Yet another electrical question - power panel

[ngiovas]

Sorry to be such a pest - I just want to make sure everything in my new shop is just right.

I originally bought a 125amp box with 12 slots for my sub panel in my garage - I knew I didn't need 125 amps, but I wanted the extra slots. After reading several posts and then looking at sonnie pies site on sub panels, I decided to return the 12 slot panel and purchase a 100 amp 20 slot panel to ensure I can expand in the future. The problem is that the box they gave me is different - it came with a 100 amp main breaker in the panel. Can I use this panel? The other one did not have any type of main breaker with it - only the breaker at the main panel. I purchased a ground bar, but didn't know if I could use it with this type of panel.

Thanks for your help.

Nick

[MadMark]

The breaker on the sub panel should be sized to carry the lesser of the maximum rating of the panel or the maximum of the main.

So if you have a 150A main service and a 100A sub panel, you'll want a 100A breaker in the sub. If the main service is only, say, 75A, then you'll want to reduce the breaker in the sub to only 75A.

Your original panel will still have needed a breaker installed, it was just sold separately.

The ground bar is a different issue entirely. There should be four buss bars in the panel, two 110V hots, a shared neutral and the equipment ground. Normally the neutrals and grounds are tied together in the box.

M

[dicklaxt]

Ground Bar ????? Where and what is this??? Please explain,we don't want you getting off on the wrong foot.

Dick

[woodmannie (Guest)]

Hi Y'all,
Mark is right on the amps.
I disagree on needing a main in the sub panel. You have a breaker in the main that feeds the sub. That is your main breaker. If your box has one, It won't hurt to have it. Just keep it lower than whats in your main box. That way it will pop in the sub and not in the main. Just easier to reset if your panel is far from the main.
My shop is fed by a 50A breaker for the main. Then I cut it to 20 and 15A cuciuts. I have yet to pop the 50A. Not bad since my shop is 120 feet from the main box.
As for the slots for breakers, remember that a 220 line takes 2 slots. And yes, you MUST feed 220 to the box. If you dfon't you'll have only half of the cuciuts working. The others will be dead.

[ngiovas]

I don't have the "Ugly's" book yet, but the book I am using states you should use a separate ground bar when running a sub panel. When I purchased my first panel it was labeled as a "sub panel" and it said right on the box "grounding bar must be purchased separately". I then bought a grounding bar kit.

My question is - if I am running a sub panel - now with a main breaker on the sub panel - do I wire it like I would the main panel, or do I still install the grounding bar and wire as a sub panel, but just through the main circuit?

(I think I am going to pick up a new book before doing any more planning.)

[MadMark]

Woodmannie, the problem occurs if his sub panel has a lower rating than the main. Then the sub could overload without tripping the main.

Also, tripping the main plunges the whole place into darkness. If there is a breaker on the sub panel that trips, then just the shop goes out (and normally at least one bulb in the garage will have house power and stay on as a 'safety' light.)

Again consider the situation with a say, 150A main panel and a 50A sub. Without a 50A breaker on the sub, then up to 150A could flow into it under dead short conditions potentially causing a fire as the circuit overloads. If the sub has a feeder breaker at the main, then the sub itself doesn't need one. But the whole concept of the sub is that there isn't enough space in the main and it's unlikely that the main has a 'spare' double-50 just sitting in it.

No, the sub needs an appropriately sized breaker in it.

As for the grounding bar, I know not. Time to call an electrician.

M

[dicklaxt]

I just went to the NEC and read the requirements for protection in panelboards. There are many scenarios, exceptions ,references to other articles that you could get lost in trying to save a few bucks and you might get yourself in trouble with local inspectors if ever at your site. This Sub panel by NEC definition is called a Power Panel . If you want to be safe put main breakers in this panel making sure they are not larger than the breakers protecting the wire that is feeding this panel and assuming every thing else up stream of breakers protecting feeder are within code requirements.

In my interpretation of the code you do not need it but there are several exceptions,if all fuses and breakers are co-ordinated properly you can go all the way back to the overcurrent device that is protecting the primary side of the transformer feeding the lihgting panel in your house. Now you can amagine where and how all this must be co-ordinated.

Put mains in your new sub panel and don't look back.

Dick

[router7529]

Just remember that in a Sub- Panel the neutral bar is to be isolated from ground bar, you must remove the grounding tab from the neutral bar that is screwed to the panal and install a seperate grounding bar in the panel. Run the ground line to the ground bar, even if you must drive a new ground rod for this.

[Sonny Edmonds]

...A pile of it!
Hell, to cut through it all, just hire a local *licenced* electrician. Many are available for "side" jobs.
Some will reduce thier rate for "beer included."

