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  1. #1
    Join Date
    Aug 2008
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    Default 150 amp service overload?

    I have a 150 amp service that may be overloaded. I thought if you have 150 amp service the total amp ratings on the breakers shouldn't equal more then 150 on each bus. If you add the breakers up I have 240 on one side and 260 on the other. Should I add a sub panel or is the combined total of breakers not an issue just the actual load? 1500 sqft house I did a load calculation and came up with 131 amps. (elec Hot water, Range & 50 amp sub panel upstairs). We used a lot of breakers (and a lot of wire)because each room has its own breaker & each appliance has its own breaker, fridge, microwave, computer, washer/dryer & jacuzzi all on there own breaker. So i don't think I am overloading a 150 amp service but I wonder if the box isn't code because of 500 amps of breakers.

  2. #2
    Join Date
    Aug 2007
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    Default Re: 150 amp service overload?

    Quote Originally Posted by rwhnze View Post
    I have a 150 amp service that may be overloaded. I thought if you have 150 amp service the total amp ratings on the breakers shouldn't equal more then 150 on each bus. If you add the breakers up I have 240 on one side and 260 on the other.

    So i don't think I am overloading a 150 amp service but I wonder if the box isn't code because of 500 amps of breakers.
    Typically around here we see 100 or 200 amp panels .... meaning that a 100 amp panel itself may be rated at 125 amps but the main breaker is only 100 ..... roughly 80 %.
    The main breakers are one of the factors determining the amount of electrical supply to your home ..... the other is the feed to the home.
    In your case if the main breakers are 150 amps ..... they will disconnect power if the load exceeds 150 amps on either of the 2 "legs" of the service.

    The load on the panel is not the cumulative rating of the individual breakers in the panel.
    It is the actual current drawn through the circuit breakers that adds up to the load.


    For example .... lets say you have a 32 space panel ..... 16 on one side and 16 on the other.

    Lets also say .... all 32 spaces had 15 amp breakers ..... 32 x 15 = 480 / 2 = 240 amps per leg ( phase ).
    However .... you may only have a load of 5 or 40 or 80 amps on the whole panel at a particluar time ....... not 480.

    If there is no current draw ..... there is no load.

    Each one of those 32 circuits would need to have maximum draw of 15 amps at same time...... which means every possible electrical device that you can gather would all have to be on at the same time drawing maximum current.

    If that were the case the main breakers would be tripping...... typically you do not use all of your electrical circuits at the same time.



    Should I add a sub panel or is the combined total of breakers not an issue just the actual load?
    If you add a sub panel that's being feed from the main this wouldn't make any difference ...... since it becomes part of the main panel load.


    1500 sqft house I did a load calculation and came up with 131 amps. (elec Hot water, Range & 50 amp sub panel upstairs). We used a lot of breakers (and a lot of wire)because each room has its own breaker & each appliance has its own breaker, fridge, microwave, computer, washer/dryer & jacuzzi all on there own breaker.
    When a proper load calculation is performed the total number will be determined as the maximum though 80 % of that value is generally used as the nominal safe wattage ( load ) range.
    In your case your panel has a capacity of 150 amps .... you mentioned your load calculation is 131.
    Obviously you are too high for a 100 amp service and you fall within approximately 80% of 150 ..... you have a 150 amp service.

    However .... if you decide to make some large additions to your electrical needs .... you may consider going up to a 200 amp service.

    Hopefully this makes sense and helps.
    Last edited by canuk; 11-16-2008 at 04:19 PM. Reason: correct those darm spelling boo boos
    "" an ounce of perception -- a pound of obscure "
    - Rush

  3. #3
    Join Date
    Aug 2008
    Posts
    35

    Default Re: 150 amp service overload?

    Thanks Canuk,
    It does make sense. There is 4/0 aluminum wire supplying the service panel but only a 150 amp main breaker. I was once told that each leg could only equal 150 amps. I thought it might be an issue at the final inspection.

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