Main service panel upgrade - SCE

[Solarisium]

I’m attempting to upgrade the main panel.
Utility: Southern California Edison
Current panel: 100 AMP with 100A main breaker
Future panel: Option 1: 225 A panel with 200A main breaker OR option2: 200 A main panel with 175A main breaker
must be Square D, outdoor, overhead, at least 30 spaces.

I prefer a 225 A panel but can find a good selection of them! Any recommendation?

I’m pulling the permit for this job, and Edison’s inspector (planner) already approved the location (the orange sticker) and determined that the current service is sufficient to support a 200 or 225A load.

Anyone with any recommendation / tip or experience with main service panel change or/upgrade?
Also I have to cut the meter seal in order to remove it. Would that be okay? No other way to remove it without breaking the seal. The planer said next steps are to get the permit, do the change out, and have the city inspect it! Dose anyone have experience with installing the meter in a separate meter socket? Do you recommend a separate meter socket and main panel or a hybrid panel/meter?

Thanks in advance

 

[400bird]

Do you really need that many spaces in the main? I don't see much for options.
You could do a 200 amp main + a sub panel.

As far as the meter seal, I wouldn't stress it. I cut mine and the PGE employee shrugged and said it saved him 3 seconds when doing the change over.

Are your old and new meters going in different locations?

 

[Solarisium]

Do you really need that many spaces in the main? I don't see much for options.
You could do a 200 amp main + a sub panel.

As far as the meter seal, I wouldn't stress it. I cut mine and the PGE employee shrugged and said it saved him 3 seconds when doing the change over.

Are your old and new meters going in different locations?

My current panel has 20 spaces, and has only 6 single space or 3 240V spaces available. I am planning to add 3 240v in the future that’s why I thought 30 spaces be minimum. So a 20 space panel probably wouldn’t be enough.
Sub panel is an option that I honestly didn’t think of! I think I can install a sub panel for the 240V circuits and probably save in wiring costs too (might)!

The meter is a net meter, and the SCE planner didnt mention the need for changing the meter. Meter wont move and staying in its current location.

Is your meter installed in the main panel? Any recommendations on hybrid or separate panel/ meter socket?

 

[zanydroid]

You need to confirm what service equipment SCE allows. Do they have a list?

I think combo meter mains are most common in California.

What is the output rating of that solar in the picture, and how is it backfed currently? Line side tap? Did you get approval to do that again? If it’s not line side tap you will need to confirm busbar calculations.

 

[Solarisium]

You need to confirm what service equipment SCE allows. Do they have a list?
I think combo meter mains are most common in California.
What is the output rating of that solar in the picture, and how is it backfed currently? Line side tap? Did you get approval to do that again? If it’s not line side tap you will need to confirm busbar calculations.

I guess I will call the Planner with those questions! didnt think of such questions when he was inspecting!
According to Electric Service Requirments on SCE website: both types are approved:
Hybrid or Combination meter / service for overhead service:


and meter remote from service panel:




The solar is 4kw, load side tap connected to a 20A breaker.
thanks for the tips, i never thought about the load calculation, although my 4kw solar should still be within the 120% rule after the upgrade, but future 240V loads will mean a load recalculation is required.

The planner did mention that the AHJ will inspect and approv according to the load. Guess the load calculation will be done through the permit application?

 

[goldserve]

If you are installing in the same location, you need to plan things out and have the crew come out and disconnect, pull your meter. If you cut the tags and pull yourself, the power company will see your meter go offline and send someone out soon to check and they can be extremely mad for meter tampering. Most electricians like to build out another meter location with the overhead service wires, get it inspected with city and schedule a cut and swing with the power company.

If you read my journey, I did the exact same thing you wanted to do and basically scheduled a cut, install everything in one day and late into the night, scheduled an inspection for the following day and pray, hope I pass inspection to get a green tag from the city to inform pg&e for a reconnect on the same day as the inspection.

It helped to have a battery system already installed and a critical loads panel for the rest of the house.

 

[zanydroid]

Are you looking to do 225A panel with 200A panel because you want to upgrade solar later? How much are you thinking of adding?

