EG4 18k PV - Need for transfer switch for whole home backup?

[zanydroid]

Hi I’m new and apologize if this is a dumb question. If you connect the utility and meter to the grid port on the kpv 18, and then connect the load port on the kpv 18 to the main service panel, doesn’t this solve the issues you bring up? If the grid goes down, the ATS on the “input lugs” (I’m assuming that’s the grid port) will shut down the kpv 18’s output from the grid port. So no back feeding the grid. However your PV system and batteries will still be able to provide power to the main service panel through the load port on the kpv. Isn’t that basically what they do in this diagram? I just don’t understand the need for a supply side tap or manual transfer switch.

The manual transfer switch hard bypasses the 18kpv if it shits a brick. So your house can have power even if the 18kpv brain completely dies or the whole box melts in a fire

The supply side tap could well be pointless or counterproductive IE requires more labor or POCO approval, or is straight up un implementable if what you have is a combo meter main. You need to pick or design a wiring diagram based on your needs.

 

[jeff.lankford]

Hi I’m new and apologize if this is a dumb question. If you connect the utility and meter to the grid port on the kpv 18, and then connect the load port on the kpv 18 to the main service panel, doesn’t this solve the issues you bring up? If the grid goes down, the ATS on the “input lugs” (I’m assuming that’s the grid port) will shut down the kpv 18’s output from the grid port. So no back feeding the grid. However your PV system and batteries will still be able to provide power to the main service panel through the load port on the kpv. Isn’t that basically what they do in this diagram? I just don’t understand the need for a supply side tap or manual transfer switch.

The MTS in that diagram allows you to still connect the grid supply to your house in the event of an inverter failure.
That switch along with the "PV System Disconnect" switch allows you to completely isolate the 18Kpv in case you need to service / remove & swap the inverter.

 

[Sonicmerlin]

The manual transfer switch hard bypasses the 18kpv if it shits a brick. So your house can have power even if the 18kpv brain completely dies or the whole box melts in a fire

The supply side tap could well be pointless or counterproductive IE requires more labor or POCO approval, or is straight up un implementable if what you have is a combo meter main. You need to pick or design a wiring diagram based on your needs.

The MTS in that diagram allows you to still connect the grid supply to your house in the event of an inverter failure.
That switch along with the "PV System Disconnect" switch allows you to completely isolate the 18Kpv in case you need to service / remove & swap the inverter.

Omg thankyou. I stared at this picture for nearly an hour yesterday trying to figure it i out. I guess the supply side tap is so that you can send 200 A to both the inverter’s grid port and the manual transfer switch?

I’m starting to see why the Gridboss is so beneficial. You can do away with 2 costly components and associating wiring. Plus it adds a bunch of smart ports and inverter ports. I thought it was so pricey but adding a MTS and supply side or feeder tap probably costs the same.

 

[jeff.lankford]

Omg thankyou. I stared at this picture for nearly an hour yesterday trying to figure it i out. I guess the supply side tap is so that you can send 200 A to both the inverter’s grid port and the manual transfer switch?

I’m starting to see why the Gridboss is so beneficial. You can do away with 2 costly components and associating wiring. Plus it adds a bunch of smart ports and inverter ports. I thought it was so pricey but adding a MTS and supply side or feeder tap probably costs the same.

If you're not sure which configuration you need, but you want a whole house backup solution, then also look at the EG4 wiring diagram "Whole House Backup using a Feeder Tap." Note that if your application doesn't require the Feeder Tap Breaker, then the diagram can be simplified as I show here...

 

[zanydroid]

I’m starting to see why the Gridboss is so beneficial. You can do away with 2 costly components and associating wiring. Plus it adds a bunch of smart ports and inverter ports. I thought it was so pricey but adding a MTS and supply side or feeder tap probably costs the same.

I think the gridboss has a built in MTS that handles a lot of oh-shit situations. Except melting down. IIRC it is controlled steam-punk style - you flip something and it is bypassed with no computers in the loop (check with the fanbois and alpha testers though, I don't own EG4 and would probably get an 18kpv over a gridboss because that ends up being easier for me)

Gridboss + flex21 isn't that bad in price compared to an 18kpv. They stripped some content out of the 18kpv for the Flex21 to help with cost reduction, and those content (breakers and whatnot) are redundant when used with Flex21 unless you wanted the 18kpv to be able to serve as a stand-in for Gridboss if the gridboss melts down completely and you really needed its capabilities while waiting for the replacement. In a more sane situation, you would be happy not to pay for the 1x smartbreaker and 200A bypass that is in the 18kpv, when you have that in the Gridboss

 

[zanydroid]

If you're not sure which configuration you need, but you want a whole house backup solution, then also look at the EG4 wiring diagram "Whole House Backup using a Feeder Tap." Note that if your application doesn't require the Feeder Tap Breaker, then the diagram can be simplified as I show here...

View attachment 276869 View attachment 276870

The feeder tap calculation for solar is a little complicated, and I'm not convinced the left diagram is correct. It makes me queasy. It might be right if the feeder is physically in between the PV and the main (I think it is, but my brain is breaking with the way it's schematically laid out).

Also, there's a lot of switchgear between the main breaker on the right, and the tap, which may give AHJ pause (and I think it's ambiguous in the code whether all kinds of switchgear can be considered part of the tap)