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Discussion Forum

How big is my electrical service?

renosteinke | Posted in General Discussion on July 22, 2006 04:40am

I just had a man tell me that he’s seen many houses with 1200 amp services. He continued to say they had “six 200 amp Panels”. I think a little explanation of service size is called for.

“Service size” is the amount of electricity the power company plans to deliver to the house. All houses have only ONE service.

The “service” is where the lines from the Power Company arrive at the house, and meet the meter and main disconnect. Ultimately, the maximum amount of electricity that can be delivered is limited by the size of the wire the power company uses, and how close you are to the transformer. It is highly unusual for a home to have more than a “400 amp” service (and those are really “320 amp” services!)

The size of the main breaker- the one that will kill everything in the house- is your “service size.”

Now, that first panel might feed an infinite number of other panels, of whatever size…. but that has nothing to do with your service size.

In a similar manner, the “size” of a panel is determined by the largest breaker that is allowed to provide it with power. The “size” has nothing to do with the number of breakers, or the sizes of those breakers.

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Replies

  1. User avater
    dieselpig | Jul 22, 2006 04:43am | #1

    I'm thinking you shoulda had this conversation with the azz-clown that was at your house earlier, no?

    View Image
    1. renosteinke | Jul 22, 2006 06:55pm | #11

      My reason for starting this thread is that the man's error has been repeated by many others. It's one of the most common errors I find in "Home Inspection" reports. I thought an explanation was in order. In a chat board, your posts will be read by thousands of folks; I try to make my answers a bit braod, so as to apply to the wider audience. Sometimes, this means explaining things that the original poster already knows- but maybe not everyone else!

      1. User avater
        dieselpig | Jul 22, 2006 07:58pm | #16

        I was just being a wise-guy... I think it's a great topic and thread.View Image

  2. User avater
    maddog3 | Jul 22, 2006 04:49am | #2

    show-off...:)

    .

    .

    .

    .Wer ist jetzt der Idiot

    ?

  3. User avater
    BillHartmann | Jul 22, 2006 04:54am | #3

    " The size of the main breaker- the one that will kill everything in the house- is your "service size."

    Now, that first panel might feed an infinite number of other panels, of whatever size.... but that has nothing to do with your service size"

    One clarification.

    If you have a 320/400 amp service then you often have two main breakers and the need to look at the total.

    1. renosteinke | Jul 22, 2006 06:44pm | #9

      Bill, while it is certainly possible for there to be several panels fed direct from the meter without a "master" disconnect.... code allows for as many as six.... all that does is make it a bit more confusing in guessing the service size. First of all, even if these were seperately metered services, the actual service size would be based upon some calculations that would have the efect of reducing the necessary service size. For example, I recently dealt with a place that had four 100 amp apartments; the total load calculations resulted in their needing a 200 amp service- and not the 400 amp you might have guessed. When someone has been "creative," then the 'final' answer will depend upon the size of the wires from the PoCo.

      1. User avater
        BillHartmann | Jul 22, 2006 07:03pm | #14

        The use of a 320 amp meter feeding two "main" panels is very common here. And without a master disconnect. As you said the NEC allows up to 6 grouped together.From what I have read of different installations POCO rules and local code modifications/practices for service installations vary a lot around the country.One example is that many locals require an outside disconnect. The NEC does not if the run into the house is "short".

  4. User avater
    BillHartmann | Jul 22, 2006 07:29am | #4

    " The size of the main breaker- the one that will kill everything in the house- is your "service size.""

    One other correction. That is IF it was all wired correctly.

    A friend of mine bought an older house where the panel and meter had been updated. A 100 amp panel, and I think a 200 amp meter.

    But the SE cable was still 80 amps.

    1. User avater
      Matt | Jul 22, 2006 06:02pm | #5

      OK, I'll play :-)

      Not an electrical guru here....

      On my house I have a meter base with a panel to either side.  See pic 001.  Meter base is not accessible as it has the power'company's 'lock' on it.  Each side panel has a 200A breaker in it.  

      Right side panel side panel has the breakers in if for the "heavy" loads like AC, range, dryer - whatever. See pic 002. 

