When I was in Guam in 1990, I saw an installation that looked like it should have been a violation of the NEC but had been approved by the electrical inspector.
Building type: 24 unit, three story residential apartment buildsing reinforced concrete block construction.
Applicable Electrical Code: NEC - 1988
Local Amendments to NEC: None
Utility: Guam Power Authority
AHJ: Guam Public Works
Service Voltage; 120/208-volt three-phase four-wire, 60 Hz. Service amps - 600 consisting of two sets of 350kcmil conductors. Service type: Aerial to building Utility: transformers: three 50kVA pole mount with single fused primary disconnects (Not Ganged)
Grounding: Consisted of one 3/4-inch 10-foot ground rod connected to a #2/0 ground conductor in the wireway with a #6 AWG bare copper conductor. The domestic water system was plastic so the grounding electrode system consisted only of the ground rod. Ground conductors toeach of the 24 panels #8 AWG.
Conductors: Copper, THW insulation.
The conductors were fed from the weather head down to a 12"x12" NEMA-3R wireway. Below the wireway were mounted 24 100-amp single-phase three-wire five-jaw, meter sockets without disconnects. From each meter socket an 1 1/4 inch IMC conduit, with three #4 AWG and one #8 AWG ground conductors ran down to the ground and under the building where it rose into a load center electric panel with an 100-amp main circuit breaker. The panel and conduit were installed within the concrete block walls of the building.
Each meter socket were connected to two ungrounded and the neutral of one of the two sets of 350kcmil conductors and the ground conductor with tape and insulating compound insulated split-bolt connectors so that the the load was evenly distributed (12 meters per set of 350kcmil conductors) and the 2/0 ground conductor. The #8 to 2/0 ground connections were not insuated All tap connectors were less tha 10-feet long
The only way to kill power to the building was to open the fused cutouts on the primary side of the three 50kVA pole mounted transformers, enter each of the 24- apartments and turn off each panel, or as suggested by a fireman to pull each of the 24 meters one at a time.
The electrical inspector said the installation was not a violation because all conductors were outside of the building or encased in 2-inches of concrete, and no the #6 AWG ground conductor from the ground rod was correct per the NEC even if it was tied to the 2/0 conductor in the wireway.
Question: Is there a code violation here?
Note: From an installation aspect the wiring was neatly laid out with all associated conductors secured with nylon straps. Each meter connection to the 350kcmil was labeled with nylon tie markers. Each meter was marked with an engraved apartment number. The #4 to 350kcmil taps appeared to be well made and insulated. The contractor could afford to because at that time an electrician in Guam was paid about $8.00 / hour and if the worker was an H2 (foreign) worker many were lucky to be making $2.00 / hr after their expenses [food, housing, transportation, and miscellaneous fees] were deducted. Metal conduits between the meter and the panels were grounded to the #8 on both ends.
Note: All conduits within the apartment were PVC and contained a ground conductor based on the largest circuit breaker trip rating, and all wiring devices including switches were bonded.
Michael L. Stoianoff, P.E. Stoianoff Technical Services 2901 Kimberlie Court Anchorage, AK 99508 Tel: (907) 269-0653 (w)
PS sorry no photos of this apartment house. Except for the electrical service it looks very nice and well constructed.
Michael Stoianoff Utility Engineer - Central Region MIKE_STOIANOFF@DOT.STATE.AK.US State of Alaska P.O. Box 196900, MS 2525, 4111 Aviation Avenue ;Anchorage;AK;99519-6900;USA
Joe, I'd like to see a main disconnet here, but I don't think that the NEC requires one. We have one sevice with multiple sets of service entrance conductors as permitted by 230-40 Exception #1. This exception permits each occupancy to have its own set of service entrance conductors. I would think that each apartment is an occupancy. 230-71(a) says that each set of service entrance conductors permitted by 230-40 Ex#1 is permitted to have not more than 6 switches to serve as the service disconnecting means. The #6 ground is ok for size based on 250-66(a), but is required to be spliced only by irreversible means by 250-64(c). The #8 GECs to each appartment would be taps as permited by 250-64(d). Don(resqcapt19)
Re: No Main Disconnect Here?#77612 06/29/0108:34 PM06/29/0108:34 PM
Isn't this a case of 2 sets of Service Entrance Conductors,(the 350s) each feeding 12 switches? By definition in Article 100, "Service Entrance Conductor Overhead System", the SE conductors are tapped from or spliced to the drop. They extend to the terminals of the service equipment (Aren't those the terminals where these meters are tapped?) None of the tap conductors to these meters are tapped or spliced to the drop, but are tapped to SE conductors. Although they are Service Conductors,I honestly don't think they qualify as SE connectors. Somebody PLEASE try & explain to me what I'm might be missing here.
[This message has been edited by electure (edited 06-29-2001).]
Re: No Main Disconnect Here?#77613 06/29/0110:28 PM06/29/0110:28 PM
The main rule in 230-40 says that each service drop or lateral shall supply only one set of service-entrance conductors. Exception #1 says that when a building has multiple occupancies, each occupancy is permitted to have a set of service-entrance conductors. The service-entrnace conductors are the conductors between the service drop or lateral and the service equipment. ( in looking at Article 100 I don't really see a difference between the definitions of "service conductors" and "service-entrance conductors") The service equipment is the apartment panel where the disconnect is. 230-71(a) says that each set service entrance conductors permitted by 230-40 Exception #1 shall have a disconnecting means. This disconnecting means is permitted to have up to 6 switches. Don(resqcapt19)
Re: No Main Disconnect Here?#77616 06/30/0107:04 AM06/30/0107:04 AM
I see your point re. SE vs Service conductors. Do you consider the tap conductors to the meters to be tapped or spliced to the drop? (I really haven't seen any multimeter installations done this way, w/ more than 6 per set of conductors that were tapped directly to the drop,other than the one we discussed in a different thread.) Then again, I've never worked outside of So Ca.
Re: No Main Disconnect Here?#77617 07/01/0101:00 PM07/01/0101:00 PM
My own words are (like this) Article 100-Service Conductors (All of)"The conductors from the service point (drop) to the service disconnecting means"(including the SE conductors). (The conductors from the meters to the panels are not SE conductors. They do not tap or splice to the service drop as they must to be SE conductors.. They are service conductors. 230-40 (1) uses the term "service-entrance conductors". This installation would require not 1 but 2 main disconnects, as there are 2 sets of SE conductors, each with more than 6 disconnects) Grounding. The #6 to the ground rod is no good, as 250-66 calls for a 2/0 for the combined equivalent of 700 MCM for the 2 sets of 350 SE Conductors. Agree or disagree??
Re: No Main Disconnect Here?#77618 07/01/0101:42 PM07/01/0101:42 PM
The service entrance conductors end at the service equipment per the definition. The service equipment is the service disconnecting means. The conductors from the taps to the 350's to the service equipment are the service entrance conductors. The six disconencts are permitted at the end of each set of service entrance conductors. There is nothing that says the SE conductors have to be continious between the 350s and the service disconnect. In this case they pass through the meter. As far as the #6 GEC, 250-66(a) never requires a GEC larger than #6 to a ground rod no matter how big the service is. Don(resqcapt19)