Distance to OCPD

[ggonza]

Is there a maximum distance to OCPD for transformer secondary conductors less than 600 v. Someone was telling me if its over 25' you would need to have a fused disc. or other ocpd. I can't find it anywhere in the 2008 code.

 

[augie47]

Look at 240.21(c)
Distance varies depending on conditions. 25 ft is a common condition.

 

[ggonza]

correct me if I'm wrong. But reading that section talks about conditions that allow no ocpd. In most cases that I'm involved with there is ocpd. Is there another way of interpreting that section.

 

[infinity]

correct me if I'm wrong. But reading that section talks about conditions that allow no ocpd. In most cases that I'm involved with there is ocpd. Is there another way of interpreting that section.

Let's start with some more information, what type and size of transformer?

 

[kwired]

correct me if I'm wrong. But reading that section talks about conditions that allow no ocpd. In most cases that I'm involved with there is ocpd. Is there another way of interpreting that section.

Read the section carefully OCP is required, just not at the secondary of the transformer. One condition allows the primary protection to protect the secondary if certain conditions are met, one allows up to 10 feet of unprotected secondary, two conditons allow up to 25 feet of unprotected secondary, another set of conditions for outside, and a condition for feeder tapped transformer.

If not protected by provisions that allow protection by the primary there will be secondary protection - where depends on conditions of the installation.

 

[davidaengelhart]

Not to wander off the beaten path, but I would like to point out that the OCP can not be more than the ampacity of the conductors at all for this situation per 240.21(C), last sentence before the sub-headings. I have reviewed a few sets of plans that indicate 500CU from a transformer secondary to a 400 amp OCD with a load calculation of 376 amps that I had to disapprove. 240.4(B) does not apply as stated in 240.21(C).
I hope this is not a repeated comment. If so, I just didn't take/have the time to look at all the comments, for which I would have to appologise for. Time to get back to work. Dave E.