Growroom Electricity and Wiring

[madpenguin]

can you explain why neutrals and ground are ok at the main panel but not ok in the sub panel?

I keep wanting to revisit this for some reason. It's a great question and I don't think I've explained it very well at all.

Any time you have neutral and grounds terminated to the same busbar, the panel in question has to be fed with SEU, or in other words, the neutral doubles up as a grounding conductor as well. Inaccurate statement but will have to do I guess.

The job of a neutral conductor is to carry the return current back to the source, as I've stated, but it's important to know that the neutral carries the imbalance of the load.

Say, in my main panel fed with SEU, One incoming hot leg (or phase) is drawing 60 amp. The other hot leg is drawing 40amp. This current draw is being utilized by your branch circuits feeding your entire house.

The return current traveling back to the transformer is not 100 amp. It's 20 amp. This is why neutrals are allowed to be smaller than the hots in some instances. This is why it's good to balance the loads in your panel also. If you know 2 appliances are likely to be running at the same time, then put them on opposite legs. On the other hand, you would put a separate AC unit and furnace on the same leg because you know they'll never be running at the same time.

Kitchens are required to have 2 - 20A small appliance branch circuits. I generally stab them onto different legs.

The same holds true when using Multi Wire Branch Circuits (Using a 14/3 to feed two separate 120v loads but sharing the neutral). If both 120v loads are drawing 10A, then the return current on the shared neutral will be 0.

So anyway, the grounded conductor (neutral) of your SEU Main Service Cable should never see a "full" load.

EDIT:

The arrangement of the hot bus bars is naturally set up to stagger but you can unbalance your panel easily if you don't think about what goes where before hand.

Say you run a sub-panel for your grow room and you choose to start attaching breakers down the left side of the panel. This is the arrangement you happen to put the breakers in (on the left hand side only)

20A Single pole - 1000w dedicated ballast for bloom - Phase A (L1) or "leg" as I call them
15A Single pole - Ceiling light fixture to throw a green CFL into - Phase B (L2)
20A Single pole - 1000w dedicated ballast for bloom - Phase A
15A Single pole - dedicated water and air pumps for reservoir. - Phase B
15A Single pole - dedicated 600w for grow - Phase A

You've got a seriously imbalanced panel there. As long as you sized the feeder cable appropriately, there still not really an issue but it's bad planning to arrange breakers like that. You should have done:

20A Single pole - 1000w dedicated ballast for bloom - Phase A
20A Single pole - 1000w dedicated ballast for bloom - Phase B
15A Single pole - Ceiling light fixture to throw a green CFL into - Phase A
15A Single pole - dedicated water and air pumps for reservoir. - Phase B
15A Single pole - dedicated 600w for grow - Phase A

Study the empty hot busbars on a de-energized panel and you'll see how they are staggered.

 

[madpenguin]

I used Sunsystem ballasts with Hydrofarm hoods. Who am I going to call to cut the plugs off and hardwire them?

Well, wouldn't that just be bad planning on your part? :smile:

Don't get mad, just pulling your chain. That's why I use Galaxy ballasts with sunlight reflectors..... As an added bonus, you can use Galaxy on 120 or 240...

So... I guess my original statement holds. With proper planning, it really shouldn't be an issue. I know things go bad sometimes after the warranty has expired. Sure. Fix it yourself, if not send it back if it's still under warranty.

I know it's not the most economical approach, but I keep backups of all my equipment. 396gph ecoplus pump goes out? No problem. Got another one in the basement. Same with a spare 600w ballast.

While I'm waiting on my RMA, I just use the new one.

But yes, you have a valid point, most certainly. Many situations arise whn you need to do the work yourself. In that case, just make sure you know what your doing 100% before you start.

 

[Phillthy]

Great information... keep it going!!!

BTW - Pigtailing does make a lot of sense so you don't lose downstream equipment if an upstream outlet goes bad, etc... Most everything in a room for me is typically on it's own circuit except for my two green light receptacles.

I like the sharing of resources and the civil way people are discussing topics and code. Thanks guys!

