No primary protection required?

[Dale001289]

I'm sure the folks who developed Article 450 (and 240) considered all your talking points.

 

[electrofelon]

I was originally going to side with the team that were saying a primary OCPD wasn't needed for the line side of the 2nd transformer myself, and felt the conductors to the 2nd transformer would be protected by 1st one that was protected by it's primary, and they are.

But then I read 450.4 (A).

Putting aside the mention of any OCP, 450.4(A) indicates 600v nominal or less shall be protected by and individual overcurrent device be installed in series with each ungrounded "Input Conductor".

That alone would lead me to believe that the "input conductors" to the 2nd transformer (although already protected by the first transformer) would still require an OCPD installed in the conductors to the 2nd transformer.

JAP>

But there is no such language in 450.3. 450.4 is about autotransformers.

 

[kwired]

I'm sure the folks who developed Article 450 (and 240) considered all your talking points.

Maybe maybe not, what I am supposed to follow is what is written and I am not seeing anything that says the point of the circuit in question isn't already protected further upstream. If you want there to be such wording requiring additional protection here you are free to submit a PI, make sure you tell them why you think there is no protection already in place in such a situation or it very well gets rejected.

 

[jap]

But there is no such language in 450.3. 450.4 is about autotransformers.

Ooops, my bad.

JAP>

 

[Dale001289]

Maybe maybe not, what I am supposed to follow is what is written and I am not seeing anything that says the point of the circuit in question isn't already protected further upstream. If you want there to be such wording requiring additional protection here you are free to submit a PI, make sure you tell them why you think there is no protection already in place in such a situation or it very well gets rejected.

Since you're the one advocating code language that does not exist perhaps you should write the PI...

 

[kwired]

Since you're the one advocating code language that does not exist perhaps you should write the PI...

How do you add something that is already covered by it's absence?

 

[Dale001289]

How do you add something that is already covered by it's absence?

It doesn't work that way. Even though your argument is correct technically there are no exceptions in Article 450 that allow it. But nice try.

 

[JFletcher]

I do not see the wording in 450.3(B), either section or table, that would require a second ocpd for a second transformer. The second transformer, its primary is the first transformer secondary (or the same amperage) and would be protected by the first transformer's ocpd. Its secondary protection is listed as not required for currents above or below 9 amps.

Although Step Up / step down schemes are used all the time, I have never installed one, and have not run across this personally, but certainly others here have done this countless times... Does the second transformer require its own ocpd or not? in answering this question, assume that the first transformer is primary only protected at the proper ocpd rating, and both transformers are identical save for Step Up step down.

 

[jap]

I do not see the wording in 450.3(B), either section or table, that would require a second ocpd for a second transformer. The second transformer, its primary is the first transformer secondary (or the same amperage) and would be protected by the first transformer's ocpd. Its secondary protection is listed as not required for currents above or below 9 amps.

Although Step Up / step down schemes are used all the time, I have never installed one, and have not run across this personally, but certainly others here have done this countless times... Does the second transformer require its own ocpd or not? in answering this question, assume that the first transformer is primary only protected at the proper ocpd rating, and both transformers are identical save for Step Up step down.

That's more or less what the OP is asking to begin with.


JAP>

 

[kwired]

It doesn't work that way. Even though your argument is correct technically there are no exceptions in Article 450 that allow it. But nice try.

No exceptions as well as no wording that disallows it. If the supply conductor is already protected why isn't the transformer? Presuming protection is no higher than max level allowed. IMO you need to submit the PI if you want the rules the way you think it should be, as is, I think what I have been saying is allowed.

 

[Isaiah]

After reading back through all the posts, I am convinced the second OCPD/Disconnecting means is required for the second transformer. The NEC is a prescriptive code and it says what it means.

Many thanks to all involved.

 

[kwired]

After reading back through all the posts, I am convinced the second OCPD/Disconnecting means is required for the second transformer. The NEC is a prescriptive code and it says what it means.

Many thanks to all involved.

What did you find that convinces you? If the second transformer is at a separate building or structure you need a disconnect for the second building or structure, but if in the same building I don't find anything that would require additional protection. Yes that transformer needs protection, but if the supply to it is already protected to the proper level, nothing says you must provide additional protection.

 

[Dale001289]

What did you find that convinces you? If the second transformer is at a separate building or structure you need a disconnect for the second building or structure, but if in the same building I don't find anything that would require additional protection. Yes that transformer needs protection, but if the supply to it is already protected to the proper level, nothing says you must provide additional protection.

The OP stated transformers are over 1700 feet apart, so how could they be in the same building?

 

[jap]

The OP stated transformers are over 1700 feet apart, so how could they be in the same building?

1700 feet is not un unimaginable distance in the some buildings.


JAP>

 

[Isaiah]

The OP stated transformers are over 1700 feet apart, so how could they be in the same building?

There are in fact, two separate buildings involved. Both are prefabricated substations. The cables are routed mostly outdoors between buildings/transformers.

 

[electrofelon]

The OP stated transformers are over 1700 feet apart, so how could they be in the same building?

There are in fact, two separate buildings involved. Both are prefabricated substations. The cables are routed mostly outdoors between buildings/transformers.

Recently the nec has made a distinction between "structure " and "equipment". I don't think the structure disconnect requirements would apply to an outdoor transformer with that in mind. Of course if you are providing transformer primary protection, it's a moot point

 

[Skokian]

Secondary OCP at the 1st Xformer.

Secondary OCP at the 1st Xformer.

Would the secondary OCP of the first transformer suffice for the primary OCP for the 2nd one?

 

[kwired]

Would the secondary OCP of the first transformer suffice for the primary OCP for the 2nd one?

It can. Such device is often protecting the supplying secondary as well as downstream circuit conductors, or anything else connected to said conductors.