Neutral & Ground Bonding

[Zyb]

I have a PV system line side tap, with PV AC disconnect. where will my neutral and ground bond location. in my MSP or PV Disconnect? is there a difference if the location is in PV disconnect or MSP or both. Thank you

 

[Another C10]

I have a PV system line side tap, with PV AC disconnect. where will my neutral and ground bond location. in my MSP or PV Disconnect? is there a difference if the location is in PV disconnect or MSP or both. Thank you

Photo Voltaic isn't my expertise although I did go to a class or two, which wont help your question I'm sure .. but the only place the neutral and ground connect in my electrical world is at the point of origin of the utility neutral, anywhere down stream from that origin point they are to be isolated from one another, basically because the neutral is a current carrying conductor and one does not want to connect that potential with a ground conductor which then could inadvertently allow a conductive path onto a metallic surface which people may come in contact with.

Research is good and you have the whole internet to study from I'm sure you could find an approved schematic which is an approved method, I'd tend to think the utility source guidelines would supersede any secondary voltage supply especially being that it sends that developed voltage onto the common grid.

Lets see what others say .. good question though.

 

[Zyb]

based on my research bond location is on the first disconnect. it's hard to tell which is the first disconnect

 

[Fred B]

Are you considering, or is the PV ever considered a SDS? If not the N/G bonding is to be at one location only.

 

[Carultch]

based on my research bond location is on the first disconnect. it's hard to tell which is the first disconnect
View attachment 2559635

Your line/load orientation is backwards on that disconnect. The line side terminals to the top of the disconnect, should be toward the utility. The line side terminals on the top of the disconnect are usually covered with a plastic shield to mitigate the risk of accidental contact. The permanently energized source belongs connected to the top terminals. This way, as much of the disconnect interior is de-energized as possible, when it is in the open position. The fuses would then be de-energized, and so would the open blades. Disconnects and fuses are inherently capable of carrying current in either direction, but voltage energization should be established on the top terminals.

It is good to draw it on your diagrams so its up/down orientation matches the way it is arranged in reality, as this is something that is easily overlooked, and could be a costly mistake requiring a new shutdown to fix. When an installer sees that you've deliberately gone out of your way to put the line side terminals on the top of your drawing, this helps comprehension. If by contrast, it looks like just a switch that is in-line with your circuit, the installer might wire it backwards and not realize that the device is meant to be wired a certain way.

 

[Carultch]

I have a PV system line side tap, with PV AC disconnect. where will my neutral and ground bond location. in my MSP or PV Disconnect? is there a difference if the location is in PV disconnect or MSP or both. Thank you

To answer your original question, this is in the gray area on whether it should count as a service disconnect or not. AHJ's are very inconsistent on their opinions on how this should be done and their enforcement. It is probably a good idea to ask your AHJ and get a response in writing for how to proceed. That, and follow the practices of others in the jurisdiction.

If in doubt, prepare for both possibilities. Wire it as if it is not a service disconnect, with both a ground and neutral connected to the corresponding busbars of the main panelboard where you interconnect. Keep the green screw, and tape it inside the enclosure, in case you need it later. Then, use the N-G bonding screw if your AHJ tells you to use it, and then connect the GEC.

Label it as if it is a service disconnect, because ultimately, it is one of the throws of the hand needed to shut down the power to the building. Follow all other rules that govern service disconnects, such as ready accessibility and service entrance ratings.

Are you considering, or is the PV ever considered a SDS? If not the N/G bonding is to be at one location only.

How does that work when you have multiple service disconnects, which the NEC allows? Given up to 6 service disconnects, and a need to bond N&G at the service disconnect, you can't do it at exclusively one point if you are required to do it in each of the service disconnects. You can if the multiple service disconnects are part of the same product and there is one place to do it, but not if they are separately-installed products.

Meter sockets also force you to bond neutral and ground, which would make a redundant N-G bond from the service disconnect.

The PV also isn't an SDS, unless it is across a transformer, or neutral-switching transfer switch from the rest of the service.

 

[don_resqcapt19]

based on my research bond location is on the first disconnect. it's hard to tell which is the first disconnect
View attachment 2559635

Both are service disconnects and need main bonding jumpers.

 

[LarryFine]

Meter sockets also force you to bond neutral and ground, which would make a redundant N-G bond from the service disconnect.

Technically speaking, not really, because there is no EGC where meters are normally installed. The meter enclosure is part of the neutral itself.

 

[pv_n00b]

If you are under the 2020 NEC you need a N-G bond in the PV disconnect. This is in addition to the usual N-G bond in the service panel.
If you are under prior NECs then there are a couple of options because the NEC is not specific, but the best place is still the PV disconnect unless the AHJ requires something else.

 

[Zyb]

Your line/load orientation is backwards on that disconnect. The line side terminals to the top of the disconnect, should be toward the utility. The line side terminals on the top of the disconnect are usually covered with a plastic shield to mitigate the risk of accidental contact. The permanently energized source belongs connected to the top terminals. This way, as much of the disconnect interior is de-energized as possible, when it is in the open position. The fuses would then be de-energized, and so would the open blades. Disconnects and fuses are inherently capable of carrying current in either direction, but voltage energization should be established on the top terminals.

