Electrical – What size grounding wire for a main lug

You can do this, but it will fill up your feeder!

Assuming that:

1. You are removing the Jacuzzi and disabling its associated dedicated circuit
2. That the "GFI Kitchen", "Wall Outlet", "Microwave", and "Dishwasher" circuits are all kitchen Small Appliance Branch Circuits (SABCs)
3. Your condo is fed with 120/240V split phase (some high-rise condos are fed with 2 phases of a 208Y/120 3 phase service instead)
4. Your feeder is 2AWG XHHW-2 aluminum, limited to 90A and 75°C by its terminations, and
5. You have a 90A feeder breaker protecting the feeder and panel

we can apply the multiunit feeder calculation methods from the Code (Art. 220 Part II) (albeit not the optional simplified calculations from Part III, as we are assuming a 90A feeder here which makes that method inapplicable) to your current configuration to get the following numbers:

• 1300sf * 3VA/sf = 3900 VA for lighting and general receptacle loads
• 5 SABCs (4 kitchen, 1 laundry) * 1500VA/SABC = 7500VA for small appliances
• Your water heater at its 4500VA nameplate load
• Your A/C at 14.5 combined Full Load Amps at 230VAC = 3335VA (the combustion blower load can be excluded as it doesn't run when the rest of the motor loads are engaged)

For the lighting and receptacle loads, we get 11.4kVA which then gets a 35% demand factor for all load past the first 3kVA to yield 5940VA. From that, we then add the 4.5kVA water heater and the 3335VA A/C to yield a total feeder load of 13.78kVA, or 57A at 240VAC. This leaves just enough room for the 8kVA (or 33A @ 240VAC) range load from Column C of table 220.55, using note 4 to treat the cooktop and oven combination as a single range load of not over 12kVA nameplate.

The resulting breaker switcheroo -- if you feel uncomfortable with this, feel free to ask your friendly local electrician to do this for you

1. Get a Siemens QT1520 breaker -- you'll need this to get rid of that single pole 15A breaker
2. Get a Siemens QP250 breaker for the new circuit
3. Run the cable for the new kitchen appliances and hook them up, but don't feed it into the panel yet. Let us (or your friendly local electrician) know if you need help with this
4. Have the power turned off to your unit at the feeder/main breaker
5. Get the front off the panel
6. Remove the existing breaker from the slot labeled "Jacuzzi" and "GFI Kitchen". Take the upper wire off (this went to the Jacuzzi) and put a wirenut on the end to cap it off. Take the lower wire off and flag it with electrical tape so that you can find it to put it on the correct half of the new double-stuff breaker. Set this breaker aside.
7. Remove the existing breaker from the slot labeled "Rooms 1-2 Lights-Outlets". Take the wire off, but do not flag it or cap it. Set this breaker aside as well.
8. Move the two breakers that were above the removed 15A breaker down a slot in the panel -- there should be two open slots at the top left of the panel once you are done with this step.
9. Install the QT1520 in the open slot in the top right. Attach the flagged wire to the 20A (upper, if the photo I have seen is any indication) slot in the breaker. Attach the unflagged wire to the 15A (lower, again based on the photo I have seen) slot in the breaker.
10. Install the QP250 in the two open slots in the top left.
11. Run the cable for the new kitchen circuit into the panel itself and attach the black and red wires (hots) to the QP250 breaker you just installed.
12. Attach the neutral from the new cable to the left-side neutral bar on your panel.
13. Attach the ground from the new cable to the ground bar on your panel (I suspect it's on the far left side, outside of view of the photo of the panel insides you have posted).
14. Button the panel back up.
15. Turn the power to your unit back on.

Option 2 is the only one that will improve safety here.

A single wire break should not create a dangerous condition. But that is exactly the situation you have, because every circuit in the subpanel has a bootlegged ground. If that neutral wire fails to make good connection, the ordinary loads in the subpanel will "pull the neutral hot". That normally wouldn't be a big deal. But because all those grounds are bootlegged, it will ”pull all the grounds hot” too. So now switchplate cover screws or the panel cover itself can bite you.

By trying to put on grounding theater, the last guy made things worse than no grounds at all. Worse, Code once endorsed this, and still does where dryer and range sockets are concerned.

Now you don't have to go back to the panel. It will suffice to reach the grounding electrode system, i.e. The bare wire running to those two ground rods.