Sub Panel

Discussion in 'Electrical Forum discussion & Blog' started by, Jul 4, 2008.

  1. New Member

    Jul 4, 2008
    Adding 1200 Sq Ft Finished Space In Basement
    Current 150 Amp Panel Is Full

    3 Bedrooms And Bath + New Furnace

    I Know That I Need A Sub Panel, But How Do You Know If The Current Service Wire To Panel Can Carry New Load?

  2. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    A 150 Amp service will carry the load unless you have an extremely large electrical demand.

    Water heater, dryer, electric range, and even an A/C can be run on 150 Amps. If you have any doubts, tell us specifically what you have and we can check it.

    You already have the space in the basement and presumably are not adding a 5 ton A/C and a complete set of equipment for an apartment.

    The only think that would be likely to push you over the limit would be electric resistance heating. That would at least require a load analysis.
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  4. Billy_Bob

    Billy_Bob In the Trades

    Apr 2, 2008
    It's not about how many outlets, lights, appliances, etc. you have connected to the electric panel, it is how many of these things you will ever use at the *same* time!

    Like one of those long long power strips on a shop workbench which may have 20 outlets along the length of the workbench. Well 15 or 20 amps may be plenty because you are only going to be using maybe one or two outlets at a time.

    But if you had 20 different things plugged in and had them all turned on at the same time, then the circuit would not be able to handle the load.

    Same thing with your house. You may be adding a room, but when in that room, you probably will not be using much electricity in other rooms. Or when other rooms, probably will not be using much electricity in basement.

    My favorite "whole house" max amperage draw is thanksgiving. Lights on all over the house. Kids in bedrooms, adults in living room. Multiple burners/oven going on range. Dishwasher going. Maybe washer/dryer going. Microwave going. Refrigerator going. Maybe garbage disposal going. Relatives have RV plugged into outlet, etc.

    Add up all the watts of everything you will ever use at the same time, then convert that to amps here...
    (Under "Single Phase")
  5. New Member

    Jul 4, 2008
    Thanks For That.
    Just To Be Clear The Main Level Uses Up All Space In A 150 Amp Panel

    We Want To Finish Basement To Include 3 Rooms (standard Layout)
    1 Bathroom

    The Only Thing Large We Are Adding Is A Heat Pump To Condition Basement (2 Ton)

    Will Sub Panel Work And Will Existing Service Wire Most Likely Carry The Load Of Added Basement
  6. Billy_Bob

    Billy_Bob In the Trades

    Apr 2, 2008
    Is this going to be a separate living space for additional people in your house like renting it out to someone? Or will the existing people living in the house just use this as an additional area? Would there be a kitchen or mini kitchen for example?

    If you heat the basement with a heat pump, and if you have an upstairs heat pump, the upstairs unit would probably not be needed as much. Something to consider. (Heat rises.)

    Are you going to have an electrician do all this electrical work? The reason I'm asking is they may have to replace your existing electrical panel and add a subpanel or just install a large main panel. Or be able to "juggle" a few circuits - maybe add some space saving breakers (two breakers on one slot), keep the existing panel and add a subpanel.

    Or maybe the existing panel is "crammed" full of wires and no room for more wires going to subpanel?

    If they need to replace the main panel, then it might not cost much more to upgrade to 200 amps.

    Or if they can keep the existing panel and add a subpanel, then it might cost just as much to upgrade to 200 amps later as it would to upgrade now. If this is the case, then I would see if 150 amps was OK, then if not, upgrade later.

    If it is not that much more to upgrade to 200 amps now, but it would cost a LOT to do it later, then I would upgrade now.

    That's one way to look at it!
  7. Bob NH

    Bob NH In the Trades

    Oct 20, 2005
    New Hampshire
    Adding a 100 Amp subpanel next to the existing panel will cost maybe $200 for materials and you can do it yourself in an hour or two without disconnecting the service.

    An upgrade to 200 Amps will require disconnecting the service, running new and larger service conductors (maybe including conduit) from the utility connections, usually a new meter socket, and often costs about $2000 if you get a quote from an electrician. It usually includes two new ground rods if you are now grounded only through a water pipe.

    One makes room in the main panel by pulling out a couple of circuits and moving them to the subpanel. A breaker is added to the main panel to supply the subpanel.

    You will need to check on the power requirement for the heat pump. A 2-ton unit operating as an air conditioner, with SEER of 10, would be using an average of 2400 Watts, or about 10 Amps at 240 Volts. It would operate with a peak a little higher than that; probably on the order of 15 Amps at 240 Volts.

    A heat pump often has supplemental resistance heating and that may be the factor that requires maximum load.
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