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Old 06-20-2011, 02:33 PM   #1
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100 Amp Service, is it enough?


I have a question on figuring out how many appliances you can run on a 100 amp service.

I have an electric water heater, a newly installed washer and electric dryer, a fridge, microwave and toaster oven, coffee brewer and 2 5000 BTU air conditioners running on a 100 amp service.

From what I have read, this is ok. Some sites suggest that if you had an electric range and central air, that you would want to move up to a 200 amp service, but that often 200 amps is overkill.

A water heater though, uses a 30 amp breaker. It has two 5600 watt heating elements in it, which is 11,200 watts. At 220 volts, this is 50 amps! And yet the unit only has a 30 amp breaker, does only 1 heating element work at a time? Even if this is true, this means the water heater uses 25 amps. The electric dryer uses a 30 amp breaker. An electric washer apparently uses about 15 amps. This is 70 amps, without the toaster, microwave, coffee brewer, refrigerator or the air conditioners. NOt to mention a tv, computer etc etc.

And yet I have had an electrician tell me this is fine, have read online that this amount of load is fine, and my fathers house has similar appliances PLUS more/larger air conditioners and a dish washer, and he has no problems.

How can I be sure my service is enough? I also had an electrician tell me that 'each bus bar has 100 amps', and read it on another electrician forum I found, but that seems impossible. There is a 100 amp breaker on the main service, I dont see how you can put 100 amps of draw on each bus bar/side of the breaker box.

Anyway, i am trying to understand this, as it seems MANY people do not, and I know lots of people like to give out advice with no idea of what they are talking about (I have an uncle who does electrical work who told me "220 volt appliances are better because they are so cheap to run - they use half the amps, so they cost half as much to run!"

Any help is appreciated.

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Old 06-20-2011, 02:47 PM   #2
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100 Amp Service, is it enough?


What is your question? Are you thinking about upgrading?

There are several 'calculators' that can be found online for calculating your load requirements. Or you could turn everything on, fire up the toaster and microwave and see what happens - JUST KIDDING.

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Old 06-20-2011, 03:37 PM   #3
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100 Amp Service, is it enough?


I also wonder what your question is.

From the sound of it you are fine.
The water heater does only use one element at a time, NEVER both. This is also only for a few minutes at a time. MOST things in a home that are high draw are only on full blast for a few minutes at a time.

Your service is 100A, 120/240V. This is 100A on EACH 120v leg, or 100A @ 240v. OR 24,000 watts of power. It is not accurate to call it 200A @ 120v, but some like to refer to it that way as an alternative.
All your calculations are quite skewed since you never mention voltage.

The water heater is 5600W, or 23A@240V.
A washer is around 12A@120v, or around 1400W.
A 5000btu AC is around 5A@120v, or around 600W.

Get the pattern?
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Old 06-20-2011, 03:41 PM   #4
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100 Amp Service, is it enough?


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Originally Posted by ShaneM View Post
How can I be sure my service is enough?
You do know that if you draw too much the main breaker will open and nothing else "bad" will happen?

If that happens, then you know you either need to move a 120v load to the other leg, use less power at the same time or upgrade.
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Old 06-21-2011, 08:07 PM   #5
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100 Amp Service, is it enough?


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Originally Posted by Leah Frances View Post
...Or you could turn everything on, fire up the toaster and microwave and see what happens - JUST KIDDING.
You get toasted popcorn
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Old 06-22-2011, 02:32 AM   #6
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100 Amp Service, is it enough?


I think you're okay dude, I have electric everything (except HVAC) I have dryer, range, 2 wall A/C, 2 garages, and it used to have the water heater on there too, but not at the moment, but all of these work fine for me no issues on 100A.
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Old 06-23-2011, 11:06 AM   #7
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100 Amp Service, is it enough?


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Originally Posted by Speedy Petey View Post
I also wonder what your question is.

From the sound of it you are fine.
The water heater does only use one element at a time, NEVER both. This is also only for a few minutes at a time. MOST things in a home that are high draw are only on full blast for a few minutes at a time.

Your service is 100A, 120/240V. This is 100A on EACH 120v leg, or 100A @ 240v. OR 24,000 watts of power. It is not accurate to call it 200A @ 120v, but some like to refer to it that way as an alternative.
All your calculations are quite skewed since you never mention voltage.

The water heater is 5600W, or 23A@240V.
A washer is around 12A@120v, or around 1400W.
A 5000btu AC is around 5A@120v, or around 600W.

Get the pattern?
Sorry for not replying earlier.

I guess I couldnt see how each leg has 100 amps, when there is only (1) 100 amp breaker for the entire box. To me it would be like saying 'well this pipe can only push 100 gallons per minute. If you try to pull more than that, this emergency switch will shut off. But then you can go ahead and hook up faucets that will pull more than 100 gallons per minute in your home, and it will be fine. And the main breaker clearly says that it shuts off if you go over 100 gallons per minute.' See what I mean? This is where electricity confuses me.

You have basically answered my question though, the service is 100 amps at 220 volts or 24000 watts (or is this what va means? 'volt amps' is basically 'watts'?)

I was adding up amps thinking I had to total less than 100, but I really needed to work with volt amps or watts, and remember that a 10 amp microwave doesn't use 1/3 of the power of a 30 amp 220v dryer, it uses about 1/6th of the power.

Thanks for the replies, it appears I am fine with my power use. And yes I did realize that if I went over, it would just trip the main breaker, I was trying to understand how much draw was being put on the service so I knew if I was really close to max, or if I had room for expansion, etc.

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