Is it OK to add a 20A circuit?

[tomtheelder2020]

Electrical system in our now 70 year old house had a 100 amp fuse box. In order to install AC, we up-graded to a 200 amp circuit breaker panel (see photos), retaining the fuse box as a sub-panel. Breakers in the panel currently include: 50+50 (fuse box), 40+40 (AC), 20 (Kitchen appliances), 20 (fridge), 15 (garage lights), 15 (garage power), and 15 (misc.) = 245 amps worth of breakers. Of course, we never have all of those maxed out at the same time. I think most of those circuits would be at less than rated capacity even if every power draw on the circuit was active at the same time. An added issue is that light sthroughout house dim briefly every time AC comes on.* I would like to add another 20 amp circuit to run a 10-gal water heater. How do I determine if it is safe to add the new circuit?

*AC is new, has done this since install, and previous one did the same, so AC not the cause.

 

[Eddie_T]

I can't think of any argument against adding it. My lights flicker momentarily when submersible well pump clicks on.

 

[afjes_2016]

Is it safe to add the new circuit for the 10 gal water heater - yes; will your present setup handle the extra load of 20amp - yes more than likely from what I see you are now powering with the 200amp service you have. The only way to know for sure would be a load calculation to be performed which you can do as an exercise to get a bit of an education on how much you electrical service can handle. Yes, you are correct you do not add up the values on the breakers to determine the power you are now using - the load calculator will do that for you and the reason is as you already stated without realizing it is because every circuit is not going to me used at full consumption at one time.

There are many load calculators on the internet. I would try a few of them. They are all basically the same but some are a bit more easier to understand overall and more user friendly. Doing this will help you in the future to determine if adding a circuit will be handled by your service. Buy again with what you have mentioned that you are powering now with the 200amp service adding one 20amp circuit is not going to be a big deal at all.

Also, just curious as to why you would save the old fuse panel to use as your sub panel? Breaker panels are so inexpensive it would really not make sense to use an old fuse panel instead of buying a new circuit breaker panel to be used as the sub panel. They would run around $35-$80+ depending on the rating.

 

[JoeD]

It will be fine.
Adding up the value of the circuit breakers in panel is a useless enterprise. You never use all the items at the same time. You never use the circuits to the full capacity of the breaker.

 

[tomtheelder2020]

There are many load calculators on the internet. I would try a few of them.

Also, just curious as to why you would save the old fuse panel to use as your sub panel?

I already have an inventory of exactly what is on each circuit so the load calculator ought to be pretty straight forward - I will try it. Thanks for the tip.

I kept the old fuse box because the guy I hired 30 years ago never suggested replacing it and it didn't occur to me then or since! That is an especially great suggestion because a couple of circuits I ran from the new breaker panel removed load from the fuse box. It is possible I could run the new 20A circuit from a replacement for the fuse box - which is located about 18 inches from the water heater!