Converting fuse panels to a subpanel in a detached garage

Question

The home i live in is an older one and when they remodeled it. They converted the in house fuse boxes to a circuit breaker panel. The only issue is they didnt update the detached garage. So looking into converting 2 prong to 3 prong outlets i ended up down this rabbit hole. So the garage is fed from 240v 30amp breaker in the panel this wired to 10/3 with ground wire to a junction box the junction box uses 10/3 with ground uf cable that lead into the garage.

Now here's where i need a bit of help. Here's how everything is set up in the garage. The cable leads into a 30 amp safety switch with ground attached to the metal box red wire connects to a 6 fuse box(they linked both reds to each bus side) black wire connects to a 4 fuse box neutral runs to the 6 fuse box and links down to the 4 fuse box There are 8 different circuits(9 wires) ive traced where they go around the garage except for 1 This last one runs in a line next to input from the house but i have to trace that later. There are 6 circuits that i want to keep wired as is. They ran each circuit in its own 12/2 with ground wire to each box/junction Lucky enough every portion seems to be grounded to each fuse/junction/outlet boxes

So i want to modernize this while not having to run any new wires but keep a few spaces incase i add 1-2 specific outlets.

I want to install a modern breaker panel and clean up the wiring a bit

So there is two paths i can take

Path 1 remove all the fuses boxes and saftery cut off switch Wire in a 30amp sub panel with the 10/3 with ground uf cable make a bunch of junction boxes to restore functionality to the 6 circuits have no space to expand or run anything else.

Path 2 Remove just the fuse boxes keep the safety switch becuase its accesible without having to open the panel and throw a disconnect. use the 3 lines from the switch and run to a 12 space sub panel reconnect all the 12/2 with ground lines to seperate 20amp breakers leaves room in case i need a to add anything or if i ever run anything needing specifically 240v

My issue with path 2 is that how do i run the ground for the sub panel to keep it seperate. The ground that leads into the garage is connected directly to the box via a screw(no grounding bar)

Im thinking to take the ground off the switch and add a grounding bar so i can run a ground to the sub panel as well.

Any thoughts or tips?

Answer 1

TL;DR Replace it all with one panel

Use a "main" panel. The main breaker will replace the disconnect switch. Get at least 20 spaces (not "circuits"), and more is better. A 30-space or 40-space panel really won't cost much extra, if any at all, because the big box stores often have bundles available that include several branch circuit breakers. While your existing circuits should be grandfathered, any new circuits will need AFCI and/or GFCI, check your local code to determine the details (it changes with each NEC cycle, and different locations adopt different versions of NEC over time, often with some local adjustments as well).

Keep neutral and ground separate. Some main panels include a separate ground bar anyway, but if not then that is cheap and easy to add.

The subpanel ("main panel style") can have any size main breaker, as long as it is equal to or greater than the feed breaker, currently 30A. So a 100A or even 200A main panel with a matching main breaker is absolutely fine. That's because the breaker is not acting as a breaker but merely as a disconnect.

If you don't have existing ground rods, you need to add them because this is a detached building. That's one with a test (which nobody does, including professional electricians) or two several feet apart. Ground rods are not needed for a subpanel in the same building (or an attached building) and are also not needed for individual circuits. But while the existing mess may well have started as an individual circuit, it is way beyond that now. In any case, subpanel + detached building = ground rods required. Note that this is in addition to the ground wire going back tot he main panel. While the ground rods and the ground wire are connected, they serve somewhat different purposes and both are required.

Then when you are ready to add more power (30A is enough for charging an EV or for standard lights and receptacles, but if you add tools and other stuff then you can easily justify larger capacity), you will need to do 3 things:

• Do a Load Calculation to determine how much power your main service can spare for the garage
• Replace the 10/3 cable with something larger. Aluminum is normally recommended for subpanel feeds larger than 30A.
• Replace the feed breaker in the main panel.

but you won't have to change anything in the new subpanel because it will be all set. If you kept the old disconnect switch then you'd have to replace it, etc. So just do it all at once and be done.

Answer 2

The other answer is pretty good, but there is one thing he missed, that is do not remove the old fuse panel, gut it. When you remove the fuse holders from the old fuse panel you can use it as a junction box so that the existing circuits do not need to be disturbed any more than necessary, then short wires to the new breaker panel.