Attention elecritians! Home electrical system question...

I work for an insurance company and when I ask potential policy-holders information about their electrical system, I get a variety of answers.

Both questions are about amps: How many amps does the electrical system use? I’ve heard of 60, 100, and 200. Are there typically more that can exist in a house (ie 75, 120, etc.)? I’ve been getting people telling me it is 220, but isn’t that voltage?

Also, if a home uses circuit breakers, does that automatically mean the electrical system is at least 100 amps?


You are likely to get a variety of answers, some will confuse voltage with current, some will use power ratings.

Service suppliers will stipulate in their supply contract to the homeowner what they deliver, I would imagine that this contract would be a very good place to look for this kind of information.

The homeowner may not know where to look in the contract to find the relevant information, but a couple of phone calls by them will soon find the answer.

Stop asking them these questions. They don’t know the answers. That’s why you’re getting such a variety of responses.

The voltage to your house is, for practical purposes, constant - around 220 V in the U.S… (It is then split in half in your breaker box to get 110 per common outlet, but you have 220 for things like the oven.)

The current – measured in amps – is a variable depending on how many appliances are actually running.

To find out how many amps you use on average do the following.

Your electrical bill should state how much energy you consumed in kilowatt-hours. Divide this by the number of hours in the period covered. If it was February, for instance, this would be 28 x 24 = 672 hours. This gives you the power you used on average in kilowatts.

Take the resulting number and divide by 220 volts. This gives you the average current going through your house in kiloamps. It should be a very small fraction. Multiply by 1000 to get it in amps.

I could almost agree with Zenbeam’s sentiments. As a homeowner and former Navy technician, I couldn’t begin to tell you how many amps my electrical system has. I could go out to the circuit breaker box and add them up, I guess. Standard house voltage should be 120 volts. The electric dryer uses 220V, and so does the electric stove. Other than that, I wouldn’t have a clue.

That’s why I come here, tgwaty, to learn something new everyday. (So pardon my previous dumb post, House)

I agree with your calculation, but did you hear about the statistician who drowned in a river with an average depth of three feet?

Of greater interest would be the maximum amps used (see OP), which you can get from usage on a bill.

. . . which you can NOT get from usage on a bill. Sorry.

Check the rating on MAIN circuit breaker----this should tell you the max capability built in to your system.

Add up all of the branch circuit breaker ratings to be sure their total value is ls LESs than the main breaker rating.

All of the branch breakers are 120 volt,nominal.

For 220 volts they are “ganged” up to conrol both legs of the 220 .

Incidentally----you should ‘exersize’ All of you breakers a couple of times each year or they will lock in on a value higher than their rating.That’s usually what they mean when they say"faulty circuit breaker" was the cause---------

Your home system can be served by a 50 -100-200-Or 400 amp service-----it all depends on what the architect decided your ultimate max load would be.

That was dependent upon how many appliances you were going to use.

What does “exercize” the breakers mean? Switching them on and off?
What does “lock in on a value higher than their rating” mean?

Good idea…I quit!


Your insurance company wants to know the service rating of the home’s electric system. This is (usually) defined as the breaker/fuse box’s maximum current rating. As stated by Ezstrete this is always engraved on the main service breaker located in the breaker/fuse box. 100 amp and 200 amp service is common. “220” likely refers to the leg-to-leg service voltage, which is not relevant to your quest.

Actually, the voltage is “split” at the transformer’s secondary. 240 VAC w/ center tap (a total of three wires) is run to your house. The voltage between either leg and the center tap is 120 VAC. (The center tap is also connected to earth ground at your house.)

Adding up the breakers is not a valid way to determine max amperage rating. The total of them will almost always be higher than the rating (on the premise that not everything in the house is running at max capacity at any time.)

Look on the two main breakers at the (usually) top of the panel. They will be stamped with a number like, 100, 200. Don’t add them together. They will both have the same number. This is the number the ins. co. wants to know.

It does mean that you should flip them off and on a couple of times each year-----say at spring and fall.

If they stay in one position for too long the trip mechanism parts take a “set” from disuse---------and it is not uncommon to find that a 30 or 50 amp breaker will stay “on” even at 50% overload.

I suggest spring and fall because you can then make it a part of your DST clock re-setting routine.

Ezstrete: I agree it’s a good idea to periodically exercise the breakers, especially if your service box is located in the garage or basement. Once a year should be adequate IMO.

NutMagnet: You’re correct about adding up the breakers. We have 200 A service and probably 400 A of breakers. On the very slim chance we ever exceeding the service rating the main breaker will trip (at least we hope!)…

Amp usage is irrelevant. Amp ratings are typically 60, 100,150, 200 amps available to the user (but the main breaker can only be loaded 80%). The restriction being the size of the feeder coming into the house from the transformer and the size of the main breaker that feeds the service. 240 is the typical voltage present between phases.

A house with breakers does not mean that the house has at least 100 amps. There are breaker panels that are rated at 60 amps with a 60 amp main breaker.

Crafter_Man - the NEC does not specify a limit of the combined cumulative ratings of the circuit breakers in the panel. In your case you could have a 200 amp panel with 1000 amps of cumulative breaker ratings and not be in violation. The only thing the code specifies is a 42 circuit limit and an 80% load on the main breaker. So in effect you can only load the service up to 160 amps continuous (for your 200 amp panel). Some larger homes will have 2-200 amp panels for the service giving them a 320 amp combined total load capability.

Whuckfistle: We’re all in agreement about “adding up breakers.” NutMagnet originally said that it’s O.K. if the cumulative rating of all the breakers exceeds the service rating, and I was simply agreeing with him. Please re-read the previous posts.

When I was the Electrical Department Manager at Hechinger’s (RIP) --kinda like a Lowe’s, I gave a book to all my new employees that we sold there. It was used to teach new electricians the “basics”, and to paraphrase them to answer your question, and based on what we sold to the public:

Depending upon the age of the house, you ususally have 60amp, 100 amp, or 200 amp services. Look at the MAIN breaker, or on the label of the panel. Keep in mind older homes use CARTRIDGE FUSES, (they remind me of shotgun shells) rated for the size of service. Minimum in new home is 100 amps, but 200 amp service is very common in new homes. We used to sell 125 and 150 amp service panels, but by far 100 and 200 amp panels were the biggest sellers. There is a good chance if the house was built before 1960 that there is a 60 amp service, and if it was built before 1940 (and never upgraded), it may only have a two-wire service (120 volts vs 120/240 volts).

If you are interested in the book, its “Wiring Simplified”, by H. P. Richter and W. C. Schwan by Park Publishing, Inc. of Minneapolis. The edition I have cost $5.50 ten years ago. And it is updated every three years, based on the current electrical code.

It is a handy book to have since it limits itself to residential wiring.

The point of my answer is that you can’t expect people to give you accurate answers to this question. Most people just don’t have that good of an understanding of electricity. 220 is almost certainly the voltage, but 120 might be also. 60 might be the value you want, or it might be the frequency the person is remembering. 60, 75, and 100 might be the wattage of the last light bulb the person remembers changing.

Presumably, your customers aren’t intentionally lying to you, but how can you legitimately have any expectation that any answer you receive is correct? If I may ask, what is the consequence of them telling you the wrong number? Does it affect their premium? Suppose the person who said they had a 220 amp service really has a 100 amp or 150 amp service, and their house burns down due to an electrical fire. Is their coverage void? There must be some consequence, or else why even ask the question.

I’ll get off my soapbox now…