Greg H
Member
- Location
- Durham, NC, USA
- Occupation
- Electrician
The customer has recently purchased an electric car and, in addition to wanting to install a new level 2 EV charger, they are also interested in being able to use their new electric car to power some critical loads in their home in the event of a power outage.
The vehicle they have purchased includes a 120V 1800W AC receptacle. The customer also has a 2200W portable battery and a 2200W portable generator each with 120V AC outputs. I want to create something for them that they safely plug any of these on-site resources into a power inlet to power their critical loads.
For now, the customer wants to back up 4 120V circuits that are currently fed from an existing 200A MSP in the customers laundry room. My plan is to install a new 125A 240V load center and 3 pole 60A 240V double throw manual transfer switch next to the existing MSP with a new 6x6x24 metal wireway run between them. The load side of the transfer switch would go to the new load center. One of the line sides would be fed from a 40A 2p breaker in the existing MSP. The other line side will be fed from a new NEMA L14-30P generator inlet receptacle that I will install outside the home by the newly installed electric vehicle charger and advise the customer to purchase a NEMA 5-15P to NEMA L-14-30R adapter. For the time being, I will only energize one of the bus bars in the critical loads panel as the customer is not currently interested in backing up any 240V loads. I will install all of the new breakers on one side (phase) in the new critical loads panel, leaving the other busbar unused for now. However, I will run an additional unused conductor between the critical loads panel, transfer switch, inlet receptacle, and MSP, so that the system could be easily reconfigured to accommodate a 240V backup supply in the future. For the same reason, my plan is to oversize all of the conductors and equipment relative to the loads that I am backing up right now.
Actuating the transfer switch will island the critical loads panel from utility power and there will only be one power inlet available (the customer can just decide which standby source they want to connect), so, to me, that seems like an optional standby system governed by 702. Reading through article 702, I am a little unsure whether or not the EV V2L output or the portable battery would be considered a separately derived system. The customer's portable generator is a floating neutral. Most of what I have read online seems to indicate that a portable battery also has the neutral floating, but there is nothing specific about it on the battery's nameplate and same with the EV output. So, I think that means that I need to bond the neutrals inside the transfer switch and leave them unbroken by the switch, but was wondering what y'all thought about it. I have sent an e-mail to the senior AHJ inspector asking what they think, since, lets be real, their opinion matters more than any of ours, but still seems like a somewhat novel installation, so, wanted to collect as many considerations about such a setup as I can. Thanks
The vehicle they have purchased includes a 120V 1800W AC receptacle. The customer also has a 2200W portable battery and a 2200W portable generator each with 120V AC outputs. I want to create something for them that they safely plug any of these on-site resources into a power inlet to power their critical loads.
For now, the customer wants to back up 4 120V circuits that are currently fed from an existing 200A MSP in the customers laundry room. My plan is to install a new 125A 240V load center and 3 pole 60A 240V double throw manual transfer switch next to the existing MSP with a new 6x6x24 metal wireway run between them. The load side of the transfer switch would go to the new load center. One of the line sides would be fed from a 40A 2p breaker in the existing MSP. The other line side will be fed from a new NEMA L14-30P generator inlet receptacle that I will install outside the home by the newly installed electric vehicle charger and advise the customer to purchase a NEMA 5-15P to NEMA L-14-30R adapter. For the time being, I will only energize one of the bus bars in the critical loads panel as the customer is not currently interested in backing up any 240V loads. I will install all of the new breakers on one side (phase) in the new critical loads panel, leaving the other busbar unused for now. However, I will run an additional unused conductor between the critical loads panel, transfer switch, inlet receptacle, and MSP, so that the system could be easily reconfigured to accommodate a 240V backup supply in the future. For the same reason, my plan is to oversize all of the conductors and equipment relative to the loads that I am backing up right now.
Actuating the transfer switch will island the critical loads panel from utility power and there will only be one power inlet available (the customer can just decide which standby source they want to connect), so, to me, that seems like an optional standby system governed by 702. Reading through article 702, I am a little unsure whether or not the EV V2L output or the portable battery would be considered a separately derived system. The customer's portable generator is a floating neutral. Most of what I have read online seems to indicate that a portable battery also has the neutral floating, but there is nothing specific about it on the battery's nameplate and same with the EV output. So, I think that means that I need to bond the neutrals inside the transfer switch and leave them unbroken by the switch, but was wondering what y'all thought about it. I have sent an e-mail to the senior AHJ inspector asking what they think, since, lets be real, their opinion matters more than any of ours, but still seems like a somewhat novel installation, so, wanted to collect as many considerations about such a setup as I can. Thanks
