Advice needed: Do I need 100 more amps if I already have 200 amps to house?

[MorrisonHiker]

I currently have 200 amps coming to my house. This panel was added about 8 years ago when the house was totally remodeled. If I add up the circuit breakers on the main panel box, it looks like I have 500 amps worth of circuit breakers. (See image below.)

From the main panel, a 40 amp line runs through the house to an attached garage approximately 50 feet away. The garage is about 30 years old and the subpanel is pretty full. It appears to have 120 amps worth of circuit breakers installed. The subpanel in the garage powers 3 garage door openers and lights, over a dozen 5-15 outlets, exterior lights and a NEMA L6-20 outlet. In another thread, Upgrade old NEMA 6-20 outlet?, I asked about upgrading my NEMA 6-20 outlet. I received lots of helpful suggestions but haven't made any changes yet.

I plan on adding NEMA 14-50 outlets to the other two bays in the garage. From the garage subpanel, the lines would have to be run about 15 feet and 50 feet respectively, so I'm guessing 6 gauge wire would be required.

Questions:
1. Should I be concerned that the 200 amp main panel has 500 amps of circuit breakers and the 40 amp subpanel has 120 amps of circuit breakers installed?
2. If I shouldn't be concerned about #1, would I be able to upgrade the NEMA 6-20 to NEMA 14-30? The 6-20 outlet is currently on 12 gauge wire but only about 6 inches from the subpanel so it wouldn't take much to upgrade it to 10 gauge. If I can't upgrade, I'll probably use a pigtail adapter or change the outlet to 5-20 based on suggestions in the other thread.
3. Should I have a new 100 amp line run to the garage (via the main panel) or is my current 200 amp line sufficient? I assume I need 100 more amps and because the main panel is already totally full, they would have to swap out the main panel in order only use one meter. Is this a correct assumption? Would it be better to get a new meter and panel for the 100 amp line or would this result in two power bills each month?

Let me know if you have any questions concerning my current setup and I'll do my best to provide answers. I already had one electrician out and he wanted $5000 for running a hundred amps plus $500-$1000 per charger. The funny (sad) thing is I didn't ask him to install chargers but had asked for 2 14-50 outlets so that I could do the 'install' myself by plugging in a UMC or EVSE. I don't trust his estimate at all. I've tried calling a few other electricians in order to schedule estimates but everyone has been very flaky so far, not returning calls or emails. :crying:

Thanks in advance for any advice!

 

[davewill]

It's not quite as bad as you think. You have 200a @ 240v coming in, so count the 120v breakers as if they were half of a pair (2 15a single breakers is just 15a). However, this isn't how you do a load calculation. You instead make a list of all of the appliances, lights and their ratings. There are lots of worksheets for calculating the service requirement, you can search online for them.

You may indeed need an upgrade, but I can't tell from what you're told us. Most places won't let you have a second service, but some will. You can physically fit more breakers in the main panel by replacing some of the full-height breakers with half-height ones. You probably need to find an electrician you can trust to do this properly. That bit with the $500-1000 to hang the EVSE on the wall and wire it up sounds pretty bogus.

 

[Lloyd]

Looks to me like you need to upgrade your panel in the garage to 100 amps (from 40) for what you want to do and that should be sufficient. If you have conduit to the garage, then that will be easy. If the garage sub is rated for 100 then you can just go 1/2 width for your present breakers and and have room for the 14-50's you wanted in the garage.

 

[brucet999]

As Davewill said, do an inventory of the loads on your 200A main panel to see what the highest likely total load at any one time would be. You have a 2pole 40, a 2pole 50 and 2pole 30 breaker - likely for Garage sub panel, stove or AC and dryer, respectively. To support two 14-50s you would have to upgrade the garage sub panel, probably to 100A, so count that load in when doing your main panel inventory.

Also, note which breakers are carrying higher loads and make sure that they are not mostly on the same phase (odd number spaces are on phase A, even number spaces are on phase B, 2-pole breakers are connected to both phases). You may have to swap some breakers (or circuit wires connected to them) from one phase to the other in order to balance the load if you are going to increase the sub-panel capacity.

Finally, ability to increase the sub-panel capacity depends on two things:
1. Native capacity of the panel itself (look for a label on the cover plate). It might be as little as 60A, although with 8 spaces that is unlikely.
2. Size of the wires connecting it to the main panel - 100A would require #3AWG wires. You probably have just #8AWG to support a 40A sub-panel. If you pull the cover you can see what you have coming in.

 

[MorrisonHiker]

It's not quite as bad as you think. You have 200a @ 240v coming in, so count the 120v breakers as if they were half of a pair (2 15a single breakers is just 15a). However, this isn't how you do a load calculation. You instead make a list of all of the appliances, lights and their ratings. There are lots of worksheets for calculating the service requirement, you can search online for them.

You may indeed need an upgrade, but I can't tell from what you're told us. Most places won't let you have a second service, but some will.

Thanks for the info. I figured out that I needed to count the 2 pole breakers once but never thought about that for the ones which aren't 2 pole. With that in mind, counting again, I have 310 amps on the main panel (of which 40 hours to the garage) and 70 on the subpanel. I will do an online search for load calculators and see what they say.

 

[MorrisonHiker]

Looks to me like you need to upgrade your panel in the garage to 100 amps (from 40) for what you want to do and that should be sufficient. If you have conduit to the garage, then that will be easy. If the garage sub is rated for 100 then you can just go 1/2 width for your present breakers and and have room for the 14-50's you wanted in the garage.

