Replies

1. 
   junkhound | Jul 15, 2004 07:11pm | #1

   But what about the green?  Where would it (green) go in the main panel? To the neutral bus, which should be tied in the main panel (but not in the sub panel) to the box, typically thru a screw thru the neutral bus to the box.

   And where in the sub panel?   to your buss bar on the case.

   The white goes to the neutral busses in each box. correct

2. 
   JohnSprung | Jul 15, 2004 10:14pm | #2

   The simple way to remember it is that a connection between ground and neutral is required at the service entrance, and forbidden everywhere else.

   -- J.S.

1. 
   brownbagg | Jul 16, 2004 12:04am | #3

   on the main and only the main. The netrual and ground can be on the same bus. BUT NOT ON THE SUBPANEL

1. 
   10man | Jul 16, 2004 02:32am | #4

   Hello Brownbag,

   I've been a residential contractor for 27 years, and usually leave the wiring to subs. I've wired a few houses myself, so I have an understanding of basic wiring, and the reasons for doing most things a certain way, but have never really fully grasped the importance of keeping neutrals and grounds seperate in a subpanel. I understand that it could keep a problem on the subpanel circuits from feeding through the circuits fed from the main, but...how important is it, really, other than satisfying code? Your post sounded like you have a firm grip on this, and I'd like to learn a bit more, if you'd be willing to share. Anyone else care to enlighten me?

1. 
   Lenny | Jul 16, 2004 02:44am | #5

   Same question as 10MAN.

2. 
   brownbagg | Jul 16, 2004 03:49am | #6

   If you have a short in the house you want it to go to the ground(ground rod) you do not want it to backfeed through the netrual. By not keeping the neutral and ground seperate you creating another path for power to feed through the house. If the hot short can get on the netrual and ground at same time it can by pass the cicuit breakers.

1. 
   pm22 | Jul 16, 2004 04:42am | #7

   Oh dear. There are certain people on this forum who are professional, knowledgeable electricians -- such as Cliff Popejoy and 4Lorn and Bill Hartman. Brownbag is half way right.

   If you have a short in the house you want it to go to the ground(ground rod)The electrons in a short to not go to dirt. A short is a direct contact between the hot wire and either the neutral or the ground wire. All the electrons in the power company's supply sense this shortcut and rush to get a free ride. Like a Brink's truck with the back door open spilling money on the street in Logan Heights. This ups the amps going thru the breaker to like 10,000 amps and the circuit breaker, like a policeman, immediately senses this and trips instantly.

    you do not want it to backfeed through the neutral. Huh? What is backfeeding?By not keeping the neutral and ground seperate you creating another path for power to feed through the house. There is as much electricity flowing through the neutral as flows through the hot wire. You get a spark when you cut a neutral which is carrying a load. Learned this at Glen Ellen high school. Also turn your wire cutters into wire strippers [the new notch].

   If the hot short can get on the netrual and ground at same time it can by pass the circuit breakers. This is not true. The circuit breaker is on the hot wire. It monitors the current passing through. If it is mildly overloaded, say 18 amps running through a 15 amp breaker, it make take a couple of minutes to trip. If there is a dead short, whether to ground or neutral, it will trip instantly. This can be a useful diagnostic tool. Reset the breaker. If it takes a while to trip, find out whats on that circuit, do some power calculations and unplug something, like the popcorn machine. If it trips instantly, start taking things apart.

   I've read a book on grounding -- not Soare's -- and it can be summed up like a star. At the main dis-connect, usually the main panel, everything comes together. The incoming neutral from the utility, all the white wires, all the green or naked copper wires, the bonding wires to the gas pipe, etc. and the "grounding electrode conductor" which is NEC double speak for the big wire to the ground rod[s].

   If the ground [green or bare] wires are connected to the ground system in a subpanel, then the aforementioned energy on the neutral would also be traveling through the building steel, water pipes, the ground wires and so on.

   ~Peter

   Por favor depositroel paper sanitarioen el inodoro

   Sign is restroom stall at Home Depot in El Cajon, Calif.

    

3. 
   BillHartmann | Jul 16, 2004 04:50am | #8

   Ground system serve a couple of purposes.

   For this discussion the two main ones are to have a path for fault currents and to make sure that all "metal" in the house is at the same potential level, ie - ground.

