Tapping wires between breakers

[don_resqcapt19]

Your opinion baffles me. :blink:

You only need to look to the section right before the one you quoted (i.e. 705.12(D)(1)) to see that a dedicated OCPD is required for the inverter(s) no matter which way they are connected.

I don't read it that way.

It's weird that you don't want to discuss the provision that applies to the OP's question.

I thought that issue was already settled.

And you only need to look at the section right after the one you quoted (705.12(D)(2)(2) to see that 240.21(B) is still in force. The rules don't modify the rules if they don't actually modify them.

Again I don't read the sections that way. We will have to agree to disagree on this one.

 

[ggunn]

I don't read it that way.

I thought that issue was already settled.

Again I don't read the sections that way. We will have to agree to disagree on this one.

Read it any way you wish, but I can pretty much guarantee that if you install an inverter without OCPD at the point of interconnection you will fail inspection in any AHJ's area that I have worked in.

 

[shortcircuit2]

Under the 2014 NEC this is a compliant installation. The one area that is a bit grey is exactly how you are supposed to size the conductors for the tap you made.

Would 705.12(D)(2)(2) tell us the tap conductors to the inverter have to be 125% of the inverter output and the 200 amp breaker protecting the feeder in the OP case?

So he had a 120amp output x 1.25% plus the 200amp OC device which means the tap needs to be rated for 350amps?

I don't understand this part?

 

[jaggedben]

Would 705.12(D)(2)(2) tell us the tap conductors to the inverter have to be 125% of the inverter output and the 200 amp breaker protecting the feeder in the OP case?

So he had a 120amp output x 1.25% plus the 200amp OC device which means the tap needs to be rated for 350amps?

I don't understand this part?

Funny you should ask me because I just submitted a comment to clarify this section in the 2017 code.

In my opinion what the CMP wanted is that you take the the 200A breaker and 125% of the inverter output, add those together, and use that value for the 'rating of the overcurrent device protecting the feeder.' Then you follow 240.21(B), or the minimum size for the output.

In other words, if 240.21(B) says your tap conductors must be 10% ampacity minimum of the overcurrent device, then in the example that would be 10% of 200A+120*1.25 = 35A. But the tap conductors must be rated for the output anyway, so it ends up just being 120*1.25, or 150A. Whichever is bigger.

If the CMP accepts my comment then the above will be right.

 

[shortcircuit2]

If 10% of the 200 amp breaker is 20amps according to the 10ft tap rule of 240.21(B)...

Wouldn't it be 20amps and 125% of the 120amp inverter output = 170amps?

 

[jaggedben]

If 10% of the 200 amp breaker is 20amps according to the 10ft tap rule of 240.21(B)...

Wouldn't it be 20amps and 125% of the 120amp inverter output = 170amps?

The language is poorly written, but if you look at it this way ...

Taps. In systems where inverter output connections are made at feeders, any taps shall be sized based on (the sum of 125 percent of the inverter(s) output circuit current and the rating of the overcurrent device protecting the feeder conductors) as calculated in 240.21(B).

...then you apply the 240.21(B) calculation to the whole sum. Which makes sense because the tap rules are based on the amount of current available, so if it's okay to have a tap with 10% ampacity of a utility supplied breaker, it should be okay to have 10% of utility+solar.

You are proposing we look at it this way...

Taps. In systems where inverter output connections are made at feeders, any taps shall be sized based on the sum of (125 percent of the inverter(s) output circuit current) and (the rating of the overcurrent device protecting the feeder conductors as calculated in 240.21(B).)

That makes just as much sense as an interpretation of poor sentence construction, but it makes less sense from any principle of code or physics, if you ask me. Also, if they wanted what you are thinking they could have just said "the sum of 125 percent of the inverter output circuit current and the minimum ampacity required by 240.21(B)."

Either way you look at it, "as calculated in 240.21(B)" is very poor wording because neither the sum nor the rating of the overcurrent device is calculated there, which is what the wording literally implies.

FWIW, here is the 2017 'First Draft'.

Taps. In systems where power source output connections are made at feeders, any taps shall be sized based on the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the feeder conductors as calculated in 240.21(B). Power source output circuit conductors, where smaller than the feeder conductors, shall be sized to carry not less than the larger of 705.60 or 240.21(B).

...and here is my proposed revision.

Taps. In systems where power source output connections are made at feeders, the output conductors shall be permitted to be sized as tap conductors according to 240.21(B) under the following conditions:
a) for calculation purposes, the assumed rating of the overcurrent device protecting the feeder shall be the sum of the primary source overcurrent device rating and 125% of the output circuit current of all other sources that can supply additional current to the feeder
b) the power source output conductors and overcurrent device shall not be smaller than required by 705.60

 

[shortcircuit2]

It is worded difficult. It seems as if the 240.21(B) result would be to small in most calculations following your math with the 10ft rule.

So the 705.60 result would apply, but consideration must be given to the rating of the equipment supplied per 2014... 240.21(B)(1)(1)b.

 

[nate.ashe]

I think what you guys should look at if your using the 2014 is 705.12(D)(2)(b).

 

[andrew.tkelly]

If this is a load-side connection, how is backfeeding 120A of solar acceptable? Wouldn't you just do: 200A * 1.2 = 240A... subtract the 200A main breaker... = 40A available for solar? Where in the Code does it say you can backfeed more than this? (I'm kind of a newbie.)

 

[jaggedben]

I think what you guys should look at if your using the 2014 is 705.12(D)(2)(b).

It's 705.12(D)(2)(2).

If this is a load-side connection, how is backfeeding 120A of solar acceptable? Wouldn't you just do: 200A * 1.2 = 240A... subtract the 200A main breaker... = 40A available for solar? Where in the Code does it say you can backfeed more than this? (I'm kind of a newbie.)

You should really re-read the whole thread. In the 2014 code the 120% rule only applies to busbars, not feeders. There are different rules for feeders, and it depends where they are fed from.

The 2014 code is not yet in force in California, it will be in 2017. California is still on the equivalent of the 2011 NEC (California 2013 code), and under that code your interpretation is generally correct. However, keep in mind that the 120% rule depends on the rating of the busbar or conductor as well as the main breaker, so it's never just multiplying the main breaker by 120%.