Transformer secoundary

[augie47]

I have lost a key (to me) element here. Once the conductors enter the building how far do they travel before reaching the overcurrent device ?
Historically locally the distance allowed has varied depending on the wiring method used (rigid or IMC conduit) and the possibility of physical damage. It is not unheard of here for an AHJ to allow a
drop from ceiling height to a main overcurrent device directly below and on the same floor.

 

[david luchini]

Let's talk about that "inside, nearest point of entrance" interpretation: The disconnecting means must be in a readily accessible location nearest the point of entrance of the conductors. The roof may or may not be readily accessible. The switchboard location in the original post could be considered to be a readily accessible location nearest the point of entrance of the conductors, being that anything above the switchboard is not readily accessible. Just sayin.

240.21(C)(4)(4)(c) addresses this.

 

[RB1]

David,

I disagree that 240.21(C)(4)(4)(c) addresses this. Actually, from a logical standpoint 240.21(C)(4)(4)(c) is entirely redundant with 240.21(C)(4)(4)(a) since, by definition, 230.6 defines when conductors are considered to be outside of a building. All of this language relating to feeders has it's origins in 230.70, a section of the code that hasn't really changed much since the very earliest editions of the Code. This is from Article 4 of the 1928 NEC (Gus' first codebook) "The switch or switches shall be placed at the nearest readily accessible point to the entrance of the service, either inside or outside the building wall." What actually has changed is the interpretation of the language. For instance, we now have to clarify in 230.6 that a mast pipe passing through the eave of a building is considered to be outside the building. It is rediculous and absurd that such language must be added to the Code. By the most conservative interpretation any panelboard or circuit breaker enclosure used as service equipment would have to be mounted on the floor where supplied from a service lateral. Using that interpretation, think of the millions of installations that would have to be considered existing nonconforming. It is a shame.

 

[david luchini]

I disagree that 240.21(C)(4)(4)(c) addresses this. Actually, from a logical standpoint 240.21(C)(4)(4)(c) is entirely redundant with 240.21(C)(4)(4)(a) since, by definition, 230.6 defines when conductors are considered to be outside of a building.

240.21(C)(4)(4)(a) and 240.21(C)(4)(4)(c) are not at all redundant. Why would they have they included (c) if it said the same thing as (a)?

240.21(C)(4)(4)(a) says the disconnecting means shall be located outdoors and 240.21(C)(4)(4)(c) says the disconnecting means shall be located indoors.

 

[jado85]

are there any "grandfathered in exeption" for installation that were done 20~30 years ago?

 

[GoldDigger]

Only if the installation met the code in effect at that time.

 

[RB1]

Your right David. List Item (a) does apply to the location of the disconnecting means. It is actually (b) and (c) that mean the same thing. Just like 695.6(A)(1) that permits fire pump service conductors to be routed through the building where installed in accordance with 230.6(A)(1) or (2), which of course is NOT through the building.

 

[augie47]

This is from Article 4 of the 1928 NEC (Gus' first codebook) "The switch or switches shall be placed at the nearest readily accessible point to the entrance of the service, either inside or outside the building wall." .

Almost....
This is the 1st Handbook a Journeyman gave me

 

[kwired]

The reasoning for this would be, to avoid having unprotected conductor inside the building to minimize the hazards. correct?

For similar situations with service conductors they are considered unprotected, for feeders they will have protection, but will be "under protected". My guess is the main reason for such rules is more for supplying separate buildings - this makes the requirement for the main supply similar to the requirements for services. One could even change from a feeder supplied building to a service supplied building without needing to make much changes to anything inside the building this way as well.

Let's talk about that "inside, nearest point of entrance" interpretation: The disconnecting means must be in a readily accessible location nearest the point of entrance of the conductors. The roof may or may not be readily accessible. The switchboard location in the original post could be considered to be a readily accessible location nearest the point of entrance of the conductors, being that anything above the switchboard is not readily accessible. Just sayin.

When you install a breaker enclosure as a service disconnecting means inside a building, do you mount the switch on the slab, or do you extend the service lateral raceway up to the switch location?

NEC does not give any specific distance - neither here or the similar section that applies to service conductors. The specific distance or other conditions has for years varied from one jurisdiction to another. Some may allow quite a bit of unprotected/underprotected conductor inside others are very specific - maybe a maximum of 3 or 5 feet of conductor is permitted in the building, and I have even read on this site there are some places you must have overcurrent protection outside as they won't allow unprotected/underprotected conductors to penetrate the building at all.

You also find places where they will let you run unlimited length - but must be encased in at least 2 inches of concrete or other methods that effectively create a situation that is considered to be outside the building.

 

[don_resqcapt19]

....
You also find places where they will let you run unlimited length - but must be encased in at least 2 inches of concrete or other methods that effectively create a situation that is considered to be outside the building.

Everywhere they use the NEC should permit that, as it specifically provided for in 230.6.

 

[kwired]

Everywhere they use the NEC should permit that, as it specifically provided for in 230.6.

I agree that they should.

 

[jado85]

I agree that they should.

would using an over current relay as in 240.92 (C)(2)(3) have the same location requirement ? since the CT's would be installed on the transformer secondary, would that be compliant with 240.21(C) in regards to the location of the OCPD?

 

[don_resqcapt19]

would using an over current relay as in 240.92 (C)(2)(3) have the same location requirement ? since the CT's would be installed on the transformer secondary, would that be compliant with 240.21(C) in regards to the location of the OCPD?

You have to comply with all three parts of that section, that is 240.92(C)(1), (2) & (3). 240.99(C)(1)(1) requires that the short circuit and ground fault protective device be within 100' from the transformer secondary terminals. (C)(1)(2) will permit an unlimited length as the differential protection will open the primary OCPD.