Service Entrance Main

[tonyjove99]

I am trying to determine if a main device is needed on the service entrance equipment. The site is serviced by an outdoor, utility-owned 1000 KVA transformer, 13.8 kV x 480/277V, where the secondary conductors are routed directly into the building. The distance from the transformer to the point of entrance well exceeds 25 ft. The service entrance equipment will be located immediately inside the building at the nearest point of entrance and will be owned by the Customer. Article 230.90 does not require a main overcurrent protection device as part of the service entrance equipment and makes no reference to a distance limitation from the transformer secondary to the service disconnect. However, Article 240.21 does require the use of a main device and, in this sense, conflicts with the information stated in Article 230.90. Since none of the exceptions in 240.21 (i.e. A thru G) apply to my situation, I assume that a main is required. Does Article 240.21 apply to my situation and why does it conflict with Article 230.90?

 

[ryan_618]

Re: Service Entrance Main

In my opinion, no the NEC doesn't require a main. That is because the transformer is utility owned, and therefore 90.2(B)(5) applies, making it unregulated.

 

[charlie]

Re: Service Entrance Main

Tony, the outside conductors are not covered by 240.21 but are covered by the NESC since they are owned by the electric utility to the service point. From the service point on is now premises wiring and covered by the NEC. Your building now is required to have a service disconnecting means that meets the requirements of Part VI of Article 230 (230.70 through 230.82).

 

[pattbaa]

Re: Service Entrance Main

Art. 240.4 Protction of Conductors----"Conductors shall be protected against over-current--- unless otherwise permitted (by par's A thru G) "

(F) Transformer Secondary Connections--- "Single- phase ( 3-wire) and multi-phase ( except 3-wire delta/delta ) transformer scondary conductors shall not be considered to be protected by the Primary over-current protctive devise----"

 

[beanland]

Re: Service Entrance Main

The cables up to the building wall are the service lateral. The cables, once they penetrate the building wall, are service entrance conductors. The service entrance conductors need to be protected by overcurrent devices. Code allows from one to six devices to act as the overcurrent protection. Most jurisdictions require the overcurrent protection to be a short distance from the building wall. If the entrance conductors are incased in concrete, they can be considered external to the building. However, wherever the cables come into the building, the overcurrent devices must be right there.

 

[tom baker]

Re: Service Entrance Main

"The service entrance conductors need to be protected by overcurrent devices"
Service entrance condutors have overload protection only, over current protection is provided by the utility on the primary side of the transformer.
As the service entrance conductors are "unfused", special rules in Art 240 and 250 apply.

 

[pattbaa]

Re: Service Entrance Main

Art 240.21 (C) Transformer Secondary Conductors, (4) Outside Secondary Conductors (2)---"the conductors terminate at a single circuit-breaker"

 

[charlie]

Re: Service Entrance Main

Patbaa, 240.21 does not apply at all to electric utility conductors. Service entrance conductors are protected from overload like Tom said. However, Tom, they are not protected from short circuits and ground fault by the electric utility.

 

[pattbaa]

Re: Service Entrance Main

The issue is the required over-current, not over-load protection of conductors connected to a transfomer secondary.
The distiction between over-load and over-current P-D's is that a over-current P-D will protect against Fault-currents in addition to protection from currents of a value that exceeds the ampacity of the conductors, such currents the result of an over-load.

Fault-currents--- "shorts" and Ground-faults --are not "over-loads". See "Definitions", Art 100.

Art 240.21, Location in Circuit reads--- "Over-current protection--- shall be located at the point where conductors recieve their suppy except as specified in ( A thu G )"

"C" applies to Transormer Secondary Conductors-----"conductors shall be permitted to be connected to a transformer secondary withour overcurrent protection at the secondary as specified in ( 1 thru 6)"

"4" applies to secondary conductors located "outside" the structure with the exception of the termination. Code-compliant if---

"2"--- "the conductors terminate on a single circuit-breaker"

"3"--- "The overcurrent device is an integral part of a dis-connecting means---"

"4"--- " The dis-connecting means is (a) outside (b) inside, nearest the point of entrance"

Greenwich Ct.

 

[iwire]

Re: Service Entrance Main

Originally posted by pattbaa:
The issue is the required over-current, not over-load protection of conductors connected to a transfomer secondary.

No not really, the issue is the NEC does not apply here.

90.2 Scope.
(B) Not Covered. This Code does not cover the following:

(5) Installations under the exclusive control of an electric utility where such installations

a.Consist of service drops or service laterals, and associated metering, or

 

[charlie]

Re: Service Entrance Main

Trust me pattbaa, I know what 240.21(C)(4) says but you are talking about the line side of the service point. Because the transformer, secondary conductors, and service drop belong to the serving electric utility this section does not apply. Bob (iwire) is absolutely correct.

 

[iwire]

Re: Service Entrance Main

Originally posted by charlie:
Trust me pattbaa, I know what 240.21(C)(4) says

 

[volt101]

Re: Service Entrance Main

Originally posted by charlie:

Trust me pattbaa, I know what 240.21(C)(4) says

CMP 10 ?

Jim

 

[tom baker]

Re: Service Entrance Main

Charlie is a member of CMP 10 and works for a POCO.

Charlie, since my statement "that they are protected from short circuits and ground fault by the electric utility" is incorrect, what would be a good way to describe the protection?
Unfused?

 

[pattbaa]

Re: Service Entrance Main

Post #1 reads---- "Art. 230.90 does not require ( an O-C P-D ) as part of the Service-entrance equiptment"

More correct to say that Art 230.91 does not require the Service O-C device to be an integral part of the Service Dis-connecting means.If the Service O-C device ( as required by 230.90) is a seperate equiptment, it is required to be "immediately adjacent ( to the Service Dis-Connect)"

 

[charlie]

Re: Service Entrance Main

since my statement "that they are protected from short circuits and ground fault by the electric utility" is incorrect, what would be a good way to describe the protection? Unfused?

Absolutely. We protect our smaller transformers with a cutout that is actually fused to protect the line itself. For instance, we use a 15 T fuse to protect a 15 kVA pole mounted transformer. The T rated fuse in a 100 ampere cutout barrel will carry 150% forever. Doing the math on our 13.2 kV system (7,620 V to ground), the fuse will open up somewhere past 170 kVA of load. If there is a short circuit or ground fault close to the transformer, enough fault current will open the fuse. If it does not, the transformer will let go and the fuse will still protect the tap after a primary to secondary fault develops in the transformer and the transformer explodes.

On larger transformers, the overcurrent is indeed sized closer to the size of the transformer. Also, other electric utilities have different protection schemes. Therefore, your original statement may be correct for your area but I am betting against it. The reason for not using small fuses is lightning strokes tend to damage smaller fuses and we would have to make an inordinately large number of service calls. Using the same logic, I believe that most electric utilities do about the same.