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Ask Kevin Your Own Question
Kevin, Licensed Electrical Contractor
Category: Electrical
Satisfied Customers: 3586
Experience:  30 years Licensed Electrical Contractor in Illinois, Adjunct College Electrical Instructor, Former Electrical Inspector, Diploma: Digital Electronics, FCC Technician License
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Two story home that was originally built in 1969 as a one

Customer Question

two story home that was originally built in 1969 as a one story, and I've almost doubled it in 1992 from 1800 sqft to 3100 sqft. It has the original forced air heater only downstairs, and a separate one upstairs. I'm in the process of getting quotes for central air and heat, and all three companies recommend a 3 1/2 ton unit down, and a 3 ton unit upstairs. One of them tells me I'll need an electrical panel upgrade to handle the load. My current main electrical panel is 100 amp, and it is nearly filled with breakers totaling 360 amps. I have an upstairs subpanel that is rated at 50 amps that has breakers totaling 160 amps. But one of the 20 amps on the main panel is for the downstairs heater, and one of the 20 amps upstairs is for the current upstairs heater. Those will get re-used for the new equipment. I have three narrow breaker slots open on the main panel and four wide breaker slots open on the subpanel. Do I really need a 200 amp main panel upgrade? It will add $2500 plus stucco work plus permits to an already costly job. Thanks.
JA: How old is the system in question? And have you consulted an electrician yet?
Customer: Everything was rewired in 1992 for upstairs and downstairs when we did the remodel.
JA: Do you plan on doing the work yourself?
Customer: No. I don't do electrical work, and I'm planning on having one of the AC contractors put in both systems.
JA: Anything else we should know to help you best?
Customer: That should be a pretty though list. I live in Cerritos, CA, in L.A. County so I will have to work within their rules and permits.
Submitted: 10 months ago.
Category: Electrical
Expert:  Kevin replied 10 months ago.

Hello and welcome to Just Answer. My name is ***** ***** I will be happy to assist you with your electrical question.

1) I recommend that you contact a local licensed electrical contractor and have them measure both of the hot service phases using a clamp-on amp probe meter with the house under as much Full Load as possible.

2) Once the phase amps are measured, subtract that number from 100 amps and this will be the remaining available amps for the new HVAC equipment. Then have the electrician perform a load calc based on the new HVAC equipment. It is very possible that you may need to upgrade to a 200 amp main service panel.

3) The total fill of breakers @ 360 does not work that way. You don't total up the quantity of the amps on the individual breakers. You need to measure the 2 service entrance conductors using an amp probe.

Expert:  Kevin replied 10 months ago.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.

Otherwise, don’t forget to rate me before you log Off.


Customer: replied 10 months ago.
Thanks for the information and recommendation.
Expert:  Kevin replied 10 months ago.

No problem, glad to assist.

If you have any additional questions, just let me know and I’ll be glad to answer them for you.