Solar Sub-Panel

[Don Martin]

I inspected a house today with a solar electric system that has two inverters. The 200 amp main panel has a 60 amp two pole breaker labeled “Photovoltaic Backfeed” that connects to a sub-panel with the two inverter breakers installed. The unusual part and were I am looking for help is that there are also two house circuits in the solar sub-panel. These would have been in the main panel but were bumped out to make room for the full size 60 amp solar feed. Is it acceptable to have two of the house circuits inside the solar sub-panel? If the main breaker is turned off and the Photovoltaic Backfeed breaker is turned off there will still be two live circuits (at least in the daytime) in the house unless they are turned off individually.

[Harold Doughty]

Don,
If the main house breaker is off, and the two inverter breakers are off, there will be no power in either panel. If the main breaker is off and the inverter breakers are on, there will be power in the sub panel and power going to the 60 amp breaker in the main panel from the sub panel. If the 60 amp breaker in the main panel is on, it will backfeed the whole main panel.
On the flip side, if the 60 amp breaker in the main panel is off, and the inverter breakers are off, the two other circuits in the sub panel will not have power.

[Jim Port]

The labels on the circuit directories do not satisfy the NEC. Plugs is not descriptive enough as there is no location specified.

[Rich Goeken]

Don,
If the main house breaker is off, and the two inverter breakers are off, there will be no power in either panel. If the main breaker is off and the inverter breakers are on, there will be power in the sub panel and power going to the 60 amp breaker in the main panel from the sub panel. If the 60 amp breaker in the main panel is on, it will backfeed the whole main panel.
On the flip side, if the 60 amp breaker in the main panel is off, and the inverter breakers are off, the two other circuits in the sub panel will not have power.
Some inverters, if they sense no commercial power, will not turn on. You will need to check the inverter instructions to determine if this applies here,

[Gunnar Alquist]

I inspected a house today with a solar electric system that has two inverters. The 200 amp main panel has a 60 amp two pole breaker labeled “Photovoltaic Backfeed” that connects to a sub-panel with the two inverter breakers installed. The unusual part and were I am looking for help is that there are also two house circuits in the solar sub-panel. These would have been in the main panel but were bumped out to make room for the full size 60 amp solar feed. Is it acceptable to have two of the house circuits inside the solar sub-panel? If the main breaker is turned off and the Photovoltaic Backfeed breaker is turned off there will still be two live circuits (at least in the daytime) in the house unless they are turned off individually.

As Rich already posted, the inverters monitor the power from the utility company in order to match the hertz. If no power from the utility, then the inverter does not provide power to the panel.

[Jim Port]

As Rich already posted, the inverters monitor the power from the utility company in order to match the hertz. If no power from the utility, then the inverter does not provide power to the panel.

Which will come as a shock to those that think they will still have power even when the utility grid is down.

[bob smit]

Rich G., your correct, and the term is 'anti-islanding".
Some notes; there are just all kinds of labeling req for PV systems, DC circuits entering a home have to be protected ahead by fuses and, conductors have to be in conduit, and don't forget the hold-down device for the back-fed breaker. Just some notes for thought:)

[Rich Goeken]

Rich G., your correct, and the term is 'anti-islanding".
Some notes; there are just all kinds of labeling req for PV systems, DC circuits entering a home have to be protected ahead by fuses and, conductors have to be in conduit, and don't forget the hold-down device for the back-fed breaker. Just some notes for thought:)
Bob, haven't seen a back-fed breaker. Do you have a pic?

[Jim Port]

A back fed breaker is where the incoming power comes into the screws that normally fed the circuits instead of the power coming from the bus. To prevent the breaker coming off the bus a clip or screw is used to make sure it stays in place.

[Rich Goeken]

A back fed breaker is where the incoming power comes into the screws that normally fed the circuits instead of the power coming from the bus. To prevent the breaker coming off the bus a clip or screw is used to make sure it stays in place.
Thanks Jim. In my installation they use two standard 240 VAC breakers, one for buss power to the grid, the other is for the sensing circuit.

[Mike Kleisch]

Solar is fairly new to me, rarely see them, need to read up on it. But, isn’t the Backfeed Breaker supposed to be at the bottom of the buss, or as far away as possible from the main disconnect, assuming there is a disconnect at the top of the panel in this case? Or, does this only apply to direct to AC solar systems?

[ken horak]

Solar is fairly new to me, rarely see them, need to read up on it. But, isn’t the Backfeed Breaker supposed to be at the bottom of the buss, or as far away as possible from the main disconnect, assuming there is a disconnect at the top of the panel in this case? Or, does this only apply to direct to AC solar systems?

From the 2011 NEC Section 705.12(D)(7)

(7) Inverter Output Connection. Unless the panelboard is rated not less than the sum of the ampere ratings of all overcurrent devices supplying it, a connection in a panelboard
shall be positioned at the opposite (load) end from the input feeder location or main circuit location. The bus or conductor rating shall be sized for the loads connected in accordance with Article 220. In systems with panelboards connected in series, the rating of the first overcurrent device directly connected to the output of a utility-interactive inverter(s) shall be used in the calculations for all busbars and conductors. A
permanent warning label shall be applied to the distribution equipment with the following or equivalent wording:

WARNING
INVERTER OUTPUT CONNECTION
DO NOT RELOCATE THIS
OVERCURRENT DEVICE

[ken horak]

Bob, haven't seen a back-fed breaker. Do you have a pic?