      Left side panel (see pic 003) simply feeds a sub-panel in the garage that has all the smaller loads like lights, etc.  See pic 004.

      BTW - those little green lights are for the surge suppressors.  House was built in 99.

      So, what size service do I have?  I'd guess I have two 200 amp?   400A?

      1. User avater
        BillHartmann | Jul 22, 2006 06:28pm | #6

        What is the labeling on the meter?A 200 amp meter has cl-200 on it (along with a buch of other stuff). I think that it stands for Class - 200 amps.I bet yours had cl-320 or cl-400 on it.You have a 320/400 amp service.BTW, I don't know enough about than to know why sometime they are called 320 amp and sometimes 400 or if that is too slightly different variations.I know that 320 would be the continous rating (80%) of 400 amps. But you don't see the same kind of references to 100, 150, or 200 amp services.And btw we I live it appears that all of the meters have been upgraded to 200 amp no matter what size the SE cable or panel is.I suspect that was done about 20 years ago when the city went to a pressurized grinder pump sewer system. And each house the power for the pumps are tapped direct off the meter.

        1. renosteinke | Jul 22, 2006 06:51pm | #10

          The reason for the "320" and "400" amp distinction is because you're pushing the limits of the equipment. Up to 320 amps (calculated load), the power company is comfortable with direct metering...passing all the juice through the meter. Beyond that point, they use a different method to measure the amount of power used. One real important thing to realise is that, when the power does not all flow through the meter, simply removing the meter will NOT disconnect the power! This is yet another reason that the PoCo resists installing services larger than "400 amp" in residences. For these larger services, you might- but not always- see a very large disconnect switch.

          1. User avater
            BillHartmann | Jul 22, 2006 06:58pm | #13

            "Up to 320 amps (calculated load), the power company is comfortable with direct metering...passing all the juice through the meter. Beyond that point, they use a different method to measure the amount of power used."I assume that you are talking about current transformers feeding a meter.

        2. User avater
          Matt | Jul 22, 2006 06:57pm | #12

          The meter is a CL200.  The power company installed a new digital meter about 4 months ago....  I wonder if they could have installed the wrong meter?  Probably not.

      2. renosteinke | Jul 22, 2006 06:36pm | #7

        That is a rather unique arrangement. In this instance, I'd have to see the service wires for a definite answer. The "normal" way things are done is to have a single disconnect to a panel, which in turn feeds all other panels. You might have this- but if so, it looks like the feeders from the "main" panel to the next panel would pass again through the meter box- a definite "no-no." My best be is that this was intended as a 200 amp service.

        1. User avater
          Sphere | Jul 22, 2006 06:44pm | #8

          Last horse farm we roofed had 4 200amp boxes. Feed a barn, pool, and geo thermal heat back up...thats a lot of juice.

          Spheramid Enterprises Architectural Woodworks

          " I am not an Activist, I am, a Catalyst. I lay around and do nothing, until another ingredient is added"

        2. User avater
          Matt | Jul 22, 2006 07:06pm | #15

          This is not any kind of after the fact install.  I built the house, and this is the way it was installed on day one.  The electrician/electrical company is very repuatable.  I've used them on other jobs as well.  The install was inspected by the county electrical inspector.  There is not a single disconnect.  The service wires are in conduit above ground.  Sorry, I'm not digging up the service wires.

          Next time I have the power company out to my job site I'll ask 'em.  Maybe I'll run it by my current electrician too...  I've got a meeting with "the main guy" next week for some bids.

        3. FrankDuVal | Jul 23, 2006 07:31am | #23

          The service shown in Matt's photos is not a unique arrangement here in Virginia and southern Maryland.In Virginia I install a 320 amp meterbase feeding two 200 amp service entrance panels (therefore two main breakers) in most homes over 3500 sq ft due to heat pumps with backup resistance heat.In southern Maryland the co-op only allows a 320 amp meterbase to feed one 200 amp panel and a 150 amp panel. Again two main breakers. I know they are limiting the ammount of power they need to provide, but a 200 amp panel is only a few dollars more than a 150 amp panel, so the homeowner is paying the same price whether I install two 200 amp panels or a 200 and a 150 amp panel.Frank DuVal You can never make something foolproof because fools are so ingenious.