Note that if you do 200A panel with 2x 100A branch breakers to two separate 200A subpanels you can backfeed a crapton into those two subpanels. You can go up to 200A of solar breakers, 100A into each)

Main panel is OK by Sum of (load) breakers rule rule (100A + 100A load breakers < 200A busbar)

Subpanels are OK by any rule. Let's say you do 120% rule (100A (main) + 100A (solar) < 1.2 * 100A busbar)

The solar is 4kw, load side tap connected to a 20A breaker.

OK, yeah, I think mathematically any legal load side tap on 100A busbar panel is also legal on 200A with maxed out breaker. Easier to check with the actual numbers sometimes.

thanks for the tips, i never thought about the load calculation, although my 4kw solar should still be within the 120% rule after the upgrade, but future 240V loads will mean a load recalculation is required.

You should only need to do load recalculation if you actually install the appliances.

Maybe with the exception of a dedicated EVSE charging circuit, my guess is a smart AHJ would force prewire to be counted.

The planner did mention that the AHJ will inspect and approv according to the load. Guess the load calculation will be done through the permit application?

This means you should fill out an appliance load calculation spreadsheet and submit it.

I think with solar they will probably always want a busbar calculation and safety stickers added on.

 

[zanydroid]

If you are installing in the same location, you need to plan things out and have the crew come out and disconnect, pull your meter. If you cut the tags and pull yourself, the power company will see your meter go offline and send someone out soon to check and they can be extremely mad for meter tampering. Most electricians like to build out another meter location with the overhead service wires, get it inspected with city and schedule a cut and swing with the power company.

I've heard a handful of stories of PG&E going nuclear over dumb stuff related to messing with the service.

I don't know if SCE is more chill, but I would get any kind of tamper seal cutting approved in writing or something.

 

[zanydroid]

A couple people here are fans of just installing a service rated breaker holder box as the main, which is enough to get power back & pretty compact. (You probably want to check with AHJ to see if they'll approve the main with your house disconnected or something crazy and non-habitable like that)

And then do everything with subpanels after that. It also lets you nuke the subpanels from orbit and start over, without involving the POCO again.

 

[zanydroid]

Is your GEC big enough for going from 100A -> 200A? I'm not super sure on the rule for that.

 

[goldserve]

A couple people here are fans of just installing a service rated breaker holder box as the main, which is enough to get power back & pretty compact. (You probably want to check with AHJ to see if they'll approve the main with your house disconnected or something crazy and non-habitable like that)

And then do everything with subpanels after that. It also lets you nuke the subpanels from orbit and start over, without involving the POCO again.

If you have the space to do this, I would absolutely do this as well because if you need to put CTs for metering or cap your sell back, it’s easier to do it on wires than some of these bus bars in meter plus cabinet combos.

 

[zanydroid]

If you have the space to do this, I would absolutely do this as well because if you need to put CTs for metering or cap your sell back, it’s easier to do it on wires than some of these bus bars in meter plus cabinet combos.

OP posted the SCE rules for service, and you are allowed to have a separate main. That will also solve the combo meter/main shitshow with consumption CTs. I think with basically every modern combo you'll have to either use ribbon CTs (assuming compatible with your system), or go into code gray area and put the CTs under the protective cover on top of the service conductors.

 

[Hedges]

I just did this with PG&E in Oakland.

Cost for utility transformer installation?

slightly OT. There was a review of the Emporia Energy Monitor on Amazon, which mentioned that the house meter records more kwh usage when the pull is unbalanced between L1/L2. Is this a possibility ?

diysolarforum.com

Couple mistakes I made:

With main breaker only panel above my brick trim and meter only box above that, meter was higher than PG&E requirements.
I did side by side, which was messy (crowded). Then switched back to meter above breaker, and uses cast stones to build a 30" x 36" platform.

The meter box I got was "ringless", lid placed over meter retains it. PG&D did not accept.
Second time I bought a ring type, and work was approved.
You can also get a Siemens 200A main breaker only box with meter side by side.

Is your GEC big enough for going from 100A -> 200A? I'm not super sure on the rule for that.

The one to water pipe has to be 4 awg. To ground rods can be 6 awg. Also bond cold/hot/gas pipes together at water heater #6 copper.


Inspector said normally people have utility disconnect, they replace box same day, reconnect.
I prefer to put new side by side, wire across, cut and swing, take out old. Power only disconnected briefly.
This one was under the eaves, not through roof. And I'm adding boxes, so all locations will be occupied.

