Second Meter vs. 400A Service Upgrade — Detached Garage Power Setup

[SemperGumby]

Getting ready to trench and finalize electrical and looking for input from anyone who’s tackled a similar setup.

Setup:

• 1989-built home with a full 200A panel (original 42-slot, aluminum wiring)
• Detached Large Garage is 140’ from the house
• Detached Small Garage is another 130’ beyond that
• This is an owner-builder project

Electrical Load (Calculated):

• Large Garage: ~150A peak
• Small Garage: ~70A peak

Utility: Florida Power & Light (FPL)

• FPL has already approved our request for a second meter
• The senior engineer has been very helpful in prepping us for this option
• Second meter run would be ~200’ from the existing transformer

Engineered plans are complete and ready to submit — the only open question is which electrical path to go with.

Option 1: Upgrade to 400A at the house

• Replace existing panel with 400A service
• Run 300 kcmil AL to a 200A subpanel in the Large Garage
• Run 1/0 AL from there to a 100A subpanel in the Small Garage

Option 2: Add Second Meter

• New 200A service drop to the Large Garage
• Feed the Small Garage from there with 1/0 AL to a 100A subpanel

Looking for feedback on:

• Long-term pros/cons of dual services vs. a single upgraded service
• Utility base fees or inspection experiences with dual meters
• Generator / backup power integration challenges
• Anything you’d do differently if you were in our shoes

Appreciate any advice before we commit and start buying materials.

 

[manwithtools]

Option 1: Upgrade to 400A at the house

• Replace existing panel with 400A service
• Run 300 kcmil AL to a 200A subpanel in the Large Garage
• Run 1/0 AL from there to a 100A subpanel in the Small Garage

I have a question for this approach. Can you upgrade just your meter base to a 320/400 and then add a 200 amp panel fed from the new meter base. This would allow keeping your existing 200 amp panel at the house. The new 200 amp panel would house a breaker to protect the feed to the Large garage.

Also have done a load calc to be sure you need the full 200 and 100 amps to the out buildings? Edit, I see you have done the calcs. Seems like a lot...

I would avoid the second meter solution if you can, it somewhat depends on what charges are for the second service vs the cost of the wire runs. Do the math to see what the payback time is, it could be many years and the meter charges are there forever.

 

[larry4406]

I like Dan’s idea.

Another thought:
- 400A service to large garage
- 200A panel at large garage
- 200A transfer switch at garage which now feeds house (house becomes sub panel)
- small garage fed from large garage’s 200A panel
- generator located near large garage so noise is away from house

 

[manwithtools]

I like Dan’s idea.

Another thought:
- 400A service to large garage
- 200A panel at large garage
- 200A transfer switch at garage which now feeds house (house becomes sub panel)
- small garage fed from large garage’s 200A panel
- generator located near large garage so noise is away from house

Great idea Larry, this would mean abandoning the existing service to the house. Would likely need POCO approval for that but otherwise this is a winner!

 

[mm08822]

Great idea Larry, this would mean abandoning the existing service to the house. Would likely need POCO approval for that but otherwise this is a winner!

Could probably cut back the lateral several feet on each end, but yeah, POCO would need to be on board with that.

 

[SemperGumby]

I have a question for this approach. Can you upgrade just your meter base to a 320/400 and then add a 200 amp panel fed from the new meter base. This would allow keeping your existing 200 amp panel at the house. The new 200 amp panel would house a breaker to protect the feed to the Large garage.

Also have done a load calc to be sure you need the full 200 and 100 amps to the out buildings? Edit, I see you have done the calcs. Seems like a lot...

I would avoid the second meter solution if you can, it somewhat depends on what charges are for the second service vs the cost of the wire runs. Do the math to see what the payback time is, it could be many years and the meter charges are there forever.

Good questions and I appreciate you raising them.

Yes, we’ve considered a 320A meter base feeding two 200A panels: one replacing the house panel, and one serving as a dedicated garage feeder. The challenge is that the existing panel is 1989 vintage, full, and has a lot of aluminum branch circuits. So leaving it untouched long-term might be a short-term patch. That said, using the new panel purely as a distribution point is something I’ll re-raise with the electrician.

On the load calc: I agree, the peak values are conservative but based on realistic concurrent use. The large garage will see welding, plasma cutting, air compressor surge, and a water well pump possibly overlapping. Small garage will have a Level 2 EV charger and tools. I’m not sizing for continuous full-load, but I am trying to avoid undersizing and regretting it later.

As for the second meter totally agree it’s not ideal long-term. FPL’s been great, but that base charge never goes away, and it complicates generator tie-in or solar later. If we can get the 400A route to pencil out with wire costs, we’ll likely go that way. Just needed to fully sketch both paths before committing.

Thanks again as this forum is a huge help as my smarter half is ready to divorce me if she hears one option for me.

 

[mm08822]

I like Dan’s idea.