          1. User avater
            BillHartmann | Jul 23, 2006 07:40am | #24

            FrankIs there a different 400 amp meter base?Why references to both 320 and 400?

          2. renosteinke | Jul 23, 2006 05:54pm | #25

            "320" refers to the maximum continuous load the meter is designed to handle. For short periods, these meters can handle up to 400 amps. For greater usages, a different method is used to measure the power, without actually having all those amps go through the meter. While the meter will look the same from the outside, inside the box things are quite different. The details are relevant only to the power company- with one exception: Services |400 amp" and larger may not be disconnected if you remove the meter! Otherwise, several folks keep returning to "I have a 200 amp panel...." I'm sure that you do. The breaker might even say "200 amp." But that is no indication of the size of the service! Nor will you "increase your service" simply by installing a "larger" panel. The size of the main disconnect is usually a pretty good indicator of the service size; but, again, there is nothing to prevent a 200 amp disconnect being used on a 60 amp service. The surest way to determine your "service size" is to see the size of the wires coming from the power company. Another way to guess, or to see if your service is adequate, is to have someone do a load calculation on the property. If calculations suggest that you need, say, 130 amps, and your service is 100 amps... then you might want an upgrade.
            Conversely, if the calculations say 130 amps, and there is a 200 amp panel.... don't be surprised if the PoCo wires are too small to actually deliver 200 amps. Such a situation may not be "correct," but it's far from unique. Incidentally, "load calculations" consider many things- but the number of panels, size of breakers, etc., are completely irrelevant. Consider this: the calculations are typically performed long before the first shovel of dirt is turned... let alone before the electrical is installed!

          3. User avater
            BillHartmann | Jul 23, 2006 06:37pm | #26

            " The surest way to determine your "service size" is to see the size of the wires coming from the power company."No, it is really the weakest link. And that may not be the service drop.Here, the HO owns the weather head and everything below it except the meter. While certain not universal I believe that is common in many areas.As I mentioned my friends house had 80 SE cable feeding a 100 amp panel through a 200 amp meter.The tri-plex was relatively new due to an ice storm a couple of years earlier. It was at least 150 if not 200 amp drop.Saw another house that had 100 amp single cable (no triplex, never seen that type before) feeded a 100 se cable to a 100 amp panel.But the meter said 15 amps. Don't know what it was really rated for, but when the POCO sent someout to check the seal they automatically replaced it. I ask POCO man did not know what the meter was actual rated for, but we both thought that it must have been much more than 15 amps.

          4. DonNH | Jul 23, 2006 07:18pm | #27

            >The surest way to determine your "service size" is to see the size of the wires coming from the power company.

            So is there any protection for these wires if the house tries to pull too much?  Is the meter fused, or will the cable from the pole start smokin'? 

            In the case of the guy with a meter & panel rated for 200A, but a service entrance cable only rated for 80, seems like he'd want to keep combustibles away from the lines.

            Don

          5. renosteinke | Jul 23, 2006 11:56pm | #28

            You are quite right; you can quite easily overload the PoCo wires to the point that they smoke. Indeed, I have responded three times to situations where there was a direct, line-to-line short in the PoCo wires; in each case, the fireworks continued until the PoCo arrived, and disconnected things at the pole. The power available from the PoCo is limited only by the "impedance" of the run... that is, the resistance in the transformer, and the wires themselves. This is but one of the reasons that "service upgrades" require permits, and the involvement of the power company. It is their duty to provide you with the power that you need; you must do your part to let them know what your 'needs' are! This thread was started, in part, because someone stated that they had six "200 amp" panels, so therefore, they had 1200 amps of service. Now, some of us may quibble as to the difference between a 100 amp and a 125 amp service.... but the fact remains that most folks have little idea as to their true service size. I would expect a "200 amp" service to be fed by 2/0 wires. Smaller than that, and what you have is a 200 amp panel on smaller service. For that gentleman's "1200 amp service," I'd expect to see wires as thick as my arms; there's just no way to get 1200 amps through anything smaller (at least without them glowing like a big toaster!). While you may own the mast and meter base, the actual "service point" (the place where the rules change) is at the meter, or the main disconnect. Everything 'downstream' from there is irrelevant to 'service size.' As you've all probably realized by now, there's a lot more to a "service change" than swapping out a panel. Keep that in mind is the local gypsy handyman approaches you with his $300 'service change special." And expect it to take a lot longer than an afternoon!

