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Thread: Electric Service Rating vs Reality

  1. #1
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    Electric Service Rating vs Reality

    At one time some houses had only 15 amp electric service This has been increased over the decades to the point where 200 amps is common. That's 240 volts x 200 amps which is in the neighborhood of 48kw. (someone will please inform us about the power factor an whatever other mistakes I have made to this point)

    When I estimated the loads that my generator would need to support it came to 11kw The 16 kw unit we installed has been fine

    I think the biggest load a normal house will put on a system is if it has electric resistance heating That might be around 20 kw (presumably A/C will not run at the same time)

    An ordinary one man workshop might draw up to 4 kw though it could go higher

    Motor starting loads may double some individual loads briefly but these would be a small percentage of the total

    Adding up my house plus electric resistance heat plus electric stove and water heater and a substantial shop load

    11 + 20 + 8 + 4 = 43 kw if it all runs at the same time, 200 amp service (48 kw) is more than adequate but 100 amp (24 kw) would be borderline

    or without the electric heat it would be 23 kw, 100 amp service (24 kw) would be good and 60 amps (12 kw) would be borderline

    So here's my question; Who has had main circuit trips and under what circumstances?

  2. #2
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    The only time my main circuit has "tripped "is when I shut it off to install something in my panel.

  3. #3
    I'm not sure what your point is. I expect the reason for 200 amp service is to make sure that very few people have to upgrade their service - which would be expensive for both the power company and the customer.

    Additionally, the power company cannot predict the future and wants to make sure that if power demands continue to grow - as they have in the past - that they won't have to upgrade their local grid and the connection to your home.

    I've seen posting here on the forum where people who had 100 amp service were upgrading to 200 amp service but I don't remember why. Maybe they purchased an electric vehicle. Many electric vehicles require a 50 amp circuit.

    Obviously, you would not want your main circuit breaker to trip from excessive current. If it did, it would indicate that your service is not sufficient, or you have some major wiring fault.

    Mike
    Go into the world and do well. But more importantly, go into the world and do good.

  4. #4
    Add a pottery kiln or welder (or both), either of which can require a 50-amp circuit. Further, pottery kilns typically run continuously for hours on end when they are fired.... (so even though on a 50-amp breaker, the wiring has to be uprated as if for a 65-amp circuit - something like that).

    In answer to the OP's question, no, I can't recall the main breaker ever tripping... IIRC, we have a 150-amp service (odd, I know)

  5. #5
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    I have never had my main breaker trip. I bet it very rarely happens today, unless a fire or flood (of/in the main panel) occurs. Individual breakers will usually trip first, shedding load, and preventing the main breaker trip. This is by design and by code.

    How long ago are you going back when homes had just 15 amp main service? The smallest I've ever seen was 50 amp service (fuse box), but I'm not an electrician.

    Andy - Arlington TX

  6. #6
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    Quote Originally Posted by Timothy Thorpe Allen View Post
    Add a pottery kiln or welder (or both), either of which can require a 50-amp circuit. Further, pottery kilns typically run continuously for hours on end when they are fired.... (so even though on a 50-amp breaker, the wiring has to be uprated as if for a 65-amp circuit - something like that).

    In answer to the OP's question, no, I can't recall the main breaker ever tripping... IIRC, we have a 150-amp service (odd, I know)
    A 50 amp pottery kiln does not draw 50 amps continuously once it is up to temperature. If it did, it would take forever to get up to temperature.

    Electric services are also often upgraded if the original service did not provide for Air Conditioning, and the house used gas heat.

    Andy - Arlington TX

  7. #7
    As Mike said, it's future proofing that costs much less at install. Just a few years ago, few people would have anticipated a situation where someone had 2 electric cars charging in their garage drawing 60A, each, for hours, continuously. That plus some A/C and you're suddenly drawing a LOT of amps.

  8. #8
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    I have 100amp service, and i have tripped the main breaker. I think the breaker was old and lost its full load rating. I tripped it twice, replaced the main breaker, and no longer have an issue. If I planned on staying in this house for years to come, i would upgrade to 200 in a flash.

  9. #9
    Quote Originally Posted by Mike Kees View Post
    The only time my main circuit has "tripped "is when I shut it off to install something in my panel.
    This is the only reason my main breaker has ever been used, even when I had baseboard electric heat in every room of my house.

