Service Conductors vs Service-Entrance Conductors

S

shieldcracker

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Location
San Juan
Per Art 100 Service Conductors begin at the Service Point and end in service disconnecting means. On the other hand Service Entrance Conductors can begin at the Service Point (connecting to a Service Drop/ Lateral), or not (connecting to the Underground/ Overhead Service Conductor), either way per NEC they end at Service Equipment terminals.
Its clear that the lines between a service drop or overhead service conductors and the meter box are indeed Service Entrance Conductors, but what about the lines going out of the meter box to a service disconnect or main breaker loadcenter?
 
The only mention of the word "meter" in the relevant definitions (basically everything in Article 100 that starts with the word Service) is in "Service Conductors, Underground" as a place that those underground service conductors might terminate. As the service conductors extend all the way to the service disconnecting means, if that disconnecting means is in a separate enclosure from the meter, the service conductors between them are Service Entrance Conductors. If that disconnecting means is in the same enclosure as the meter, then there are no SECs, as per the Informational Note.

In all other cases, the meter is not mentioned in the definitions. So the identity of the service condcutors on the line side and the load side (if any) of the meter are the same. If the meter is on the building with the service disconnecting means (as opposed to, say, on a post 300 feet away at the edge of the property), then the conductors on each side of the meter (barring that underground case above) would be Service Entrance Conductors.

Cheers, Wayne
 
I think that we had a thread a few years ago asking why we need two different definitions. :unsure:
 
wwhitney said:
FWIW, service entrance conductors need to be sized with a 125% factor for continuous loads (barring 100% rated OCPD), while other service conductors do not.
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Then perhaps the important distinction here is that Service Entrance Conductors are present in all installations (sized to above) and Overhead/Underground Service Conductors will depend on the actual Service Point location. I suppose the latter are sized to 100% CONT+NCONT because the conductors are mostly outside the building...
 
wwhitney said:
Because one end of the service entrance conductors terminate on an OCPD?

Cheers, Wayne
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I don't know and have always found the current wording to be confusing and poor. I never really understood the distinction between the two definitions or why we need them both. Just take the different rules and combine them into a single definition.
 
wwhitney said:
FWIW, service entrance conductors need to be sized with a 125% factor for continuous loads (barring 100% rated OCPD), while other service conductors do not.

So there's that.

Cheers, Wayne
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I leafed through the NEC2026 and could not find the rule for the other service conductors (OHSC and UGSC) Can you point me in the right direction?

Sent from my SM-G973U using Tapatalk
 
shieldcracker said:
I leafed through the NEC2026 and could not find the rule for the other service conductors (OHSC and UGSC) Can you point me in the right direction?
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2026 NEC 230.42(A) has the usual two part criterion where the minimum termination rating (60C or 75C ampacity, no derating) includes a 125% factor for continuous loads. But it covers only Service Entrance Conductors.

Other service conductors are only mentioned in 230.23(A) and 230.31(A) which do not have any 125% factor.

Cheers, Wayne
 
wwhitney said:
Other service conductors are only mentioned in 230.23(A) and 230.31(A) which do not have any 125% factor.
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Both 230.23A & 230.31A state the ampacity of the OHSC, UGSC conductors should be no less than the calculated load.
The load imposed on OHSC and UGSC is the same as the load imposed on the service entrance conductors as it is a series connection.
I fail to see how the of load & demand for the service entrance conductor would not apply.
 
shieldcracker said:
I fail to see how the of load & demand for the service entrance conductor would not apply.
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230.90 plays into this. A couple examples:

Suppose we have an underground service lateral to a post at the edge of the property. The post has the service point, a 200A meter base, and underground service conductors to a building (no OCPD on the post). And suppose the calculated load on the service is 165A, of which 80A is continuous. And NEC 310.12 does not apply. The underground service conductors terminate in a handhole adjacent to the building, and service entrance conductors run from the handhole to one or more service disconnects/OCPD. All conductors and wire connectors are 90C rated, as are the meter base load side terminals (this is allowed by the UL standard for meter bases, not sure how common it is for a meter base to be so labeled).

Case 1. A single service disconnect/OCPD. Per 215.3, It has to be rated at least 165A + 25% * 80A = 185A because it supplies a feeder (either wire type or just panelboard busbars) carrying the full load, and the OCPD is not 100% rated. So a single 200A OCPD.

The service entrance conductors need to have a 75C termination rating of at least 185A per 230.42. So they need to be 3/0 Cu or 250 kcmil Al.

In contrast, the underground service conductors from the post to the handhole have no limit on their termination rating, and need only have an ampacity (which can be based on the 90C column) of 176A (the greater of the load of 165A and one more than the next lower OCPD rating per 240.4(B)). So that means they could be 2/0 Cu or 4/0 Al.

Case 2. From the handhole two sets of SECs go to two separate service disconnects/OCPDs. Now the underground service conductors only need to have a (90C) ampacity of at least the load of 165A, per 230.90(A) Exception 3. So they could be 1/0 Cu or 3/0 Al.

Cheers, Wayne
 
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