There's no conduit yet but that should be pretty easy to run along the back of the house. I don't want to go through the house as they did with the current 40 amp line since the basement is finished and it would be a lot of work to redo that.

 

[MorrisonHiker]

Finally, ability to increase the sub-panel capacity depends on two things:
1. Native capacity of the panel itself (look for a label on the cover plate). It might be as little as 60A, although with 8 spaces that is unlikely.
2. Size of the wires connecting it to the main panel - 100A would require #3AWG wires. You probably have just #8AWG to support a 40A sub-panel. If you pull the cover you can see what you have coming in.

Thanks. I will use a load calculator and take a look at the line into the subpanel. I'm betting it is only 8 gauge. Would they be able to pull 3 gauge through and remove the 8 gauge without tearing up the finished basement or do you think conduit on the outside is the way to go?

 

[MorrisonHiker]

I used an online calculator and it looks like my household usage is probably less than 100 amps but it is close. If I could route 100 amps to the garage instead of just 40, I might not need another 100 amp line. I see Tesla added a couple new recommended electricians for my area so I guess I'll try giving them a call next.

Is there a buffer I should plan on not using or seeing aside for the future? 200 might just be enough but I don't want to find out the hard way that it isn't!

I really don't think the garage would use all 100 amps at once since I could stagger charging to begin at different times.

 

[dj905]

One thing to keep in mind is that you can manually set the maximum current that the car draws during charging. My system can provide a maximum of 48 amps (60 amp breaker), but often I charge at 30 amps, since this is sufficient to fully charge my car overnight.

I also have a 200amp service, and have a 100amp subpanel in the garage. I've looked at my usage online for the purposes of sizing a generator, and my peak whole house usage is less than 15 kW, which is approximately 70 amps, including the car.

David

 

[chriSharek]

Does your car have dual chargers? If you don't plan on getting duals or ever upgrading, you only need a 50 amp circuit to maximize the charging rate on the HPWC, which is 29 miles/hour of charge.

I just installed the 50 amp dual pole breaker, conduit and wires at the house last weekend. I'm months off before taking delivery, but I didn't want to be digging the ditch in August . . .

- - - Updated - - -

One thing to keep in mind is that you can manually set the maximum current that the car draws during charging. My system can provide a maximum of 48 amps (60 amp breaker), but often I charge at 30 amps, since this is sufficient to fully charge my car overnight.

I also have a 200amp service, and have a 100amp subpanel in the garage. I've looked at my usage online for the purposes of sizing a generator, and my peak whole house usage is less than 15 kW, which is approximately 70 amps, including the car.

David

DJ905, you hit the nail on the head. You really need to pull an amp reading when everything is running. I had both ACs running, and my Volt Charging and I was only pulling 36 amps - and my panel is only a 150 main! I'm fairly confident I'll be fine even with the Tesla AND the Volt!

 

[FlasherZ]

You are not permitted to use user-configured currents in load calculations. If the receptacle is a NEMA 14-50, you must use 50A in the load calculations. Likewise, for HPWC, you must use the breaker size that the installer sets in your load calculations, even if you can dial the car down to 5 amps. HPWC is considered an "installer-configured" appliance. This also means that you must use 100A in the calculation if you install an HPWC on a 100A breaker, even if your car only has a single charger.

Typically a 200A service will have room for a 50A charging load, even with an all-electric home. The only exception would be a very large home using electric baseboard or ceiling heat. HPWC's at 100A circuit size will typically require 400A service, unless it's a very small home, gas-only.

I can pretty much guarantee your transformer isn't sized to 200A, and it's likely your entrance conductors aren't sized to 200A by NEC standards, anyway. Those are the things I would be worried about first, as long as you have 200A service.

Note that your subpanels don't have to "route" 100A exclusively to the garage. Load calculations are based on the entire service, then each feeder to subpanels are sized appropriately. On my grid-only panel (200A from 400A service), I have a 100A breaker to my machine shed, a 60A breaker to the pool panel, a 50A breaker to the hot tub panel, and a 100A breaker to my garage's car charging panel. This is all ok, as long as the projected loads fit the load calc.

 

[brucet999]

I can pretty much guarantee your transformer isn't sized to 200A, and it's likely your entrance conductors aren't sized to 200A by NEC standards, anyway. Those are the things I would be worried about first, as long as you have 200A service.

How could a panel with a 200A main breaker get signed off at inspection if the transformer or entrance conductors were too small for that load? Edison would not allow me to install a 150A panel - even with only a 100A main - to accommodate a larger solar array (to connect 30A solar under the 120% rule) because the entrance conductors are only #2AWG, too small for that capacity, even though they would never have to carry such a load.

 

[FlasherZ]

How could a panel with a 200A main breaker get signed off at inspection if the transformer or entrance conductors were too small for that load? Edison would not allow me to install a 150A panel - even with only a 100A main - to accommodate a larger solar array (to connect 30A solar under the 120% rule) because the entrance conductors are only #2AWG, too small for that capacity, even though they would never have to carry such a load.

Power companies work under a different set of rules, sometimes different sets of rules depending upon state. Each can set its own requirements for connection, aligned with PUC requirements.

Prior to my installation of EVSE, my home's 200A meter pan was fed by 2/0 AL (NEC rated 135A at 75 deg) from a 10 kVA transformer (rated ~40A at PF=1).

The NEC takes over at the base of the meter... #2 AL is good to only 90A on most terminations (75 deg), so perhaps they took issue with that.