Electrical panels can often be configured a bunch of different ways, depending on whatever parts the electrician orders for them. Different parts can be added or subtracted. Here’s a 225 amp panel that has been configured to use a main breaker.

Above the main breaker, you’ll see a section of the panel that was configured for something else, that wasn’t used.

http://forums.pelicanparts.com/uploa...1761070220.jpg

Is that a meter next to the panel? If so, why do you say you must install the new breaker hot?

More: if there is a meter there, this is a main panel. I don't know where I got off track and considered this mess to be an existing sub. It doesn't look to me like that now.

Here's one more item to be corrected although you say the 100a breakers will be removed. If not, the 100 amp breakers could be for 240 volt lighting, in which case the unidentified wires should be marked green.

If it were me, I’d punch the Meter service circuit through the bottom left of the breaker box into a fused disconnect switch box hanging on the left side. Run the switched source back into the breaker box. Agree, I’d run breaker protected four wire from this box to the new sub panel.

NEW sub panel needs local ground rod too.

HOWEVER,,, I wouldn’t touch a thing without knowing the service to the meter. I also don’t like the size of what I think is the service neutral.

Or as has been said, nuclear option is replacing the guts of the panel with new tech. In any case,,, I’d put this on the homeowner for responsibility.

IDK how to rebuild the panel to get a disconnect. I suspect an electrician (what I would do) is swap the whole panel.

There are also meter pans with disconnect breakers. Some areas require that now so in case of emergency (fire/water) they can cut power outside.

Also of concern, and I'm not sure anyone said it, is I don't think you can use a standard panel exposed to the elements. I've had to build roofs & plywood box around even temporary electrical services. Pool subpanels (typically mounted outside) have gasketed doors, etc.

All good points. Apparently the thing has been there and in service w/o incident. I am advised that a new Square D will fit that space w/o mods. AFA the disconnect goes, I wouldn't be w/o one. Just this proposition of working in that panel tells me that. But requirements for outside disconnects at the meter apply to occupied buildings and apparently not skeet ranges. Not saying this was done anywhere near right. We have all pointed out many flaws.

Don’t need to rebuild the panel for a disconnect. A separate fused disconnect box mounted on the left side of the service panel would do. There’s enough service wire from the meter to reach the left side box IMO. Would need new service wire from the disconnect switch to the panel service lugs. A breaker for the panel service is probably not required being so close but, like Zeke, I wouldn’t NOT have a disconnect. I like beefy bladed disconnect switches. A fused disconnect allows a tailoring of the fuse rating somewhat.

I'd bet there isn't a ground rod at that panel. Not seeing one, anyway.

I was looking too. Maybe coming in from the meter service box but, not how I would have done it. We’re now required to have two ground rods per breaker panel with a minimum 6’ rod separation. I added a second rod for our residential panel even though our original service is grandfathered from 1961.