I've got 30A...what are my limits?

[diggler306]

I have 30 amps (10-3) feeding my detached garage. I WISH I would have gone bigger when the garage was built but... I didn't know much of anything at the time (PRE-garage journal days) so c'est la vie. What I want to know is, what are my limits?

Will I be able to run a gas unit heater, tv, stereo, 9-12 4' two-bulb T8's... plus a 15a compressor and whatever woodworking tools I may use (mitre saw, table saw, router, etc)?

My next question is: I have a small, 4 breaker panel. Currently I have 2 duplex breakers in there. I like to keep things very organized, so for me, the more circuits the better. But how many circuits can I realistically have for a 30amp feed before they basically become pointless? I'm not even sure if that question makes sense... but humor me. lol

Thanks in advance.

 

[jvitez]

The answer is easy: simple arithmetic.

Start with Ohms law. 30 amps x 240 volts= 7200 watts. That's the max you can run at one time without popping the breaker.

Next, add up the wattage, not amperage, of everything you would consider running at the same time. Is it less than 7200 watts? You're good to go. If not, time to reconsider how you'll use electricity at the same time.

A NG unit heater will have the motor amperage rating with the data sheet, and it will say at what voltage it's spec'd. For eg, 1.9 amps at 115 volts. So 1.9X115= 218.5 watts, or 220 watts for ease of addition. Fluorescent fixtures will have a ballast amperage rating. Again multiply by voltage to equal wattage, in this case use 120 which is 1/2 of 240 that's coming into the subpanel.

You get the idea. Find the wattage of everything you're interested in and start adding things together.

 

[jvitez]

Now for completeness, I'll add the code type disclaimer.

Everything that's considered a continuous load (more than 3 hrs use at a time) needs to be multiplied by 1.25 as a heat/fire/safety factor. Your woodworking appliances and branch circuits are intermittent. The unit heater and lights are continuous. So add up continuous load, multiply x 1.25, then add the rest of loads at straight numbers.

 

[theoldwizard1]

Will I be able to run a gas unit heater, tv, stereo, 9-12 4' two-bulb T8's... plus a 15a compressor and whatever woodworking tools I may use (mitre saw, table saw, router, etc)?

My next question is: I have a small, 4 breaker panel. Currently I have 2 duplex breakers in there. I like to keep things very organized, so for me, the more circuits the better. But how many circuits can I realistically have for a 30amp feed before they basically become pointless? I'm not even sure if that question makes sense... but humor me. lol

Don't worry about the panel. It is designed to protect itself and you ! Besides how many times are you going to be running more than 1 of those tools at a time (you forgot shop vac).

By duplex I assume you mean tandem (two circuits, one slot). Sure, put in 2 more tandem breakers, but I would make sire they are 20A, each circuit and then use 12 gauge to all outlets on those circuits.

 

[RivennHewn]

Don't forget start up load for most tools is higher than running load.

Should calc in some fudge factor.

 

[hidollartoys]

30 amps

 

[vartz04]

I have a 30 amp feed to my garage as well. I tested it.

Mini fridge on
Compressor on 15 amp
1500 watt heater on
Shop vac on
4-t8 4' 2 bulb lights on
Circular saw on

Didn't trip. I'm pretty happy with that. I'd never change it except I want a 220 outlet in their for a heater so I'm gonna pull some 6's and get 60 amps.

 

[pattenp]

Just how long of a run is the 10-3 to from panel to panel? This will also effect your load capacity.

 

[FrankieD]

I owned a converted bungalow/house. When I first bought it I did not know the main was one screw in glass fuse. We had a house warming party. Everything was on,ac,coffee maker, stereo,fridge. When the sun went down thats when I learned the limits of that 30A fuse! You can have all the circuits you want you just can't use them all at once.

 

[Larwyn]

I ran my little woodworking shop in the shed out back off of 75 feet of 12 gauge extension cord plugged into a 15 amp 120 volt outlet on the back of the house for a couple of years before getting the 240 volt 60 amp service out there. Reason for delay was the need to upgrade the service at the house first.

For heat I used a propane space heater (no fan), and for cooling a good sized osculating pedestal floor fan. It became routine to turn off the fan and all but one light before starting up most machines. It still dimmed that one light on start up and was inconvenient but it worked. And I'm sure that experience has only served to enhance my enjoyment of having plenty of power out there now. I can run the table saw with the shop vac hooked up, leave all the lights and the fan going and never dim a light. Those tools which allowed for it were changed over to 240 volts, mostly to better balance the current demand on the two legs of the supply to the shed (not sure how important that was but it sounds like a good idea).

 

[zmaxmotorsports]

Youll be fine as long as you aren't running lots of big stuff at same time,if you have access to a clamp on meter clamp it around one of the feeds to the panel and it will tell you what kind of load youre actually pulling.

 

[ddawg16]

10-3? Confirm 240Vac? If so, your fine.....

You have up to 30A on each 120Vac. I initially was running the same to my garage....I NEVER tripped a breaker....

Say you have a compressor...240Vac....it might pull 10A....still leaves you 20A on each leg....

Your only going to run one tool at a time.....

Yea...your fine.

 

[tfi racing]

You'll be fine with what you have,just don't expect to run the welder,air compressor,coffee maker and toaster all at the same time.The 30A breaker will let you know when you have loaded it up too much-the danger arises when someone gets frustrated and installs a larger breaker than permitted.

