Electrical – Garage subpanel wiring


I recently bought a house that has a subpanel in the garage served by a 50 amp circuit from the main breaker. The breaker has 4 wires coming in: red, black, green, white. Currently, the subpanel feeds a 30 amp and a 20 amp circuit Each served be a 3-wire connection where the third wire goes to green for one, white for the other.

subpanel photo breaker in main panel

I want to rewire to install a NEMA 14-50 with a single 50 amp breaker in lieu of the 20 amp service (bottom right exit), and leave the second circuit unused. That would require a 4 wire connection, do I just use green and white? What about the second circuit? Disconnect it? Leave it in place?

I'm looking to connect an EV (Model 3) that draws under 45 amps. Based on the cerrowire application chart, 8 AWG would be sufficient? => https://www.cerrowire.com/products/resources/tables-calculators/applications-charts/

Did I forget to ask anything else I should?

Best Answer

Looking at your sub it was done correctly , the white neutral bond was not connected so you can connect the 14-50 , you will need to remove one of the double pole breakers and yes you use all 4 wires 2 from your new 50 amp breaker 1 ground and 1 neutral. , great question and good photos. Make sure to get the correct brand and type of breaker for the sub I can’t quite make out the brand but the main is a Murray , but the tandem breaker is Bryant this is something I have seen many times and usually not code compliant for 2 reasons , Bryant breakers were not listed for a Murray panel even though they fit. Item 2 is early panels were limited on the total number of spaces so manufacturers came up with “cheaters” early tandem breakers that did not have a rejection feature allowing the buss to be overloaded, these breakers usually have a sticker stating they are Non Current limiting. (Just want you to know). If you can find the proper double pole breaker for the sub all may be fine but I would want the main panel updated so there is not a problem if there is a fire later even though everything on the sub is correct there could be problems because of the alien breakers in the main.