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Question DetailsAsked on 3/2/2018

What happens if i have a125 amp meter box on a 70 amp service panel

I have a temporary service pole with a meter pan that is rated for 125 amps and my service panel is only rated for 70 amps will it overload the 70 amp service panel and what size service wire is needed for that

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What the capacity of the service is has no great relevance - that just means that box can safely handle providing more power than your panel can draw, which is a common situation. Actually, unless it actually has a sticker or label saying "125A Service Installed" or "Demand Limited to 125A" or something like that (sometimes just felt-tip marked on the inside of the box on the bus bars), just having 125A or maybe CL125A (meaning rated for Continuous Load of 125A rather than intermittent max load of 125A) stamped or factory-marked on the box just means that box is rated for maximum 125A load connection - not that the service wiring is necessarily sized for that. For houses with breaker panels of 100A or less (unless very old) the incoming service wires are commonly sized for 25-50A more than the main breaker and household box load, if 125 or 150A load commonly 150-200A service wiring, if higher household load capacity commonly 50-100A greater service capacity - though varies by utility and of course that assumes the household capacity has not already been increased in the past. The meter box itself may be sized based on house design load - or may be sized based on the incoming service rating - different utilities use different rules, and sometimes depends on who pays for the meter box.


Also - the service will only provide the power which the breaker/distribution panel draws, at least up to the point where there is an overload which starts causing a significant voltage drop. Think of it like your water line - street main is maybe 8-36" pipe and can supply hundreds or thousands of gallons a minute - but your service line to the house and main shutoff valve are only 3/4 to 1" usually, capable of maybe 20-50 gpm or so at normal household pressures. Having it connected to a larger capacity service pipe does not change the flow into your house - your incoming pipe only carries as much water as the fixtures in the house which are turned on demand. Much like a distribution/breaker panel, you may have several different water lines in and outside the house using water - the incoming line only provides the amount the fixtures are demanding (commonly only a few gpm each), regardless of its much greater capacity of the service pipe and the public water main.


In fact the incoming service is commonly sized significantly larger thn the design house demand - both to eliminate the problem of excess voltage drop if the wire is highly loaded near its carrying capacity, to allow for future household panel upgrades, and also to use the same size wire for basically all houses regardless of what breaker panel main breaker rating they have. So - a new subdivision or street service might be sized for say 200A or even 3000A household demands - but if someone build a bungalow with 100A breaker panel, their incoming service would be significantly oversized for the house. Ditto for natural gas versus all-electric houses - there might be a 2:1 or even 3:1 difference in household panel sizing in those cases, but all might have the same incoming service cable size.


Anyway, all that deals with the ability of the incoming service to provide power - your panel being rated for 70A (assuming you mean the 2 main breakers are 70A breakers, not that the box is stamped 70A, which would make it tiny by current stndards) means it will not draw more than about 70-90 amps for an extended period of time - potentially more for a short time in the event of a major short circuit or overload before the main breakers trip out.


But as long as the main breakers (be they at the top of the breaker panel or separately installed next to the meter box or in some cases even in the meter box itself) are properly rated for the size household wiring (including the main feed wire from meter panel to breaker panel) and are also not more than the total amperage rating of the breaker panel, you are good.


Note - for normal 220/240V service to a house, the service is actually two 110/120V live leads and a neutral (plus ground however it may be wired), so actually each "side" or live lead is rated for 70A in your case - so the main breaker will be two mechanically interconnected (with a tiebar or two breakers with one central handle) or "paired" 70A breakers protecting your household wiring and breaker panel. As long as you have a properly sized main breaker for your household wiring, an oversized service connection (within reason) is not an issue foir concern.

Answered 8 months ago by LCD




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