Metal vs Plastic boxes for series wiring


  #1  
Old 03-09-05, 01:28 PM
Mangi
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Metal vs Plastic boxes for series wiring

I am running 12-3 wire through two basement storage rooms. 6 receptacles, one of which is a GFI, and two single light switches in the middle of the run to light each room. 1. am I better off using metal boxes and ground at each or should I use plastic and pigtail the grounds? 2. Should I bother with a GFI as the first receptacle, as this is in a workroom with power tools? 3. Is a single box big enough to accomodate the wires for this run, power to a receptacle, out to another, then to a light switch with a lead to the light, then to another receptacle, then to another light switch and lead for the light, and finally to a final receptacle.
Any advise on the method of wiring, types of receptacles/switches and boxes would be greatly appreciated.
JOhn
 
  #2  
Old 03-09-05, 02:04 PM
R
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I am going to assume you mean 12-2 wire. Unless you plan on running switched power and constant power from box to box, 12-3 won't gain you anything.

You need to pigtail the grounds no matter what you do. You can only have one wire under a screw. You need to pigtail to the receptacle or switch AND to the box, if the box is metal. They do make wire nuts with a hole in them where you can feed one longer ground wire all the way through.

Use plastic boxes, but get good quality large ones.

You need to GFCI any receptacles in unfinished areas of the basement. That means the workroom. I would NOT GFCI protect the lights. Being in the dark after a GFCI trip is no fun. Either run the lights on a different circuit (good to prevent darkness if you overload the circuit), or at least pull them off the circuit NOT GFCI protected.

You need to describe your layout better. Try again, and be specific.
 
  #3  
Old 03-09-05, 05:15 PM
Mangi
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Thanks Bob. YOur right in that it is 12-2 wire. I ran two 12-2 lines to my work room. One line feeds all the way around the room and adjoining storage room and the second line was going to feed an electric base board.
Line one was set up to feed a GFI, then to two receptacles, then to a light switch (@ leed to the light), then to another receptacle, back to the workroom light switch (@ leed to the light), and finally to two more receptacles.
So I have a total of 6 receptacles and 2 light switches on one 12-2 line with a 20amp breaker.
Most of my tools are small and wont draw that much power. When I finally get a table saw I will figure out how to bring the one pre-existing receptacle that was already installed the middle of the garage by the previous owner for his big table saw. So I think I'm okay with the power not tripping the GFI, unless it is more easily tripped than I'm thinking!
Bob, can you walk me through the wiring sequence for this series I have described? If so, please also indicate what size boxes I should install as well.
THanks in advance.
JOhn
 
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Old 03-09-05, 06:25 PM
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I still don't follow the wiring sequence. You don't mention lights at all (just switches) and it almost sounds like you have a loop, which is not good at all.

This is what I think you have:

Power---R1---R2---R3---S1---R4---S2---R5---R6

Where R1 is a GFCI receptacle, R2-R6 are regular receptacles and S1 and S2 are switches.

Where are the lights? Do they feed directly off the switches at a right angle in my drawing? Please advise.

As for the GFCI issue. A GFCI tripping is from a ground fault. A ground fault is not the same as an overload. A GFCI trips when there is an imbalance between the current on the hot line and on the return line. That extra current must be going somewhere, so to prevent it from going through you (a human), the GFCI trips and shuts off the circuit. Ground faults do occasionally occur, especially with motors (ie tools). You don;t want to be in the dark when one trips.

If you are using plastic boxes, look for 22 cubic inch boxes.
 
  #5  
Old 03-09-05, 07:24 PM
Mangi
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Hey Bob,
Yes, the lights are at right angles off the switches. Your diagram is exactly right. The power lead goes from the panel to R1. A separate piece of 12-2 goes from R1 to R2, a separate piece of 12-2 goes from R2 to R3, separate piece of 12-2 goes from R3 to S1, and so fourth around the room. I'm wondering if you can explain the wiring based on this layout. When I say a separate piece I mean that the wire was cut at the box and a new run was layed to the next box.
You said to use 22 cu inch boxes. Would that apply for s1 and s2 also. There are three lines going to the one box. The 12-2 that comes from R3, the line going form s1 to the light and the continueing feed to R4.
John
 
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Old 03-10-05, 04:41 AM
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The wiring for this is straight forward. I say to use 22 cubic inch boxes because they are typically the largest of the single gang plastic boxes. The larger the box, the easier it is to work with.

Again, I recommend that you don't wire this way, because of the GFCI issue with the lights. Instead, I would use 6 GFCI receptacles and make all connections on the line side of the GFCIs. GFCI receptacles are available in 3 packs.

