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Old 10-09-2013, 04:29 AM   #1
jpalarchio
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Default Electrical Panel Capacity Question

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?

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Old 10-09-2013, 06:35 AM   #2
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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? $$

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Old 10-09-2013, 06:44 AM   #3
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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.

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Old 10-09-2013, 02:06 PM   #4
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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.

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Old 10-09-2013, 03:24 PM   #5
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You are limited by the load on your service. You can calculate the load based on this blog post. The actual rules on how to calculate your service load being in section 220.24 of the 2011 NEC code (page 67 of the PDF).

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Old 10-09-2013, 03:28 PM   #6
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Quote:
Originally Posted by jpalarchio View Post
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:


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
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Old 10-09-2013, 03:56 PM   #7
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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.

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Old 10-09-2013, 04:17 PM   #8
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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.

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Old 10-09-2013, 04:29 PM   #9
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Quote:
Originally Posted by jpalarchio View Post
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.
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Old 10-09-2013, 04:30 PM   #10
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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

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