Easy Question Regarding Breaker Box Capacity

[LlamaSchool]

The large main at the top of a breaker box is labeled "100 A" on the handle. It has the two large gauge black wires coming in from the outside to this main switch. However, when I add up the individual breakers that run vertically down the two sides of the box, they add up to about 300 amps.

What's up with this? I was about to add a few breakers to the box and trying to figure out how much more capacity I have on the house main but it's just not making sense to me...

 

[growshower]

i think what you are becoming confused about is that even though it adds up to be 300 amps, that is just maximum possible amps which you would most likely never use, you could have empty breakers as well that electricians install because they come with breaker boxes, no expert at this though

 

[The Southpaw]

your AC Service is capable of delivering 100 amps total.. each circuit is capable of the amps on the individual breaker. if the current (amps) on any circuit exceeds the rating the breaker trips.. if the SUM of all your circuits exceeds 100 amps, the breaker trips (even is the entire load is only coming from a few circuits)

Maybe I should gently suggest that if you dont understand this you should not be making changes inside your breaker box....it is not complicated but it should be done correctly

 

[LlamaSchool]

Thanks for the advice. This is sort of what I figured but I wondered if it was standard practice to allow maximum capacity of individual breakers to exceed and thus potentially trip a main. Of course I doubt anyone would run every circuit at 100% capacity.

Southpaw - Your concern is legitimate but my plan is fairly simple I think. I will be removing two linked 30amp circuits that feed a (30 amp 240v I believe) central A/C unit that we never use and replacing it with two individual 30 amp 120v outlets that will run through conduits along the basement ceiling to work boxes (protruding outlet boxes) in the adjoining basement room. That's about as basic as it gets, right?

I need to do a little more research to understand whether I should run the ground wires (green) back to the ground in the box or whether I should ground them somewhere closer to the outlets.

 

[madpenguin]

I wondered if it was standard practice to allow maximum capacity of individual breakers to exceed and thus potentially trip a main.

Sure. Not a problem with that. That's why your main breaker is there. It's sized accordingly to protect your service entrance cable that comes from your meter.

and replacing it with two individual 30 amp 120v outlets that will run through conduits along the basement ceiling to work boxes (protruding outlet boxes) in the adjoining basement room. That's about as basic as it gets, right?

Not really. I hope your not planning on using the standard 49 cent receptacles on the end of those 2 30A runs.

I need to do a little more research to understand whether I should run the ground wires (green) back to the ground in the box or whether I should ground them somewhere closer to the outlets.

I have quite a few questions overall. Are you using the same #10 AWG wire that fed your AC unit and re-routing it to your new receptacle locations? Sounds like your planning on using conduit with individual THHN conductors?

My pizza is getting cold so I'll post back in a few. I'm also making some hash so I need to finish that quick...

I will say that you need a few pointers here before you start unless you want a fire on your hands. I'll post back in an hour or two.

 

[madpenguin]

You should probably post back with some clarifications on your setup/equipment. Not sure what your talking about with the grounds and I assume you want 2 - 30A 120v receptacles to feed your equipment.

Clarify what you mean about the grounds and list all the equipment you need to run in your room. That would help towards the most proper wiring for what you need.

Are you out of space in your panel? Is this why you want to abandon your A/C unit?

 

[LlamaSchool]

I'll definitely be posting AND researching more before I lift a finger.

1. I need 30 amp rated receptacles I imagine to fit into the workbox (haven't researched yet) - definitely understand the receptacle needs to tolerate more amperage than a 10amp/15amp/etc. Not quite sure what a 49 cent receptacle is but I'm guessing it's no good. I want like heavy duty garage-rated type stuff.

2. As far as wiring, I'm not reusing anything. The run from the breaker panel to the outlets will be about 30'-40' so I don't mind buying some good heavy wire (I think 8 gauge for 40 amp but need to double check). No re-routing of anything. Just disconnecting the A/C breakers (240v) and replacing everything from the breakers to the new outlets. There aren't even workboxes in there yet.

Here's what I haven't planned out really yet but just pictured in my head...

1. Turn off main; (not in right order) hook hot to breaker, neutral to neutral bar, green/ground wire to ground (ground is in panel somewhere I imagine but I get it confused with the neutral bus)

2. Run all the wiring through a conduit of some sort to protect the wires as they will travel along the cieling to another room; terminate conduit in workbox where I wire in the receptacle.