   For the later all water pipes, HVAC ducting are bonded to the grounding system and off course electrical equipment (including appliances) are grounded via grounding system.

   The only way to guarantee that everything is at the same potential is to not have any current flowing through the grounding system. If you have any current flowing through the wire then you have a voltage drop. If the sub-pannel used the neutral as the "ground" then anything that used the ground connection of a piece of equipment connect to the sub-pannel would be at a defference potential than equpment or say a water pipe that is grounded via the main pannel.

   And if you either had a poor neutral or a large fault current then that difference can be very high.

1. 
   10man | Jul 17, 2004 02:50am | #9

   Hey...I almost get it. Thanks for the info. These are the clearest explainations I've heard. I've asked a few subs and only get mumbles like "it's just code". I like to understand the reason for doing things a certain way, not just because "it's code", etc..

   10man

2. 
   brownbagg | Jul 17, 2004 04:49am | #10

   " the netural bar must not be connect to the panel frame - only the grounding bus can do this in a subpanel. this is to prevent netural current from flowing through the grounding system on the load side of the main breaker ( which is a code violation). Doing so would place current throught the metal conduit and ductwork, creating a shock and fire hazard."

3. 
   edwardh1 | Jul 17, 2004 02:13pm | #11

   To all -

   what about a switch box (son in law just built a big big playhouse out in the yard and ran two wires (one for receptacles , one AC) to a "box" (mounted up under the playhouse floor) that has two switches (breakers) in it - is that a sub panel??? sounds like it to me. feeds comes straight from the house breaker panel breakers.

   1. How is the outside of this sub panel/switchbox kept grounded and safe for the kids? by the bare wire (ground) that comes in on the feed wires - attached to the box ground screw?

   2. and you say the neutral conductor (white wire?) bar inside the new box (I assume even a two breaker box has one) should be isolated from the box frame? Hope my terms are OK here

   Edited 7/17/2004 7:14 am ET by wain

4. 
   edwardh1 | Jul 17, 2004 02:21pm | #12

   To all - (please excuse double post - the "to all" toggle was not there??????????????

   what about a switch box (son in law just built a big big playhouse out in the yard and ran two wires (one for receptacles , one AC) to a "box" (mounted up under the playhouse floor) that has two switches (breakers) in it - is that a sub panel??? sounds like it to me. feeds comes straight from the house breaker panel breakers.

   1. How is the outside of this sub panel/switchbox kept grounded and safe for the kids? by the bare wire (ground) that comes in on the feed wires - attached to the box ground screw?

   2. and you say the neutral conductor (white wire?) bar inside the new box (I assume even a two breaker box has one) should be isolated from the box frame? Hope my terms are OK he

5. 
   brownbagg | Jul 17, 2004 06:00pm | #13

   1) yes

   2) yes

6. 
   BillHartmann | Jul 17, 2004 06:57pm | #14

   If this play house is treated as an "outbuilding" then there are a couple of other rules that come into play.

   But I suspect that most people would treat this more as a yard object the same as a gazabo.

   "one AC) to a "box" (mounted up under the playhouse floor) that has two switches (breakers) in it - is that a sub panel???"

   Exactly what is it. Does have switches or does it have breakers.

   The only two pole devices that I have seen are used not as sub-pannels, but as disconnects. Square D has one box that comes with with a double pole molded switch that is in the same configuration as circuit breaker. That is used for AC disconnects.

   You can also get the basic box and install a GFCI breaker (or as a package) and use it for GFCI protection and a disconnect for SPA's.

   It has been a while since I looked at one, but it is really not designed for distribution, as a sub-pannel, and has limited connections. I *think* that is just has 2 or 3 spots for grounding and none for neutrals.

7. 
   edwardh1 | Jul 17, 2004 07:08pm | #15

   thanks

   I guess the question for the son in law is, is there a white bus bar inside the box, or are all the (two) whites just wire-nutted together ith the incoming feed white.

   box has only two breakers.

8. 
   BillHartmann | Jul 17, 2004 07:17pm | #16

   No matter what is it used for or where it is located the main important thing is that neutrals still need to be isolated from the ground and the case, if it is metal (Sq D has a plastic version), has to be connected to the ground wire.