Lowes doesn't return anything for "225A"
Home Depo shows an indoor panel:

Square D QO 225 Amp 42-Space 42-Circuit Indoor Main Lug Plug-On Neutral Load Center with Cover, Ground Bar QO42L225PGC - The Home Depot

The Square D QO 225 Amp Main Lugs Only 42-Space 42-Circuit Convertible Indoor Plug-on Neutral Load Center for Plug-on Neutral breakers is UL Listed for residential, commercial and industrial power distribution,

www.homedepot.com

They may be able to look up and order others.

I'm not readily finding 225A outdoor.
Consider a 200A main breaker only panel, and fan out to multiple sub-panels and safety switches with Polaris like I did.

 

[Solarisium]

The change out is proving to be more challenging than what I initially thougth.
1- I dont have much wiggle room to install meter socket above the man breakers, if I choose separate socket / breekers box. The same is ture for the sides. Thus I am limited to a combination service .. "CSED"
2- why the selction of CSED is very limited? when I filter my shopping for Sqauere-D overhead/200A/20 or 30-space, I am left with one or two! that are taller than my availabel space.

If you are installing in the same location, you need to plan things out and have the crew come out and disconnect

Guess I have two options: A- be as fast as a pro and change it out during the day while my sunny boy inverter is supplying max 2 kWh, or B- But a small inverter generator for night times, and take my time (maximum a few days I guess) to install under no time pressure!

Most electricians like to build out another meter location with the overhead service wires, get it inspected with city and schedule a cut and swing with the power company.

The space is the challenge: how do electricians install a new main panel/meter without connecting the service conduit (the one supplying the service) to the new panel? It literllay requires removing the current panel or at a minimum disconnecting the serivece lines form the meter. Am i missing something?

If I plan to re-route the service like a 90 degree turn to the left and install a new panel next to the current one, get approval, then remove the current one, would that be Okay? I woudl look awkward a bit!

Are you looking to do 225A panel with 200A panel because you want to upgrade solar later?

will be installing 240 V circuits: ESVE and water heater and electric cooktop. The current panel busbar cannot support those. No solar upgrade for now! I dont want to give up my NEM 2.0. well, I can legally upgrade by 1KW. and remain under NEM 2.0.

You should only need to do load recalculation if you actually install the appliances.
Maybe with the exception of a dedicated EVSE charging circuit, my guess is a smart AHJ would force prewire to be counted.

Prewire? you mean 240V wiring for new loads?

I don't know if SCE is more chill, but I would get any kind of tamper seal cutting approved in writing or something.

Will be calling SCE on Monday. The planner didnt mention anything about the seal. He gave the Ok to proceed with change out. and said do not remove the orange tag until the City inspection. How would I chaneg out the panel and leave the orange tag for the inspector? I wasnt home during the planner visit and didnt get to ask any of these questions!

installing a service rated breaker holder box as the main, which is enough to get power back & pretty compact

This is a vey good idea, giving me flexibility with future sub-panels. The approval would be the AHJ call, right? It sounded like all SCE cared about was the location of the meter for the new panel:

s your GEC big enough for going from 100A -> 200A?

It's #6. Fortunately the water pipe is very close to run a #4 ground.

OP posted the SCE rules for service, and you are allowed to have a separate main. That will also solve the combo meter/main shitshow

I drew a diagram, seems doable:
Option1: Combination panel. only drawback is that I will have to add sub-panel anyway since I cant fit a tall combo panel in that space.
Option 2: a meter socket/main breaker and a sub panel. This option requires more qork to install but seems the favorable option among folks here:




I mean I look at all of this, seems like the simplest option is #1, to take out the current, and replace it with a similar panel, except bigger rating. I thought I can add a subpanel indoor where the water heater/cooktop will be installed. Somewhere close to the kitchen area.

 

[Solarisium]

meter was higher than PG&E requirements.

SCE gave my the max/ min height for the meter. So I can avoid this.

I did side by side, which was messy (crowded). Then switched back to meter above breaker, and uses cast stones to build a 30" x 36" platform.
The meter box I got was "ringless", lid placed over meter retains it. PG&D did not accept.
Second time I bought a ring type, and work was approved.
You can also get a Siemens 200A main breaker only box with meter side by side.

