Supply Side (line side) Interconnections and the 7th disco

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This is fixed in the 2014 code. 125% of the inverter's maximum output current is carried all the way back to the service for the 120% rule calculations. The size of the OCPD is no longer used.

thanks all for the help.

The conversation here has brought up another question.
Suppose I have 167A of Inverter output, all run into an AC combiner panel. This number time continuous duty (125%) is : 166.7 x 1.25 = 208.4 Amps. But I can only fit (physically) a 200A switch into the gear. SO, I use fully rated fuses in the 200A switch, lets say they are 175A (just above the 166.7 amp) (note - I checked with littlefuse who says that all fuses under 600A are 100% rated). The point is that I save myself from having to install a 400 switch with 225A fuses. I would however size my conductors for 208A.
Additionally could I not install a utility required 200A non-fused PV disco (external to gear) ahead of the gear. these are fully rated.

Does anyone see an issue with this?
 

Smart $

Esteemed Member
Location
Ohio
thanks all for the help.

The conversation here has brought up another question.
Suppose I have 167A of Inverter output, all run into an AC combiner panel. This number time continuous duty (125%) is : 166.7 x 1.25 = 208.4 Amps. But I can only fit (physically) a 200A switch into the gear. SO, I use fully rated fuses in the 200A switch, lets say they are 175A (just above the 166.7 amp) (note - I checked with littlefuse who says that all fuses under 600A are 100% rated). The point is that I save myself from having to install a 400 switch with 225A fuses. I would however size my conductors for 208A.
Additionally could I not install a utility required 200A non-fused PV disco (external to gear) ahead of the gear. these are fully rated.

Does anyone see an issue with this?
Not sure what you mean by putting the switch in the gear, but as far as using the 100%-rated exception, the entire assembly needs to be listed as such... not just the fuses.
 

jim dungar

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PE (Retired) - Power Systems
(note - I checked with littlefuse who says that all fuses under 600A are 100% rated).

They have effectively misled you.
While fuses may be 100% rated, there are almost no switches which are rated that high.

As Smart mentioned, if the gear was not specifically ordered with a 100% rating, you are out of luck.
 

Carultch

Senior Member
Location
Massachusetts
They have effectively misled you.
While fuses may be 100% rated, there are almost no switches which are rated that high.

As Smart mentioned, if the gear was not specifically ordered with a 100% rating, you are out of luck.

Usually it is unfused disconnects that are fully rated, while fusible disconnects are not. It likely is the same blades that they use in both cases. And being built with standard rated fuses in mind, the fusible disconnects are only listed to be rated at 80%.
 

jim dungar

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Usually it is unfused disconnects that are fully rated, while fusible disconnects are not. It likely is the same blades that they use in both cases. And being built with standard rated fuses in mind, the fusible disconnects are only listed to be rated at 80%.

No.

For all practical purposes, all fuses are 100% rated in open air.
The same goes for molded case circuit breakers.

All devices become 80% once they are put into enclosures. The excepteion is when the enclosed device have been specifically designed for 100%.

It is all about heat dissapation, not the construction of the current sensing elements.
 

shortcircuit2

Senior Member
Location
South of Bawstin
thanks all for the help.

The conversation here has brought up another question.
Suppose I have 167A of Inverter output, all run into an AC combiner panel. This number time continuous duty (125%) is : 166.7 x 1.25 = 208.4 Amps. But I can only fit (physically) a 200A switch into the gear. SO, I use fully rated fuses in the 200A switch, lets say they are 175A (just above the 166.7 amp) (note - I checked with littlefuse who says that all fuses under 600A are 100% rated). The point is that I save myself from having to install a 400 switch with 225A fuses. I would however size my conductors for 208A.
Additionally could I not install a utility required 200A non-fused PV disco (external to gear) ahead of the gear. these are fully rated.

Does anyone see an issue with this?
Your first switch after your Line Side Connection needs overcurrent protection. 240.4 or 230.90(A)

Use a 225amp Circuit Breaker Disconnect.

How is metering done with the existing service? Is there a location to connect to the service conductors ahead of the switchgear after metering?

You have provided very little detail on the service. An engineer familiar with Solar should be able to lay this out for you.
 

Zee

Senior Member
Location
CA
Suppose I have 167A of Inverter output [....] This number time continuous duty (125%) is : 166.7 x 1.25 = 208.4 Amps. But I can only fit (physically) a 200A switch into the gear.

Can you switch inverters around so that you get down to 200A?

I would think so, from 208.4 Amps.... you're getting mighty close.
Usually you would find that you have extra capacity left over on some inverters and so you may choose to replace those inverters with smaller W models, or combine two inverters into one that is a bit less than the sum of the two. This will reduce W and hence output Amps.

Can you give details on how many solar panels on what make and model of inverters?
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Can you switch inverters around so that you get down to 200A?

I would think so, from 208.4 Amps.... you're getting mighty close.
Usually you would find that you have extra capacity left over on some inverters and may reduce teh W and hence output Amps of some.
Can you give details on how many panels on what inverters?

Unfortunately, even in [2014] the NEC requires use of the rated output of each inverter as a starting point, even if there are not enough panels connected to ever deliver that output.
If you actually change the inverter size, you would have a chance to adjust that number. And pre [2014] you would still be stuck with the amperage corresponding to the required breaker, which is usually above the actual inverter output.
 
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