4 wire, 30a dryer circuit question

[Medical_Man_420]

Im tring to figure out all my options with a 4-wire, 30A, dryer circuit. I'd like to plug a sub-panel into it, but I have a few questions on how many circuits I can branch off of the sub-panel. From searching on the internet (please correct me if I'm wrong), a 30A circuit at 240v can handle around 6900w (way more 240v juice than i need), and a 20A 240v circuit can handle around 4600w. So I thought a 20A 240v circuit would be perfect for all my lights (with over a 1000+Watt safety margin). So one 20A double breaker(240v) in the sub-panel taking up 4600w out of 6900w total capacity (leaving 2300w free at 240v), how many 15A 120v single breakers can I add? I was thinking 1800w per 15a 120v breaker, so I'm thinking one 15A 120v, and that would leave 500w to spare on the sub-panel? That would be great if i could run one 20A 240v line, and one 15A 120v line all off the 4wire 30A dryer circuit, then all my electrical problems would be solved. I know messing with 240v/120v is dangerous shit, so i have full respect for the power gods This tutorial is what im going off, quite a bit, -----------------> http://www.hammerzone.com/archives/elect/p...01/overview.htm


Peace and Grease

 

[Guest]

You can easily do this,what you want is a 120/240V 30 amp subpanel.You can remove the dryer receptacle and mount the subpanel directly over the box coming in the back of the panel through the knockouts in the back.Now you simply tie your two hot wires to the "hot lugs" in the panel,the neutral on the neutral bar and the ground on the ground bar.From this panel you can run both 120V and 240V circuits,the difference being the 120V circuits will utilize "single pole" breakers and the 240V circuits will utilize "2 pole" breakers.The 30A subpanel should be fed by #10 AWG sized wire and be fed from the main panel by a "2 pole" 30 amp breaker.

 

[Medical_Man_420]

excellent, thanks SKELETOR! now what are my breaker limits? can i use a 20a double pole, and a 15a single pole, to there max potential, and not melt the 10gauge wire goin back to the main panel, 30a double pole breaker?

woohoo, i found a 30a sub panel i belive will werk, is this what your talking about ---------> http://electrical.hardwarestore.com/14-51-breaker-boxes/main-lug-panel-607112.aspx

peace and grease

 

[Guest]

Count up your total amperage and if shouldnt exceed 24 amps.The max amperage on a 12 wire 20 amp circuit is 16 amps regardless if its 120V or 240V,the max amperage on a #14 wire 15 amp breaker is 12 amps regardless if on a single pole or 2 pole breaker.So,if you had both circuits loaded to capacity,you would be drawing 28 amps,slightly over the max 24 amps.The thing is,I doubt seriously that you will be using both circuits to max capacity,it just doesnt normally happen.What you need to do is add up the nameplate amperge ratings of everything you want to power.If you're running a 1K fixture at 120Vits normally about 9.5A,if you run it at 240V it only draws about 4.5 amps.Using 240V allows you to get more fixtures on a single circuit.

 

[Medical_Man_420]

Thank you so much for answering the question with pure FACTS! woohoo, you da man. you just dont find SOLID advice like that everywhere!

You da man SKELETOR, i have everything i need to know now. If your ever in oregon, ill buy ya some tasty beers at some fine microbrewerys, hehe.

Peace bro

 

[IronLung OG]

wow that was really helpful! exactly what i was looking 4!

 

[packn2puff]

It's all good info..80% of the circuit's rating is the magic number i.e 30A=24A or max load allowed..
The panel in the link only has 2 slots..so you get 1 240V or 2 120V but not both..
240V in single phase utilizes a breaker on each pole..
each breaker is the same current rating and their only connection to each other is the toggle bar..
so when either one is tripped it disconnects the other as well..what this means is each conductor can be loaded to 24A..
or 4-(single pole) 15A 120V breakers(circuits) or 2-(double pole) 15A 240V circuits or 2-120V 15A and 1-240V 15A circuits..
the panel has to fit 4 breakers(4 slot) worth at least..The lines are 180 degrees out of phase so they can share the same size neutral..
so each line is worth 30A in relationship to neutral giving you 60A worth of current at 120V..

