What does 2002 NEC require for nipple between meter base
and breaker panel? Clients ex is an electrical contractor, want metal rigid with lock washers. Job Contractor wants has Rigid PVC with bonding wire
running through nipple to bond both boxes. Can anyone help
They prefer PVC here because you don’t have the problem of paralleling the neutral. It gets a 3 wire service conductor set (120/240 1p). The NEC has cleaned up that language a bit, basically making that parallel neutral legal on the line side of the service disconnect, but you are still putting current on a grounding path, if the PoCo grounds the neutral in the meter base. Most do.
Why would he run a bonding wire through the nipple on a PVC…really depends on the POCO as greg stated…as in our area they want nothing bonded into their meter can when using PVC for the nipple…
Bob, advise them that IF you use the metal nipple then you WILL have issued that greg so correctly spoke of…using PVC is a much better route in my opinion and I never use metal nipples for back to back connections.
If he is worried…use Sch. 80 and he should be fine.
Here…this may help explain what greg was speaking of :
Now just picture the left one on the bottom as the meter…and the one of the right as the main panel…same basic principle applies.
Here’s another one…
Fire Hazard. When objectionable current flows on metal parts, a fire could occur because of elevated temperature, which can ignite adjacent combustible material. Heat is generated whenever current flows, particularly over high-resistive parts. In addition, arcing at loose connections is especially dangerous in areas containing easily ignitible and explosive gases, vapors, or dust.
Bob …here is another article for you to pass on to the contractor…enjoy !
"An approved grounding electrode system is listed in NEC 250.52.A.1 through 7**.**The grounding electrode conductor is normally sized by NEC Table 250.66 A normal grounding electrode for a structure is usually a ground rod serving a dwelling NEC 250.52.A.5, or a metal water pipe in contact with the earth for at least 10’. NEC 250.52.A.1If a water pipe is used then this metal water pipe must have a supplemental or auxiliary grounding electrode that is required to be associated with that metal water pipe. NEC 250.52.A.The supplemental grounding electrode is usually found to be a ground rod. NEC 250.53.D.2The grounding electrode conductor may be run from the ground electrode system to the fourth grounding lug of the meter base that is electrically joined to the grounded [neutral] conductor and to the metal frame of the meter base itself. NEC 250.24.A.1OR The grounding electrode conductor may be run from the grounding electrode system to the neutral / grounding combination bar or bars located in the main service rated panel or disconnect. NEC 250.24.A.1 The grounding electrode system serving a dwelling is usually a ground rod, because most grounding electrodes listed in NEC 250.52.A.1 through 7 are not available. You must land the grounding electrode conductor somewhere between the utility company’s point of attachment, most commonly either inside the meter base or inside main panel. The NEC allows you to use the neutral service conductor anywhere from the point of connection of the Utility Company to within the main service rated panel or disconnect. It is my opinion that should not run both a grounding conductor and a neutral conductor connecting in both the meter base at one end and the main service rated panel or disconnect at the other end of these two conductors. If you do you are creating a paralleling that sets it up so that if the big insulated neutral conductor fails that little bare grounding conductor will try to take that neutral’s place because they are both coming from and going to the same place. The NEC does not declare this paralleling on the line side of your main service rated disconnect or panel but I see it as a bad idea to invite this paralleling condition. If you create this paralleling condition you would never know you have a shock hazard because the little bare wire is taking the place of the neutral service conductor. Sounds like a bad idea to me. If the neutral service conductor installed on the line side of the main service disconnect acts as both the neutral service conductor and as the grounding conductor acting as a dual purpose wire as allowed in NEC 250.142 then if that neutral fails your 120 volt circuits will start causing your trouble by dimming etc. At least then you would know you have a problem. Bad part of this is that if your neutral service conductor fails then the 220 volt appliances may try to act as a neutral causing possible spikes in your electricity. My best thoughts on the subject is don’t create the paralleling design by installing the 4th wire being the grounding conductor between the meter base and the main service rated panel unless your power company or AHJ rules that you must do that.
It is advisable not to run a fourth conductor between the meter base and the main service panel, this would cause a paralleling affect not considered to be safe in the electrical field. A neutral service conductor carries the unbalanced load between the two hot conductors. If you ran a fourth bare grounding jumper between the meter base and the panel, and you happened to lose that larger, insulated, current carrying, neutral service conductor’s connection, then that little bare grounding jumper, installed parallel with that neutral and connected to the same places as that neutral, would try to take over the job of that larger insulated neutral. If this happens a bare, smaller, inadequate, conductor would suddenly be a current carrying conductor that has energized all metals exposed to people it is in contact with. This energized metal can provide a difference of potential to ground seeking an easier path to earth, probably, through your body. The neutral wire [white or gray service entrance conductor found between the meter base and the main panel is allowed to act as a duel purpose conductor, that is insulated and much larger. This neutral conductor [whiter or gray service entrance conductor] is allowed to serve as both the neutral and the equipment grounding path between the meter base and the main panel, regardless where you install the grounding electrode conductor coming from the grounding electrode system. Just my opinion, didn’t mean to become redundant on the subject of paralleling the neutral service conductor and the grounding conductor, it just happens to be one of my concerns in electrical design NEC 250.142.A and 250.24 "
P.S. Not my QUOTE…just passing it along!