          6. alfie | Jul 24, 2006 03:00am | #29

            Very useful thread, thanks for starting it. I hope others will also create threads that clarify fundamentals of something they know well. Some of that already happens, looking forward to more.

  5. User avater
    basswood | Jul 22, 2006 10:17pm | #17

    I have a commercial service with 6 meter sockets on my house rated for 2400 amps total. I will never get close to needing even half of that total. I could use all the sockets though.

    I should explain that my house is a 3000 s.f. 1850's vintage Inn with a 2000 s.f. Big Band era dance hall attached. I wanted plenty of options for my little compound. I created a MIL apartment in the back of the house that I am renting out (but may need for my MIL who is fighting cancer). The apartment has its' own meter.

    My well, commercial size water softener and septic with lift pump are shared by three households and I wanted to be able to meter the common power consumption separately (though I have not yet).

    When I finish renovating the dance hall into a workshop, it will get its' own meter and 200 amp panel so I can easily write off the shop power use.

    Also, my place is on 2 acres and I have approval to build a guesthouse/rental duplex on the property (adjacent to a city park and State land with a trout stream).

    My electrician found a deal on the meter six pack and I found a well hidden location (under the MIL apartment stairs)...so I said, Why not?

    1. renosteinke | Jul 23, 2006 12:55am | #18

      Large as your place is, a quick "load calculation" suggests that a 200 amp service would be plenty large enough; chances are the PoCo wires are size 2/0 or smaller.

      1. User avater
        basswood | Jul 23, 2006 03:49am | #19

        I think each meter in the six-pack is considered a separate service rated for up to 400 amps each.My house uses just a 100 amp main (though the service can handle 400 amps). As I said I don't ever see using anything close to the amp ratings...I just wanted the ability to meter different facilities separately.

  6. User avater
    BruceT999 | Jul 23, 2006 06:50am | #20

    Since you brought up service size, maybe you will be willing to answer related question for me.

    I recently did work at a pet hospital and staff members told me that whenever they ran the washing machine and gas dryer at the same time as the x-ray film processor machine(I think there may be other things on that circuit as well), the breaker trips.

    I thought I might run a new dedicated circuit for the x-ray developer, but when I looked at the panel (Bulldog Pushmatic box), I found a 100A 220 breaker labeled x-ray, a 70A 220 labeled AC, one 15A and 11 20A breakers. Meter panel has a 100A fuse block (type you pull out and rotate to shut off power), so I assume they must have just 100 amp service, yet the breakers add up to 405A.

    I know that electricians size breakers for more than expected load, but 400%? Is this within acceptable standards? I guess the actual load is not too high for the service size, given that the fuse on the meter panel is not blowing.

    BruceT

    1. User avater
      BillHartmann | Jul 23, 2006 07:18am | #22

      You are proving his point.The needed size of electrical service has nothing to do with the total number and size of breakers in the panel.I have not been through the calculation for comercial, but here is a link for doing the calculations for residential.http://www.taunton.com/finehomebuilding/pages/bh0019.aspWhat you have to realize that for fixed appliances you need to look at the ACUTAL NAMEPLATE LOAD DATE. For example that AC might be on the order of 30-40 amps.And for the convience outlets I the load is either based on the number of receptacles or the sq ft. Lets look at the a office room with 6 receptacles in it. You might have all the receptacles in that office and another one in a 2nd office. Or you could run a separate 20 amp circuit to each of the 12 recpetacles. And if you did that theroretically you could draw that much more current.But in actuality you still only have a computer, fax machine, radio, and desk like in each office.

  7. User avater
    BruceT999 | Jul 23, 2006 06:52am | #21

    Thanks for starting this thread.

    BruceT

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