NEC 690.41(B) Ground-Fault Protection > 400VDC

[Bill541]

I'm installing a ground mount solar system with an 8S3P panel configuration. It will have a maximum Voc of 424 VDC in winter. The panel Isc is 8.9A so with the 3 parallel strings, it would be rated for 26.7A. The PV circuit will need to be sized for => 41.7A. The inverter I am using is an MPP LVX 6048 and the manual requires the PV array to float. I'm curious to what others have used with similar floating inverters with high DC voltage to comply with NEC 690.41(B) Ground-Fault Protection? The solutions I am finding cost as much or more than the inverter or they require the battery (-) to be grounded. I do not believe the LVX 6048 will tolerate a grounded battery though I do not see that it says one way or the other in the manual. Bench testing the inverter, the battery does center itself about earth ground. Ideally, a differential DC relay would be used to shunt trip a DC breaker but I have yet to find a cost effective solution.

Thanks, Bill

 

[FilterGuy]

I'm installing a ground mount solar system with an 8S3P panel configuration. It will have a maximum Voc of 424 VDC in winter. The panel Isc is 8.9A so with the 3 parallel strings, it would be rated for 26.7A. The PV circuit will need to be sized for => 41.7A. The inverter I am using is an MPP LVX 6048 and the manual requires the PV array to float. I'm curious to what others have used with similar floating inverters with high DC voltage to comply with NEC 690.41(B) Ground-Fault Protection? The solutions I am finding cost as much or more than the inverter or they require the battery (-) to be grounded. I do not believe the LVX 6048 will tolerate a grounded battery though I do not see that it says one way or the other in the manual. Bench testing the inverter, the battery does center itself about earth ground. Ideally, a differential DC relay would be used to shunt trip a DC breaker but I have yet to find a cost effective solution.

Thanks, Bill

Yup.... that is a problem with that class of inverter. Getting the PV set up to meet the Ground-Fault, arc-fault, and rapid shutdown NEC requirements is a major challenge.

Most All-in-ones do not have isolated MPPTs so neither PV conductor can be grounded. The only way I know of to detect a ground fault on these is using a Hall Effect sensor and as you have found, these solutions are very expensive. What is worse is that some of the products that did this are no longer available so the options are extremely limited. If you find a good solution, please let us know.

Because of this set of problems, I advise anyone that is going to need NEC compliance to make sure the inverter has arc-fault and ground-fault protection built-in before they purchase.

Ground Fault Protection On Solar Panel Arrays.

To get the paper, click on the orange button at the top of the screen. This paper provides a summary of what a PV ground fault is, what NEC requires for PV Ground Fault Protection and how PV ground Fault Protection is typically implemented...

diysolarforum.com

Solar Array Arc Fault Protection summary

To get to the paper, click on the orange button at the top of the screen. Most DIY Solar implementations do not have PV Arc Fault protection, but in many cases the NEC requires it for fire safety. This Resource is a brief summary of what Solar...

diysolarforum.com

 

[Bill541]

Thank you for the reply.

I agree, if any part of the PV system is to be installed on or inside a non-exempt structure, it is much easier, and more cost effective to purchase a LISTED inverter and or combiner that has all the necessary protections built in. Roof top array installs have it even more difficult having to break up the arrays into 80V segments during rapid shut-down.

For those who like the more budget minded equipment, opting for an exempt PV equipment only structure may be the way to go. Then only run AC circuits to and from any non-exempt structures.

As for me, I'm leaning towards a separate, exempt structure to hold the PV equipment. The additional protections required by a non-exempt building may end up making the system less reliable and certainly more expensive. However, I'm not looking forward to providing additional heating and cooling for the equipment!

-Bill-

 

[Old_Skewler]

Most All-in-ones do not have isolated MPPTs so neither PV conductor can be grounded.

What about in stand-alone MPPT applications? Could one easily implement a DC GFP Breaker connecting the battery negative to the grounding conductor?

I ask because I am trying to implement DC GFP breaker to a Victron MPPT and it is not clear to me the implications of connecting the battery negative to the breaker making it a grounded conductor.

 

[FilterGuy]

What about in stand-alone MPPT applications? Could one easily implement a DC GFP Breaker connecting the battery negative to the grounding conductor?

I ask because I am trying to implement DC GFP breaker to a Victron MPPT and it is not clear to me the implications of connecting the battery negative to the breaker making it a grounded conductor.

View attachment 161617

That is going to depend on the individual charge controller,

I would have to go check, but I am pretty shure Victron, Outback and Midnite can all handle a grounded conductor on the PV input. However, please check before you buy. It has been quite a while since I looked at this.

 

[Old_Skewler]

That is going to depend on the individual charge controller,

I would have to go check, but I am pretty shure Victron, Outback and Midnite can all handle a grounded conductor on the PV input. However, please check before you buy. It has been quite a while since I looked at this.

Here is what the Victron installation manual states:

 

[FilterGuy]

I am glad you checked!!!