This is an older picture and not in a PV system.
Notice the incoming conductors, in the pvc, go to the output side of the circuit breaker. This set up has the electricity going through the circuit breaker in the opposite direction then it normally would. Thus the term "Backfed". Think "backwards"
http://www.nachi.org/forum/attachments/f19/225d1136467979-unusual-sub-panel-wiring-img7.jpg

[Jerry Peck]

This is an older picture and not in a PV system.
Notice the incoming conductors, in the pvc, go to the output side of the circuit breaker. This set up has the electricity going through the circuit breaker in the opposite direction then it normally would. Thus the term "Backfed". Think "backwards"
http://www.nachi.org/forum/attachments/f19/225d1136467979-unusual-sub-panel-wiring-img7.jpg

It's not that the electricity is going through the breaker backward, it is that the electricity is *connected to* the breaker such that the exposed metal parts *may be live* when the breaker is removed.

The normal method of connecting power to the terminals on the bus within the panel allows the breaker to be removed, and when the breaker is removed, there are no live parts of the breaker which are exposed - the live connection between the breaker and the panel is made and un-made where the breaker mounts on the bus.

The back-fed breaker is much less safe as the terminals to the back of the breaker itself are fed live. remove the breaker and those terminals are *still live*, and if that removed breaker is accidentally flipped from 'off' to 'on', then the even more exposed breaker connections to the panel bus are *live* too.

Thus the requirement that back-fed breakers require a tool or other similar secondary means to remove the breaker and not that the breaker can just be snapped out like a normal breaker.

[Gunnar Alquist]

It's not that the electricity is going through the breaker backward, it is that the electricity is *connected to* the breaker such that the exposed metal parts *may be live* when the breaker is removed.

The normal method of connecting power to the terminals on the bus within the panel allows the breaker to be removed, and when the breaker is removed, there are no live parts of the breaker which are exposed - the live connection between the breaker and the panel is made and un-made where the breaker mounts on the bus.

The back-fed breaker is much less safe as the terminals to the back of the breaker itself are fed live. remove the breaker and those terminals are *still live*, and if that removed breaker is accidentally flipped from 'off' to 'on', then the even more exposed breaker connections to the panel bus are *live* too.

Thus the requirement that back-fed breakers require a tool or other similar secondary means to remove the breaker and not that the breaker can just be snapped out like a normal breaker.

I exhumed this thread because I was hoping to get clarification on something regarding backfed breakers and PV systems.

My understanding is that the inverter monitors the utility feed and will not energize the breaker if there is no power in the panel. Therefore, (theoretically, at least) when the breaker from the PV system is snapped out of the panel, power should be interrupted at the inverter.

So... does the backfed breaker from the PV system need to be secured?

[Kevin O'Hornett]

Kudos to all who have posted on this thread. In my experience, understanding photovoltaic systems is no small challenge for home inspectors. Inspectors consistently tell me that understanding electrical systems is their greatest weakness. Notwithstanding the time-worn water flow analogy used to explain basic electrical theory and Kenn Amdahl’s humorous “urge to party” analogy in his book “There Are No Electrons”, it seems that the electricity’s “invisibility” is an ever-present stumbling block for inspectors when it comes to understanding the what-to-do and what-not-to-do aspects of electrical system inspection.
As residential solar (photovoltaic) electric installations become more common, home inspectors will find that their customers expect them to include the examination of such systems in inspections. That said, even the electrical industry and the NEC have been playing catch-up as the rate of technological development outpaces electrical industry standards and building codes. It’s time for the home inspection industry, through its various teaching/training coursework and trade association seminars, to begin the process of teaching the rudiments regarding the types of photovoltaic systems currently and commonly in place.

[Jerry Peck]

So... does the backfed breaker from the PV system need to be secured?

I don't recall there being an exception for any backfed breaker.

[Gunnar Alquist]

I don't recall there being an exception for any backfed breaker.

Thanks Jerry. I was wondering if there might be an exception if the circuit to the backfed breaker had some kind of automatic lockout. It might be in the manufacturer's installation instructions; however, I suspect the manufacturer would be unlikely to be permissive and would just let the requirement to secure a backfed breaker stand.

[Jerry Peck]

I was wondering if there might be an exception if the circuit to the backfed breaker had some kind of automatic lockout. It might be in the manufacturer's installation instructions; however, I suspect the manufacturer would be unlikely to be permissive and would just let the requirement to secure a backfed breaker stand.

Well ... :) ... when you lose utility power ... a backfed service disconnect is no longer energized either ... ;)

[bob smit]

wow! this thread is an oldie but goody :) I remember back when... I was fighting with the utility co. over some issue where they wanted something and it was a violation of the NEC.
Don't ask, I have a case of CRS in this regard:o

[jack davenport]

I don't recall there being an exception for any backfed breaker.

Jerry

Just some quick FYI:
(I don't have time right now to cut & paste code sections ,but can at a later time )

In the 2008 NEC they stated in article 690 that backfed breakers do not need to adhere to 408.36(D). That is the section that requires the additional fastener to hold the breaker in.

In the 2014 NEC Article 690..10(E) they state that stand alone and multimode stand alone systems need to use the additional fastener to hold the breaker in.

Most residential systems are not stand alone alone systems, they are interactive systems. These do not require the additional fastener to hold the breaker in.

The reason is the stand alone systems have power storage capability ( batteries) thus the power stays on when the utility power fails.
Interactive systems do not have storage capability thus when the utility fails the PV invertor shuts off.

This section keeps getting changed every code cycle as the PV systems evolve. Just enough to keep most confused .

[Jerry Peck]

In the 2008 NEC they stated in article 690 that backfed breakers do not need to adhere to 408.36(D). That is the section that requires the additional fastener to hold the breaker in.

I found it at:

2008 NEC 690.64(B)(6)

2014 NEC 705.12(D)(5)

... thus I stand corrected - that breaker is not required to have the additional anchor when back-fed.

Thank you for the correction and update, Jack.

[Gunnar Alquist]

I appreciate the information. Of course, the report went out with the comment about the retaining device. Oh well. :cool: