About 100 amp house wiring

Written by jay p. whickson
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About 100 amp house wiring
(Michael E Whicker)

If you're about to buy a house, most lenders want to know what amperage the wiring is. 60-amp service is not adequate anymore. Even insurance companies consider the smaller amperage a liability. Today's homes, with the heavy variety of electrical appliances and gadgets, require a larger service, like 100 amp.


You can identify 100-amp service house wiring by looking at the main circuit breaker. It identifies the service by its amperage. The main circuit breaker is in the box above the other breakers. It controls the flow of electricity from the outside power lines. You use this breaker to shut off all the electricity in the house at one time.


Don't let the number on smaller breakers in the box fool you. They may total more than 100. Electricians put in the breakers for specific areas. If a breaker says 15 amps, usually the load is only about 80 per cent of that amount. The logic for so many breakers is that you'll probably not use everything at once, and they don't load all the breakers to full capacity.


Determine how much of a load you place on one of the circuits by calculating the amount of amps they use. For instance, an iron has a wattage rating of 1200. A portable heater has a rating of 1500. You divide the wattage rating by 120 volts to convert it to amperes. The iron is 10 and the electric heater is 12.5. If they both were on the same 15 amp circuit and turned on at the same time, they overload the circuit and the circuit breaker clicks to the off position.


Circuit breakers have a purpose in a 100-amp house wiring service. They prevent overload of electrical flow and potentially a fire. Before you reset the breaker, find out what caused the overload in the first place. It might be a short in a wire or a bad ground requiring repair, or just too heavy a load on the circuit.


Check the grounding of the 100-amp service in your home. There's a main ground wire from the box that usually connects to a metal water pipe and a metal grounding wire buried outside in the ground, which gives the excess current a direct path to travel into the ground. Each outlet, ceiling box and switch in the house also has a grounding system. Grounding prevents you from getting a shock if there's an abnormal flow from a short circuit. It also prevents fires. In damp areas, make sure that your 100-amp service has GFCI breakers for additional safety.


If you're installing 100-amp service, why not upgrade for future use? Often the 200-amp panels are cheaper because there's more of them sold. This accommodates for expansion and changes in code that may occur in the future. Check the prices before you begin your project.

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