Feeder Tap

[newt]

Do feeder tap rules apply for pv we have a 1200 feeder that the installer did a feeder tap to a 200 amp disconect that is 16 feet away according to the feedre tap rules that disconnect should be 400amp he said that it being a solar disconnect tap rule doesnt apply but i cant find anything in the code that allows this. Thanks

 

[augie47]

For clarification, does his "tap" connect to a service or a feeder ?

 

[newt]

Feeder

 

[ggunn]

Do feeder tap rules apply for pv we have a 1200 feeder that the installer did a feeder tap to a 200 amp disconect that is 16 feet away according to the feedre tap rules that disconnect should be 400amp he said that it being a solar disconnect tap rule doesnt apply but i cant find anything in the code that allows this. Thanks

FWIW, for a supply side tap in a solar installation I did here in Austin a year or so ago, the utility engineering department's determination was that the tap rules did not apply.

 

[jaggedben]

In my opinion the tap rules apply.

 

[Smart $]

The feeder tap rule of 240.21(B)(2) does not cover the equipment or overcurrent device rating. The one-third stipulation is for the ampacity of the feeder tap conductors... nothing more.

Even under 240.21(B)(1), it is only specified that the tap conductors' ampacity be not less than the equipment or overcurrent device.

 

[augie47]

I would agree with jaggedben in post #5 that the tap rules apply, in fact 690.9 supports that by stating Art 240 is applicable to PV systems. As you pointed out in you post the tap does not comply with 240.21 tap rules.

 

[Smart $]

I would agree with jaggedben in post #5 that the tap rules apply, in fact 690.9 supports that by stating Art 240 is applicable to PV systems. As you pointed out in you post the tap does not comply with 240.21 tap rules.

As I noted, 240.21(B)(2) only covers ampacity of tap conductors. It does not specify equipment or OCPD ratings. Newt did not provide the tap conductors' ampacity rating. If he posts again, it would be nice to know what Code cycle the installation is under and other information regarding ocpd ratings, conductor sizes, sets, ampacities, and any other relevant detail.

 

[jaggedben]

As I noted, 240.21(B)(2) only covers ampacity of tap conductors. It does not specify equipment or OCPD ratings. Newt did not provide the tap conductors' ampacity rating. If he posts again, it would be nice to know what Code cycle the installation is under and other information regarding ocpd ratings, conductor sizes, sets, ampacities, and any other relevant detail.

I think we can agree, though, that the installer was making an invalid argument when he "said that it being a solar disconnect tap rule doesnt apply".

Hopefully Newt can properly apply the tap rules given that answer to the main question.

 

[Smart $]

I think we can agree, though, that the installer was making an invalid argument when he "said that it being a solar disconnect tap rule doesnt apply".

But if the response was regarding equipment rating, it was a valid statement.

Also valid if regarding tap conductor ampacity. We're talking about utility-PV interconnection conductors where 705.12 would apply... rendering 240.21(B) tap rules moot.

 

[electrofelon]

FWIW, for a supply side tap in a solar installation I did here in Austin a year or so ago, the utility engineering department's determination was that the tap rules did not apply.

I am not quite sure i follow what you are saying. By "the tap rules" I assume you mean the feeder tap rules in 240 and those are not for service conductors so why would this ever be a question of applicability for a "supply side tap"?

 

[jaggedben]

But if the response was regarding equipment rating, it was a valid statement.

I don't think the purpose of this forum is to validate right answers that are reached by the wrong reasoning.:happyno:

... We're talking about utility-PV interconnection conductors where 705.12 would apply... rendering 240.21(B) tap rules moot.

No, that's not what we're talking about. See post #3, and the subject line of the thread.

I am not quite sure i follow what you are saying. By "the tap rules" I assume you mean the feeder tap rules in 240 and those are not for service conductors so why would this ever be a question of applicability for a "supply side tap"?

I agree. 240.21(B) tap rules apply to feeders, not service conductors. Whether solar is involved is irrelevant.

 

[Smart $]

I don't think the purpose of this forum is to validate right answers that are reached by the wrong reasoning.:happyno:

No, that's not what we're talking about. See post #3, and the subject line of the thread.
...

Hmm. Re-reading the thread, I may have misunderstood... but then again, I may not have. :huh: Newt will have to clarify...

 

[ggunn]

Hmm. Re-reading the thread, I may have misunderstood... but then again, I may not have. :huh: Newt will have to clarify...

