NEC 2014 690.16(A) fuse pullouts

hhsting

Senior Member
I have fuses in inverter with integral disconnect on the line side of the fuse. The fuses have pullouts. Based on NEC 2014 Article 690.16(A) do I have to add disconnect at the load side of the fuse or fuse pullouts are ok?
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I have fuses in inverter with integral disconnect on the line side of the fuse. The fuses have pullouts. Based on NEC 2014 Article 690.16(A) do I have to add disconnect at the load side of the fuse or fuse pullouts are ok?
Just to be clear, what are you calling line and load side of the fuses? Most inverter integrated DC discos I've seen have been between the fuses and the inverter; I would call that the load side of the fuses.
 

hhsting

Senior Member
Just to be clear, what are you calling line and load side of the fuses? Most inverter integrated DC discos I've seen have been between the fuses and the inverter; I would call that the load side of the fuses.
Fuse side that faces the utility is being called line side and fuse side that faces the solar panel is being called load side. The fuses are inside the inverter. The side that faces the utility has a disco integral to the inverter.

The side that faces solar panel has no disco but their is fuse pull out. Would pullout instead of disco on solar panel side be code compliant disconnecting means per NEC 2014 690.16(A)?
 

Carultch

Senior Member
Location
Massachusetts
String inverters are generally designed to meet code without DC Balance of systems equipment between them and the DC string wiring. The exceptions are rapid shutdown and DC optimizer systems, or an inverter which hasn't caught up with the code cycle. It is usually not necessary to have a "pre-disconnect" before string inverter string fuses.

The fuse servicing requirement, requires that the fuses be capable of being replaced in a "touch safe" manner, after the inverter is shut off. Either by handling only non-metallic components (like rockout fuseholders or fuse pull-outs), or by disconnecting both sides of the fuse from energy sources on both sides (PV & inverter capacitors).

The place where you usually find this requirement affects your design as an EPC, is on a central inverter system with a fused subcombiner at the inverter. These fuses usually need to be unbolted to be replaced, which required separate disconnecting means on both sides (prior to the fuse, and after the recombiner busbar).
 

Carultch

Senior Member
Location
Massachusetts
Fuse side that faces the utility is being called line side and fuse side that faces the solar panel is being called load side.
Line/load sides generally work the opposite way on the DC side of the inverter. The array is the energy source, the inverter is the load. You want your disconnects to have the "hinge side" toward the inverter, and open blades toward the utility or toward the PV.
 

hhsting

Senior Member
I got solaredge three phase inverter for the 208v grid SE9KUS/SE14.4KUS.
String inverters are generally designed to meet code without DC Balance of systems equipment between them and the DC string wiring. The exceptions are rapid shutdown and DC optimizer systems, or an inverter which hasn't caught up with the code cycle. It is usually not necessary to have a "pre-disconnect" before string inverter string fuses.

The fuse servicing requirement, requires that the fuses be capable of being replaced in a "touch safe" manner, after the inverter is shut off. Either by handling only non-metallic components (like rockout fuseholders or fuse pull-outs), or by disconnecting both sides of the fuse from energy sources on both sides (PV & inverter capacitors).

The place where you usually find this requirement affects your design as an EPC, is on a central inverter system with a fused subcombiner at the inverter. These fuses usually need to be unbolted to be replaced, which required separate disconnecting means on both sides (prior to the fuse, and after the recombiner busbar).
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pv_n00b

Senior Member
Location
CA, USA
I have fuses in inverter with integral disconnect on the line side of the fuse. The fuses have pullouts. Based on NEC 2014 Article 690.16(A) do I have to add disconnect at the load side of the fuse or fuse pullouts are ok?
If you can touch the fuse terminals after pulling out the fuse then it requires an outside disconnect. That's why finger safe fuse holders are used almost universally.
Using SolarEdge I guess you could argue that the optimizers cut off the voltage to the PV side of the fuse.
 
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Carultch

Senior Member
Location
Massachusetts
I got solaredge three phase inverter for the 208v grid SE9KUS/SE14.4KUS.

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At one point, the 14.4k-US model had fuses in the DC connection area with touch-safe rock-out fuse holders, but those have since been retired in the inverter design. Now they just have a group of DIN rail terminal blocks, bussed together for the two polarities to connect 3-4 strings. SolarEdge has a whitepaper substantiating the removal of string fuses in their inverters, even in the case of 3+ strings, due to the nature of how the DC optimizers work and prevent backfeed. The single phase counterparts that are also designed with 3 strings in mind, 10k-US & 11.4k-US, are the same way.

The 9k-US models never had fuses in the DC connection area, because it was expected that you would connect no more than 2 strings to the inverter.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
At one point, the 14.4k-US model had fuses in the DC connection area with touch-safe rock-out fuse holders, but those have since been retired in the inverter design. Now they just have a group of DIN rail terminal blocks, bussed together for the two polarities to connect 3-4 strings. SolarEdge has a whitepaper substantiating the removal of string fuses in their inverters, even in the case of 3+ strings, due to the nature of how the DC optimizers work and prevent backfeed. The single phase counterparts that are also designed with 3 strings in mind, 10k-US & 11.4k-US, are the same way.

The 9k-US models never had fuses in the DC connection area, because it was expected that you would connect no more than 2 strings to the inverter.
Many AHJs still require fusing when combining three SolarEdge strings despite what SE says in their white paper.
 

Carultch

Senior Member
Location
Massachusetts
Many AHJs still require fusing when combining three SolarEdge strings despite what SE says in their white paper.
Seems like SolarEdge should've just left them in there, in order to AHJ-proof their system. I was surprised when I found out that the fuses I assumed in a design from the manual when I was doing the drawings, turned out to not be in the units that made it to the site. It passed inspection anyway, and I didn't even need to show the white paper.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Seems like SolarEdge should've just left them in there, in order to AHJ-proof their system. I was surprised when I found out that the fuses I assumed in a design from the manual when I was doing the drawings, turned out to not be in the units that made it to the site. It passed inspection anyway, and I didn't even need to show the white paper.
Another thing to be careful with when designing with SolarEdge is the length of your strings. With some modules it's possible to put too many in a string for the circuit to comply with rapid shutdown.
 

Carultch

Senior Member
Location
Massachusetts
Another thing to be careful with when designing with SolarEdge is the length of your strings. With some modules it's possible to put too many in a string for the circuit to comply with rapid shutdown.
In those instances, not only do you get to use the two-module optimizers, in some cases, you have to do so. It is usually the case with the 277/480V rated inverters where you encounter that situation. In my experience, the 120/208V Solaredge inverters give you a choice.
 

pv_n00b

Senior Member
Location
CA, USA
At one point, the 14.4k-US model had fuses in the DC connection area with touch-safe rock-out fuse holders, but those have since been retired in the inverter design. Now they just have a group of DIN rail terminal blocks, bussed together for the two polarities to connect 3-4 strings. SolarEdge has a whitepaper substantiating the removal of string fuses in their inverters, even in the case of 3+ strings, due to the nature of how the DC optimizers work and prevent backfeed. The single phase counterparts that are also designed with 3 strings in mind, 10k-US & 11.4k-US, are the same way.

The 9k-US models never had fuses in the DC connection area, because it was expected that you would connect no more than 2 strings to the inverter.
Is SolarEdge still sending out that letter they had Bill Brooks write justifying the fuseless combiners? Bill's theory is reasonable but it does not change the NEC requirements. The NEC needs to be updated to take into account how DC optimizers work. Until then contractors are having to ask AHJs for an alternative methods approval to install them if the AHJ catches it and asks.

It seems like kind of a low blow to the contractors for SolarEdge to put out a product that does not comply with the NEC and then tell the contractor it's their job to sell it to AHJs.
 

hhsting

Senior Member
At one point, the 14.4k-US model had fuses in the DC connection area with touch-safe rock-out fuse holders, but those have since been retired in the inverter design. Now they just have a group of DIN rail terminal blocks, bussed together for the two polarities to connect 3-4 strings. SolarEdge has a whitepaper substantiating the removal of string fuses in their inverters, even in the case of 3+ strings, due to the nature of how the DC optimizers work and prevent backfeed. The single phase counterparts that are also designed with 3 strings in mind, 10k-US & 11.4k-US, are the same way.

