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Thread: Old house, 100A fusebox, should we replace w. breakers?

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    Question Old house, 100A fusebox, should we replace w. breakers?

    Our house is about 60 years old, have 100A service, fuses.
    Its getting more difficult to purchase fuses, and we were thinking of changing to a new breaker box.
    We have 3 220v. appliances, stove, dryer, and water pump. And the rest is all 110v.
    We would have it done professionally, my husband used to do all our plumbing and elec work, but not any more at this age, and there are new rules and regs.

    Wondering if this is actually necessary, if the old fusebox is fine, and we have no plans to add to our house. Doesnt seem to be a safety issue, fuses blow when needed. Like when our cat chewed thru my router wire and shorted it out, the cat was OK. Blew the fuse but not the fur off the cat.
    Thank you.

  2. #2
    Electrical Contractor/Instructor jwelectric's Avatar
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    I am a firm believer in if it ain’t broke don’t fix it.

    Changing to Type “S” fuses might help the issue. Be sure to replace the fuse adaptor with the proper size according to the wire and this will help

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    Thank you, I think he has some screwed into the old sockets. Its the Knife/cartridge fuses that are hard to find now.
    The big ones that fit into the main fuse thingie are hard to find, and the fuse holder itself cracked one day when the power was whacky when a tree fell on the line and my husband yanked it out. He glued it together, but we could not find a replacement anywhere, Square D. was on the side of it.
    I did find one on ****, but they wanted $100 for it.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Fuses have both good and bad points...CB are certainly easier to restore power with than finding an appropriate fuse in the dark. Today's homes like electrical appliances, and 100A may not be adequate. If you ever broke down and added an a/c unit or two to the thing, then you'd likely have problems.
    Jim DeBruycker
    Important note - I'm not a pro
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    Moderator & Master Plumber hj's Avatar
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    I am not sure where you are buying fuses, but I have never had any problem locating either the screw in or cartridge fuses. They do make "circuit breaker" screw in fuses with a button you push when it trips.
    Licensed residential and commercial plumber

  6. #6

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    We do occasionally use an AC, but rarely do we need one with our constant seabreezes here in summer.
    We do use a dehumidifier most all summer in our cellar.
    Reason its difficult to find fuses, is we are a small town, but could easily get the cartridge fuses in Hyannis.

    Thank you all for this advice, perhaps this summer we will go ahead and upgrade everything. We did get one estimate for about $700 so far.

  7. #7
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by capecod12 View Post
    Thank you, I think he has some screwed into the old sockets. Its the Knife/cartridge fuses that are hard to find now.
    The big ones that fit into the main fuse thingie are hard to find,.
    Something else to bear in mind is that a non-time delay cartridge fuse will blow within 6 cycles or 1/60 of a second but an inverse time breaker can carry 6 times its rated current for up to two minutes. The fuse will blow when loaded to 100 amps in less than a second but a 100 amp breaker can let through 600 amps for as long as two minutes but in most cases when loaded to 600 amps will trip in a few seconds, (between 2 and 30 seconds)

    A non-time delay fuse is 6 times safer than a breaker. A type “S” or time delay fuse is 4 times safer than a breaker when it comes to the amount of time it takes to open them.

    It has been my experience over the past 44 plus years that those who had a service upgrade changing from fuses to breakers without addressing All the issues of the interior wiring of their homes have ended up having more problems in the long run.

    Please understand that I am not trying to talk you into or out of something that you desire to have done, I just want you to be aware of the facts. The price you quoted, if the service is being changed for the same size is about a third of my price. I have a hard time believing that the job can be properly done at that price but then again I have never done work in your area nor have I looked at the job. I will say this, it is about what I include in my bid for labor and expenses for a service change.

    Also be aware when you decide to hire someone to do this work one of the most important questions you must ask is about their liability insurance. Should something go wrong and they don’t have liability insurance you might be stuck with a larger bill than what was bid.

    Also for the sake of your homeowners insurance be sure that the job is permitted and inspected.

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    Excellent info! Thank you, I am soooooo glad I found this forum, we started with the plumbing one, as we were replacing a toilet and needed to research a good replacement.

