It's difficult to tell from the photo if there's even a grounding conductor run along with the two ungrounded (hot) conductors, so you'll have to verify that before you go shopping for supplies. You'll also have to verify that the ungrounded (hot) conductors are the proper size. You said the panel is fed through a 60 ampere breaker, so you'll need at least 6 AWG copper conductors (solid or stranded, it makes no difference).
Shopping
Here's what you're going to need.
- A grounding bus bar.
- 6 AWG copper THWN wire with white or gray insulation, long enough to reach from the main grounded (neutral) bar to second panel grounded (neutral) bar.
- 6 AWG bare or green copper conductor, long enough to reach from the main grounding bar to the second panel grounding bar (which you'll install).
If the current ungrounded (hot) conductors are undersized, you have a couple choices. You can replace them, with appropriate conductors. Or you can install a smaller feeder breaker in the main panel, and down size the grounded and grounding conductors accordingly.
Installation
Once you have the supplies, here's what you're going to do.
- Remove the brass bonding screw from the existing bus bar in the second panel.
- Install the grounding bus bar (the one you purchased), in the panel.
- Move all the grounding conductors from the old grounding bus, to the new grounding bus bar.
- Pull the required conductors between the panels.
- Connect the grounded (neutral) conductor to the grounded (neutral) bar in the main panel.
- Connect the grounding conductor to the grounding bar in the main panel.
- Connect the grounded (neutral) conductor to the grounded (neutral) bar in the second panel.
- Connect the grounding conductor to the new grounding bar in the second panel.
- Connect the grounded (neutral) pigtail from the GFCI breaker, to the grounded (neutral) bar in the second panel.
Now you should be all set.
NOTE: Depending on where the second panel is installed. You may need to install a grounding electrode, and bond the panel to it. Check with your local building department, to determine if this is required.
That is an old "rule of six" panel, which while grandfathered, is illegal under its grandfathering becuse it has 7 main breakers. Going to five is a good plan.
It is a classic "CH" panel which is a very good industrial grade panel, except that the 3/4" breaker width make non-ordinary breakers very expensive (a trait it shares with Square D QO). That makes it perfect for what you plan.
On your subpanel which would be near this panel, I would get a panel with a main breaker, with an eye toward (at some point in the future) cutting it over to be the main panel. In a subpanel, the "main breaker" is nothing more than an on/off switch, it is OK for it to be larger than the feeding breaker.
I would also get a rather large panel, at the very least 42 space and even 60 or 84 if practicable: because panel spaces are dirt cheap and often even come with free breakers, whereas running out of space is painfully expensive.
I would aim for an industrial grade panel of good repute (one available in 3-phase variants, not Homeline, BR, or second tier brands) and avoid the expensive 3/4" breakers (not CH or QO).
Over time, as you find it convenient, i'd migrate all your 1-pole and smaller 2-pole circuits over to the new panel.
For your garage panel anything would do, but I'd go for the same type as your indoor panel, so you can use some of those bonus breakers. Again it's false economy to scrimp on spaces, I'd go 20-30 at least.
Also, since garage spaces need to be on GFCI, consider getting a subpanel which has a "main breaker" which is GFCI, that way all the breakers in that panel would be protected (at the cost of potential nuisance trips, a big deal if you keep a freezer in the garage).
Ed Beal raises some very good concerns about overall capacity. One problem with these "rule of six" panels is there is literally no main breaker to stop you from drawing more than 150A. So it pays to be conservative.
It's a difficult situation because you have two big loads that operate sporadically - the EV charger and the range. And the A/C as a wildcard.
One thing I might suggest, is feed the garage subpanel from the new primary subpanel. And then move everything but the range over to the new subpanel. At that point the only things still in the CH panel would be a 60A range breaker and a 100A subpanel breaker. Even at max, those two could not overload the 150A service (by enough to matter). This would force your entire house (from A/C to EV charger) to share 100A, but would remove the possibility of an overload. This would also save you the $85 you'll spend on a second 100A CH breaker.
Best Answer
Regardless of what all the individual breakers add up to, the maximum you can draw through that subpanel is 60amps. Realistically you want to be a bit lower then that to allow for some spikes.
To determine if you can support the tub, you need to take a measurement of the current (amps) on the circuit with some or all of the existing devices in use (i.e. normal use). Ideally you would use a clamp meter around the hot wires in order to measure this, but alternatively you could add up the loads on the circuit. If you subtract this value from 60, and you have enough capacity for the tub, then it should be OK to run from that sub-panel.