Back feeding a breaker without a main breaker

[NYSolar]

Is it possible to back feed a breaker in a panel that doesn't have a main breaker? It's a 3 phase 120/208v service that goes to a 6 breaker 800amp main panel. I'm trying to back feed a PV system where the OCP needs to be 110amps. In this situation how would I go about doing calculations for what I can back feed?

 

[Dennis Alwon]

Back feeding a panel is often done but a retainer clip must be installed to insure the breaker is fastened. Look at art.408.36(D)

I don't do solar but I believe you may not need to use the retainer clip

 

[NYSolar]

Reply

Reply

Trying to find out if I can back feed solar with this set up. The only calculation I have to back feed solar on a panel requires a main breaker. Any suggestions?

 

[Smart $]

Trying to find out if I can back feed solar with this set up. The only calculation I have to back feed solar on a panel requires a main breaker. Any suggestions?

What you're looking at is a supply side connection which falls under 705.12(A). The sum of all 'backfed' breakers cannot exceed the service rating. Your service rating will be the lower of service conductor ampacity or MDP equipment rating.

 

[ggunn]

Back feeding a panel is often done but a retainer clip must be installed to insure the breaker is fastened. Look at art.408.36(D)

I don't do solar but I believe you may not need to use the retainer clip

Backfed breakers supplied by solar are not required to be clipped. I believe the reason for that is that if the breaker is pulled under load the inverter shuts down; i.e., the breaker cannot be energized from the inverter side alone.

 

[NYSolar]

Thanks

 

[kwired]

Back feeding a panel is often done but a retainer clip must be installed to insure the breaker is fastened. Look at art.408.36(D)

I don't do solar but I believe you may not need to use the retainer clip

Backfed breakers supplied by solar are not required to be clipped. I believe the reason for that is that if the breaker is pulled under load the inverter shuts down; i.e., the breaker cannot be energized from the inverter side alone.

Very possible they don't need secured but just some more commentary here - when dealing with 800 amp panel the likelihood of using "plug on" breakers also diminishes and the "hold down" requirement is met with a bolt on type breaker.

 

[Carultch]

Back feeding a panel is often done but a retainer clip must be installed to insure the breaker is fastened. Look at art.408.36(D)

I don't do solar but I believe you may not need to use the retainer clip

Solar applications specifically do not require a retaining method for the backfed breaker, when you connect the inverter side to the branch terminals.

The reason for requiring a retaining clip is that, in the event that the plug-on breaker is unplugged from the busbar, you want to avoid energizing the breaker. If an inverter breaker is unplugged from the busbar, the circuit is still deenergized, even if the inverter was recently operational.

An interesting case not explicitly covered by the code, is what happens when you use a plug-on branch breaker as the main breaker of a panelboard that is backfed? I recently built a load center to combine two 40A inverters into an 80A output, with an 80A branch breaker used as a main. The circuit is still energized, even if you unplug the 80A plug-on breaker. Therefore, it is my opinion, that even though this breaker is forward fed per the power flow direction, it is still reverse energized by grid voltage on the branch terminals. And thus it should have a retaining clip.


Another check you always have to do, is whether the breaker is built to be backfed. If it is not marked "line and load", then it is suitable for backfeed. This can be a difficult thing to look up, because you are trying to prove a negative. You look at the only part of the breaker you can see, in the existing main panel, and you prove that it isn't already marked line and load.

The typical off-the-shelf ordinary breaker usually is suitable for backfeed. It is usually breakers with additional functionality, such as AFCI and GFCI that might not be. Microinverter users are in a Catch-22. They need to tie-in at an AFCI breaker, but no backfeedable AFCI breakers exist yet.

 

[Carultch]

Is it possible to back feed a breaker in a panel that doesn't have a main breaker? It's a 3 phase 120/208v service that goes to a 6 breaker 800amp main panel. I'm trying to back feed a PV system where the OCP needs to be 110amps. In this situation how would I go about doing calculations for what I can back feed?