Did you use a eter socket with main breaker? I see ones with a breaker like the one in my drawing, and others with no breaker, only a simple socket for meter. My meter is a rink type, limiting me to a few choices
I would wun into a window if I do side by side. there is a window next to the arrow:

The one to water pipe has to be 4 awg. To ground rods can be 6 awg. Also bond cold/hot/gas pipes together at water heater #6 copper.

I am lucky I have a #6 to the earth rod. the water pipe is close and will be replaced! The inspector made me bond cold/hot/gas at the water heater duirng the solar system approav! I guess I'm covered here!

Inspector said normally people have utility disconnect, they replace box same day, reconnect.
I prefer to put new side by side, wire across, cut and swing, take out old. Power only disconnected briefly.
This one was under the eaves, not through roof. And I'm adding boxes, so all locations will be occupied.

Does the utility need to shut off the electricity from the pole? envisioning the cut and swing step, will the service wires be still energized during this?
basically I am envisioning I will do this in this order: determine the right/approved equipment-> plan the installthat works with the space available and submit it in the online permit -> once plan is approved, break the seal, pull the meter, disconnect service wires, remove the old panel, install the new equipment (meter socket and panel), connect the service wires to the new socket, install the meter,, and call the buidling safety inspector to inspect and approve.
Am I missing anything here, specially a step involing my utility provider, SCE?

They may be able to look up and order others.
I'm not readily finding 225A outdoor.

Yes I gave up on 225A.

Consider a 200A main breaker only panel, and fan out to multiple sub-panels and safety switches with Polaris like I did.

Something like Option 2 in the picture attached? This is a meter and a 200A main breaker combined. I thought it would be nice to shut off the power from the meter socket so the entire subpanel is safe, during manitennace or work.


I see a disconnect like this in your post. is that what you are referring to as polaris safety switch? would that be installed between the main breaker and the subpanel?

PS I just noticed this safety switch costs like $1200 or $2000! you must be refering to something else!

 

[goldserve]

When I say some pros build a parallel main panel and do a cut a swing on the same day, they literally put up a new panel in a nearby location, make a new roof penetrations anyways because you are usually stepping up the imc mast/conduit to 1.5” or 2” for 200A anyways so they complete all the house circuit moves, get it inspected and then the power company will cut wire from original service entrance wire and swing it to the new service entrance. Hopefully the existing wires will still reach it. If you look carefully around your neighborhood, you will see some houses with two masts and one of them is abandoned. Usually much smaller because they were for 75A or 100A service.

Your order of operation is not quite correct. You would schedule a time with the power company after they approve your service upgrade to come cut the wire and temp tie it off so it is not a hazard. At this time, the worker will remove the smart meter ring and unplug the meter for you. You would the do all the electrical work, run the service entrance wire up the conduit and leave enough wire to make a U shape after installing the weather head. Make all the necessary connections to meter socket and torque down everything because there is no servicing these connections after the meter is installed. If this is your new main panel, make all the branch circuit connections and make it look pretty and correct. Most inspectors are weary of home owners doing their own electrical work so if something doesn’t look right, they will keep on probing to find something that is not to code. For me, I made my existing main a sub now so I just had to install one set of breakers, separate the neutral and gnd bond in my old main (they didn’t even check this) and this was all that was inspected. You need to set up an inspection before anything is energized or meter is plugged in (you definitely don’t get to do that yourself) because the inspector will give you a tag or okay the the electrical permit work before the power company will come over and do the reconnect of the service wires before the meter is plugged in again and the meter ring locked with the approved power company tags.

Hope this helps!

 

[Hedges]

Some 200A safety switches are $thousands.

Here are Siemens unfused and fused for $265 and $385

Siemens 200 Amp 240-Volt 3-Pole Non-Fusible General Duty Safety Switch GNF324 - The Home Depot

Siemens offers a wide range of switch products to service the residential, commercial and industrial markets. Safety switches are available in 30-1200 Amp ratings in all enclosure types. The VBII safety

www.homedepot.com

Siemens 200 Amp 2-Pole 3-Wire General Duty Fused Outdoor GF224NR - The Home Depot

General Duty Safety Switches are intended for applications where reliable performance and continuity of service are needed. But where duty requirements are not severe and usual service conditions prevail.

www.homedepot.com

Polaris is a multi-port lug. I used a couple to fan out from L1/L2 of 200A breaker and feed several sub-panels. The breaker box I got had sufficient L and G lugs. With this 250 MCM size, I can slip it over insulation of 3/0 wire and make connection somewhere in the middle (having stripped off about 1" of insulation.)

