It is a single family home. Everything is electric in the house. Heating system will be geothermal.

I agree with you - just wanted make sure.

Thanks.
AJ

I have 400A in my house. Overkill? Perhaps, but with two 200A panels in the house, I have plenty of slots for surge protection, etc. Plus my two geothermal units use a total of 10 slots (5 different 220V circuits).

Water heater too? Tankless electric? That would make a difference. Or traditional water heater?

It is possible that the post misquotes one or both of the electricians- but the statements as written concern me.

I have a desuperheater and two traditional hot water tanks. The first one is turned off and is used as a buffer tank. The second one has power (30A) but since the DSH gets the incoming water to 120F, it only has to heat a little. Of course, in the spring/fall when the weather is nice, the unit isn't running so no "free hot water". I have power running to both tanks for a total of 4 slots. However, I've never turned on my buffer tank's breaker. Probably a waste of a breaker and 10awg cable.

My 4ton unit has a 50A circuit for the compressor, etc, a 60A/30A circuits for the 15KW emergency heat for a total of 6 slots. I also have a 2ton unit in the attic that handles the upper floor. It has a smaller emergency heat so just 2 220V circuits for another 4 slots.

That totals 14 slots just for my HVAC & hot water system.

You do not size the supply based on the highest possible load. There is never a situation where your water tank is drawing full power, oven is on full blast, heat is on full, a/c is on full, all lights are on, vacuum is running, hair dryer is blowing, etc. etc.

And (as bus_driver said) I hope you misunderstood and misquoted what the electricians said because it is not just all about the amps. Voltage is considered too. A 200 amp service is supplying 200 amps at 240 volts. Which can be considered 2x200A at 120v. But your actual usage will have some devices that require 240v, and some at 120v. So it isn't a cut and dry calculation (although it should be fairly simple for an actual licensed electrician).

Yes, I do have a tankless electric. I was just looking at an ecosmart unit on Amazon and spec says - 112 amps for one heater.

Thanks everybody - Geothermal information is also very helpful. Good to know how amps are calculated. I have to list all 120 and 240 appliances, add it all up and apply some sort of discount factor to account for non-simulateous usage. There must be some heuristic or more firm guidance to do that...

Thanks.

The easiest way is to just ask the electricians if they did a load calculation or how they came up with what they are recommending.

If you want to get a general idea if they are in the right ballpark, you could google a website that will do the calculation for you where you just have to punch in the values. I linked to an example below, but I haven't actually used it or even read the instructions or anything, so I'm not actually recommending this one as a good one.

Maybe try a few different calculators and see if they agree.

But be aware that there may be something specific about your situation that isn't taken into account by these general calculators. Which is why a good electrician's opinion is probably the better option.

Here is a link that might be useful: Calculator

The electric tankless will also pull even more than 112 A when it kicks on to heat water.

Resistance heating elements pull their rated power AFTER they have heated up, but just like induction motors (like in your heat-pump) pull significantly motors current for a very short time.

Incandescent bulbs do the seating, but the filament is so small it is not usually many cycles of the power line (though many an engineer has blown out his drive transistor by using the running wattage to determine the starting current of a bulb).

Larger heaters prolong the starting draw (more mass meas longer heat up time) and large induction motors can really stretch it out till they come up to full speed ('hard start kits' and more start capacitance to shorten the start up on time).

The heat pump should have a LRA (Locked Rotor Amperes) number on the name plate.
This provides a decent estimate of the starting current the motor will pull, but you still need to round up (often you end up going to the next larger available breaker size anyway and that covers the problem unless the feed run is long).

There are a couple methods for doing load estimates in the NEC.

Ask to see at least one of them on paper.

For habitable rooms that require receptacles every 12 feet, put them in every 6 feet.

Not using extension cords on every lamp you need to plug in is nice (and safer).

That is lots of good information. Thank you all.

I will use the calculator and report back, right not aI am away on a business trip.

Thanks again!!

AJ

Hi All,

regarding load discount factor:

Loads are not just summed up to compute the service size needed. There are discounts and multipliers, such as:

Lighting load beyond 3000VA is discounted to 35%.
Water heater rating has a multiplier of 125%.