    You would get some pretty good amps if you are running the washer, dryer, dishwasher, oven, cook top, water heater, well pump and electric heat at one time. I've seen that many loads in my house. Not to mention tv and lights.
    Last edited by Lee Schierer; 02-10-2020 at 1:52 PM.
    Lee Schierer
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  10. #10
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    Quote Originally Posted by Andy D Jones View Post
    ...How long ago are you going back when homes had just 15 amp main service? The smallest I've ever seen was 50 amp service (fuse box), but I'm not an electrician.
    50 years ago I had a house with a 60 amp fuse box. All the fuses were warm to the touch. I taught myself electrical wiring and installed a 200 amp service, rewired much of the house, and fed my first small shop with an underground cable. I learned then to love underground wiring.

    I'm not an electrician either (except in Mexico) but I've done all our wiring since, upgrading a 100 amp service to 200 amps in the second house we bought as well and rewired 1/2 the house.

    This (and our final!) house came with a 200 amp service fed from the meter next to a 7200 volt transformer on a concrete pad in the woods near the house. When I built the shop I rewired at the meter to keep 200 amps to the house and provide 100 amps to the shop. (I have four things in the shop that want 50 amp receptacles, never .)
    There are four other sub panels fed from various places to elsewhere on the farm. (Every bit of the power is underground starting at the pole at the street. There are wires and pipes everywhere!)

    I think it's far better and not much more initial cost to have more capacity than needed.

    And also, never had a main breaker trip. And I'm happy about that.

    JKJ

  11. #11
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    I never had the main breaker trip in my current house with 200 amp service. I have never had the 100amp shop sub-panel circuit break trip either. Like others stated, if your main is tripping, your electric has some major problem. Heck, even when lightening hit between my house and my neighbor's house, individual breakers went and so did gfci's that were affected by the zap.

    Also if any break trips too many times, it does weaken the breaker and once you fix the reason for the breaker being tripped, you should also replace the breaker.

    Electric kills - if you are not sure, hire a licensed electrician to fix the issue.

  12. #12
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    My understanding of it is that they must assume that everything in your house is going to start up all at once. All ovens and electric stove burners, all motors and compressors. Then they add in a safety factor. They they go up to a handy round number. When we built our little in-law quarters, we were fortunate that the main house already had a 400A service. They added a 125A breaker and gave us that which was overkill. But then I put a 70A breaker in our box and wired up a subpanel for my shop. Now the 125 doesn't look so crazy.

    In my shop about the most power I would draw would be the 3hp table saw and a 1.5HP dust collector + about 700watts of lights. I seldom run more than one thing at a time since it's just me.

  13. #13
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    One of our wood netters was considering upgrading his service so I thought it would be good to get a reality check.

    Roger
    If 'they' required a service equal to the greatest conceivable connected load very few would pass. A healthy diversity factor is applied. So it is possible to trip the main breaker under unusual circumstances (everything starts up at once).

    When the power goes out some loads do not start up instantly. An electric clothes drier and some motors in your shop must be restarted, a gas furnace will have to heat up before the blower comes on, not everything else will be on. Still it's a good idea to switch off some things to reduce the startup current when it does come back on.

  14. #14
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    Depends on your friend's ultimate plans too. Im a unique situation in that i have a very small home service(100amps), and ive tripped a main breaker. It was a faulty breaker, but still. More so than the faulty breaker, ive passed on things and been limited because of my service. If I had 200-250 amps, i would have more than likley gone over to 100% 3 phase equipment off a converter. As it stands, im limited to to 5-5.5hp, which is on the low end for most bigger/better equipment. I wont tolerate another 100amp service if i continue in the craft and move.

  15. #15
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    We originally had 200 amp service and bumped that to 400 amp service when I put a full panel into my shop building back in 2005. The house and the shop are on the same meter but have separate feeds from the meter with separate main breakers. (this work was all done by a licensed electrician and code inspected) However, the power company refused to change the aerial feed wire from the transformer. They said it was adequate...despite it looking "small" to my eyes...for anything we would be able to throw at it. My generator is a 22Kw, only powers the house, and is more than adequate to run both HVAC systems and everything else we normally use. We've never sprung either the main breaker on the house or the main breaker for the shop.
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