 

[packn2puff]

madpenguin..Sorry left yesterday after my last post..I'll concede you are probably right and a single circuit probably is allowed to be spliced at the yoke..
I mostly work on 120/208v..277/480v 3Ph systems..and do a lot of office buildings..we pigtail everything..
more for the reason Phillthy just stated..
When a receptacle gets used alot..plug-in/plug-out like a vacuum location..I've seen this as a failure point..
especially when using the stab-in connections..and the mounting isn't solid to the wall(spongy)
I've had two service calls in homes where the problem was open neutral at a yoke and also took out devices downstream..
If it had been pigtailed..then the failure will most likely stay at that one device..Klein twisted solid wire, then nutted connections rarely fail if done right..

Sub-panels and N & G..At some point at the service entrance(step-down transformer, main panel, main disconnect) at or before the 1st means of disconnect..we bond Neutral & Ground together..(Neutral is also known as the Grounded conductor..and Ground is known as Grounding conductor)
Since in residential this is usually done at the main panel..you may see a green screw bonding the N bus to the enclosure..(this screw or wire is called the Main Bonding Jumper)
After this bond is made..all downstream devices or Sub-panels need to isolate the ground and neutral from each other..
So if your new sub-panel comes with a bonding screw you won't use it..
The reason is if there is a fault (hot to ground) on the load side of your sub-panel, it will only travel on the green grounding conductor all the way back to the main bonding point..which is also tied to Earth Ground
If it were bonded again at the Sub..the fault current could travel down the neutral feeder from the sub to the main..or normal return currents from the neutral could travel down the Green to the main..
If all is wired right..no current should be on the green in a non-fault situation..
Since they are usually(not always) bonded at the main
panel in residential..some guys don't install an Equipment Ground Bus at the main and just use unused neutral lugs..
not acceptable at sub-panels fed from the main..

 

[~SYK~]

FWIW - These posts are GREAT.

Respect to those adding to the discussion!!

Just an FYI for those trying to do more research ... those GREAT pictures that madpenguin has been nice enough to share ... can be found in the excellent electrical resource :

Black and Decker's Complete Guide To Wiring ...

http://www.amazon.com/Black-Decker-...bs_sr_1?ie=UTF8&s=books&qid=1239730408&sr=8-1

Hope it Helps

SYK

 

[Phillthy]

It is my understanding that the new code states that sub panes for out buildings and such are now required to travel back to the main for earth ground. It is no longer appropriate to have a separate earth ground for a sub panel. Anyone have more info on this?

 

[~SYK~]

I recently heard of a code inspection for 2 - 200A Subs that *some guy* put in *his* garage.

The subs were bonded together (technically this was done using the unistrut which it was mounted on) - but for the inspector *this person* added a shielded #6 between the panels.

The Grounding Bus was then taken to a grounding rod (also using #6), buried 8 feet deep.

In Addition - *they* ran a #4 back from the panels to the main SE (250') where it was connected to *their* new 400A main panel and dual grounding rods.

Inspector said it was overkill and *his* install/work was akin to jobs that he had seen done for Hospitals and Schools.

Not sure if that helps?

SYK

 

[madpenguin]

It is my understanding that the new code states that sub panes for out buildings and such are now required to travel back to the main for earth ground. It is no longer appropriate to have a separate earth ground for a sub panel. Anyone have more info on this?

That's correct. ie - You still need to run 3 conductor w/ground to your outbuilding. It was allowed to use 3 conductor w/out ground (hot-hot-neutral) as long as you had no other conductive path's back to your main structure. Say I had a barn I wanted to install a sub-panel in. It had no water lines, no gas lines, no phone lines, nothing spanning the distance from the house to the barn (the main electrical service originates in the house). I could run 2 hots and a neutral out to the barn and not have to have a dedicated grounding conductor. This is no longer the case. You need to run 3 conductor w/ground in all instances now (if you are on 2008 code). Even if your still on 05' then you should probably run 3 conductor w/ground anyway. Were you to run hot-hot-neutral and then later add a phone line to the barn, your now in violation.