3. Repeat. Then turn power on.

I really haven't gone over any of these last steps so please don't waste too much time critiquing. I know you know your stuff and could prevent disasters elsewhere.

I am out of room in my box. It seems like a few 120v single breakers are "double size" breakers that take up twice the room of most of the other breakers but feed only one hot line and have one breaker switch. These are not the linked 240v breakers that take up two slots but these large 120v breakers take up the same space as the linked breakers for 240's. I'm not sure if I can replace these with the smaller profile breakers and open up more room.

Losing the A/C is no big deal as these linked 120's (making 240) will open up the space for two unlinked 120's (making 2 x 120). I don't use the central A/C because of the power bill.

What's Running:
-edited-

Again, I'm not about to jump into this, madpenguin so no worries about getting into specifics. I have not fully satisfied my research requirements beyond the very basic planning.

 

[madpenguin]

Ok.. Sounds like your on the correct train of thought. Just wanted to make sure.

A "49 cent receptacle" is the standard 15A blue-backed receptacle that you see at Lowes or HD.

Yes, you will need 30A rated receptacles if your using 30A breakers. You need atleast #10AWG to feed them. If you run your wire in conduit then it has to be individual THHN conductors and not sheathed romex. You can't strip the conductors out of #10 romex either. Has to be marked THHN and the grounding conductor has to be sheathed as well.

I assume by "linked breakers" your talking about 2 single pole breakers that are joined at the handle to form a 240v double pole breaker. As for the double pole breakers (with one handle) that only feed one hot conductor, that's not making too much sense. If it takes up 2 spaces, then it should serve 240v across 2 hot conductors.

There is a "Growroom Electricity and Wiring" thread floating around here somewhere. Pretty much all of the basics are covered there if you want to read it, but it sounds as if your on the right track. Just remember that you can only safely go up to 24A on those 30A circuits, no more. So, one of those circuits should be dedicated for your lights only.

If you add 2 more lights in the future, then that takes up your other 30A run. There will be no room to run a dehumidifier if so.... 24A on each circuit and not a watt more.

You might just consider running a sub panel to your grow room instead. Would allow for the most versatile installation.

Post back if you have any questions.

 

[PharmaCan]

Ok.. As for the double pole breakers (with one handle) that only feed one hot conductor, that's not making too much sense. If it takes up 2 spaces, then it should serve 240v across 2 hot conductors.

When he says, "It seems like a few 120v single breakers are "double size" breakers that take up twice the room of most of the other breakers but feed only one hot line and have one breaker switch.", he's talking about slimline breakers vs. standard breakers.

remember that you can only safely go up to 24A on those 30A circuits, no more. So, one of those circuits should be dedicated for your lights only.

If you add 2 more lights in the future, then that takes up your other 30A run. There will be no room to run a dehumidifier if so.... 24A on each circuit and not a watt more.

You might just consider running a sub panel to your grow room instead. Would allow for the most versatile installation.

Post back if you have any questions.

Two 1000w lights ~ 17 amps. How do you figure that that maxes out a 30 amp circuit?

You're right about the sub panel. That would be the cleanest and easiest way to do things.

PC

 

[narutonut]

in my estimation it would be easier for you to build one of these http://www.hydroponics.net/learn/grow-light-controller.asp
This is very simple to do and instead of putting the pig tails on the ends you could just run this right to your work boxes all nice like. You run 240v from the panel to the relay box and step it down 120v if you don't want to rewire 120v ballasts for 240v. ElCap built one of these a while back and here is what he said about it.

Check out this rig I built, a 240v 4-outlet light controller that uses any simple timer, so you don't need some heavy duty specialty timers, there's a big 30A dual pole contactor relay in there.

Plug that baby in your common 30A dryer outlet, and you have 4 NEMA 6-20 style 240v/20A plugs to run your lights, heavy power tools, air conditioner...whatever. It's a pretty versatile thing, done DIY with instruction from the web that were sweet ass sweet in detail with tons of pics. I over-spec'd the wiring on the plugs/outlets, it's 12/3 SJO. Took maybe 10 hours of work and two trips to the home improvement stores, about $115 total. I could have done it for $95 if I hadn't oversized, and got the box I was actually looking for (they were out), and you take off the $8 or whatever for a wire stripper/crimp tool.