Polaris 250 MCM - 6 AWG Bagged Insulated Multi-Tap Connector, Black IPLD250-4B - The Home Depot

IPLD series insul-tap connectors have wire entry ports on both sides of the connector to allow for access from either side. Eliminates the need for cover and taping. Insulated with high-dielectric strength

www.homedepot.com

Here is a Siemens 200A Meter Main. Since it doesn't have busbar, just 200A main breaker, doesn't matter so much that this is not Square D. All your branch breakers can go in your sub panels.

https://www.amazon.com/Siemens-MM0202B1200-200-Amp-Meter-Combination/dp/B000UEJY2Q

If you rerouted that one conduit to left of inverter, more room to put a couple boxes side by side.

Utility does Cut and Swing hot, in a plastic bucket and with electrical gloves.
I haven't been involved in a one-day changeover, but what Goldserve describes with hot wires capped off and disconnected makes sense.
Took me a couple tries to get my work accepted by both inspector and PG&E, so new install next to old was convenient.

 

[zanydroid]

(EDITING)

Guess I have two options: A- be as fast as a pro and change it out during the day while my sunny boy inverter is supplying max 2 kWh, or B- But a small inverter generator for night times, and take my time (maximum a few days I guess) to install under no time pressure!

Note that inverter generator requires supervision in inclement weather and is noisy. You may run afoul of local noise rules. It might just be a warning.

I have both an inverter generator and an EV that gives 120V out. The EV does not require supervision, I've left it feeding my house for 24 hours during power outages. Maybe you can rent one off Turo (EG Toyota Prime or Hyundai/KIA EVs I believe generally have big 120V out).

will be installing 240 V circuits: ESVE and water heater and electric cooktop. The current panel busbar cannot support those. No solar upgrade for now! I dont want to give up my NEM 2.0. well, I can legally upgrade by 1KW. and remain under NEM 2.0.

OK. Note that couple of us have discussed justifying adding an ESS by noting that it also serves as emergency power in case you can't cut it over fast enough. Dunno if that is real or just justifying toys. Certainly it is real for projects that intend to add an ESS anyway. For your case it's cheaper to rent an EV for 2 days (or borrow from someone) or borrow a generator. The EV is less work once you can find it.

<some stuff I said about car charging>
Prewire? you mean 240V wiring for new loads?

On new construction many places in California require EVSE prewire, which is stronger than what NEC asks for (they're inching towards this nationally, I looked it up and it is a 120V @ 20A receptacle in each bay, but not a dedicated circuit per bay or something easy to convert to 240V. Sigh. Baby-steps).

This is a vey good idea, giving me flexibility with future sub-panels. The approval would be the AHJ call, right? It sounded like all SCE cared about was the location of the meter for the new panel:

The POCO will still care about the location of equipment near stuff they have to work with. It has to pass both.

Option1: Combination panel. only drawback is that I will have to add sub-panel anyway since I cant fit a tall combo panel in that space.
Option 2: a meter socket/main breaker and a sub panel. This option requires more qork to install but seems the favorable option among folks here:

I mean I look at all of this, seems like the simplest option is #1, to take out the current, and replace it with a similar panel, except bigger rating. I thought I can add a subpanel indoor where the water heater/cooktop will be installed. Somewhere close to the kitchen area.

What is on the other side of the wall? You could put a subpanel there if it is clear or clearable. And then extend the circuits into it.

How many circuits are in the existing main? Have you looked into whether you can get a small combo that supports tandems, and squish everything from current main into it? You are exempt from AFCI if the circuit extension on retrofit is within some distance. If you do need AFCI then consider Siemens panels since Siemens is AFAIK the only brand with tandem AFCIs. (Though, if you already need AFCIs it may behoove you to use the same panel brand in the sense that you can reuse those $$$ AFCI breakers that you already have).

Subpanels can be helpful, but do keep in mind you need enough working space in front of it. A common way to do that is to use a space like a hallway where you won't put anything there anyway, and then hang a painting over the panel to make it look nicer.

 

[zanydroid]

Here are Siemens unfused and fused for $265 and $385

Are any of these cheaper 200A switches service rated? If the difference between $350 and $1000 ones is service vs not service rated, and I don't have much space budget... I think I'd rather pay $700 more so I can consolidate.

