Electricians? I have a panel question.

I have a very ancient panel in my house. Easily from the 80's, possibly even older. I have run a sub panel off of an old 50 amp double pole breaker already.

I'm planning to run power to my carport this year, another 50 or 60 amp sub panel, and my original plan was to run it out of the sub panel I already have.

Unless by some miracle I win a welder, 220 compressor, AND figure out how to run both at the same time, I feel my potential load is safe to run a sub panel from a sub panel.

But I was doing some thinking and figure better safe than sorry.

Now, the main panel is presently full. I actually think I can eliminate a few circuits if I take the time to trip them on and off and figure out what they belong to because there aren't a lot labeled. But if there aren't any I can completely eliminate, I've been thinking about minimizing the breaker count.

Most of the panels I see for sale these days are 20 spot/40 circuit, like they were made with breakers like this one in mind.

Are these style breakers universal? Murray is the preferred OEM equivalent, and I know they make them in this style.

But looking at this diagram

I'm curious if this panel would support those 2 in 1 breakers. To me, the slots with a line through them seem like they should work for one of these breakers.

So that is my question, I think the panel diagram says I can use them, if I can find a matching brand, but I want to make sure before I start an electrical fire or something.

The main is 125 amps, and only exists in block B on the diagram, not sure if that makes a difference or not.

Those are called tandem breakers, and they should work if you can find the correct ones. Why such a large service for a carport?

Because I presently just have extension cords for power, and kind of want to overdo it. I may also buy a 220 compressor in the future, and would rather have the power there ahead of time instead of needing to upgrade.

Looking at a 6 spot, 12 circuit panel for in there. Lets me do lights, 2 different circuits for outlets, and the option of 220/240 in the future.

Find or order some of these. They are thin breakers that allow you to put two breakers where one fits now. They will allow you to free up spaces to add additional circuits.

just remember, for 220 you need two legs

In reply to Toyman01:

That's the plan, but with my luck, I wanted to know if my panel might be too old for them somehow.

2 of those and a double 20 and I'll be good.

Mad_machine

Yea, I'll be running 4 #6 copper lines down through conduit. And putting in a grounding bar.

Wow, reading comprehension fail on my part.

Pull a breaker out of your panel and carry it up to the hardware store.

A quick googles turned up this as well.

https://www.youtube.com/embed/1aYnTtfnLrs

It looks like, if you breaker panel is gray, the above thin breakers will fit.

In reply to Toyman01:

This just got really easy.

It's strange, you look at something every single day, and parts in your mind just don't click until you look like an idiot asking questions. There already is a tandem in the panel.

Put the hot water tank and the dryer on tandems, and plenty of room for another breaker.

Although I just added everything up, and see 420 amps of breakers on a 125 main. I feel like there's a formula for a maximum that I'm forgetting about.

I have no idea what my current max current draw is, but I can borrow a tool to find that out.

Figures I had the answer all along, just didn't notice until after I asked.

In reply to RevRico:

The shop at my last house was fed off of a 50 amp breaker in a 150 amp panel. It pulled the welder, air compressor, shop AC and heat without any problems. In 10 years, I never tripped it.

I wouldn't worry too much about the totals. A 150 amp, 40 circuit panel, full of 20 amp breakers, is 800 amps. I've also seen a 400 amp main, transfer enough amperage to peg a Snap 9 meter at 900 amps. Starting loads, like a air compressor, are pretty much ignored by the breakers. Welders also pull a lot less than most people think, unless you are running them wide open, which you will almost never do.

I'm no electrician, but my concern of running a 50 amp sub panel on a 50 amp sub panel would be voltage drop out at the car port over the total run back to the panel. The existing run from the house to the garage might not be heavy enough.

In reply to BrokenYugo:

It is. I replaced the old wire that was there with 6 gauge direct bury wire, it's only about 5 feet from panel to panel. Only difference is I'll be running 6 gauge THHN to the car port through conduit, which is 95 ft from the panel in the garage and 100 feet almost exactly to the main panel.

My concern about feeding a sub panel from a sub panel is that somehow I do have a current spike, like the steel building gets hit by lighting, or I weld through a cable or something, that it could overload the sub panel and cause some damage before it hits the main breaker.

Typing that out, and realizing how far away I am from owning a proper welder and compressor, it sounds like a completely crazy fear. At most I can see me running a shop vac alongside a drill, sawzall, or angle grinder while I have lights on. But that's 3 circuits that will be put into the car port panel anyway spreading out the load.

I over think things sometimes, but I've had some really E36 M3 times working on this house in the past. It also doesn't help matters that the friend with all the right tools has a crappy antique 60 amp main service panel at his house and forgets the rest of the world isn't so old fashioned.

If they're 5 feet apart you might as well just make room with a couple 15 amp cheater breakers and run it off the main buss. Seems like the more proper way to do it.

You can't put both legs of a 220 circuit on one of those piggyback breakers because they are both pulling off the same 110 lug in the panel. For 220, you need to take up 2 side by side lugs. On the top of the panel there are 2 big 110 lines coming in from the street. Each feeds every other lug in the panel. Every lug by itself is 110. Add two from the same 110 feed from the street and you still have 110. Add one from each of the feeds and you have 220 because the 110 feeds are independent of each other. Had a weird one last winter. One of the 110 feeds from the street was only delivering around 30V. The other was fine. Nothing fed by the 30V line was working and nothing requiring 220 was working. All the lights in the house were working, but unfortunately the heat and hot water were not. House was in between seller moving out and closing. Everything froze solid. Spent a week there fixing frozen pipes. At least the boiler was in the basement and it didn't freeze. Power thing reminded me of working on a British car.

I agree, 50A service is plenty for a garage. A 220V welder draws a max of maybe 25A running full hot. You will need 2 full 50A breakers on your main, each on a different pole like tr8todd said. That is how 220V works. You are grabbing 2 seperate lines of 110V. You should be able to free up 2 spots by moving other household circuits to duplex/thin/tandem breakers. For the sub-panel, you should get one with a neutral bus bar, NOT bonded to garage ground, to prevent ground loop.

This is how I put 100A service to my detached. I can run a 220V welder, 220V pottery kiln, 30A 220V heater, 220V baseboard heater, a power tool, and all 10 light fixtures at the same time. Ask me how I know :)

http://www.garagejournal.com/forum/showthread.php?t=169211

I would just run a subpanel in the carport off your subpanel. This is done all the time for 2nd buildings. I added a subpanel in the house for my feed to the garage panel. I would have the carport panel actually be in the carport so you run 1 big Romex for the feed.

When you get to this point, please ground everything properly and install GFCI protection.

I'm an Electrical Engineer. (RUN AND HIDE.)

I do power design for datacenters, among other things. I know we're talking about commercial vs. residential, but I would not recommend running a sub panel off of a sub panel.

Not recommended but it works. I have a 200 in the house. It feeds a 100 amp sub panel 125 feet away in the garage. That feeds a 30 amp sub panel in the kids clubhouse that is another 125 feet away, and a sub panel in the shed that is also 125 feet away. As long as you sink a ground rod at each panel, it will be fine. Then again, I was educated as an electrical engineer, but I'm now a plumber. Run faster and hide better.