You also need a ground rod (grounding electrode) driven at the detached structure regardless. This includes rinky-dink sheds. If the structure is not physically attached (wall to wall) with the house, then it's considered detached. So, an 8' steel rod that is copper plated needs to be driven. If you measure 25 ohms of resistance or more, then you need to drive another rod. Ground rods are cheap, I usually drive 2 just so it's a non issue. It's also very hard and time consuming to accurately measure resistance on a grounding electrode. When driving 2 rods, the first one must be outside the drip edge of the roof. You want it in contact with moist earth. Then the second one needs to be atleast 6 feet away from the first. I do it at 8 feet. Clamps used to connect the ground rods to the isolated ground bus in the sub need to be rated for direct burial. You would use #6 bare copper to connect the ground rod/s to your isolated grounding busbar. This is all in conjunction with your dedicated grounding conductor leading back to the house (part of the feeder cable). Also pretty sure any exposed GEC/EGC (Grounding Electrode Conductor - #6 bare wire) needs to be protected from physical damage on the outside of the structure. Don't think shedule 40 will do it, has to be schedule 80 PVC or RMC/IMC. Rigid Metal Conduit or Intermediate Metal Conduit. Inspectors usually overlook this but some can be pricks about it. I challenge anyone to severe a #6 with a weed eater. A lawn mower will do it tho so make sure it's adequately buried and plumb/flush with the structure if your not using conduit to protect it.

Any detached structure being fed from the house also needs a main disconnect, on the outside of the structure, or immediately inside the structure. What I usually do is buy a Main Breaker Panel (not a MLO) and as soon as the feeder cable enters the building, it goes directly into the panel. Basically the same principle as your main panel in the house (even tho the feeder cable is now fused by the main panel at the house).

Even if your not installing a sub-panel, you need a disconnect imediately inside the detached structure. Say I just wanted to run 2 lights and have one receptacle in my shed. I could use 14/2 UF romex coming out of my main panel and just direct bury the cable. But as soon as it entered my shed, I would need to run it into a junction box with a single pole light switch. All power to the shed needs to be killed when I throw that switch.

There is also burial depth requirements for cable and conduit.

Table 300.5

So, If I wanted to protect that 14/2 direct burial UF cable with a GFCI breaker in the main panel, then I would only have to bury it 12". You also wouldn't need a grounding electrode in this instance. Only when your feeding a sub-panel.

If the framing of the detached structure is exposed, then you need to run all your wire in conduit. Not romex but individual THHN conductors. Or, you could sleeve all romex with EMT or Electrical PVC conduit. Up to a height of 8 feet I believe.... If the structure has metal framing, then you need to ground the framing to your isolated ground busbar as well.

Ugh... Lots of stuff but that's it in a nut shell. Just use common sense and protect your wire and you will automatically comply with much of the NEC.

 

[Phillthy]

Excellent information. Thank you for sharing!!!

 

[madpenguin]

I added more pics on page 2 of this thread. The post concerning a sub panel installation..

I'll go ahead and wrap up and post branch circuit runs and installing breakers in the sub panel for those of you who are interested. Pretty simple but some of you probably have never done it so I'm going to be very basic.

Set your junction boxes first. Don't worry about putting cable into them, just set them (so ignore the cable inside the box below). If this is a new room with exposed framing, all the easier. A typical rule of thumb for receptacle boxes is hammer height to the bottom of the box. If your studs are exposed, then new work boxes are what you want. They have the nails in them that attach to the side of the 2x4. This is a double gang new work box. Will accept 2 devices.

See those 2 little peg things that are in front of the 2x4? Blue and part of the box? The ends should butt up against the front of the 2x4. Using those as guides to set the box, when you go to hang drywall, the front of the outlet box will be flush with the drywall.

Grab your roll of cable and start at the set junction box and work your way to the panel. Don't try to fish the cable thru the knockout in the back of the box, just start in the stud cavity that your box is in.

When unreeling romex from the roll, Take the outer loose end and step on it so it's flat. Then start walking with the roll and unraveling it and keep stepping on the romex as you go. Hope that makes sense. Don't just grab the cable and pull it off the roll while it is laying on the floor. You'll have a kinked and twisted mess. Your cable should be nice and straight with no kinks. Once you "walk off" 20 feet or so, put the roll down and run your cable. Rinse and repeat until you get to where you need to be (the panel).

Once you reach the panel, leave the cable attached to the spool still. It should still be sitting back at your outlet box. Approximate how much cable you'll need to take into the panel. Always try to take your cable into the top of the panel. Looks really shitty when you use the sides and bottom.