Another thought:
- 400A service to large garage
- 200A panel at large garage
- 200A transfer switch at garage which now feeds house (house becomes sub panel)
- small garage fed from large garage’s 200A panel
- generator located near large garage so noise is away from house

Good plan. OP would need to understand that only house is backed up with the 200a xfer switch.

If he wanted the garage also, would need a 2nd 200a switch or one 400a xfer switch for all.

 

[SemperGumby]

I like Dan’s idea.

Another thought:
- 400A service to large garage
- 200A panel at large garage
- 200A transfer switch at garage which now feeds house (house becomes sub panel)
- small garage fed from large garage’s 200A panel
- generator located near large garage so noise is away from house

Appreciate the alternate layout. And, that’s actually a really interesting angle.

A 400A service directly to the Large Garage with a 200A panel + transfer switch there, then feeding the house as a subpanel, could simplify generator integration and shift the hub out to where the heavy loads live. That also solves the backup power issue cleanly — especially since the generator would be far enough from the house to keep noise down. I do live in hurricane alley (Irma and Ian).

My only hesitation is feeding the house from the garage. It would mean trenching a 200A feeder back to the house (~140’), and I’d need to confirm the load calc works cleanly in reverse (house load + garage loads balanced off the same 400A service).

Definitely worth bringing up with the electrician (he is a friend that does big commercial projects) especially if it gives me better long-term flexibility for generator, solar, or a future battery install.

Thanks ! This is exactly the kind of thinking I needed.

 

[manwithtools]

If he wanted the garage also, would need a 2nd 200a switch or one 400a xfer switch for all.

And one Big *** Generator to go with it!

 

[SemperGumby]

Good plan. OP would need to understand that only house is backed up with the 200a xfer switch.

If he wanted the garage also, would need a 2nd 200a switch or one 400a xfer switch for all.

Good catch

Yes, if the transfer switch is 200A and only ahead of the house feed, then the garage wouldn’t be backed up unless I added a second switch or went with a 400A whole-service transfer switch.

That’s one of the reasons I’ve been leaning toward keeping everything fed from the house with subpanels: a single generator/ATS setup could cover it all cleanly. But if the generator is going near the garage, the reverse layout (garage as service entrance) might still be cleaner overall, even with the added complexity of coordinating transfer switch coverage.

Appreciate the detail as this helps frame the tradeoffs clearly. The smart half will be so happy to hear this over a beer

 

[SemperGumby]

And one Big *** Generator to go with it!

We live in Fort Myers and Hurricane Milton took a week to restore power

Hurricanes Ian and Irma took > 2 weeks

And, no fuel available for the first week

 

[manwithtools]

My only hesitation is feeding the house from the garage. It would mean trenching a 200A feeder back to the house (~140’), and I’d need to confirm the load calc works cleanly in reverse (house load + garage loads balanced off the same 400A service).

This approach is no more trenching than this diagram you shared earlier. Only difference is FPL would feed large garage and not the house:


Load Calc is already done for the house, if it works on 200 today, it will tomorrow, just will be fed from the large garage and not FPL.

 

[SemperGumby]

Luck have it - my electrician called me

He too likes @larry4406 and Dan's idea: bring in the 400A service to the Large Garage, then feed the house from there as a subpanel. Generator and transfer switch would be located at the garage, which simplifies the whole backup system and keeps the noise/maintenance away from the living space.

He concurs on future flexibility and easier generator integration i.e., one main switch, everything backed up. I’d just need to trench the ~140’ run back to the house, but wire size would match what I’d be doing anyway if I were sending power to the garage.

Going to run final numbers, but it’s starting to look like the cleanest all-in-one solution.

Appreciate the feedback

This thread has been a huge help in framing the beer-world tradeoffs.

 

[mm08822]

Good catch

Yes, if the transfer switch is 200A and only ahead of the house feed, then the garage wouldn’t be backed up unless I added a second switch or went with a 400A whole-service transfer switch.

That’s one of the reasons I’ve been leaning toward keeping everything fed from the house with subpanels: a single generator/ATS setup could cover it all cleanly. But if the generator is going near the garage, the reverse layout (garage as service entrance) might still be cleaner overall, even with the added complexity of coordinating transfer switch coverage.

Appreciate the detail as this helps frame the tradeoffs clearly. The smart half will be so happy to hear this over a beer

If the garage is currently a blank canvas, you can at least leave room for the xfer switch(es) so they are easy to cut in later.

 

[SemperGumby]

This approach is no more trenching than this diagram you shared earlier. Only difference is FPL would feed large garage and not the house:


Load Calc is already done for the house, if it works on 200 today, it will tomorrow, just will be fed from the large garage and not FPL.

My electrician concurs with your plan

The house electrical is so dorked up now that getting the situation right will save us pain for the next storm too.

 

[manwithtools]

He too likes Dan's idea

Thanks for the acknowledgment, but it was actually @larry4406 who suggested that approach, not me!