 

[diggler306]

The answer is easy: simple arithmetic.

Start with Ohms law. 30 amps x 240 volts= 7200 watts. That's the max you can run at one time without popping the breaker.

Really good info - thanks!

Don't worry about the panel. It is designed to protect itself and you ! Besides how many times are you going to be running more than 1 of those tools at a time (you forgot shop vac).

By duplex I assume you mean tandem (two circuits, one slot). Sure, put in 2 more tandem breakers, but I would make sire they are 20A, each circuit and then use 12 gauge to all outlets on those circuits.

Yes, sorry I meant tandem (and I DID forget shop vac!) I asked this question because I've been wondering if it was worth it to buy a panel with more spaces, just to be able to get more circuits. So far, this is what I have planned for circuits:

1 - Interior lights
2 - Exterior lights
3 - Exterior outlets (2)
4 - Left side & workbench #1 outlets (5)
5 - Right side & workbench #2 outlets (7)
6 - NG Unit heater outlet (1)
7 - Ceiling outlets (3) (Garage doors & cord reel)
8 - BLANK

All my outlets are currently on 15A circuits run with 14-2. While my walls are exposed, should I consider upgrading to 20A circuits? Or at least replace one side of the garage with 20A circuits, since I have to split the circuit into two anyway (currently all 12 interior wall outlets are one)?

I have a 30 amp feed to my garage as well. I tested it.

Mini fridge on
Compressor on 15 amp
1500 watt heater on
Shop vac on
4-t8 4' 2 bulb lights on
Circular saw on

Didn't trip. I'm pretty happy with that. I'd never change it except I want a 220 outlet in their for a heater so I'm gonna pull some 6's and get 60 amps.

That's a great example - thanks!

Just how long of a run is the 10-3 to from panel to panel? This will also effect your load capacity.

About 45'.

10-3? Confirm 240Vac? If so, your fine.....

You have up to 30A on each 120Vac. I initially was running the same to my garage....I NEVER tripped a breaker....

Say you have a compressor...240Vac....it might pull 10A....still leaves you 20A on each leg....

Your only going to run one tool at a time.....

Yea...your fine.

Yes, 10-3, 240Vac.

 

[VHF]

Just get a 20-space 100A subpanel. These are frequently on sale for around $50 bundled with a few breakers thrown in. You won't need to worry about running out of space for a long time (and certainly not before you upgrade that 10-3 feeder!)

 

[IONH]

My detached garage also only has a 30A 220V box. I expect that was to get by some of the codes when you go larger.. like needing a grounding rod or a main breaker in the garage box.

Anyway, I've never popped the circuit but I am conscious about what I do at the same time just so I don't pop it.

I have a 220V 3.5hp 60 gallon compressor, 8 or 10 T12 fixtures, 220V welder, 110V welder, hanging 110V LP heater, numerous chop/circular saws, more lights, more extension cords, etc etc. I would never run either of the welders while the compressor was on, that's just silly to even try. My larger chop saws may also be a test with the compressor or welders going. So I don't do that and I've been fine for over 5 years now.

I do, however, desperately want to upgrade the feed at some point, just have not had the time to do it yet.

 

[Alchymist]

My detached garage also only has a 30A 220V box. I expect that was to get by some of the codes when you go larger.. like needing a grounding rod or a main breaker in the garage box.

Detached garage needs ground rod, any panel with more than 6 breakers needs a main breaker.........

 

[theoldwizard1]

...I asked this question because I've been wondering if it was worth it to buy a panel with more spaces, just to be able to get more circuits.

IMHO, no, it is not worth the cost as long as you can still get breakers for your load center.

So far, this is what I have planned for circuits:

1 - Interior lights
2 - Exterior lights

Combine these 2 on to one 15A circuit.

3 - Exterior outlets (2)
4 - Left side & workbench #1 outlets (5)
5 - Right side & workbench #2 outlets (7)

I would put the exterior outlets on the interior circuits. One on each would be good. These should be 20A circuits (which means 12 gauge wire). That many outlets on one circuit is likely to NOT be compliant with current code, but I wouldn't worry about it, especially if you upgrade to 12 gauge wire.

6 - NG Unit heater outlet (1)
7 - Ceiling outlets (3) (Garage doors & cord reel)

If the cord reel is primarily for a light or light duty power tools (drill, circular saw, etc) you could put this on the lighting circuit, but then I would consider bumping that to 20A (12 gauge). It might be easier to just leave it on its own 15A circuit.

 

[theoldwizard1]

Detached garage needs ground rod, any panel with more than 6 breakers needs a main breaker.........

In the case of the OP, with an old load center, there may be no ground bus or it maybe bonded, which met code at the time it was installed.

Is is worth the effort to try and retrofit a non-bonded ground bus ?

 

[Alchymist]

In the case of the OP, with an old load center, there may be no ground bus or it maybe bonded, which met code at the time it was installed.

Is is worth the effort to try and retrofit a non-bonded ground bus ?

True, but if he replaces the panel......

 

[theoldwizard1]

True, but if he replaces the panel......

Some people are on a budget !

The recent kitchen remodel at my daughters house probably should have had a new load center, but I did not want to spend another $500-$1000 when I could just add some tandem breakers (which still cost $40 each).

 

[IONH]

Detached garage needs ground rod, any panel with more than 6 breakers needs a main breaker.........

It only has 6 breakers, so maybe that was another piece of the code I had forgotten. The garage is probably 40 years old now.