You need a proper pair of wire strippers:

Notice towards the tip, there is a place for 14/2 cable and then 12/2 cable. That's how you strip the outer sheathing off of romex. Not like this:

That's the sign of a hack. If you don't own wire strippers then you have no business doing electrical work in the first place.:wink: Don't write all over your cable like that either. Looks like an 8 year old did it. Don't twist all your ground wires together like that either. This panel is absolutely horrid. Notice how he over stappled everything in the pic below as well.

Possible bending radius violation along with unsightly side entrance cable and 8 year old writing... (ignore the arrow)

You'll need to remove a knock-out from the top of the panel. Use a flathead screw driver and your lineman's pliers to break it loose. Then install a NM connector with the screws on the outside of the panel. Never put more than 2 cables in one 3/8" NM connector. 2 - 14/2's or 2 - 12/2's. Only one 10/2. One 14/3, one 12/3 and one 10/3.... Pretty much common sense.

Here is a crappy plastic one. Much prefer the metal ones.

Once you have your NM connector installed and tightened down really good, pull your 14/2 cable into the new sub-panel. Pull enough in so all conductors in the cable will reach their intended destination. It should still be attached to the roll at this point if you started working from the outlet box.

When you have enough, take a black sharpie and mark the cable where you want to strip it as it enters the panel. Remember to leave 3/8" of the outer sheathing inside the panel and remove the rest. Once you crimp it with your wire strippers where you marked it, the entire sheathing will pull right off the conductors. Helps to wiggle your strippers from side to side so it cuts all the way through the sheathing (but it will not damage the individual conductor insulation). Remove the paper wrapping that surrounds the ground wire as well.

Once your branch circuit cable is in place, stripped and the nm connector has been snugged down onto the cable (do not over tighten the screws), work backwards towards the outlet box. Start stapling your cable down and pulling any excess with you back towards the outlet box. You might want to hold off stapling until all your cable is run. You can fit 2 - 14/2's or 2 - 12/2's under one staple. If you staple each branch circuit as you go, you might find yourself pulling staples down the road to accommodate for new branch circuits....

Your cable must be atleast 1 1/4" inch from the face of the framing member. This is to prevent drywall screws from hitting your cable. So, always staple dead center of the 2x4. Same deal when you drill through a 2x4 to run horizontally. Put the hole dead center, otherwise, a drywall screw could pierce your cable. No need to use anything larger than a 3/4" auger bit when drilling. You should also only have 3 cables in one hole. If you need to drill more than one hole, put twice the width of your auger in between holes. So, if using a 3/4" auger bit and you need to drill 2 holes, from inside edge to inside edge of the holes, give yourself 1 1/2" of space.

When driving staples, just make sure the cable is snug to the 2x4. Don't over do it. If you take a pair of dykes (side cutters) and pull the staple up and you see a noticeable indentation in the outer sheathing, then your probably driving your staples too much. Cables should be stapled to within 12" of an outlet box and every 4 feet there after (I like to do it 6" and 3' respectively). Watch your bending radius with the cable. No sharp 90 degree angles. Same reason we don't want kinks taking it off the spool. Your likely to get increased resistance at those points.

Once you make it back to your outlet box, measure how much wire you will need to have atleast 6-8" sticking out the front of the box, then cut it off the roll. You can always cook a rare steak more but once it's over cooked your screwed. My point being, always leave extra. If you cut the cable too short, you need to pull the entire run and start over. Don't even think of making splices outside of an approved junction box. That's their main purpose. To contain fire if it starts. Also, don't even think of installing a junction box to splice wires and then cover it up with drywall. All junction boxes need to be accessible at all times. If you cut your wire too short and don't want to re-do the entire run, then you must install another outlet box just as you did for the receptacle location. Then once your drywall is up, you would put a blank plate on the junction box so you can still get at the wires later.

When you insert the wire into your box, do not break the tab off. For that matter, don't even bend it down too much. Just jab at it with a screw driver to break the initial "lock" it has, and then carefully fish the end of your cable into the box. You want the plastic tab to retain it's "springyness" and to firmly hold the cable in place.

Always leave 3/8" inch of outer sheathing in your outlet box as well as your panel. I forget what the NEC says. Pretty sure it's 3/8". From the point where the cable enters the outlet box, you need at least 6" of conductors. That will typically leave you with at least 3" sticking out of the box. Make sure you do this! Old timers back in the day would leave 0" sticking out of the box. How they even managed to device anything out is beyond me. I hate working with short conductors. Really pisses me off and it will you too...