However, I will give instructions based on a single GFCI as receptacle R1.

At all the boxes you will connect the ground wires together. I recommend that you use wire nuts with a hole in them. You leave one ground wire longer than the other(s), and that wire extends through the hole. If it's too late for that then just use large wire nuts and use a pigtail. A pigtail, in this case, is a piece of 12 gauge bare wire. The pigtail connects to the ground screw on the receptacle or switch. If the boxes were metal, you wouold also have to connect the grounds to the box, but with plastic this isn't done.

At R1 connect the power wires to the line terminals of the GFCI. They will be marked LINE, and there will be a gold one and a silver one. They may also be marked hot and return or hot and neutral. The gold screw is for the black (hot) wire, the silver screw is for the white (return/neutral) wire. Connect the outgoing wires to R2 to the LOAD terminals of the GFCI. Again, black to gold, white to silver.

At R2 and at R3 connect each white wire to one of the silver screws of the receptacle, and each black wire to one of the gold screws of the receptacle. Do not break the tab between the screw terminals.

At S1 connect all white wires together with a wire nut. Connect the black wires from R3 and R4 together with a wire nut and include a pigtail (a short piece of 12 gauge black wire). The pigtail gets connected to one terminal of the switch. The other switch gets connected to the black wire going to the light.

At R4 connect each white wire to one of the silver screws of the receptacle, and each black wire to one of the gold screws of the receptacle. Do not break the tab between the screw terminals.

At S2 connect all white wires together with a wire nut. Connect the black wires from R4 and R5 together with a wire nut and include a pigtail (a short piece of 12 gauge black wire). The pigtail gets connected to one terminal of the switch. The other switch gets connected to the black wire going to the light.

At R5 connect each white wire to one of the silver screws of the receptacle, and each black wire to one of the gold screws of the receptacle. Do not break the tab between the screw terminals.

At R6 connect the black wire to a gold screw and the white wire to a silver screw. Make sure the tab is not broken on either side of the receptacle.

12 gauge wires are harder to work with than 14 gauge wires, and can be tough to push back into the boxes. Use your finger or a blunt object to gently push the wires to the back of the boxes. Never use a screwdriver blade or anything else that might damage the insulation. make certain that the bare ground wires do not come anywhere near the side of the receptacles or switches. If the grounds contact a hot wire, you will trip the breaker and possibly the GFCI. If the grounds contact a neutral wire then you will trip the GFCI
 

Last edited by racraft; 03-10-05 at 05:03 AM.
  #7  
Old 03-10-05, 07:54 AM
Mangi
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Bob, thanks for the detailed explaination. Very understandable. My last question re. the GFI is, I thought that if a GFI was the first receptacle in a series, than all other receptacles would be protected by the GFI and would trip it if necessary? Is this correct. If you really think I need GFI's at every receptacle I will install them, but I'm assuming you have a diffent wiring plan as well.
 
  #8  
Old 03-10-05, 08:02 AM
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Bob is concerned that a tripped GFCI will leave you in the dark. My personal opinion is that this is not a significant concern, especially with the newer, better GFCIs they make these days. I've been left in the dark much more often by power failures than tripped GFCIs. You could always plug in one of those emergency battery-backup lights if being left in the dark concerns you, and that would cover all manner of power outages.
 
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Old 03-10-05, 08:20 AM
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"I thought that if a GFI was the first receptacle in a series, than all other receptacles would be protected by the GFI and would trip it if necessary?"

This is correct, as long as the other receptacles are on the LOAD side of the GFCI, which is what my directions indicated.

As John stated, I am concerned about you using a table saw, for example, and having the lights go out in the middle of a cut because the GFCI tripped. The surprise of the trip just might startle you, and being startled near a sharp saw blade can be hazardous.

If you are willing to put up with the idea of being in the dark because of a GFCI trip, then only use one GFCI. However, make it a new one. Don't reuse an old one or even a new one that you have from years ago.

However, if being in the dark if the GFCI trips is a concern, then go with multiple GFCIs, or modify the wiring slightly so that the lights aren't on the load side of the GFCI.
 
  #10  
Old 03-10-05, 10:38 AM
Mangi
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THanks to both of you for your advise. If the GFCI poses a problem I will tie one more light from the garage into the workroom. Then I will never be in the dark. Thanks again for your responses. This site is excellent.
John
 
  #11  
Old 03-13-05, 05:40 PM
Mangi
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Bob,
I may end up taking your advise on running a separate receptacle line so my lights don't go out. Can you tell me if it's possible to extend the existing 220 volt outlet to another location in my garage. The electrician mounted this wierd three prong outlett near the ceiling and I was told it is for a powerful table saw. If this outlett can be moved to the far end of my garage, I will see if I can hood an electric Modine blower heat unit to it. Then I will have the other 12-2 (20 amp) line free for my receptacles.
 