The 9k-US models never had fuses in the DC connection area, because it was expected that you would connect no more than 2 strings to the inverter.
I have solaredge inverter SE14.4KUS however their are fuses inside of them. Exactly what you said it has Din rail and utility side has integrated safety disconnect but PV side does not. Would PV side of fuse require disconnect?

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jaggedben

Senior Member
I have solaredge inverter SE14.4KUS however their are fuses inside of them. Exactly what you said it has Din rail and utility side has integrated safety disconnect but PV side does not. Would PV side of fuse require disconnect?
It really depends on what your AHJ thinks. If you're in a hurry and need to play it safe you should probably put in fuses. If you want to try to save that money then best to get the AHJ's approval before you need to install.
 

hhsting

Senior Member
It really depends on what your AHJ thinks. If you're in a hurry and need to play it safe you should probably put in fuses. If you want to try to save that money then best to get the AHJ's approval before you need to install.
I know fuses are required in inverter. Fuses are in the inverter. Their is already one disconnect integarted in inverter fuse dc facing utility side.

Nec 2014 690.16 says fuses need to be isolated for servicing. Question was regarding if disconnect is required on the inverter fuse side facing pv even though their are fuse holders.

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I know fuses are required in inverter. Fuses are in the inverter. Their is already one disconnect integarted in inverter fuse dc facing utility side.

Nec 2014 690.16 says fuses need to be isolated for servicing. Question was regarding if disconnect is required on the inverter fuse side facing pv even though their are fuse holders.

Sent from my SM-G935U using Tapatalk
If the fuses have plastic (non-conducting) pullouts or finger safe tiltout holders, that is sufficient. They generally
aren't load break rated so you have to open the switch between the fuses and the inverter first to stop the flow of current.
 

jaggedben

Senior Member
I know fuses are required in inverter. Fuses are in the inverter. Their is already one disconnect integarted in inverter fuse dc facing utility side.

Nec 2014 690.16 says fuses need to be isolated for servicing. Question was regarding if disconnect is required on the inverter fuse side facing pv even though their are fuse holders.
Sorry for any confusion. It had been mentioned that some of these inverters are being supplied without fusing.

I still think it's somewhat open to AHJ interpretation. With that said, I've never ever been asked to add an additional disconnect on this type of installation. And, from a practical point of view, an additional disconnect is really unnecessary with optimizers, because the inverter side disconnect effectively de-energizes the fuses. Since the code language refers to fuses energized from both directions, you have a pretty strong argument that no additional disconnect is needed.
 

Carultch

Senior Member
Location
Massachusetts
I have solaredge inverter SE14.4KUS however their are fuses inside of them. Exactly what you said it has Din rail and utility side has integrated safety disconnect but PV side does not. Would PV side of fuse require disconnect?

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No external "pre-disconnect" would be needed. The touch-safe fuses are not load break rated, but you have to break the load by opening the inverter's main DC disconnect anyway, in order to access them in the first place. This disconnect is on the inverter-side of the fuses. The entire purpose of touch-safe fuseholders is so the fuse is disconnected when opening them by design from both sides of the fuse holder, so it is de-energized and touch-safe to remove.

The inverter's integrated disconnect is NOT on the utility-side of the inverter, as it is a DC disconnect. At one point, some of their inverters had the disconnect operate both AC and DC, but that is no longer the case. It is common that a string inverter will be co-located with an AC disconnect anyway, such as the breakers in an AC combining panelboard, where you aggregate the outputs of a group of inverters. One application with SolarEdge inverters where you would have to add a separate AC disconnect specifically for each inverter, is a non-readily accessible location like up high on a parking canopy column. You need to be able to reach or walk to the AC disconnect, from where you access the inverter. Not climb down a portable ladder.
 
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Carultch

Senior Member
Location
Massachusetts
It seems like kind of a low blow to the contractors for SolarEdge to put out a product that does not comply with the NEC and then tell the contractor it's their job to sell it to AHJs.
Especially when they initially HAD an otherwise identical product that complies with the NEC.
 
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