A CAP MLC-4 by comparison, cost about $200 retail and on sale as cheap as $120. But you can only run 1000w per plug because their wiring is undersized and they use dual chained style receptacles instead of individual plugs. And you can't have one of the plug-ins always "hot" while the others are on the timer.

And, I KNOW how well this one is put together because I did it with my own damn hands. Not some random line worker in a factory, bored off their ass and slappin' shit together. They're faster, no doubt, but if something has the capacity to burn my house down and kill my family if done wrong I'll do it slow and right.

I can plug the 120v trigger cord straight into an outlet and the outlets will always be on, I can plug the trigger into a timer and it will control all the outlets. Within 5 minutes, I can configure it to have 3 outlets on the timer and 1 always having power...or 2 and 2. Handy feature if you want to run a 240v ac or dehuey all the time but time control the lights. It's a flexible tool and would be ideal if you move around a lot...just find a space with a clothes dryer outlet and use a gas dryer or the local laundry.

Now I can get my light and fans and stuff off the 120 circuit.

So anyway if you do it this way all you need is to run new 240v line to the breaker the ac was using from this relay and your done. Controlled by one cheap digi timer is the kicker though. Hope this helps.

 

[PharmaCan]

in my estimation it would be easier for you to build one of these http://www.hydroponics.net/learn/grow-light-controller.asp
This is very simple to do and instead of putting the pig tails on the ends you could just run this right to your work boxes all nice like. You run 240v from the panel to the relay box and step it down 120v if you don't want to rewire 120v ballasts for 240v. ElCap built one of these a while back and here is what he said about it.



So anyway if you do it this way all you need is to run new 240v line to the breaker the ac was using from this relay and your done. Controlled by one cheap digi timer is the kicker though. Hope this helps.

That is a nice looking power box - the only problem is that it doesn't fit with what LlamaSchool wants to do because the box is strictly for 240v and doesn't have a neutral. While including a neutral in the run from the panel to the box would be easy enough, it could pose a problem for someone without electrical knowledge because it would mean modifying the step-by-step instructions.

I'm not trying to dis you or what you posted - it's just that it really doesn't apply to this situation.

PC

 

[The Southpaw]

I need to do a little more research to understand whether I should run the ground wires (green) back to the ground in the box or whether I should ground them somewhere closer to the outlets.[/QUOTE]



You should run them back to the box..Peace!

 

[madpenguin]

PC, I was speaking in regards to a dehumidifier. Your average dehumidifier draws around 9A. Add 2 more lights and those 2 - 30A runs are not enough.

It's possible to squeeze 3 120v lights on one of those runs but without knowing the amp draw, no one can say for sure.

A Tandem should still only take up one space tho (as well as having 2 ungrounded conductors).

A sub-panel is really the only way to go here IMO.

 

[LlamaSchool]

Well I got on this a few days ago. I ended up running 240v through THHN 10 gauge wires in a conduit to a new sub panel that I set up with 3 20 amp circuits at 120v. I really like this set up. From here 3 different conduits go to 3 20 amp rated receptacles in 3 work boxes.

I haven't put anything under load yet as I don't have anything going yet but everything works just fine. This was way easier than I thought although I did pick up a book called "Home Wiring" by Black and Decker. I would definitely recommend this book for anyone whose experience is limited.

 

[madpenguin]

Yea, that is a good book.

But, um.... #10 to feed your subpanel? Now you only have 30A total instead of 60A which was your original plan (This sub needs to be fed from a DP 30A breaker since you used #10). That leaves you no room for those future lights.

I assume you used #12 THHN (black,white,green) for the 3 different receptacle runs out of the sub panel?

Well.... If you ever need to add more equipment, you'll have to re-pull larger conductors to your sub. Just remember not to exceed 16A on those 20A branch circuits coming out of your subpanel. Even if you load all 3 20A runs up to 16A, the main breaker for the sub back in the main panel will kick. Even if your draw on that subpanel winds up being 28A, the main won't kick but your #10 will be seeing too much current for continuous loads. That's not good. You really should have pulled larger conductors to your sub and that makes me nervous TBH.

To be safe with your current setup, you shouldn't draw any more than 24A on that sub panel.

And I'll assume you pulled a red,black,white and green conductor to feed your sub and have isolated your neutral and ground buss at the subpanel. The book should have covered that pretty well.

