Electrical Panel Capacity Question

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jpalarchio

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I'm in the process of switching over to electric and plan to bring in an electrician to install a spa panel in the garage. Before I waste someone's time with what is probably an unusual request, I was looking for a quick assessment of my capacity.

I'm trying to determine if I can plan for a 50 amp setup or if I'm restricted to 30 amp.

My breaker box has physical capacity although I'm sure doesn't mean you can just add until you're full. The house was built in 1997 and the main breaker on my panel is 150 amp; the usage is probably much lighter than when the house was built as the dozens of pot lights have all been replaced with CFLs.

One thing I added after moving in was I had AC installed which doesn't appear to have a breaker in the box but I believe is wired direct to the panel (?) and has a fused disconnect outside next to the unit. Stove and dryer and both electric.

Does a pic of the panel help?

How can I tell if 50 amp or 30 amp is in my future?
 
I'd go with a 50A.
If you can, try and mount it as near to the main breaker as possible.
You'll need to find two singles together with enough wire to move to the bottom. You can extend the wires and use wirenuts inside the panel.

Also, choose the side of the panel that has the most room for the the #6 wires.

Worried at all? Get some battery lighting, shut off the main and then do the C.B. swapping.

'da Kid

Are you going with the GFCI breaker? $$
 
I guess my question was more along the line of how do I know that I have actual capacity to put in a 50 amp connection?

Obviously the sum of the breakers far exceeds the main breaker and the concurrent usage of devices in the house is fairly small (we're not running all the lights, microwave, dryer, stove and AC all at once 24x7).

How do I know whether 50 amp or 30 amp is appropriate? Do I need to be concerned about drawing too much amperage and tripping the main breaker?

My thought was to install the 50 amp spa panel with GFCI in the garage (about 10 ft of wire from the panel) and then either a 50 or 30 amp breaker in the panel.
 
This is what I am trying to do. Since my house is about to be totally rewired within the next year, I am going to have it so I can add in a 50A breaker. Installing the breaker is the easy part, Making the panel for me is the hardest part.
 
I guess my question was more along the line of how do I know that I have actual capacity to put in a 50 amp connection?

Obviously the sum of the breakers far exceeds the main breaker and the concurrent usage of devices in the house is fairly small (we're not running all the lights, microwave, dryer, stove and AC all at once 24x7).

How do I know whether 50 amp or 30 amp is appropriate? Do I need to be concerned about drawing too much amperage and tripping the main breaker?

My thought was to install the 50 amp spa panel with GFCI in the garage (about 10 ft of wire from the panel) and then either a 50 or 30 amp breaker in the panel.

The unused spots in your panel are there for a reason . . . . . to be properly used for future expansion. Heck, a builder could kindly fill every one from the git-go.

You do not want to exceed 80% of that main 150A breaker.

One way to know this is to measure the 'draw' with everything in the house on. Equipment nameplate data will need to be added to what can't be turned on during the draw test.

The tool to use is:
spin_prod_214591101


You will want to be comfortable using the meter before ever attempting the test. You will be never be closer to the full current supply available to your house than during this check. Possibly 1000's of amps. Not to scare you, but you must not be insecure with the task.

Shut off the main power the first time you ever pull off the panel cover. I'd wear leather gloves for physical and electrical protection. Look for improper wiring methods that may get you in trouble. AKA crappy workmanship. Shut off every branch breaker in the panel.

Locate the two service wires coming into the main breaker. There must be room for the clamp meter to clamp around each wire. Clamp it around one wire. I like to place it at a viewable position.

Main back on. Then each branch breaker back on. Turn every load on you can and take an amp reading. You can gingerly move the meter to the other service wire, or you can reverse the procedure. Shutting off each branch breakers, swap the meter and repeat the above.

If this makes procedure makes you queasy, you can add the loads mathematically using nameplate data for all the appliances. This will give you an elevated number as the nameplate data is using stated as 'full load'.

Some safe steps:
Avoid shutting off/on the main breaker under load with the cover off.
Don't have any distractions.
Watch for wires near the panel cover screws.
Don't sweat the 50A breaker. The panel and breakers will protect you from overloading anything.

The remote Spa panel is the way to go.

'da Kid
 
Thanks for all the info guys.

Running through the calculations seems like it could still be a bit of a guess but I'm sure this is a time tested way of doing it.

I imagine we're quite a bit below the limit given the number of open breaker spots, all the energy reductions we've done and the number of breakers that I look at that have virtually no load. There's a 15 amp GFI breaker for the lights on the deck outside which I converted a while back to a string of LEDs that use very little power and operate on a photocell. There's another breaker dedicated to the outlet in the garage where the air compressor is plugged in, something I use about 4 times a year.

I suspect I have room to go with 50 amp.


One last somewhat unrelated question... Is it normal for my air conditioner to be wired how it is where there's no breaker but instead a fused disconnect outside? I had this installed by a contractor and I guess it seems a bit odd to me that it doesn't connect into the breaker panel.
 
