I live in a Duplex (build in 1979) with a 200A distribution panel which has 2 meters and 2 100A breakers (one for each unit).The distribution panel is on the outside of the garage and is fed underground by the utility. I live in California and the code currently references NEC 2014.
Each unit has a sub-panel and is about 1200 sqft. There is an aluminum 3 conductor + ground cable going to each unit, I believe it is a #2 AWG Al (but I'm not sure). I assume it was sized correctly in 1979 to be protected with a 100A breaker in the distribution panel.
I wanted to add a sub-panel in the garage (between the distribution panel and the unit sub-panel to charge my EV (14-50R outlet) and add a couple of 20A outlets. In the near future I plan to connect a PV inverter to this panel (20A 240V breaker installed for this future use).
I think based on the tapping rules specified in [240.21(B)(1)] I’m allowed to tap into the cable that runs from the distribution panel (with a 100A breaker) to the sub-panel in the unit. I used a #2 3 conductor, copper, NM-B cable between the junction box where I did the tap back to the distribution panel (<10ft of cable). I used #2 copper conductors between the tapping junction box and the panel below. I did this work without permit, but would like to get it permitted when I get my solar installed.
According to NEC Table 310.15 (b) (7) “These are the permitted ratings for Dwelling Unit service and feeder conductors which carry the total load of the dwelling”. 100A, Copper #4, Aluminum #2. #2 Copper can provide 125A. But is this still relevant now that some of the load of the dwelling is coming from the sub-panel in the garage.
Here is the load calculation according to the optional method of 220.82 For the unit only (excluding the garage):
1200 sqft @ 3 w/sqft=3600 3 kitchen 20A appliance circuits: 4500 Dishwasher NPR: 1188 garbage disposal NPR: 1224 microwave NPR: 1350 washer: 1500 gas fired dryer:720 Sauna NPR 6000 Total: 20082 1st 10,000W @100%: 10,000 remaining at 40%: 4032.8 Total: 14,032 W (58.47 A)
If I add the EVSE in the garage (32A NPR), the total load goes to 71.3A. Do I need to multiply the EVSE rating with 125% (operation >3 hrs) ?
Am I allowed to run a #2 Cu cable from my tapping junction box back to the main distribution panel? Southwire states it is rated for 95A only, but the main breaker is 100A.
Is it OK to use a #8 wire between the 50A breaker at the 14-50R outlet based on the 75C rating of the outlet and the breaker? I read somewhere that you have to use 60C in residential applications
If I add a 40A 240V inductive stove to the unit, can I keep my existing aluminum cable? I had an electrician tell me that it needs to be upgraded, but I figured as long as I keep my 100A main breaker, there should not be a problem. I checked the ‘feeder and service load calcuations’ in [220.82] using the optional method and it is within 100A (including the loads on the sub-panel in the garage. I do need to replace the sub-panel in the unit, because it is a Zinsco panel and it is located in a closet.
Any other problems you see in the pictures provided?