Glad you got everything running. Sounds like you might have had fun and learned something in the process as well... ;-)

 

[LlamaSchool]

Hopefully I did this right...I haven't loaded anything up so I will wait to confirm here. My original plan was 60 amps of 120v not 60 amps of 240v and this is what I ultimately did.

The 240v breaker in the main box said 30amp on each pole so I thought that meant that the total output there was 30 amps of 240v. In fact, I'm pretty sure that is true. I looked at some breakers at the hardware store and they looked the same and were sold as 30 amp/240v breakers.

According to the chart in the book, 10 gauge wire was good for 240v/30 amp. You feel that is too small?

Therefore, that gives me 60 amps of 120v to play with once in the sub panel and on 120v circuits no? There are two hot buses in there - one fed from black, one from red (obviously). I have 3 x 20 amp 120v receptacles coming out of sub panel. I used 10 gauge for the receptacles. I guess this was overkill but I don't think it can hurt.

All my wiring jives with what you are saying. I do have separate neutral and ground in the sub and the 4 wires running from main box to sub. What I don't quite understand is what you are saying about amperage. I thought that if I was running my sub off of 240v/30 amp then 10 gauge was fine.

Why would the circuit in the main box kick if I loaded up all 3 20A/120V receptacles to 16A? Wouldn't that be 48A/120V (which is the same as 24A/240V) on a 30A/240V circuit?

Do you mean I shouldn't run more than 24A of 240v? My only way of understanding your last post is if you thought my equipment was all 240v. I could understand that but my receptacles are on 120v circuits since all my equipment is 120v. I'd like to do this all to code just to be safe so please tell me what I am misunderstanding if you can.

Thanks as always for entertaining newbie questions. I am certainly enjoying this.

 

[madpenguin]

An amp is an amp is an amp.

You can draw 30A @ 120v or 30A @ 240v. Either way, once you hit that mark, your 30A main back in your main panel will kick. It doesn't know or care what voltage your running your equipment, only that when you exceed 30A it's time to shut down. That's why it says "30" on the handle. If it were voltage dependent, then the handle would say "60A@240v 30A@120v". Doesn't work that way. 30A period.

Your only option now is to run everything you can at 240v or pull new conductors to your sub.

Is there anyway you can take a close up picture of your main panel? That or just say exactly what breaker you used for the main? It is one solid piece, right? One breaker? Takes up 2 slots? Has one handle that spans the entire thing?

This is what you should have used: It looks like 2 breakers but is just one.

If you really wanted 60A, then you should have pulled #6 THHN and used a double pole 60A breaker for the main.

 

[madpenguin]

I'm sorry, rarely do I pull in conduit. I have romex on the brain with regards to ampacities.

If you wanted 60A then #8 THHN is what you want. The #10 grounding conductor could stay where it is according to Table 250.122 of the NEC if you were to upsize to #8/60A

 

[LlamaSchool]

According to the Black and Decker book, we want #6 to run 60 amps (from main breaker to sub panel) so I think I will go with this to be safe. However, if you think it's OK to keep my #10 ground (green) from main breaker to sub panel then I will not mess with this one.

I did use the double-pole 240v breaker in my main circuit box as pictured in your image above. Mine says "30" on each side of the connected pole (just like the one in your picture). However, as I understand it this is still only a 30 amp 240v breaker and I need one marked "60".

I will upgrade this to the same style but with a 60 amp trip capacity and upgrade all wires to the sub panel except for the grounding wire. This will allow me to use all 20 amp 120v receptacles to their full capacity if I need.

 

[BigTex]

If your main service is 100Amp you barely have enough ampacity to power your home, much less a Indoor Grow. If you dedicate 60 amps to your grow that leaves 40 amps for your home @ 100%!!! You can expact virtually every all your appliances to have a very short lifespan. You will probably burn up the compressor on your fridge, AC and other related stuff. Try and run a skill saw or something & it'll probably make your lights dim and stuff.

If you wanna be safe upgrade your home elec. panel to 200Amp and use that 100Amp for your growroom sub-panel. Go buy yourself a cheap Amp Probe or Amp Clamp and just see for yourself how many Amps you are using. You can upgrade for less than replacing a major home appliance. I'm a Master Electrician and I know what I'm talking about. If you do what you are saying you're gonna do you are asking for trouble and possibly a burned home. If you want some sound advise PM me & I'll help you out. .....you should invest in that amp probe too......