240.21(C) Help

[Jerramundi]

I'm reading 240.21(C) Transformer Secondary Conductors and, barring the latter 240.21(C)(1-6), there seems to be only TWO iterations of transformer secondary conductors that are acceptable without overcurrent protection...

#1 "...a set of conductors feeding a single load..."
#2 "...each set of conductors feeding separate loads..."

I'm curious where #3 (see diagram below) falls under this explicit verbiage, if at all...

 

[augie47]

As I read 240.21(c), your diagram is correct 1 & 2 are allowed, #3 is not

 

[wwhitney]

I would say that the distinction doesn't matter for 240.21(C)(1), as it has no requirement for OCPD at the load. It only matters for 240.21(C)(2)-(6).

Cheers, Wayne

 

[Jerramundi]

I would say that the distinction doesn't matter for 240.21(C)(1), as it has no requirement for OCPD at the load. It only matters for 240.21(C)(2)-(6).

Cheers, Wayne

Are you sure Wayne?

I think the beginning of 240.21(C) is pretty clear in that these two instances (i.e. 1-a set of conductors feeding a single load, or 2-each set of conductors feeding separate loads) applies to the whole of 240.21(C)(1)-(6)

 

[Jerramundi]

Just out of curiosity, how would one "provide protection at the point at which the conductors recieve their supply?" Would the OCPD have to be an integral part of the transformer? I've never worked with transformers that have a built-in OCPD....

My 2014 Handbook states the following in an author's commentary...

The requirements for overcurrent protection of transformer secondaries apply only to the protection of transformers, not to the protection of conductors.

The sections in Article 240 referenced in the informational note apply only to the protection of conductors, not to the protection of transformers.

The overcurrent protection required by Article 450 may also satisfy the requirements in Article 240 for conductor protection, and vice versa, but it is also possible that they do not.

Barring the exceptions of 240.21(C), it seems the only way to accomplish both types of protection, would be to have an OCPD as an integral part of the transformer...

 

[wwhitney]

Are you sure Wayne?

Sure, just call the green wires and the two "loads" you have all one "load". 240.21(C) (2) - (6) would require you to provide OCPD there, at the end of the single pair of red conductors.. Since 240.21(C)(1) doesn't require OCPD, there's nothing to do.

Cheers, Wayne

 

[goldsborough]

Sure, just call the green wires and the two "loads" you have all one "load". 240.21(C) (2) - (6) would require you to provide OCPD there, at the end of the single pair of red conductors.. Since 240.21(C)(1) doesn't require OCPD, there's nothing to do.

Cheers, Wayne

The primary fuses or circuit breaker provides protection for the transformer. Secondary Protection protects the load. Its very important to read article 240.4 F Single Phase (other than 2 Wire) and multi-phase (other than delta delta 3 wire) the transformer Secondary Conductors shall not be protected by the primary Overcurrent Protective Device.

Sent from my SM-G965U using Tapatalk

 

[wwhitney]

Not sure what your point is, the secondary circuit shown is a 2-wire circuit, so 240.4(F) does allow the secondary conductors to be protected by the primary OCPD.

Cheers, Wayne

 

[Jerramundi]

The primary fuses or circuit breaker provides protection for the transformer. Secondary Protection protects the load. Its very important to read article 240.4 F Single Phase (other than 2 Wire) and multi-phase (other than delta delta 3 wire) the transformer Secondary Conductors shall not be protected by the primary Overcurrent Protective Device.

Sent from my SM-G965U using Tapatalk

I would be careful here. "Primary protection" doesn't necessarily mean both (1) the primary of the transformer itself and (2) the secondary of the transformer itself are protected.

450.3 never explicitly says that primary protection alone = protection of both (1) the primary of the transformer and (2) the secondary of the transformer.

Table 450.3 only says that "secondary protection" of the transformer itself is not required in certain instances...

We're talking about two distinct things with Articles 450 and 240: (1) The transformer itself (primaries and secondaries) and (2) secondary conductors. I think that distinction is crucial. There is a key distinction in verbiage here between (1) secondary and (2) secondary conductors.

The 2014 Handbook has an interesting author's commentary that says: "The requirements for overcurrent protection of transformer secondaries apply ONLY to the protection of transformers, not to the protection of conductors..."

It goes on to say that "...The sections in Article 240 referenced in the informational note apply only to the protection of conductors, not to the protection of transformers..."

It concludes with "...The overcurrent protection required by Article 450 may also satisfy the requirements in Article 240 for conductor protection, and vice versa, but it is also possible they do not."