Here's what I do. Your strippers should be 8" long. Crimp the outer sheath as shown above where you need it. Put the tip of your strippers at the cut point of the sheathing you just made. Mark where the cable meets the end of the handles. Cut there. That leaves you 2" extra beyond what code requires.

Once the wire is ran, cut and stapled, go back to the panel. You should have 3 loose conductors from the branch circuit you just ran. Remember the order in which to hook things up (ground, neutral, hot) and reverse to unhook (Hot, neutral, ground).

Terminate the grounding conductor: No more than 2 grounding conductors under one screw.

Terminate the grounded conductor: One conductor per screw. No more.

Then attach the ungrounded conductor to your breaker:

Put the hooked end in first:

Then push it into place so it makes contact with the hot busbar:

Your done in the panel. Go back to your outlet. The cable is already cut, stripped, stapled, 3/8" of sheathing enters the box and at least 3" of conductors are sticking out the front.

Making up receptacles is very easy. Just remember "Black to Brass will save your ass". Black to brass, Ground to green and white to silver. Again, remember your connection order (even tho every thing is cold). Just get into the habit of it. Also, again, never backstab a receptacle. They are the little holes in the back:

Use the screw terminals. If it's a spec grade receptacle (heavy duty), there will be slots right by the screw terminals. Use them.

If it's a spec grade receptacle (or 20 amp receptacle), you don't need to put little loops in the end of your conductors to attach. Just leave them straight, strip the ends and insert into the slot and tighten down the screw. Tighten them down good. You can usually do better with a flathead than with a phillips.

Stripping the ends of your conductors:

If it's not spec grade and just your standard 49 cent receptacle, put little bends at the ends of your conductors. There is a little hole on your wire strippers that is made for this. Look at the above pic. Inbetween his thumb and the neutral wire, right below the word "only". Stick the end of your stripped conductor in that hole. Just have a hair of wire sticking out the other end and then use your wrist and do a 180 degree bend (with the stripper hand, not with the conductor hand). The wire will wrap around the edge of the strippers to form a hook.

As someone already mentioned, hook the conductor onto the terminal screw so that when you tighten down the screw, it grabs the wire and pulls it tight. If you do it the other way, it will start to squeeze the wire out.

Always push the bare grounding conductor into the back of the box first. Treat it the same way as you make connections. Push the excess ground in first, then neutral, then hot. You don't want that bare grounding conductor to accidentally make contact with a hot or neutral screw terminal.

Anyway... That's branch circuits 101.

 

[fishheadbob]

It would be nice if we had a dedicated electrical section where anyone could post topics, but only a qualified few could respond.


The info posted here is very helpful

It would indeed be nice if we could separate the electricians advice from the 14 year olds opinions. After watching this site for a few years you can get a good idea whose advice is professional, and who is blowing smoke; I know I've seen examples of both. I still wonder if one guy ever burned his house down, he was trying hard to; what scared me was his comment about his girlfriend and child living in his grow-op with the lousy wiring job.
Another good option is to pick up a good DIY book about simple wiring, and don't get in over your head. Especially, don't get in over your head.

 

[yamaha_1fan]

Well, wouldn't that just be bad planning on your part? :smile:

Don't get mad, just pulling your chain. That's why I use Galaxy ballasts with sunlight reflectors..... As an added bonus, you can use Galaxy on 120 or 240...

Well when setting up a 30KW grow, you can only plan so much. The original plan was ballast kits which would have required hard wiring anyway but it turned out the Sunlight ballast was the best deal and it was alast minute change. I wasnt going to spend hundreds of dollars on adapters.

But I have learned alot from here and my BIL. I already had a basic understanding of electricity, and got the more advanced stuff from here.

Who said there friend got hit with 277? According to my BIL, thats not something you usually wind up regretting. Your friend is lucky.



If you dont know what you are doing, get advice or help. Theres alot of people here that can help. Take pictures, give detailed info, etc.

And to the experienced sparkies, stick around and try to answer as many questions as you can.