Every branch circuit must have over current protection at the panel, even an A/C unit. Is this the only panel in the house? A pic of the panel with the cover off would be helpful.

You should have plenty room for a 50a sub panel, if you have a problem do not use the dryer, oven, etc. while brewing.
 
One last somewhat unrelated question... Is it normal for my air conditioner to be wired how it is where there's no breaker but instead a fused disconnect outside? I had this installed by a contractor and I guess it seems a bit odd to me that it doesn't connect into the breaker panel.

Extremely odd. However, my well is connected directly to the meter and the fuses are at the pump house. That was done by a contractor in 1975.

It might be that the A/C draws too much additional power to be added to the main breaker.
 
What type of Air Handler?

If your heat is all electric, the outside condenser may be getting fed from a sub panel at the Air Handler.

It would be a major error to feed a condensing unit disconnect straight from the main panel buss.

'da Kid
 
The10mmKid said:
It would be a major error to feed a condensing unit disconnect straight from the main panel buss. 'da Kid

I just looked and the wiring from the air conditioner goes from the outside fused disconnect right into the meter.

I had this installed like 10 years ago and we originally planned on using an interruptible service where your AC is on a second meter and the power company can shut you off during peak usage (you in return get a discount). It turned out when they came to install that the interruptible service wasn't available at my address.

So is this an unusual install? Did the installer maybe take a shortcut when he found out he couldn't do a second meter?
 
:off: But I think it is important and interesting to talk about. In my awfully wired house, my furnace is hooked to my hallway lights, sump pump to my master bedroom, stove hood vent to furnace.....
 
Aside from hoping what I have is safe, we plan to move in a couple years and I don't want someone having an inspection and the buyer coming back with a list of major issues.
 
Well, if you are lucky, they just used the meter base as a chase into the main panel. There is usually an oversized hole for the service cable. Is your panel directly behind the meter inside the house?

I would never attach a small amperage wire into a meter base . . . . never.

I'd put this on your knockout-before-moving list.

'da Kid
 
The panel is behind the meter but about 4 ft down as it's in the basement. I looked at all the wires going into the top of the panel and there's nothing that size other than the two I know are for the dryer and stove. So it must terminate at the meter.

If I had the interruptible service I assume it would be wired this way with the difference being that I'd have a dedicated meter for the air conditioner.

So is this not allowed or just not preferred?
 
If you are going to have an electrican install your new circuit and gfci protection in the brewery then just ask him to inspect the A/C circuit while he is at it. He will tell you if there is a problem. The 50amp circuit for brewing will work great and if you will ever want to run more than one heating element at a time you will need the 50 amp circuit. Make sure he knows you need a 4 wire circuit. We only run 3 wire circuits to most water heaters and if the electrician hears you talking about water heater elements for your kettles he may misunderstand the needs of this circuit and what it will need to power other than the elements. But he should know since it will have gfci protection. Good luck brother.
 
If you are going to have an electrican install your new circuit and gfci protection in the brewery then just ask him to inspect the A/C circuit while he is at it. He will tell you if there is a problem.

That's kind of what I was thinking at this point. I really don't have too much of a concern about doing this myself but I'd rather just bring someone in so I don't end up with a list of homeowner DIY mistakes when we go to sell. As it is, the previous owner did a number of things that I've since corrected.

I guess when we sell the house in a couple years, we can market the garage as being "electric vehicle ready".
 
Figuring out load calcs on an electrical panel can be a little goofy. As you stated your main is 150 amps. That is actually a little bit larger than a lot of houses out there.

When an engineer designs an electrical circuit for a house, there is a de-rating factor involved when "assuming" a total potential load. Though off the top of my head I do not know what the actual de-rating is. It is assumed that a homeowner will never have all their lights on, and be using every single receptacle to its full capacity in the house. So for lighting and receptacle circuits I think you can pretty much assume 70% use at highest value. If you open up your panel and add up all your 15/20 amp single phase breakers by their value, then reduce that by 30% you will have an estimated load potential for your general use breakers.

*edit. I left one part out on accident. For the general purpose breakers there are two phases in your panel. So as long as you had a good electrician do the install, then your loads should be fairly balanced. Add up all the breakers 20 amps, and divide by two. Then all the 15 amp breaks and divide by two. Then add em up and take 30% off that value. My bad. I had a few beers already and forgot about that until a few minutes after I posted this.

There are also the single use breakers to account for though. If you have electric stove, dryer, furnace, or heaters in the house then the breakers supplying that load should be added into that total load value at their full ratings. Usually those can be easily identified because their 240 v breakers that occupy two spots in your panel. That and since your home is newer you should assume that you have one dedicated breaker for your microwave at 20 amps (calc at full load).

This may be more than you actually need to know, but in all probability you do have the capacity to add a two pull 50 amp breaker in your panel without dealing with nuisance breaker trips. (Your main breaker being the nuisance)

I am being a little agressive with the 70% value for the general purpose breakers I think. It may actually be able to be de-rated a bit more. I haven't looked at that section of the NEC in a while.
 
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