Update wiring questions

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  #1  
Old 11-14-06, 04:36 PM
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Update wiring questions

I am currently doing some remodeling. I noticed that the metal flex conduit doesn't have a grounding wire. Does the metal flex conduit serve that purpose or should I be adding a grounding wire as I update wires?

Also I notice that some curcuits were sharing the same neutral wire, is that ok?

Thanks,
Pete
 
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Old 11-14-06, 08:01 PM
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Pete, Some more info is needed.

The flex for the range does NOT count as ground.
For the shared neutrals, What and where are these ckts?
 
  #3  
Old 11-15-06, 02:15 PM
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It depends on where/how the FMC is used. NEC 2005 348.60 & 250.118(5) permits properly bonded FMC to act as the ground when it's not used in a flexible application, is shorter than 6', is 20A or less and grounding fittings are used. In all other cases, a separate equipment grounding conductor must be installed. I'd never rely on conduit as a grounding conductor, though- I always run a ground wire regardless.

Shared neutrals are OK in some instances, but we need more information before we can tell you if it's OK or not.
 
  #4  
Old 11-18-06, 07:47 PM
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If you don't know what a shared neutral is, I'll tell you it's one of the best means to electrocution. Keep playing and your family will miss you when you're gone.

That's Mr. Stripes to you!
 
  #5  
Old 11-18-06, 11:59 PM
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I tend to avoid using shared neutrals as well. However, when designed and installed correctly (i.e., to code), they are no less safe than other circuit types.

My concern with shared neutrals is primarily in residential settings, where wiring is often modified over time by many different homeowners with varying levels of electrical knowledge. Since they are a bit out of the ordinary for most people, they can be easily rendered disfunctional and unsafe.

If you need to modify shared neutral circuits and aren't sure about them, I recommend studying them with a good homeowner electrical book, and understanding the particular circuits you have in your home, before modifying them.

Interestingly, using metal conduit for grounding in a home can pose the same type of problem as other inordinary conditions - like shared neutrals - because some homeowners may not be familiar with them and so are not aware of the need to preserve the continuity of any metal conduit being used as a ground in their home.
 
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Old 11-20-06, 10:22 AM
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Thanks for the replies and a follow up question

So as I make updates I should update both these issues.
If I update the wires I should also do the following:
1. add a ground wire
2. ground the metal box
3. fix the maze of shared neutrals if possible. (I am pulling through 1/2 inch MC. ) May run up against box or MC capacity issue.

Questions:
For 12/2 to wire does it matter if I use a 14 AWG grounded wire versuses 12 AWG? I would guess it does but if it does it could save me a few bucks.

I know shared neutrals is kind of playing with fire in residential setting but how about shared grounded wires?



My hot wire detector has saved life in this remodeling project.
 
  #7  
Old 11-21-06, 01:20 AM
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Pete,

The shared neutrals are OK, provided you understand them, and in particular, the circuits that are in your house.

Sharing grounds between unshared, individual circuits is dangerous because the ground wire must be capable of carrying the ampacity of a potential fault produced by the load of the circuit it protects. If you "overload" a ground conductor it could fail during a fault and cause injury, fire, and/or a fatality.

For example, let's say you "share" a 14 AWG ground wire from a 15 amp circuit to provide a grounding path for a 20 amp circuit. 14 AWG is rated for 15 amps. If a fault occurs on the 20 amp circuit, the 14 AWG wire could fail (i.e., melt down) resulting in electric shock to some unlucky person, or a fire.

This is one of the reasons you may not use a 14 AWG ground wire to protect a 12 AWG circuit. The wire is simply too small to provide proper protection.

As to the type of wire/cable. Are you referring to FMC (flexible metal conduit) or type MC (metal-clad cable)?

FMC is a flexible metallic conduit specifically designed to pull unsheathed, individual insulated wires through. Like rigid conduit, it comes with no wires inside.

MC is a type of cable - meaning it is a prefabricated flexible metallic sheathing, inside which there are individual insulated wires.

These are not the same thing, in that MC is not to be used like a conduit. You should not attempt to pull additional wires through type MC cable. In fact, I am guessing that it will be virtually impossible to do so - there just isn't room.

Also, bear in mind that any ground wires run through conduit must be insulated. There is also a "grouping" requirement to protect against induced voltages on the metal sheathing.
 
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Old 11-21-06, 04:17 AM
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In a residential setup you run one ground wire through conduit. The ground wire must be sized for the largest conductor in the conduit, and the ground is shared between ALL the circuits.

Further, in a residential setting, at each junction box you connect all ground wires together, even if they are from different circuits.
 
  #9  
Old 11-21-06, 07:29 AM
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Thanks again great points (I have .5" FMC)

OK so I will go pick up some 12 AWG tonight as well. Where is the best place to find "grouping" requirement information? So I can better determine if I can separate the shared neutrals.
 
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Old 11-21-06, 07:32 AM
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"Where is the best place to find "grouping" requirement information? So I can better determine if I can separate the shared neutrals."

I don't understand this question.
 
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Old 11-21-06, 08:53 AM
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"If I update the wires I should also do the following:
1. add a ground wire "--- You will be adding an Equiptment Grounding Conductor which is required to be the color Green--- no other color is permissibl.

A #14 EGC for a 15 amp circuit and a #12 EGC for a 20 amp circuit






"2. ground the metal box"--- A Code requirement








"3. fix the maze of shared neutrals if possible. (I am pulling through 1/2 inch MC. )" --- If you are referring to two Branch-Circuits extended from the panel as a "3-wire" connection- two wires connected to circuit-breakers, and one wire connected to the Neutral terminal bar, you must adhere to an exact color-code, presuming you are pulling new conductors thru Flexible Metal Conduit. For a "3-wire" 15 amp B-C, this would consist of one Black, one Red, one White, and one Green, all #14 copper.The Black & Red colors indicate 220 volts between the Black& Red conductors.