I see that your real intention is to ask about how to work out 705.12(D) calculations.

The question I would ask, is are there any overcurrent devices UPSTREAM of this panelboard? Such as a fused disconnect, or a breaker integrated in the meter enclosure?

If so, I would use that overcurrent device, as the OCPD protecting the main supply of the busbar. And then do your 705.12(D) calculation on it. Suppose it is an 800A disconnect fused at 800A. You then try to interconnect a 110A breaker for PV, which means your calculation is (800A + 110A) <= 1.2*800A. And it turns out that this is indeed the case. In such a situation, the maximum you could connect is a 150A breaker, or if NEC2014 applies, a 175A breaker with only 160A of it utilized. Provided that you place it at the opposite end of the busbar.

NEC2014 now rewrote the language, such that rounding errors aren't a showstopper. Such as if 1.25*inverter current would round up to a breaker that would be too large to interconnect, but 1.25*inverter current itself is low enough that it can meet 705.12(D).

You can also use the rule that the sum of the breakers excluding the main supply, cannot exceed the busbar ampacity.


If there isn't a main OCPD anywhere, then you'd have to treat this as a supply-side interconnection per 705.12(A). This would be an interconnection on the supply side of the 6 "service disconnects". PV interconnections get a special exception not to count as one of the six.

 

[PWDickerson]

NYSolar, please clarify the details of the electrical service and how you are considering the interconnection. It sounds like your service panel is rated at 800 amps 208/120 and does not have a single main breaker, but instead has 6 breakers that are all service disconnects. Are you considering interconnecting at one of the 6 service disconnects in the main panel? Is there space for a 7th that the PV system could tie in at? If yes to either question, this would be considered a supply side connection in most jurisdictions (check with your AHJ to be sure), and the backfeed breaker could be sized up to 800 amps.

Are you intending on interconnecting at a panel fed by one of the 6 service disconnects? If yes this would be considered a load side connection and would be subject to the 120% rule or others if you are under the 2014 NEC.

Give us more details please.

 

[jaggedben]

Another issue might be the 6-handle rule.

In my opinion, the code allows 6 handles for each set of service conductors, and you are allowed to install a new set of service conductors for a PV system. However, if you are wishing to add a 7th breaker as a new service disconnect on an existing panel, then you have 7 handles on that set of service conductors which would be a violation.

With that said, there has been a plethora of debate on this forum and elsewhere on this particular subject, and the most important thing is to be one the same page with your AHJ.

 

[NYSolar]

Reply

Reply

Yes there is an 800amp disconnect before this panel. However I was told by one of my AHJ that because the disconnect is not in the panel with the breakers the breaker panel becomes a sub panel. With that being said I cannot combine neutrals and grounds together. And if I was to back feed a breaker that would be my first means of disconnect for my PV installation and would need to have the ground and neutral bonded. Do you see a way around this? This is why I thought the easiest solution would be to take out the 800amp disco. By the way the reason I can't do a line side tap on the disco is because the utility meter is after the disco ( cold sequence).

 

[jaggedben]

And if I was to back feed a breaker that would be my first means of disconnect for my PV installation and would need to have the ground and neutral bonded.

That's wrong. By thinking this is necessary you're creating a problem where there isn't one.

 

[Dennis Alwon]

So when the inverter sees no load it shuts off?? That doesn't sound right. I am trying to understand how the array could feed the inverter and the there would be no voltage on the load side of the inverter. This goes to the clip on the back fed breaker. I understand the clip is not needed but why would the inverter shut down especially if there are batteries that it may charge ahead of the inverter

 

[Smart $]

So when the inverter sees no load it shuts off?? That doesn't sound right. I am trying to understand how the array could feed the inverter and the there would be no voltage on the load side of the inverter. This goes to the clip on the back fed breaker. I understand the clip is not needed but why would the inverter shut down especially if there are batteries that it may charge ahead of the inverter

This gets into different types of inverters. The ones mentioned that shut down are grid-tied inverters (GTI's). They are required to disconnect their output automatically on loss of grid voltage.

