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Question DetailsAsked on 2/15/2018

why does power usage by main appliances trip 100 amp main breaker when two or more are operating?

Cooking and running dryer does not trip their breakers respectfully, but, trips main 100 amp breaker every time.
If refrigerator, oil furnace, electric water heater and both sump pumps intermittently run; and dryer or washer or range or microwave is used, same effect occurs. Outside of required specific breakers for range and dryer, the main panel has primarily 15 amp breakers and a few 20 amp breakers. none of which trip their own breakers, but are bypassed and main is tripped.

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While it is possible individual breakers are not tripping like they should, that is fairly rare - especially since you are talking multiple breakers serving multiple devices here. And you said nothing about wires getting hot or appliances not working right, so it is quite likely wach item is pulling the amperage it should, hence no reason for individual circuit breakers to be tripping.

What is more likely happening is either that you are just plain overloading the household service (100A is quite undersized for a mostly electric appliance house like yours), or possibly your devices are imbalanced with respect to load so one "side" of the 220/240V service is carrying more than its share of the load. (220/240 devices like range and dryer and water heater and such are actually fed by two 110/120V circuits feeding into paired and interlocked breakers, making that a 220/240V demand but the current is actually carried in two 'hot" leads at 110/120V each.)

Your normal 220/240V device breakers (vary by age and make) have about the following power demands - water heater probably about 50A (amps) or even more (on each "side" of the service feed), range 50A, dryer 30-40A, dishwasher or washing machine electric steam generation (if steam unit) 20-40A.

Microwave, sump pumps, clothes washer and dishwasher NOT including heat-dry or any steam generation unit, handheld hair dryer generally nor more than about 10-15A each. Oil or gas-fired furnace no more than 10A that I have ever seen - EXCEPT if you have a heater (with or without recirculating pump) on an outdoors oil tank to prevent fuel gelling, that can add another 10-15A. Reefer/freezer can be 10-20A range depending on size. Most other house electronics and lights commonly only an amp or two each - unless you have a large old (non-electronic) cathode ray tube TV, which can pull up to about 3-5A.

So - reefer plus furnace plus some lights and home electronics and such miscellaneous household devices probably around 20-50A total draw, water heater maybe 50A, 2 sump pumps maybe 10-15A or so total = 80-115A - so that is up to your 100A breaker capacity right there just for the items regularly on or turning on by themselves. So - any otehr high-demand item - range, microwave, toaster, waffle iron, coffee maker, dryer, washert, dishwasher being used could, any one of them and certainly any two simultaneously, push uyou to the point of the breaker tripping because your total household load exceeds design capacity, even though no one item is causing breaker trips.

Air conditioner - you did not mention, but 15-20A for small unit, on up to 30-50A for large house unit.

So - I think your house is just underpowered for what sounds like basically (except for furnace) an all-electric home. I would guess when it was built the larger appliances (water heater most likely, maybe dryer and range also) were probably oil or gas fired - or maybe even older than the days of using clothes dryers if built before 1960's. These days most houses have 150-200A capacity - yours sounds like probably a typical 1960's or maybe early 1970's house, or a very small bungalow-size house which was designed for fuel-fired spadce and water heating.

What you need is a circuit load test - testing by an Electrical contractor (your Search the List category) for the normal load operating on each circuit, what the peak loads are from the larger demand items (from physical measurement or nameplates), and then with that info look at which are on which "side" of the breaker box. Could be general overloading (which I suspect), or could be your uses are concentrated on one side of the box and some juggling around of breakers (which required some rewiring at the box at a minimum) to balance the two sides out might help.

Once he tells you the results of that (probably around $300-400), then he should recommend one or a combination of things:

1) converting one or more of the major loads to gas or oil, if suitable for you - cheapest would be water heater probably unless you have natural gas to the house, in which case dryer ($300-600) and range ($700-1000) for economy models would also be candidates for changeover (which would also in most areas dramatically reduce your power bills, natural gas generally being about 1/2 the cost of electric for those uses).

The above prices would be if there is already natural gas plumbed to those appliance locations - commonly about $500 range plus or minus to run gas from existing meter to an appliance if no gas piping in the house, PLUS repair of drywall and repainting if the line cannot convenientlyh be run around the outside of the house. Of course, if gas does not already serve the house, then you are talking (assuming there is gas distribution line along a property line) a larger project to bring gas service into the house. Commonly pays for itself if going to stay there indefinitely (15+ years say), not if you are expecting to move soon, but in your case you would be looking primarily at reducing electric load, not the cost savings.

2) upgrading the main power supply into the house - in the couple to few thousand $ range generally, can be much more if power utility has to come more than just from the street or a nearby pole transformer to upgrade your service drop. Fair number of previous questions with answers about that in the Home > Electrical link, under Browse Projects, at lower left.

3) if incoming power supply (service drop) is high enough capacity already (commonly is sized larger than house is designed for to allow for future upgrading), possibly splitting your load into two breaker panels - putting in an auxiliary one pulling from the meter panel to a new second panel which (with its own main breaker, so above and beyond the 100A current main breaker capacity) which might serve say the furnace and water heater and maybe one other high-demand item like dryer or range - getting much of the heavy loads off the existing breaker panel. This is generally, IF the service drop has the capacity, quite a bit cheaper than doing a total upgrade of incoming lines and breaker panel.

If service drop needs upgrading, depends on what utility charges for that - some charge little or nothing, figuring they will recoup the cost in electric usage over the years, others (more so with most electric bills being split between installation and power charges) charge a thousand or two to do this, sometimes quite a bit more for long run or $ hungry utilities.

4) to limit simultaneous use - but with the combinations you gave, the first list of basically uncontrollable items (ones that come on by themselves - furnace, reefer, sump pumps, water heater) plus any one of the other large demand items kick it off, that indicates (unless you have a LOT of lights on all the time) that your system is probably just undersized for your house use, so trying to limit simultaneous use does not sound like a solution for you. Some people get by with say not using the dryer or a shop air compressor or welder at the same time as microwave or range, or not using microwave at same time as toaster or multi-burner/oven range use, but in your case sounds like any one of those coming on can trip it out - not a functional or safe situation.

Plus continued tripping of the main breaker can affect its funtionality, so eventually it either breaks (cutting of all power) or starts malfunctioning, which in some instances can be dangerous. And of course, because it is tripping out, that means you are overloading breaker box and wires too - also not a good thing.

I would say get a well-rated electrician (and should be a Journeyman or Master electrician, not just an apprentice) to check it out and then look at whwre you go from there.

Good Luck

Answered 2 years ago by LCD

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