At the outlet-box where the 3-wire B-C splits into two seperate 2-wire B-C's, you can use Black & White for one 2-wire B-C which extends from the O-B, and Red & White for the other.

It's not necessary to "break" the Red wire at this point--you can pull the Red wire directly thru to the next O-B without a connection or splice in the first O-B. A wire that enters/leaves an O-B ,wihout any connection or splice in the O-B , is "counted" as 1 wire, not 2, when calculating the conductor-fill of the O-B. Eliminating an un-necessary connection is an example of "If it's not there ( a splice), it can't fail"






May run up against box or MC capacity issue.


"For 12/2 to wire does it matter if I use a 14 AWG grounded wire versuses 12 AWG?" --- Yes-- #12 required

" but how about shared grounded wires?"--- If the two B-C's which extend from the panel "share" the same Neutral, a "3-wire" connection at the panel, they can "share" the same EGC



My hot wire detector has saved life in this remodeling project.[/QUOTE]
 
  #12  
Old 11-21-06, 09:10 AM
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On Grouping: How many wires can a 1/2" FMC have?

I guess have two questions:
1. What was meant by this:
"There is also a "grouping" requirement to protect against induced voltages on the metal sheathing."

2.
How many wires (12 AWG and 14 AWG) can a 1/2" FMC have running through it?

I am assuming most code books will have # of wires in boxes depending on the box size. So I won't bother you for that.

Thanks
 
  #13  
Old 11-21-06, 09:54 AM
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> "There is also a "grouping" requirement to protect against
> induced voltages on the metal sheathing."

I think what the poster meant was that the hot wire(s) and neutral wire(s) for any given circuit must run together in the same conduit. If two hot wires share a neutral, all three conductors must travel through the same conduit. Violation of this prinicple causes an imbalance in the magnetic field around the wires which has bad side effects.

> How many wires (12 AWG and 14 AWG) can a 1/2" FMC have
> running through it?

You can put up to (9) #12 wires or (13) #14 wires in a 1/2" FMC. However, there is another rule called derating which can further reduce that count. If you have more than (6) conductors in a conduit, not counting the ground, post back and we'll discuss derating. Also, as you suspect box fill could become a limiting factor if you have that many conductors; for #12 your box must have 2.25 cubic inches for each wire entering the box; for #14, 2 cubic inches for each wire entering the box.
 
  #14  
Old 11-22-06, 12:33 AM
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racraft is correct regarding the grounding analysis.

However, I was thinking that an attempt was being made to simply extend a ground from a single higher rated circuit (i.e., 12 AWG, 20A) with a single lower rated wire (i.e., 14 AWG, max 15A). In my view, this could be dangerous under fault conditions.

Sorry if my earlier note caused any confusion.
 
  #15  
Old 11-22-06, 02:52 AM
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MC??? FMC??? Grouping??? Here it is.

Do - Run an equipment grounding conductor, in addition to any metal conduit and / or neutral; but only in an approved conduit, and in the same conduit, not separately or outside of the conduit as an individual conductor. Not in MC or BX.

Type MC (metal clad) Cable, as earlier stated by someone, has wire installed in it at the factory. It has additional insulation around the already insulated conductors, plastic or paper depending on the type. It was never intended, nor is it "OK" or National Electric Code worthy, to remove and replace conductors, or to add conductors in these types of cable.

If you have FMC (flexible metal conduit) "Flex", it would be something that I have never seen in my 30 years experience as an electrical contractor. (Not to be so arrogant to say that it couldn't be so) different parts of the country have different trends. I've worked in Utah, Nevada, California, Connecticut, and Ohio. ?????

Also as earlier stated, a 15 amp circuit must have #14 or larger wire for all of its conductors, including its grounding conductor, and a 20 amp circuit must have #12 or larger wire for all of its conductors, including its grounding conductor.

Grouping – What they meant by this is that you need to run all the conductors of a circuit i.e. all currant carrying conductors “Hot and Neutral” and an equipment grounding conductor ( Only one grounding conductor required per conduit, no matter how many circuits are in the same conduit, and it must be sized for the largest of the other conductors amp rating) must be in the same conduit. In short: DON’T RUN THE HOTS IN ONE CONDUIT AND THE NEUTRALS IN ANOTHER. IT WILL CAUSE A MAGNETIC FIELD, HEAT UP THE CONDUITS AND CAUSE A FIRE!

Hope this all helps Rog
 
  #16  
Old 11-24-06, 03:09 PM
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I live in a 60s ranch in Minnesota which is mostly .5 in. flex conduit. Thanks for all the responses.
 
  #17  
Old 11-26-06, 02:12 PM
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I'm in the same boat as you. I also live in Minnesota and most of my house is FMC. I always thought it was BX until I had an electrician out who told me I had Flex. I'm not sure what the I.D. is (maybe 1/2" or 5/8"), but the O.D. is just under 1". He also told me that the Flex was the ground - although now I see that he may not have known what he was talking about (nearly all runs in my house are more than 6'). I'm not entirely sure if I should just leave it alone (as it has been for 40 years), or have it corrected.
 
  #18  
Old 11-27-06, 03:52 PM
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Grounding old metal electrical Boxes

How do I ground old metal electrical boxes? The screw sizes seem goofy. Are they off? Am I having trouble because the boxes are old? Or is it me?
 
  #19  
Old 11-27-06, 04:01 PM
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> How do I ground old metal electrical boxes?

Buy a box of green, self-taping hex ground screws in the electrical aisle. If there is not an adequate hole in the back of the box, drill one. Ideal sells a 10pk of pre-assembled ground screw, green pigtail and wirenut combos that make the job quick.
 
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