 

[sparkjumper]

Just about all flourescent lighting circuits in commercial office bldgs come from 277V circuits.Its bad enough being hit by the hot but if you get in between the neutral and ground its soo much worse lol

 

[madpenguin]

Electrical Theory 101

Electrical Theory 101

This is kinda silly but for those of you who aren't familiar with electricity, I find everyday comparisons an easy way to explain it.

I already said this on another post but I'll say it again. You can compare electrical wires with water pipes.

Your water pressure is the same thing as voltage. The actual water volume in the pipe is the same thing as amperage. The amount of water that comes out of your faucet is the same thing as wattage. You can view a single water molecule as an electron. Just as there are millions of water molecules traveling in a water pipe, there are millions of electrons traveling in a wire.

Voltage is the electromotive force that pushes electrons down the wire. Electron flow will happen whenever there is a difference in potential between two points (Voltage)

View a light bulb in a ceiling fixture. If you have excessive voltage drop, the light bulb will barely light up, just as if you have excessive water pressure loss in a water pipe, you'll get barely a trickle coming out of your faucet.

Current (Amperage) is the flow of electrons from one atom to another (copper atoms in the case of copper wire).

Here is a copper atom:

The red and green dots in the middle is the nucleus of the atom. It's comprised of protons and neutrons. Protons are positively charged and neutrons have a neutral charge. The yellow dots are electrons and they have a negative charge. You know the phrase "opposites attract". The positive charge of the protons in the nucleus hold the negatively charged electrons in place. Generally, there are an equal amount of protons and electrons in an atom.

The reason why copper is such a good conductor is that the outer shell of the atom contains only one electron. This electron is loosely held by the nucleus of the atom. This outer electron is called a free electron or valance electron.

When you apply voltage to a wire, that electromotive force will dislodge the outer free electron and it travels to the adjoining copper atom. Kinda like a pool table, when 2 balls collide. The free electron hits it's neighbor free electron and knocks it out of place, but at the same time, takes the place of the one it just hit.

So current is nothing more than electrons hopping from one atom to another. The number of electrons moving past a certain point in one seconds time is the Amperage (current intensity). When 6.24 x 10 to the 18th power of electrons move past a given point in one seconds time, you have 1 amp worth of current. That's 6,240,000,000,000,000,000 electrons in one second.

So anyway, take mikecar's earlier post with why you separate neutrals and grounds in a sub panel. Here's another silly analogy.

You can view your house as a city and all the wires in it as roads.

Say a ground fault occurs. This ground fault is a car. The neural wire is one side of a street heading one way and the hot is the other side of the street heading the other way. View the ground wire as a back alley that runs parallel with the street. You want to force this car to take the back alley and not get on the road (neutral wire). Sure.... It can take either road because they both go the same way. But the main road is already congested. So put a road block up and force the car to take the back alley. It still winds up going to the same place but yet see's no traffic while it's traveling...

If you want to take it a step further, this is what a GFCI does. By all rights, that car should have gotten on the main road and traveled with the rest of them. The GFCI instantly knows that someone tried to be sneaky and cut down the back alley so it throws up a red light on the hot wire and stops all traffic until that rouge car get's back to the main panel.

I just kinda over did that one, but whatever.... Whatever helps you understand better, then look at it like that. :wink:

 

[nephilthim]

yea my friend got zapped with 277 he was a licensed electrician, I believe their was a loose connection somewhere he touched metal ..zap..he was shook up whenI found him a few minutes afterwards,he was fine no physical damage..mental..yea that scared the shit out of him as he was nearing retirement age.I think we all know who is licensed here so I defer to their knowledge,as all others should.

 

[nephilthim]

this thread gets a bump back up as so many posts are germane to posts here.

 

[madpenguin]

Old Working branch circuits

Old Working branch circuits

Many times when you set up a grow room, the room is already there. Drywalled, painted and finished. In that case, you can't use new work boxes with the nails, you have to use old work boxes. They are also called remodel boxes.

Old work boxes are designed to be installed into existing drywall.

They have 2 tabs on them instead of nails:

Once the box is inserted into a cut hole in the drywall, you use the screws attached to the tabs to pull the box tight to the drywall.

Here is a pic from the back side of the wall so you can see how it's held in place:

If you have access to the back side of the wall, as the above pic demonstrates, then using an old work box isn't the way to go. Especially if your cutting your hole right next to a 2x4 stud. You should probably use a new work box in that instance. Just nail the new work box from the back side of the wall. The nails will almost touch the back side of the drywall, but you can still "slide" your hammer along the back side of the drywall to nail it down.

