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Question DetailsAsked on 4/17/2015

how do you determine if an electrical panel is overloaded?

I have a 200 amp panel with several "double-tap" breakers. Should I upgrade to a higher amp panel?

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Certainly if the panel or any area near it on the wall feels noticeably warmer than the adjacent surfaces or you smell any odor coming from it, you should have it checked for overloading or a wiring problem.


The panel will have a label sheet or embossed rating on it, showing the "rated capacity" - sometimes for the entire panel, sometimes also for several specific areas of the panel if it has an internal protective sub-main breaker - meaning the box is divided into a couple of service blocks.


The electrical load you are putting on the panel is calculated by a "demand load" formula which all electricians can figure. The "demand load" load or the maximum amperage you actually expect to draw at any time varies by types of circuits (lighting, outlets, dedicated appliances, heating systems, motor starting amperages, etc) and assumes only a certain percentage of lights and outlets and appliances are in use at a given time, that electric furnace and A/C will not run simultaneously for instance, and factors in the likelihood that major appliances like clothes dryer and range and furnace and electric water heater etc will all be used at the same time. So, the "demand load" at the panel will be significantly less than the total number you get by adding up the total breaker ratings of the breakers in it - commonly by 20-50%.


The "demand load" should not exceed the rated capacity printed on the panel on either legof the 220V feed (load should be roughly balanced between the two legs of the panel both by amperage and by types of circuits), but the total of the breaker ratings very commonly will exceed the rated panel capacity.


The electrician and you should also discuss how you use your house - for instance if you livealone the percentage of installed load in use at any time will be a lot less than if you have big family get-together dinner parties with multiple people preparing food he might increase the estimated kitchen appliance/range demand and assume the dishwasher and washer/dryer may be working the same time as counter appliances like blenders and mixers and coffeemaker as well as the range/stove working near capacity. Likewise, if you have large parties where most of the lights are on in the house (or you leave most lights on at times in the winter) the demand percentage rating on them would be increased, adding in other items likely to be used at the same time like entertainment loads (home theater, pinball machines, etc), hot tub/sauna, pool and pool lighting, etc. I have seen houses where during a party or multi-aged family get-together the total demand load can come close to the total ofthe rated breaker capacities - bringing the party to a crashing halt when the main breaker trips. Teenagers can also cause this effecton individual circuits - loading up every outlet in their bedrooms or family room and tripping out individual breakers from chronic overload.


Also, you should (by code) have a "master breaker" to protect against the demand load estimate being too low. Sometimes at the top of the panel on the incoming main feed wires where they come into the panel, probably more usually these days in a separate master breaker or breaker/disconnect box right next to the meter. This master breaker should not be rated higher than the LESSER of the rated capacity of the meter, the service line to the meter, the service feed wire from the meter to the breaker box, or the breaker box itself. That way if the rated capacity is exceeded by accident, the main breaker should trip out to protect against overheating and fire hazard.


Having "double-tap" or half-width breakers is certainly an indication that the demand of your house MIGHT be approaching capacity for the box, but you have to check to actually know - a 150A box is adequate for most normal size houses unless you are in a cold area AND have an all-electric house, or have a lot of unusual demand like major outdoor lighting or electric hot tub/sauna- so with a 200A box (assuming your main breaker and service are similarly rated) you are most likely good to go. I know in my box the rated capacity of the breakers is probably over double the box and main breaker capacity yet I have never tripped out the main - because half that capacity is in large breakers each dedicated for table saw, welder, or air compressor and I never use more than one of them at a time, and never use the welder at high amperage without tagging-out the dryer and oven so they will not be used at the same time.


One comment - just because a box or main breaker or meter says it is rated higher than your demand does not mean all is well - the electrician should check all the wiring to the boxes and breakers against the breaker size on it to be sure the breakers are properly sized for the wire size. While he is there, I would hve him check the connections too - tighten up all the connections at the breakers and bus bars, ESPECIALLY on any aluminum wiring, as they tend to get loose over time as the screw/clamp pressure causes the aluminum to creep and loosen up, potentially causing a loose connection that can overheat.


Cost for a service feed and breaker/box capacity check and grounding check probably in the $200 range - a good safety measure for peace of mind, and especially if you are looking at adding loads.



Answered 5 years ago by LCD




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