Appliance (not including dryer, water heater etc.) load beyond 4 is discounted to 75%.

In short, it is best left to the professional but make sure that he is taking everything into account AND doing the calculation.

Mine arrived at 200 amp because 99% of the people get 200 amp service AND the fact that materials for 300 amp service add another $1k or more to the cost.

If your new 200A service is almost maxed out with the geothermal loads and normal house loads, I would strongly advise to upsize the service now, while it's still relatively cost effective. If you wait and need it later, the $1k in materials plus the cost of labor will look like a bargain. Appliances are not accounted for in a load calc unless they are fixed in place- dishwashers, garbage disposal, etc. The online calculator linked to in this thread doesn't look like it takes the largest motor load into consideration, which would be a major oversight. Leave the calculations to professional electricians. Guess what happens when the service is undersized? It doesn't work correctly (trips), gets ripped out, and redone, all at significant expense. Don't get a 200A service because that's what 99% of other services are; have several load calcs done by qualified electricians, decide how much room you want for future expansion, and go from there. FYI- there's a standard and an optional calc for dwellings. Cheers, Mike

At this stage the labor is pretty much the same for 200 vs. 300 vs. 400 service.

The cost of the material will add up, but like mm11 says - it's cheap now and big $$$, hassle and mess if you need it later.

Also, people don't really have a grasp on how much power electronics can use. A good home theater can can draw 2000-3000 watts and 25 + amps while running. Have a workshop ? Saws, Air compressors and dust collectors, welders can draw huge loads at startup and consume breaker slots fast. Most kitchens can consume 20 breaker slots by themselves.

Sure you could split the 200 into a couple of sub panels, but why not get the xtra juice too ?

Thanks for your suggestions.

I agree with you that extra cost at this stage could prove to be money well spent. I do have a table saw and I hook up a shop vac to it when I use the saw.

Thanks again.

aj

I have a 20 KW furnace on 2 60 amps, a tankless on 3 40amps, both were running and tripped the mains, 200 amamp, if you are running a all electric house 200 will not be enough in the winter time.

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?

He probably isn't around to answer (this thread started in 2013). Probably not too much difference in price. We put in 400A which turns out to be somewhat silly as we never get anywhere near that kind of load even with almost everything (with the exception of the tankless hot water) being electric.

That's funny, Ron - I tend to look at the date of the last response, not the original posting. My mistake.

It's interesting to read these 200 vs 400 amp service discussions. I've only lived one place that had 200 amp service (it originally had electric heat). Every other place has had 100 amp service.

I've also never had a main breaker trip.

A friend of mine owns an old house in France, and just had it rewired. She has electric heat and water heating. The electrician said he was giving her plenty of extra capacity for future expansion. The main breaker is 60 amps. How many years has it been since builders put 60 amp service in US houses? I don't think since the 1960s or 1970s, but I might be wrong.

In France and Spain,, possibly in other EU countries but those are the ones I know about, older houses typically have 30 amp or even 20 amp service. That's partly because the utilities level a higher "standing charge" (base rate) for a larger service. People just manage their loads.

If the main trips, it's no big deal; the panel is usually close at hand, in the kitchen or laundry room. A typical one is about 14" x 6" (estimate, I haven't measured) and has maybe 12-14 breakers.

It's something to think about. It certainly makes me realize how much more energy we use here than people do in other countries.

A load that wasn't much considered in 2013 but should probably figure into planning for new installations is a car charger. They can require 60-100 amps each, if you need two that can be a considerable impact.

European electric is 220/240volt the US is 120/240. all electric and electronics run higher voltage and less amperage. you cannot compare the two. that is why (with a few exceptions) you cannot use electronics from the two, interchangeably with out a converter. just an fyi…. that is also why they have different plugs on electronics. it keeps you from plugging in your american stuff and frying it.(hopefully) lol

When will you ever have every single thing running in your home all at the same time probably highly unlikely

Does a 300A meter ok for a facility with a total load of 283A considering starting currents of central ACs