Is 200 amps really 200 amps?

15 years ago

We're adding some living space to our existing home, and have no more slots in our breaker box to feed the added electrical needs. We need to add a few circuits (sunroom, bathroom including electric instant hot water heater, laundry room including washer and electric dryer).

We have 200 amp service, but the amperage on all the individual breakers adds up to 600+ amps. That, as well as a conversation with the local utility, seems to indicate that it's ok to hook up more circuits than the service, presumably because you never have everything turned on at once. Is this truly ok by code? If so, how high can you go?

So now we need to add some circuits. We can up the service to 320 amps without running new wire, but need to add more than 120 amps to our capacity, as the instant water heater alone requires 120 amps. Alternatively, they'll run new service, which, given our distance from the hookup, will be around $1000.

Can we live with the 320 or do we need to take the thousand-dollar plunge? Also, can we hook up a second breaker box to the first to add more circuits to the existing service?

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Comments (6)

hexus
15 years ago
first off, there is no way that you're instant water heater is 120 amps, I think you mean that it's 120 volts.
200 amps is pretty standard service size for an average size house. You do not add up all the breakers in your panel to determine what service you need, as you can see that just doesn't work. There are load calculation formulas you can search for the web if you want to get a more accurate calculation.
As for your question of how high can you go. Personally the biggest residential service that I've installed is 600 amps. The house was 13,400+ square feet however (no, that's not a typo).
My suggestion in your situation would be to contact an electrician to have a sub panel added for the new circuits that you need.
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wired_lain
15 years ago
If the OP is talking about a tankless on-demand water heater to supply the whole house, and not just one of those little undersink hot-water dispensers, it could easily require 120 Amps.

Here is a link that might be useful: tankless water heaters
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the thing about upping the service is you run into other issues. i KNOW that inspectors in my area will try to, and usually will, force you to bring other items up to current code. a good friend had a bad panel replaced, the EC pulled a permit for it, and the inspector made them go back and GFCI the outdoor/bath outlets before he would sign off. heck nothing was touched on those other than disconnecting fromthe old panel and pluggin most of the same breakers back in the new one. but he insisted tha tbecause the circuit was "touched" it had to come up to current code. With 100 amp service, you are limited to about 5 circuits total. common misconception, totally wrong, but common. at my house i have all my 240v breakers in the outside panel. there are 2 100A breakers, 2 60 amp breakers, 4 50A breakers, 2 30A breakers. that is a total of 580A! do i have 600A service, NO. i DO have 300A service though( i posted before that it was 400, but a friend who is a sparky corrected me). 1 of the 100A breakers feeds my indoor panel which feeds all the 120v circuits inteh house. this is a 24 slot panel with 22 20A breakers in it(the whole house is wired with 12/2 even the lights). that is 440A worth of breakers! you can have 20000A worth of breakers on a 100A service. it is not the size of the breaker, it is the size of the actual LOAD that determines service size.
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I had an interesting variation on this situation (I've posted it here before). When my house plans were being formulated, my plumber, who was going to install the electric boiler and electric DHW, recommended 400A service. But, when the electric service was installed, only 200A was run (??, I don't know why, same GC). While the house was being built, one of the first things they did after enclosure, was to run the in-floor radiant heat (this was during the winter at temperatures as low as -20°). No problem, the workers kept warm enough, even though the window and door openings only had plywood over them. THEN, the GC realized his mistake and decided to upgrade to 400A which meant running a new line from the pole transformer to the meter (on a stand 150 feet away from the house), replacing the meter, and running a second 200A buried line to the house and installing a second load center. He said it was his mistake and would only charge me for the additional materials, but I'm not sure. My boiler can use up to 100A by itself (it's on a 120A circuit). Anyway, I still don't think the extra 200 was necessary but it's nice to have the second load center, the first one is full! Are your quotes for 200 or 300 Amps, or is that the difference?
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petey_racer
15 years ago
The OP is adding up breakers which is a meaningless number.
By 120 amps he means the unit requires three 40A/240v circuits.

Weedy, IMO if it were not for that stupid on demand water heater you'd have been fine the way you are.
With it you probably have no choice but to go 320a.

I am confused by your explanation about the service. I SERIOUSLY doubt you can go from 200A to 320A without changing the service wire. Even so, $1000 is not even close to what it would cost to upgrade from 200 to 320.

It' NOT just a matter of adding a panel. The service cable, meter pan, grounding/bonding, panels, etc, all need to be rated for the service size
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weedyacres
Original Author
15 years ago
Ok, realized I didn't explain the situation perfectly clearly. The existing service coming in can handle up to 320 amps. The existing breaker box says it's a 200 amp box. So hexus is probably right, we can get up to the 320 amps by adding a subpanel.

To go higher, we've got to pay the utility ~$1000 (6-something per foot) to run the new wire and hook up the new meter.

I googled and found an online load calculator, so we're going to run around the house and figure out what all our appliances need, and get educated on how that all figures into what we can really load onto our existing service.

Our house, with the addition, is 4300 square feet. Does 320 feel sufficient for that square footage? (2 sets of A/C and furnaces, 3 1/2 baths, double laundry hookup)

And the instant hot water heater (necessitated by the fact that the bath and laundry are on the far side of the house from the existing hot water heater, and we don't want to waste all the water needed to move hot water that distance) really does require 120 amps.
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petey_racer
15 years ago
First off, you DO NOT have a 320A service. You have a 200A service. Even if you add a sub-panel you will STILL only have a 200A service.
THAT is what the POCO wants the $1000 for, to upgrade the lateral to the house. Even then, you still need to add another 200A panel and replace the meter pan.

IMO there is NO way you will get by with just a 200A service. That silly insta-hot is killing you. (Can you tell I HATE those things)

Have your electrician (or the POCO if they will) do a load calculation to REALLY see what you need. Everything else is just guessing.
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hexus
15 years ago
I would 100% scrape that water heater, and either get one that goes under the sink (normally they just require a normal outlet and don't draw too many amps.)
OR (the best option IMO), have a plumber come in and add a recirculating pump to your hot water system. The pump will require to be wired, but it will be A LOT cheaper than what you're looking at doing. It keeps the hot water circulating around so you don't have to wait for hot water on the other end of the house.

Both options will save you a lot of money. Upgrading your service is not cheap, and like was said, it will not only cost you $1000, you'd be looking at around at least $2500 normally. Get rid of that dumb water heater and you'll be fine with the 200 amp service that you already have.
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Is 200 amps really 200 amps?

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Is 200 amps really 200 amps?

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