For craps sakes! #1-The neutral IS grounded, HAS to be or it is a floating neutral. Floating neutrals can cause a lot of trouble, and makes a ton of money for electrical folks like ME.
Put an Ohm meter on ANY neutral bus and see for yourself. There is a bonding screw on convertable panels, (which you won't, or I dought will, find at a "home improvement" center.) There is an electrical bond TO THE BOX. Adding a grounding bus, (which is also bonded to the box), allows you the convinence of a dedicated
grounding point for your sub-panel. Or you can use the neutral bus, but in most new panels they are sepperate bus's.
Normally one grounding bar (5/8" copperclad steel) is connected
at the HOUSE main panel to the grounding bus which is bonded to the neutral bus. The bonding wire for the main has to AT LEAST be armored with flex. Some areas require steel ridgid conduit.
We at the power companies also ground the neutral at our transformers, on the pole, or at the pad if a pad mount transformer. And we won't hook you up unless it is right. Inspectors be damned. It gets checked so some error won't cost a life. PERIOD.

Now, you also have to have a main CB at your house panel. That protects US from YOU. It also gives you a convinent place to shut off ALL power to your house.
Then your end breaks up on CB's for your homes distribution needs. Typically, 30 amps @ 240 volts for an electric dryer outlet, 50 amps @ 240 volts for your range, 30-50 amps for your electric water heater, (if so equipped). And a monster for your air conditioning/heat pump (if so equipped) or two even.
And on down the line, a dedicated 15 amp for your microwave outlet, at least 2 individual circuits to your kitchen besides, so your toaster and an electric skillet or what have you doesn't cause "neusance trips".
You may have a GFI CB in your panel for your bathroom(s) and outside recepticals and one or more garage convinence recepticals. Or they may have fed one GFI outlet and protected the rest with a GFI protected feed from that GFI outlet.
The rest of your home is split up on a mirad of CB's.
The biggest trouble with ALL home wiring is NO SCHEMATIC. Not a roadmap to be found! NADA! ZILCH!
Just some scrawl in the panel, if you are lucky. But who gives a damn.
We want to wire a shop, right?

OK, to the root of the problem. IF you have an available spaces IN THE MAIN PANEL OF THE HOME, indicated by square KO's in the panel where the CB's are at, GREAT! You'll need 2 for a 240 volt CB of your choosen amperage. A CB that will connect to both L1 and L2 in your main panel.
And you will need enough wire to go from your main panel to a SUB-PANEL in your intended shop. This panel NEED NOT HAVE A MAIN CB IN IT.
Hello? Remember it is a panel AFTER your MAIN panel. You have a CB protecting the wire feeding this panel at THE MAIN PANEL. All this stuff is on YOUR side of the main and meter. The utillities don't tell you what kind of dryer to buy, or stove. That's your problem and choice. (I LOVE America)
SUB-panel. GOT IT?
OK, Now good prudent practice would be to protect yourself from yourself. Run 3 wire w/ground (2 hot, 1 neutral, one bare) cable, from your MAIN PANEL to your SUB-panel.
If in the dirt use UF type cable. UF stands for Underground Feeder.
If inside, like through an attic and walls, no exposure to the sun or elements, use NM. NM stands for Non-Metalic sheithed cable.
#10 for 30 amps; #8 for 40 Amps, #6 for up to 60 amps.
Anything over that and I want to buy stock in your power company and the place you are buying your supplies from. Email me before you go shopping!
Now what DO you need FROM your sub-panel?????
Well, just how much can you operate at one time?????
One TS. One DC. One shop vac. And shop lights. Maybe an air filter as well. Continous at one moment, under load.
Or
One this and one that and some others.
Point is this: you setting up a business or a home shop that won't see but one soul once in a while? Or maybe two days a week? Or in my case, every night and most of the weekend?

Right..... you aren't really going to need 100 or more amps out there. And getting so much power out there is going to be real expensive. Money you could better spend to enhance your shop, right?
Put a 50 Amp, 240 volt, 2 pole CB at your main house panel, feeding a sub-panel large enough to have a 240 volt CB for all your dreams that will need 240 volts. Possibly 6?
And two 15 amp lighting circuits. More than enough for all lighting needs.
And maybe two, 120 volt, 20 amp circuits for outlets.
Because you will never run EVERYTHING all at once, at full load.
What the hell are you? An octopus???
So we are at 10 total circuits, 16 openings in a SUB-panel.

Want to know what I have? 8 openings. And two aren't used yet. That might go for the bandsaw-jointer 240 volt circuit. Because the 240 volt also feeds some of the 120 that runs with it.

Notice I never once called it 110 or 220. That went out with barbed wire for telephone service.

Come on over and see my page on a sub-panel for your shop. This crap here is ratherly pissing me off.

Sonny
http://home.earthlink.net/~sonnypie/

"Precision Firewood Specialist"

[dicklaxt]

Sonny ,I only recommend a panelboard with mains as a means of convenience in the shop. It appears Mr "X" is starting from scratch and being able to isolate his shop would be a good practice to keep unwanted hands and fingers from operating or turning on tools.

Dick