 

[Dennis Alwon]

This gets into different types of inverters. The ones mentioned that shut down are grid-tied inverters (GTI's). They are required to disconnect their output automatically on loss of grid voltage.

Thank you

 

[kwired]

Yes there is an 800amp disconnect before this panel. However I was told by one of my AHJ that because the disconnect is not in the panel with the breakers the breaker panel becomes a sub panel. With that being said I cannot combine neutrals and grounds together. And if I was to back feed a breaker that would be my first means of disconnect for my PV installation and would need to have the ground and neutral bonded. Do you see a way around this? This is why I thought the easiest solution would be to take out the 800amp disco. By the way the reason I can't do a line side tap on the disco is because the utility meter is after the disco ( cold sequence).

It is done with standby generators by not bonding the neutral at the generator, and running a separate neutral and EGC from the generator to the transfer equipment which may or may not be part of service equipment. But ultimately neutral and EGC are bonded together at the main/system bonding jumper wherever it may be. I can't really speak for what is common or even required with PV installs without doing some reading though.

 

[Smart $]

Yes there is an 800amp disconnect before this panel. However I was told by one of my AHJ that because the disconnect is not in the panel with the breakers the breaker panel becomes a sub panel. With that being said I cannot combine neutrals and grounds together. And if I was to back feed a breaker that would be my first means of disconnect for my PV installation and would need to have the ground and neutral bonded. Do you see a way around this? This is why I thought the easiest solution would be to take out the 800amp disco. By the way the reason I can't do a line side tap on the disco is because the utility meter is after the disco ( cold sequence).

AFAIK, your PV System neutral(s) and ground(s) are not required to be bonded at the PV System disconnecting means.

Is that an 800A fused or unfused disconnect?

If not fused, it is not an NEC-qualified service disconnecting means... and the MLO panel would be where the service disconnecting means/MBJ are located. Adding PV System breaker there would make it a supply side connection.

 

[jaggedben]

This gets into different types of inverters. The ones mentioned that shut down are grid-tied inverters (GTI's). They are required to disconnect their output automatically on loss of grid voltage.

FWIW, the code term is "Utility Interactive Inverter".

AFAIK, your [AC] PV System neutral(s) and ground(s) are not required to be bonded at the PV System disconnecting means.

Make that not allowed to be bonded at the PV System disconnecting means, unless 1) the disconnecting means happens to be in the same enclosure as the normal main-bonding jumper (i.e service panel), or 2) it's an offgrid, non-utility-interactive inverter that is the primary source of power to the premises. Not allowed because of 250.6.

It is done with standby generators by not bonding the neutral at the generator, and running a separate neutral and EGC from the generator to the transfer equipment which may or may not be part of service equipment. But ultimately neutral and EGC are bonded together at the main/system bonding jumper wherever it may be. I can't really speak for what is common or even required with PV installs without doing some reading though.

If the PV system has a backup capability (i.e. not merely utility interactive), then treat it the same as you would any other type of backup generator. Either there's no N-G bond at the generator, or there is one and the neutral is switched by the transfer equipment. (Right?) AFAIK most off-grid inverters do not come with an N-G bond; it should be made somewhere else.

If the PV inverter is only utility-interactive, as in 99% of cases, then there's no AC N-G bond (i.e. none additional to the one at the service).

 

[kwired]

If the PV system has a backup capability (i.e. not merely utility interactive), then treat it the same as you would any other type of backup generator. Either there's no N-G bond at the generator, or there is one and the neutral is switched by the transfer equipment. (Right?) AFAIK most off-grid inverters do not come with an N-G bond; it should be made somewhere else.

If the PV inverter is only utility-interactive, as in 99% of cases, then there's no AC N-G bond (i.e. none additional to the one at the service).

Correct - my response was to say that in general you need separate grounded and equipment grounding conductors for any additional power sources unless they are service equipment or separately derived. Most PV AFAIK are not separately derived and they definitely are not service equipment.