For better or worse and subject to the failings of my memory, and withholding the name of the AHJ, here's my best recollection of what happened in my case:

We had a smallish (<100kW) PV system to interconnect in a fairly large building. There would have been electrical space (a la the 120% rule) to feed the PV into the MDP through a backfed breaker (which is what we had intended to do), but as it turns out there was not enough physical room to land the breaker on the MDP busbars. The owner did not want to spend the money to add another section to the MDP, so the only way to interconnect was a supply side tap. The feeder from the utility transformer was entirely underground to the MDP and the utility did not want us to land on the transformer, so our only alternative was to land our conductors on the input busbars of the main breaker of the MDP.

Incidentally, the electrical room was interior to the building and not adjacent to an exterior wall and there was no room to put the inverters' AC combiner panel in the electrical room. Moreover, the inverters and combiner were already hung on the outside wall and the conduit and conductors run into the electrical room when it was discovered that the busbars in the MDP did not extend to the top of the MDP enclosure, which meant that the breaker we had intended to put into the MDP could not land on one of the busbars. Bummer.

The conductors from the transformer to the MDP were very large - something on the order of six sets of 500kcmil copper. Our equipment on the outside wall was some 30-40 feet away as the conductor flies. I was concerned about the ramifications of the tap rule, specifically as to what size conductors it would direct us to run from the tap point to our gear, so I went to the AHJ's engineering department for a code interpretation.

They ruled that our equipment did not qualify as a tap under the code and was therefore not bound by the requirements of the tap rule. Running those relatively small unprotected conductors through the building out to our gear made me nervous, though, so although the AHJ did not demand it I put in a fused disco in the electrical room right next to the MDP to protect them.

BTW, I am an engineer, not an electrician, and therefore not as accustomed to dealing with the finer points of code as are a lot of you guys. My decision to place the fused disco in the electrical room was one of common sense and what I considered to be prudence rather than one of code compliance.

That's my story and I'm sticking to it.

 

[jaggedben]

...The feeder from the utility transformer was entirely underground to the MDP and the utility did not want us to land on the transformer, so our only alternative was to land our conductors on the input busbars of the main breaker of the MDP. ...

Common usage notwithstanding, that's an incorrect use of the term 'feeder.' Conductors between a utility transformer and an MDP are 'service conductors' or 'service entrance conductors'. That's why the tap rules in 240 didn't apply in your example.

 

[ggunn]

Common usage notwithstanding, that's an incorrect use of the term 'feeder.' Conductors between a utility transformer and an MDP are 'service conductors' or 'service entrance conductors'. That's why the tap rules in 240 didn't apply in your example.

Ah. Well I fessed up to not being an electrician, didn't I?

It's good to know that the AHJ was not in error in their interpretation of the code, since I will likely encounter similar situations in the future.

Would you have put the fused disco near the tap as I did? The AHJ had no problem with me adding it and it seemed to me to make for a safer system.

 

[jaggedben]

Yes, I think the closer is the better.

A service disconnect needs to comply with 230.70.

i.e. "at a readily accessible location either outside of a building or structure or inside nearest the point of entrance of the service conductors." And not in a bathroom.

(And now someone will dispute whether the PV disconnect is a 'service disconnect' and this thread will continue to go on... :roll

 

[texie]

Ah. Well I fessed up to not being an electrician, didn't I?

It's good to know that the AHJ was not in error in their interpretation of the code, since I will likely encounter similar situations in the future.

Would you have put the fused disco near the tap as I did? The AHJ had no problem with me adding it and it seemed to me to make for a safer system.

I think that by your addition of the fusible switch at the point of connection made this compliant and the AHJ was wrong. As noted by others these are service conductors up to the disconnect and as such you could not have extended these to the outside unless you treated them as service conductors and installed accordingly.

 

[Smart $]

I think that by your addition of the fusible switch at the point of connection made this compliant and the AHJ was wrong. As noted by others these are service conductors up to the disconnect and as such you could not have extended these to the outside unless you treated them as service conductors and installed accordingly.

I don't believe the AHJ was wrong, as 240.21 tap rules do not apply to service or service entrance conductors. However, you are correct that to not provide OCP at/near the inside tap would require the conductors to the exterior combiner panel to be installed using a considered-outside method.

 

[texie]

I don't believe the AHJ was wrong, as 240.21 tap rules do not apply to service or service entrance conductors. However, you are correct that to not provide OCP at/near the inside tap would require the conductors to the exterior combiner panel to be installed using a considered-outside method.

Yes, I agree this is not a tap and in that regard I agree with the AHJ. I'm just saying that the fusible disconnect is required at the point of connection is required. I'm agreeing with you that while these may not be service conductors they have to be treated as such, as you say, if the disconnect was at the outside end.