4 slot panel
1 30 amp 4 wire Dryer Plug
1 Double Pole 15A 240VAC breaker
2 Single Pole 15A 120VAC breakers

What you get..2-120V 15A circuits and 1-240v 15A circuit..mount the box and just plug it in to the dryer receptacle..
your selection of device receptacles is up to you..you can gang both 120V circuits together or each in it's own box..
but each needs it's own neutral conductor back to the sub-panel..MC cable flex 12-2 solid (only 14-2 is needed..but bigger is OK..
nothing wrong with de-rating) is good choice if you want to run the receptacles to a location near the devices..
MC is easy to work with and fairly sturdy and you can use the same wire 12-2 on the 240V 15A circuit as well..

Otherwise you can mount the J-boxes to the sub-panel with 1/2" nipples..
Make sure the sub-P and breakers are meant for each other(brands and type; like Homeline, Square-D, Murray etc...)

at least this way you can easily remove the setup by just unplugging the sub-panel from the dryer receptacle..and all is back to as it was..

Hope this helps some

 

[Guest]

I wouldnt get that panel,thats an ultra cheapo 2 space panel.I'd get a minimum of 4 spaces,2 for a 2 pole breaker and 2 for 2 single pole breakers.With a small panel like that,you'll probably have to buy the ground bar seperately although youy may find one with a ground bar.The difference between the neutral and ground bar is the neutral bar should be up on insulators,it should have no continuity with the metal enclosure of the panel.The ground bar on the other hand should be screwed directly into the can itself so there is continuity between the ground bar and the panel enclosure.Have you added up the nameplate ratings of everything you want to power yet?Too many people use wattage and ohms law,this is incorrect a 1K fixture doesnt draw 1000 watts it draws a certain amount of AMPS at a certain voltage.Ohms law is great to know,but not to do circuit sizing with.EDIT Also if it were me I'd definately hard wire the panel and mount it right on the wall over the dryer plug box,I wouldnt get a plug in deal but thats just me.Why would you want to do that anyway?

 

[tuttlebudd]

 

[Medical_Man_420]

SKELETOR - "Have you added up the nameplate ratings of everything you want to power yet?"

yes i finnally did, heres the total amp draw id like to use,

six, 600w HPS at 240v, for a total of 18amps at 240v

and 8amps of 120v items (fans, pump, aquarium heater, etc.)

 

[packn2puff]

If that's the case..since most of what you want is 240V on a 30A circuit..just make a 4 wire plug to 6 receptacle adapter and just use the breakers in place..
would save a lot of money..and use another 120V circuit (like the washer's)..this way you can just use J-boxes and nipples or cables..
no sub panel or extra breakers..just some 12gauge wire (14 would OK too) for the branches..similar to tuttlebud's diagram..just with 6 outlets.. My

 

[Medical_Man_420]

packn2puff: that makes perfect sense, and I can use the washer 20a, 120v. I understand most everything you said, but... I'm kinda lost on the "just make a 4 wire plug to 6 receptacle adapter" part. the 4 wire is #10, and i know i dont want to use that to wire up outlets. if you could help me out with this "6 receptacle adapter" that would be great. Oh yeah and thanks for the nice diagram tuttlebudd, but it dosnt make a whole lot of sense to me, hehe.

Peace and grease

 

[packn2puff]

You get a dryer plug(usually comes with 6 ft cord..copper)..any hardware store has um..a lot of 240V dryers don't come with plugs..
run it to a j-box..from the box (this is where I don't know what you want to do) if you want all the outlets in one area..
then you can buy like 3" long or so 1/2" pipe nipple connectors..knock out the knock outs and connect the nipple(conduit) between say 3 double gang j-boxes..
so you would have a deep j-box connected to three metal double gang boxes..
you can then run 12 gauge THHN wire or so to each box and make connections..in the main box just wire
with big wire nuts like "blues" ..twist L1 (one of the hots) from dryer plug with the 3 12AWG wires from the L1 wires coming into box from outlets..
4 wires under nut..
Twist L2 with the L2 outlet wires..4 wires under nut..Cut of conductor and cap the neutral from dryer plug wire(not used)..
connect the green or bare wire ground to the main j-box and all of the outlet's grounds..
you can get the receptacles and plugs for each ballast at the hardware store as well..some ballasts have a 120/240 switch..
some you have to open up and re-tap the transformer..you can usually buy the 240V cords for your ballast..
then just match the plug with the receptacle you need..just don't use 120V receptacles..
too easy for a dangerous situation..240V 3 wire twist locks are a good choice (2 pole 3 wire; 2 hots and ground)..
This way you don't have to open the dryer box..if the dryer wires are aluminum..you would have another can of worms to deal with..you move..just unplug the adaptor from the wall..done..
We set up similar setups with various outlets on a new job site when we establish temporary power at the power pole or such..
so the other contractors have a good choice of power for their tools..some use twist lock 120V or 240V or standard 15A 120V or 20A 120V..etc..
We use sub-panels and j-boxes usually mounted on a piece of plywood..after power is in the building..
we disconnect the main home run and take the set-up to the next job..connect to the meter and ready to go again..