 

[SemperGumby]

If the garage is currently a blank canvas, you can at least leave room for the xfer switch(es) so they are easy to cut in later.

The garage design is CMU / block for hurricane proofing

Large Garage is 45' wide by 32' deep at 16' high

Small Garage is 25' x 25' x 11'

Engineer sent me the final drawings for approval. We submit for permit at end of the month.

 

[mm08822]

We live in Fort Myers and Hurricane Milton took a week to restore power

Hurricanes Ian and Irma took > 2 weeks

And, no fuel available for the first week

Was that vehicle fuel (gas stations) or utility fuel also?

 

[mm08822]

The garage design is CMU / block for hurricane proofing

Large Garage is 45' wide by 32' deep at 16' high

Small Garage is 25' x 25' x 11'

Engineer sent me the final drawings for approval. We submit for permit at end of the month.

Play with the "furniture" layout inside/outside now so it works best for you for both electrical requirements and garage/shop requirements.

 

[SemperGumby]

Was that vehicle fuel (gas stations) or utility fuel also?

No electric - powers nearly everything in SWFL

Most gas stations lacked the personnel or back-up systems to either pump or take payment

Toss in SWFL common courtesy you got to figure everyone is "conceal and carry" player lacking the training to be one. So line queuing is a **** shoot

We had a boat so 65 gallons available several vintage 4x4s with enough fuel to power us for a week or so. That said, we help our neighbors out

 

[SemperGumby]

Play with the "furniture" layout inside/outside now so it works best for you for both electrical requirements and garage/shop requirements.

As of the moment, the layout is a blank canvas besides agreeing on a four post lift bay position

 

[Fav Onefour]

Whole house is aluminum wiring or just the main line?

I bet the electrician would like to avoid messing around with a whole panel. The plan of feeding the house as a sub would sure clean up the installation.
We're doing a remodel in a place with aluminum wiring. In the end is is probably cheaper to run a sub panel for the new circuits.

 

[mm08822]

No electric - powers nearly everything in SWFL

Most gas stations lacked the personnel or back-up systems to either pump or take payment

Toss in SWFL common courtesy you got to figure everyone is "conceal and carry" player lacking the training to be one. So line queuing is a **** shoot

We had a boat so 65 gallons available several vintage 4x4s with enough fuel to power us for a week or so. That said, we help our neighbors out

I asked regarding which fuel for generator to consider. (See we already added scope creep to your project!!)

 

[SemperGumby]

I asked regarding which fuel for generator to consider. (See we already added scope creep to your project!!)

I see

Propane seems to be the "go to" in the 'hood - I do not operate a diesel truck anymore

 

[SemperGumby]

Whole house is aluminum wiring or just the main line?

I bet the electrician would like to avoid messing around with a whole panel. The plan of feeding the house as a sub would sure clean up the installation.
We're doing a remodel in a place with aluminum wiring. In the end is is probably cheaper to run a sub panel for the new circuits.

The house is vintage 1989 electrical next level genius work for SWFL

Aluminum wiring for the larger amp circuits 30A to 60A.

We just found an energized 30A line buried in a wall with stucco covering it.

 

[mm08822]

It is not uncommon or an issue for higher amperage circuits to be AL.

I would be more concerned with the "happy homeowner specials," like you just mentioned!

Could that have energized the metal lathe used with the stucco?

 

[Codyboy]

Wow didn't realize they were still running aluminum branch circuits in 1989. I thought that stopped around 1972, 1973? Other than larger circuits like #2AL or is it #4AL. ?

As to the plan suggested to the op of installing a 320/400a service at the garage and feeding the house from there as a subpanel....
Wouldn't that add a lot of distance from the source(FPL transformer)? (320 ft to the house) Would a larger wire be required for that house panel like 250mcm just due to distance?
And what about wire and size from the transformer ? Does op provide that wire or does the POCO?
Seems like a lot of big wire being run for a longer distance parallel 4/0 or 350mcm 180ft vs. a single 4/0 140ft from the house .
ETA
I see op clarified my question while I was typing on the AL branch circuits.

 

[Fav Onefour]

The house is vintage 1989 electrical next level genius work for SWFL

Aluminum wiring for the larger amp circuits 30A to 60A.

We just found an energized 30A line buried in a wall with stucco covering it.

Uffda.
Makes you almost want to quit digging around.
This week, we were running snake through a soffit run some hack threw together. Dang snake hit a zapper hard enough to trip the circuit. Oh well, finished soffit run is gone for now. We found an open box connection with no wire nuts. Who does stuff like that and then buries it?

Honestly, the find was great reinforcement for the decision to add the sub panel. I was starting to get nervous about doing long work runs with tools. All the old aluminum stuff is in flex. We've found neutrals tied together all over the place without boxes. It has been a real riot trying to narrow down circuits. We've solved quite a few mysteries with spark taps. We'll probably end up pulling out a bunch of that stuff and tying into the new sub panel.