A sub panel must have the neutral and ground isolated. Panels come with a very long, rather thick (about 1/4 x 20) green bonding screw that connects the neutral bar to the can in the case of a primary panel. You don't get a neutral from your utility, you create one with that bonding screw.
Sub panels should be fed with 3 insulated conductors of appropriate size, and a ground that need not be insulated (but can be, if you want). So the first part of your question is, yes, that sub panel must be grounded, but the grounding conductor should be attached to the can using a ground lug, not by landing it to the neutral bar.
Sub panels must also have a fused disconnect, which means they need to be fed from a breaker, and there can't be anything else on that breaker. Don't double tap. You have two options here:
- Increase the size of the existing sub panel
- Put in a new double pole breaker in the existing sub panel and use that to feed your new sub panel. Land the circuits you had to pull out of the existing sub panel into the new one.
As others have noted, you need to watch your loads. If all you need are a few convenience receptacles or a lighting circuit, you should probably be o.k. (hard to tell with what you've given).
Either way, get an amprobe and look at what each incoming phase is pulling in your existing sub panel prior to doing anything. Make sure everything is on when you do. If it's only pulling 25 - 30A on average, you should be o.k. to add a small 8 circuit sub panel. Since it's directly in the line of sight with the existing sub panel, the new sub panel need not have a main breaker since the means of disconnect is right next to it.
A six to eight circuit sub panel runs about $80 without breakers, they typically start at 50A, but you don't have to feed them with 50A. You could feed it from a 30A breaker if all you want are convenience receptacles and lights.
Here is an amprobe being used:
(source: amprobe.com)
Do that on your sub panel first (one phase at a time) just to be sure you have room to add more. If not, you need to replace your existing sub panel, and an electrician is really your best bet there.
Another good thing to do is measure the draw of the circuits you'll have to move to the sub panel in order to make room for the breaker that will feed it. Obviously, you want to move the circuits drawing the least to the new panel in the end. Some re-arranging might be needed to make that happen.
Since this is a garage, take care what you connect to the sub panel. If you are going to be powering something like a compressor (or anything else with a decent sized motor), carefully consider the locked rotor amperage when determining the load. It will be printed on the motor.
Finally, if any of this sounds overwhelming, call an electrician. If you get into any kind of trouble, call an electrician.
You can do this, but it will fill up your feeder!
Assuming that:
- You are removing the Jacuzzi and disabling its associated dedicated circuit
- That the "GFI Kitchen", "Wall Outlet", "Microwave", and "Dishwasher" circuits are all kitchen Small Appliance Branch Circuits (SABCs)
- 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)
- Your feeder is 2AWG XHHW-2 aluminum, limited to 90A and 75°C by its terminations, and
- 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
- Get a Siemens QT1520 breaker -- you'll need this to get rid of that single pole 15A breaker
- Get a Siemens QP250 breaker for the new circuit
- 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
- Have the power turned off to your unit at the feeder/main breaker
- Get the front off the panel
- 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.
- 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.
- 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.
- 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.
- Install the QP250 in the two open slots in the top left.
- 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.
- Attach the neutral from the new cable to the left-side neutral bar on your panel.
- 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).
- Button the panel back up.
- Turn the power to your unit back on.
Best Answer
The trick is adding up the loads not the breakers you might have close to 200 double pole amps on a 125 amp panel and it could be ok but the size of the loads and the diversity of loads like heating / cooling all come into play but if you are putting in a new panel go big they don’t cost that much more.