
hitehm said:
No, I can't actually. If you look at the panel label I attached on post #37, it clearly shows the max for the upper slot is 100A. Whoever installed the 125A feeder for the apartment is already 25A over. Technically I should've said I'm limited to 100A.
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Okay I stand corrected.

That's kinda bizarre though. I almost wonder if Siemens made a typo on the label, for two reasons:
1) How can the whole thing be 400A rated if the max allowed service disconnects are only 300A?
2) Upthread I said I'd been looking at this same model service panel the other week. I went back and looked at my pics and it turns out to be the Murray labeled version, evidently a couple years older. Panel itself looks exactly the same as far as I can tell, but the Murray label clearly states 200A for the upper slot.
 
jaggedben said:
Okay I stand corrected.

That's kinda bizarre though. I almost wonder if Siemens made a typo on the label, for two reasons:
1) How can the whole thing be 400A rated if the max allowed service disconnects are only 300A?
2) Upthread I said I'd been looking at this same model service panel the other week. I went back and looked at my pics and it turns out to be the Murray labeled version, evidently a couple years older. Panel itself looks exactly the same as far as I can tell, but the Murray label clearly states 200A for the upper slot.
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That's very interesting and I bet anything you're correct - they made a mistake on the labeling. Thanks for all the help on this. I have another question I'm gonna post soon concerning load calculations for residential MSPs that have a feeder or branch circuit for an RV and some other issues. Please jump in when you see it.
 
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