  #12  
Old 03-13-05, 06:00 PM
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Yes, it's certainly possible to extend a 240-volt circuit to a new location. Unlike 120-volt circuit, however, 240-volt circuits are not general purpose and you'd need to be lucky indeed if the existing circuit matched the electrical requirements of what you want to use it for.
 
  #13  
Old 03-13-05, 06:02 PM
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You can extend your circuit if you wish. You will need to install a plain junction box with a cover where the receptacle is now, leaving the receptacle box accessible, and then run the cable to where you want it.

However, if this line was for a table saw, you may not be able to use it for a heater to it. It will depend on the size of the circuit (wire gauge and breaker size) and the requirements for the heater.

I am confused. How will extending the 240 volt circuit free up a 12-2 120 volt circuit?
 
  #14  
Old 03-13-05, 07:03 PM
Mangi
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I initially ran two 12-2 lines to my new workroom. One was for the receptacles and light. The other was going to power an electric baseboard. YOu advised me to wire the receptacles independent of the lights to avoid black outs with the GFCI. Now I'm considering tapping into the pre-existing 220 line for a heavy duty Modine heater, if possible...
 
  #15  
Old 03-14-05, 04:27 AM
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Ah , now I understand. You are considering using the 240 line for heat, and therefor having the other 12-2 line for lights.

As John and I stated, you can use the 240 line if it meets the requirements of the heater. Tell us what the heater's requirements are and what the 240 circuit is (wire size).
 
  #16  
Old 03-16-05, 06:21 PM
Mangi
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I made a mistake on the power saw outlett. The receptacle matches my book for 20 amp, 125 volts. The breaker is made up of two 20 amps that are tide together with a bar. My question is, can I hot wire an electric heater to this receptacle and is the heater shown below compatible with the power I have. The heater says 20.8 amps, then it says you need a 30 amp breaker? Will the two 20 amp breakers cover the requirements? Also, will this type of heater cost me an arm and a leg to use it for maybe 2-3 hours a night?
thanks, john


Powerful Electric Garage & Shop Heater
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Powerful Electric Garage Heater with up to 17,100 BtuH. This electric garage and shop heater operates with both 208 & 240 volts, 20.8 Amps, 4 different heat setting's, built in thermostat, and an automatic fan delay control. Perfect both for primary or supplemental heating in garages, workshops, factories, stores, warehouses, public buildings, service stations, stockrooms, basements, toll booths, and any large exposed areas or additions. It's SAFE - A high limit thermal cutout automatically shuts off the electric shop heater in the event of overheating. Choice of wattage and BtuH settings. The electric heater element features rugged plate fin.



Utility Heater Description - Heats up to 500 sq. ft:

* Horizontal and downflow heating in one unit.
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* Built-in thermostat with a range of 25-85 degrees Fahrenheit
* Automatic fan delay control
* Heats up to 500 sq. ft. or 5,000 cubic feet
* 12 1/2 H x 14W x 11 1/4 "D
* KW: 5/4.1/3.3/2.5
* Requires a 30 amp circuit
* BtuH: 17.1/14.0/11.3/8.5
* Volts (60Hz): 240
* Fan CFM: 270
 
  #17  
Old 03-16-05, 06:59 PM
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You already asked this question. I am not going to give you a different answer.

A 240 volt 20 amp breaker gives you 20 amps at 240 volts. You need 30 amps at 240 volts.
 
  #18  
Old 03-17-05, 07:36 PM
Mangi
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So the fact that 2, 20 amp breakers are tide together doesn't mean it has 40 amps total. Why are the two breakers tide together with the bar. What function does this have...?
Thanks,
John
 
  #19  
Old 03-18-05, 06:41 AM
J
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Breaker handles are tied together any time it would create an unsafe condition if only one of the breakers tripped. In a 240-volt circuit such as for a water heater, you want to ensure that both hots are deenergized before you work on it. The double handle does that. Also in multiwire circuits where both hots are connected to devices, you also need to make sure that both hots are deenergized together. Of course the main breaker is also two breakers tied together.

The above are situations where you are required to tie them together. But you are allowed to tie them together any place else you might want to. One common case is a multiwire circuit where the two hots are not ever connected to any one device. This is where you probably want to tie the handles, but don't have to. You also might want to if you have any boxes that contain wiring from two different circuits. Or maybe they're just tied together because you got a great deal on a double-pole breaker.
 
 

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