 

[packn2puff]

btw..tuttlebudd is showing you how to make a 3 wire 240V to 2-120V outlet adaptor..

 

[Medical_Man_420]

packn2puff: very nice explanation. I guess I should have mentioned that I need the plugs/outlets in the next bedroom over. I was goin to run the 12-2 up into the attic, and drop it down into the spare bedroom (50ft max wire length I'm thinking). I was hoping I could just run one 12-2 wire ( to save money) and run the outlets/gang boxs in series (all off of one 12-2 wire), spaced every 4 feet in the spare bedroom. i suppose it would be much safer to run 3 seperate 12-2 wires (or 3 seperate 14-2 wires) from the j-box to more evenly share the load of 18amps total.

Anywho it makes perfect sense to just wire nut the 12-2 and dryer cord, but i didnt know it was just that simple, hehe. So what do you think about the # of 12-2/14-2 wire (1,2, or 3) i should use for 18amps of draw, i know 12-2 wire is rated for 20amps, but im nervous about when all six ballests turn on at once, only using one 12-2 wire. from what I understand ballests draw double or so the amps when first being fired up, and 6 ballests could over do it? not sure, you have been tons of help, thanks man!

Peace

 

[packn2puff]

When you connect one outlet j-box to the next to the next and on with one run back to the source..it's called a "daisy chain"..
I assume that's what you mean by series..because circuit is still a parallel circuit..all the L1's connect together and all of the L2's like a ladder(parallel)..
anyway you could do a daisy chain, electrically by code we would have to run 10AWG the last whip is gonna have all the total current on it..
Really the last way I told you should have wire that can handle 30+ Amps , ie: 10AWG, but since you were going to dedicate each ballast to each receptacle..
I wasn't gonna worry about it with 12AWG on each..if this was a permanent circuit installation that someone could plug into later..
See that was a dedicated dryer plug..now you're gonna make a circuit..so the whole circuit has to be able to handle 30A from any outlet
then the same size wire has to run to each outlet so any one outlet and wiring all the way to the breaker can support a 30A load..
Now here is what you can do..purchase 12-2 MC cable...this is a flexible metal conduit whip with wires in..
you can buy a cutter for it too..makes things go real quick..after you cut it you just insert a plastic bushing..
and snap it into a 1/2" connector or use a screw clamp type..it's probably the most used method of commercial office building wiring these days..
Well what you could do is run two whips of 12-2 in parallel with each other doubling your capacity..
if it's just you using the circuit and you're spacing out the loads, then just double the whips from the dryer plug to the first box in the daisy chain..

 

[Medical_Man_420]

"Well what you could do is run two whips of 12-2 in parallel with each other doubling your capacity.."

that sounds like a good option. im not to sure on how that is exactly put together, so im going to have to do some research online, about that subject. thanks for the great advice.

peace

 

[packn2puff]

It's just doubling up the pathway adding another lane on the highway..so to speak..instead of one wire each L1, L2 & Ground..you run 2 wires each..bigger wire sizes are the same thing (multiple strands of wire under one insulator)..this is just 2 strands of 12AWG each with it's own insulation..they are connected to each other so they act as one..
industrial do this all the time..rather than buy a wire the size of a baseball bat ..they just run several strands of a smaller gauge..
if you ran water from one bucket to another with a hose..you could handle twice as much water flow with two hoses..same thing

 

[Guest]

Thats not going to work bro,cant hook those inseries period and I wouldnt use 12 wire on an 18 amp load.What you you have is 26A total,slightly over the 24A max for a 30A panel.Pulling 18A on a 12 wire circuit on a 20A breaker is real iffy,I dont think I'd do it.

 

[oldnslow]

HAHA, smoke another one SKELETOR. Youre a stoner for sure! Youre also kinda fast to answer Q's you dont get! Please read the Q before firing off a halfassed reply that is no help. Peace ONS