A box nailed to a stud will always be more sturdy than an old work box positioned in the middle of 2 studs.

First, make sure you are able to fish wire into that stud location before you cut your hole. If you think it's going to be impossible to get wire into that cavity, then choose another location before you cut your hole.

Once you've decided upon a location for your receptacle or light switch, cut your hole for the box. Take the front face of the box and lay it flush with the drywall. Make sure it's level and plumb. Take a pencil and outline the box.

Look at this pic again:

There are 4 "tabs" that are a fixed part of the box. The guys thumb is on one of them. Don't trace around these when you make your outline. Those are what holds the box to the front of the drywall and the adjustable tabs get pulled tight to the back of the drywall.

You need a keyhole saw:

Cut out the hole you just outlined. There's not really a need to drill holes in the corners to get started. Just bang on the handle of your saw with lineman's pliers. It'll punch thru.

Once you have your hole, and you've made sure the box fits good:

Fish your cable. This can often be an exercise in patience as well as ingenuity. You'll figure it out one way or another.

Once you see your cable in the stud cavity, your home free. Pull it out.

Strip the end of it's outer sheathing and pull it into your old work box, just like you would a new work box, as covered on the previous post. Then put the box in the wall:

And tighten down the 2 screws:

Pretty easy, all in all, but it is time consuming and often frustrating. This is why electricians charge big bucks to old work stuff. It's much nicer when you can see studs.

If your working in an old house that has plaster and lathing strips, it get's even more frustrating. Best to use a utility knife and score your outline first. You'll be very lucky if you are left with a perfect hole that your receptacle plate covers up everything. Be prepared to do some minor drywall repair and touch-up painting when working with plaster. The stuff loves to crumble, not cut.

Also be very careful with the lathing strips when cutting. You can pull down an entire section of plaster if your saw grabs a hold of the lathing strip. You can also blow out a giant hole on the opposite side of the wall your working at if your keyhole saw goes in too deep and hit's the opposite sides lathing strips. Just take your time when working with plaster.

Here is an old work box designed for a ceiling light fixture:

Same deal with installing those.

It helps to have a basic understanding on how houses are constructed when your old working cable. Otherwise, your going to have a rough time. Often times, you can't get a clear shot from the basement panel up to the second floor. Your best bet is to locate the bathroom plumbing and use a drop chain to fish your wire.

If that's not even remotely where you need to be, then often times, pulling baseboard and punching a hole is about the only way to get from the second floor down to the first. Once you put your baseboard back on, the hole will be covered up. Use this hole behind the baseboard to drill down into the 2x4 plate. This will give you access into the first floor stud cavity**. Then go into the basement (hopefully you have an exposed ceiling in the basement) and drill up through the first floor plate to get into that same stud cavity.

Make sure you don't drill up through your floor, missing the wall cavity. That would really suck. Make sure your where you need to be before you drill.

** = Sometimes. Other times you will need to drill through 2 plates with almost a foot of dead space in between in order to get into the 1st floor stud cavity. In this instance, consider going to the first floor and punching a small hole in the wall by the ceiling. Destruction is sometimes the name of the game when doing shit like this. Do what you deem necessary to get the job done. Drywall repair sucks ass, but sometimes it can't be avoided.

 

[nephilthim]

i have to bump my two fav threads too much info too let this one die thanks too all you electricians who put in the hard work of data entry.perma_bump.

 

[madpenguin]

GFCI and AFCI requirements

GFCI and AFCI requirements

Haven't really mentioned this yet but it's good to know. The 2008 code introduced some pretty strict requirements for branch circuit protection (above and beyond Over Current Protection).

GFCI requirements:

AFCI requirements:

Whether or not you choose to adhere to them is another matter. I would strongly suggest that you do.

Also, tamper proof receptacles are now a requirement as well...

406.11 Tamper-Resistant Receptacles in Dwelling Units. In all areas specified in 210.52, all 125-volt, 15 and 20 ampere receptacles shall be listed tamper-resistant receptacles.

210.52 is pretty large but it basically covers all dwelling unit receptacles.

 

[billy_big_bud!]

lots of helpful knowledge!