Is there is a Standard on how much main service panel / main circuit breaker amps should be?

Question

Is there is a standard how much main service panel / main circuit breaker should be rated for?

Below example.

Here's current line up of my electric loads:

• Electric Range - 50 amps
• Electric Vehicle level 2 charger - 50 amps
• Dryer - 30+20 amps (4 spaces breaker, 2 phases)
• Air conditioner - 40+15 amps (4 spaces breaker, 2 phases)

These four main loads add up to 205 amps !

There are additional circuit breakers (10 of them):

15 amps circuit breakers - seven circuit breakers:

• Furnace, refrigerator
• Bed 3
• Family room, basement
• House gfi, loft
• Up hall, garage
• Master bed+ bath
• Bed 2 + living room

20 amps breakers - three circuit breakers:

• Kitchen + washer
• Kitchen plugs, disposal
• Dining room + dishwasher

Is there is a standard how much main service panel / main circuit breaker should be rated for? I will be adding EV Level 2 charger (50 amps breaker). Currently have 150 amps main circuit breakers, but I feel it should be at 200amps there. This topic was starter primarily to understand if I have to increase main circuit breaker to 200amps with the additional EV charger.

Thanks.

Answer 1

Article 220 and you

Without the last year of utility usage data in hand, we have to use Article 220 of the NEC as our guide to sizing your service -- this is one of the toughest articles in the Code, so don't feel bad about being bamboozled by it (it's hard for many of the pros, even). However, now that we have the information necessary in hand, we can go through the process together.

We start with the general receptacle load -- this is 3VA (volt-amps) per square foot of house, or 3*2635 = 7905VA. To this, we add the small appliance load -- this is allocated at 1500VA per kitchen and laundry small appliance branch circuit (1 laundry and 6 kitchen in your case, conservatively treating the dishwasher and disposal circuits as SABCs) for 7*1500=10500VA. Totaling these two numbers, we get 18405VA, which we then apply a 35% demand factor to for everything over 3000VA, giving us 8392VA of factored load.

From there, we then deal with major appliances. You don't have any major motor loads (such as a dedicated circuit for a well pump) in your house, and your primary HVAC load is your air conditioner at 26.8A; also, it appears that you have a gas water heater to go with your electric dryer and electric range. This means that we can use 9.6kVA as an allowance for the range (this handles ranges up to 50A, based on the Table 220.55 logic) and 5kVA as an allowance for the dryer as per NEC 220.54, to go with a 26.8A*230V=6164VA air conditioner load. Adding this all together gives us 29156VA of total demand (before the car charger), which we divide by 240V to give us 121.5A of service load.

Adding the 9600VA (40A continuous) car charger to the existing load gives us 161.5A, which is over the current 150A service size, thus requiring an upgrade to 200A to fit this.

As to fitting the breaker in...

Here's the bad news -- you need to install a subpanel to get the breaker for the EV to fit into your setup, since Square D does not make a HOMT240250, and it does not appear you have enough spare spaces otherwise to fit things in. The best bet is to move the range breaker (top left) out to the new subpanel -- this frees up space for a 100A breaker (HOM2100) that can then feed a 1AWG aluminum feeder (3x1AWG aluminum XHHW-2 in metal conduit) to a subpanel (I would use a 2 or 2.5" conduit to accommodate a future upgrade of the feeder to 200A, and use a 200 or 225A main lug panel with ground bars and 42 spaces minimum for the sub), which can then mount a 40A 2-pole breaker for the range and a 50A 2-pole breaker for the EV charger.

Answer 2

Both of the previous answers are correct, but you may be confusing your actual electrical usage (the demand) and your actual connected load which is as if all of your devices were operating at the same time.

Nec Article 220 is the article we use to calculate the demand to size the service and needless to say it is intense. In fact there are two methods to calculate this size.

But you are lucky. We are not dwelling in speculation about what your dwelling is using in the way of electrical power. All you really need to do is to contact your utility provider or in many states it is listed on you utility bill the winter and summer maximum demand that you used the previous 12 months. NEC 220.87 Determining Existing Loads. We take the maximum demand you used in the last 12 months which is in KW or KVA divide it by 240V and you will have the maximum demand in amperage. If we take that amount and add 25% to it, the NEC will allow that as the maximum demand for your dwelling.

If you are going to add to that demand the you will need to use NEC 220.83 to calculate how it will effect your service size.

The point being is just this, if you add up all of the breakers or all of the loads in your panel, it usually exceeds the service feeder and the main breaker. So we are allowed to use calculations to determine how much power you will use at any given time (the demand) and size everything accordingly.

Hope this helps explain things.

Answer 3

Is there is a standard how much main service panel / main circuit breaker should be rated for?

This is generally up to what the builder ordered when the house was built, at least with some latitude. Some places may mandate a minimum or maximum for a residence, and that may depend on occupancy limits, floor space, etc.

The service also depends on when the house was built. Customary service levels have been rising slowly over time. For example, my house was built in 1985, and it has 200 A service.

Here's current line up of my electric loads:

This is nothing to do with what your service is. In fact, it works the other way around. The total appliances you can have on at any one time is limited by the service you have.

Currently have 150 amps main circuit breakers, but I feel it should be at 200amps there.

If you want a higher service level, talk to your electric company. Upgrading may be expensive, since it probably includes running thicker wire from the last transformer to your panel. The electric company may want to make any changes themselves, particularly outside your house, or inspect changes made by someone else before turning the power back on. Either way, this is something a licensed electrician needs to to, at least.

Answer 4

Yes, the National Electrical Code in the USA (similar standards exist for other jurisdictions) has specific procedures for calculating the required breaker sizes for various combinations of load.

Answer 5

The NEC has a section called load calculations article 220, we don't get an accurate idea what our loads are by just adding up breakers. For example do you run your furnace and air conditioner at the same time? So part of the calculation is using the larger of the 2 not both 220.83. How large is the home a small house requires less lighting so we multiply the square footage by 3 volt amps to get the minimum required 220.12 . with LED & Flouresents it will be lower but this is the minimum. If you have multiple ranges, wall mounted ovens, counter mounted cook tops you don't turn everything on high so there derating values 220.55. There are some minimum standards like 20 amp circuits 2 for kitchen, 1 for bathroom and 1 for laundry. An electric dryer minimum is 5000w There is a bit more to it but you can see the total of the breakers will usually be much higher than the size of the main breakers. I find many homes with gas heat and AC pulling well under 100 amps in summer while cooking dinner and there panel is usually 150 -200 amp range but may have breaker totals of 200-250 or more. I hope this points you in the correct direction just 1 last note for a single residence the minimum size panel is 100 amps and the max is usually 400 amps 230.79.C. There are service calculators that ask the needed questions. Like square feet appliance types furnace and AC loads put the answers in and it will provide the calculated load and they are free. Check out wireyourownhouse.com/tools/housecalc.html it was the first one I looked at after searching online.