How big is the current NEM2 system? If it is less than 7.6kW-AC and you don't plan to add EG a powerwall then you have a lot of flexibility with a 200A busbar. If you plan to hang storage inverters into it then some additional optimizing is warranted.

will be installing 240 V circuits: ESVE and water heater and electric cooktop. The current panel busbar cannot support those. No solar upgrade for now! I dont want to give up my NEM 2.0. well, I can legally upgrade by 1KW. and remain under NEM 2.0.

In what way is the busbar unable to handle this? I have 100A feeders and service, the main reason I upgraded my subpanel (DIY) was so I had enough breaker spaces; even with crazy amounts of tandem and quad breaker I was always 1 double pole too short. You can also get the EVSE to fit using EVEMS (EV specific load management), and this might be cheaper/less PITA than a service upgrade. For overhead service the cost of an upgrade is a lot lower, but the PITA stays similar.

In my case I am fed underground to a non-compliant service location at my house, so upgrading would cost > $15K, thus I got very educated at load management.

 

[Solarisium]

Still pending SCE to return my call. cant get a hold of the Planner!

From the responses here It sounds like I might have other options.
Current panel 100A
Loads (ball park):
AC 7.5 KWH (30A)
Hot tub: 5 KWH (20A)
Solar backfeed (is it a load?!): 4KWH, 20A
others small loads: 10 KWH (10 A)


Future loads:
ESVE 10 KWH (~40A)
Electric water heater: 12 KWH (~45A)
Cooktop: ~5 KWH (20A)

Total current loads: (~27kwh) ~80 A,
Future loads: 27KWH, 100A


Total estimate maximum loads after upgrades: 54 KWH, 180A

Pretty obvious a panel upgrade is necessary. I need to find the efficient solution considering the space available. I am comfortable working with electricity, and have installed the grid tie string inverter solar myself.

This is the space available.
My preference is to use the current space. I am open to combination panel or separate meter socket and sub panel too. Or if possible, as hinted by @zanydroid,if I can use sub panels, and tandems in the current setup, I guess I will be happier.

In what way is the busbar unable to handle this?

given the loads, I thought it cant! please But I am not nowhere near being expert here.





The circuits on the current panel:
(I know it is not organized and labeled! I'm the new owner, so bear with me! the future panel will be proper!)

What is on the other side of the wall? You could put a subpanel there if it is clear or clearable. And then extend the circuits into it.

This and @goldserve gave me an idea to move the service to the other side of the hot tub. only if not doable in its current location.

How many circuits are in the existing main? Have you looked into whether you can get a small combo that supports tandems, and squish everything from current main into it? You are exempt from AFCI if the circuit extension on retrofit is within some distance. If you do need AFCI then consider Siemens panels since Siemens is AFAIK the only brand with tandem AFCIs. (Though, if you already need AFCIs it may behoove you to use the same panel brand in the sense that you can reuse those $$$ AFCI breakers that you already have).

Subpanels can be helpful, but do keep in mind you need enough working space in front of it. A common way to do that is to use a space like a hallway where you won't put anything there anyway, and then hang a painting over the panel to make it look nicer.

they literally put up a new panel in a nearby location, make a new roof penetrations ..........If you look carefully around your neighborhood, you will see some houses with two masts..

I understood it now! Makes it much easier.
That is exactly the case with my neighbor.

Your order of operation is not quite correct. You would schedule a time with the power company after they approve your service upgrade ..... You need to set up an inspection before anything is energized or meter is plugged in (you definitely don’t get to do that yourself) because the inspector will give you a tag or okay

Thank you for taking time and clarifying this! I wasn't going to pull the meter right away, but I seriously thought it is going to be as simple as me pulling metro, me installing again ;-)
Now I see how installing the meter in a new location makes things simple!

Here is a Siemens 200A Meter Main. Since it doesn't have busbar, just 200A main breaker, doesn't matter so much that this is not Square D. All your branch breakers can go in your sub panels.

https://www.amazon.com/Siemens-MM0202B1200-200-Amp-Meter-Combination/dp/B000UEJY2Q

This is alsmot perfect! then I would only need sub panels.
do I have to use a safety switch between this panel and the subsequent sub panel? it already has a main breaker? should be sufficient?