    Your first paragraph is extremely interesting, I had read something about this years ago, and thats one reason that he stuck with fuses.

    My husband said that they used fuses on the ships for some reason, will have to ask him the reason for that(by the way, he is a retired marine engineer), and knows a lot about DC.
    I am learning so much here! From now on, before we do anything elec or plumbing, will run it by you all first.

    We will certainly have to think about this, perhaps we are better off leaving our fuse box the way it is, its always worked perfectly.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    I made a mistake in that paragraph. It should have said one tenth not one sixtieth

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    Jack of all trades DonL's Avatar
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    Quote Originally Posted by jwelectric View Post
    Something else to bear in mind is that a non-time delay cartridge fuse will blow within 6 cycles or 1/60 of a second but an inverse time breaker can carry 6 times its rated current for up to two minutes. The fuse will blow when loaded to 100 amps in less than a second but a 100 amp breaker can let through 600 amps for as long as two minutes but in most cases when loaded to 600 amps will trip in a few seconds, (between 2 and 30 seconds)
    How did You come up with these figures ?
    Theory only works perfect in a vacuum.

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    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by DonL View Post
    How did You come up with these figures ?
    It is a calculus math problem but there are many sites on the internet where this information can be found. I have a book by Cooper Bussmann at school that I use in the class for fuses. I also use the Square “D” trip curve booklet for breakers.

    Fuses and breakers are used to protect electric motors along with running overload protection that is either internal or separate of the motor. Motors in AC and heat pumps will have running overload that is internal the motor and auto reset while motors like garbage disposals will have manual reset overloads.

    Look at your AC or heat pump and find the minimum circuit ampacity. This is used to size the circuit conductors.
    Now find the maximum fuse or HACR overcurrent device. This is what we use to size the fuse or breaker with.

    The overcurrent protective device will always be larger than the circuit conductor ampacity. The reason is because for the compressor to start it must overcome locked rotor ampacity.

    Looking at Table 430.248 of the NEC we can see that the running ampacity for a single phase 5 horse power motor at 240 volts is 28 amps. Table 430.52 says that the inverse time breaker (breakers sold at the supply house, HD, Lowe’s ect) is to be sized at 250% or a 70 amp breaker. Why? Because the breaker must hold until the locked rotor ampacity is over come and the motor reaches full speed.

    Look at Table 430.251 and we will find that this motor will have a locked rotor ampacity that is six times that of the running ampacity or amperage of 168 amps. The breaker must hold this inrush current until the motor reaches full speed. Under load this can take several seconds.

    Using this same rule of thumb we can apply it to the breakers in our home. It will not work out to the exact number as the calculus math but will be real close.
    This same method is used in drivers education. Take the speed of your car and divide by 2 then add it back to the speed to see how many feet per second you are traveling. Example; At 60 miles per hour divided by two is 30, added back to 60 equals 90 feet per second but calculus figures to 88 feet per second.
    A non-time delay fuse on the other hand is a lot quicker to open.

    Edited to add:

    In most cases during a fault condition most breakers will open between 120 and 180 cycles or two to three seconds.

    While teaching at DCC we did a test using a GE 20 amp breaker and a very large rheostat. We loaded the breaker to 30 amps for over two minutes before it opened. We loaded the same breaker to 120 amps and it took just under 10 seconds but over 9 seconds to open. (The watch had 10.2 seconds but we subtracted the reaction time to operate the stop watch)

    We did the same test using Square “D” home line and Siemens breaker with similar results.
    Last edited by jwelectric; 01-14-2012 at 11:50 AM.

  12. #12
    Self Employed Electrician / Master ESCO's Avatar
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    People are afraid of fuses but they do open circuits [ disconnect] faster than most breakers
    But you are right they are less user friendly

  13. #13

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    I sure appreciate all this information, and I now agree with you all and my husband, the fuse box will stay.
    We have plenty of fuses and managed to find a replacement for the big main knife fuse, used but in perfect shape, from a local electrician.
    Thank you!
    Jane

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