It is good to draw it on your diagrams so its up/down orientation matches the way it is arranged in reality, as this is something that is easily overlooked, and could be a costly mistake requiring a new shutdown to fix. When an installer sees that you've deliberately gone out of your way to put the line side terminals on the top of your drawing, this helps comprehension. If by contrast, it looks like just a switch that is in-line with your circuit, the installer might wire it backwards and not realize that the device is meant to be wired a certain way.

I think this is interchangeable. I was corrected by my instructor before. I took up a class and install the wire from the load side and she said it should be on the line side because the PV system is the source.

 

[Carultch]

I think this is interchangeable. I was corrected by my instructor before. I took up a class and install the wire from the load side and she said it should be on the line side because the PV system is the source.

Your instructor is incorrect. It is understandable how someone can get confused by this, because the designation of source and load isn't as cut and dry in this application as it applies to standard power-consuming loads. The reason I take this seriously, is that it can be a costly mistake for both your company and customer, with the additional shutdown needed to correct it.

When installed this way, fuses are not serviceable without a utility-controlled shutdown. There will also be a lot more exposed live parts within the unit on the load side, if you install it this way. The blades are exposed, the load side terminals are exposed, the fuse mounting clips are exposed. You want as much of the exposed metal to be de-energized as possible, when the handle is in the off position.

Both the PV system and the utility are sources of different aspects of the power. The utility is the source of the voltage and frequency, and the inverter provides the current. The inverter monitors grid voltage, and solves Ohm's law through a feedback loop, generating a slightly higher voltage at its terminals that enables it to function as a current source. Upon shutting off the disconnect, the inverters automatically shut down, since the voltage is no longer within the tolerance of their internal relay. A standard grid-following inverter is required by the UL standards to not feed power to a blackout grid.

The circuit elements inside a fused disconnect, both the fuses and blades, can withstand power flowing in either direction, and don't care which side consumes and which side produces. But you are asking for trouble if you don't wire the top terminals to the permanent source of energization. Treat a standard grid-following inverter as if it were any other load, and wire all blade disconnects with that thought in mind.

Some components do get wired with the inverter(s) as a source and the utility as a load, but a blade disconnect is not one of them. Customer-owned metering, and its corresponding current transformers (CT's) are the examples in my familiarity, such that the meter counts production as positive. If a utility is the recipient of a meter's data, the utility likely has their own standard for wiring orientation & sign convention that would apply instead.

 

[PWDickerson]

Carultch is absolutely correct about the line-load orientation of the fused disconnect. When a solar fused disconnect is opened, the inverters instantly shut down and no longer send voltage to switch. That is why the solar conductors are connected to the load side. Yes, there is a concern that an expensive utility shut down would be required to replace the fuses if the switch were wired the wrong way, but the bigger concern is that someone could get electrocuted replacing fuses if they didn't realize that the fuses were still live when the switch was open. Make sure your instructor gets this right!

 

[PWDickerson]

Also, the PV system is the source when everything is working correctly. But that is not when the fuses come into play. The fuses will only blow when there is a short circuit between the fuses and the inverter, and when that happens, the source of the short circuit current is the utility, not the inverters.

 

[ggunn]

Both are service disconnects and need main bonding jumpers.

Not universally; here in Texas there are only two AHJs I know of who want to see this. The rest want an EGC through the disco to the PV system and N and G unbonded in the PV AC disco. Botttom line: look at any documentation that there may be in the AHJ PV system requirements, or if there aren't any, ask them.

 

[BradPV]

This causes confusions with the AHJ's in NC so much that there are example drawings on the fire marshal website. Think about it like this, if you turn off the main breaker will the PV system still have power? If so you need to bond the neutral in the PV disco, as this is the first means of disconnect.

 

[ggunn]

This causes confusions with the AHJ's in NC so much that there are example drawings on the fire marshal website. Think about it like this, if you turn off the main breaker will the PV system still have power? If so you need to bond the neutral in the PV disco, as this is the first means of disconnect.

Again, many AHJs here in Texas do not see it that way.

 

[BradPV]

Again, many AHJs here in Texas do not see it that way.

I understand they get to run their own jurisdictions but I don't quite get the logic behind that decision either. Do they require the fused AC disco to be marked as "service equipment"?

 

[ggunn]

I understand they get to run their own jurisdictions but I don't quite get the logic behind that decision either. Do they require the fused AC disco to be marked as "service equipment"?

They do not require us to label the PV AC disconnect with anything other than what NEC 690 requires.

 

[BradPV]

They do not require us to label the PV AC disconnect with anything other than what NEC 690 requires.

So I get the 690 requirements of course but it also falls under the definition for Service Equipment which has it's own requirements for bonding and marking. I know this is a moot point I just find it curious.

 

[ggunn]

So I get the 690 requirements of course but it also falls under the definition for Service Equipment which has it's own requirements for bonding and marking. I know this is a moot point I just find it curious.

The AHJs that direct us to leave G and N unbonded in the PV AC disco also require us to run a grounding conductor through the disco back to the main distribution panel from the PV system, so they do not consider it to be a service.