Anyone have any experience in connecting solar into a panel with a GFI main? 2011 705.30(3) says it has to be connected on line side. There is an exception that it can be connected on load side if GFI protection will still work. In my situation I can't attach on line side because it has cold sequence cts and the main is upstream from the cts. I have to connect behind the metering. I am not sure that the GFI protection would work if the load on the building is small and the system is exporting a lot of power. This is because the inverter would be sourcing the fault current and it would not go through the neutral ct. It would work on a low impedence fault but not reliably if there were impedence in the fault limiting the current. I have seen this done many times but I don't think it meets code. Any ideas?
PV into load side of 2500A Main with GFI
- Thread starter coop3339
- Start date
- Status
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
I don't know the answer to your question, but it might get more attention if it were posted over on the Photovoltaics forum.
No they don't and the GFP on the main could be compromised by fault current sourced from the PV, so I think the best way to handle it is to add a self contained GFP breaker before the interconnection. It could be set at a low value so that it will only allow the PV to source say, 30A of fault current before it trips. The only problem is this may cause it to trip on a small fault in the facility.
Have no experience in GFP ratings/settings, but 30A seems high for GFP.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Since transformerless inverters do not have galvanic isolation between the DC and AC sides, would the GFP on the DC side suffice?
I suspect not...
With GFP triggered by net current imbalance on the circuit conductors, the DC side would not realize any. The AC fault current would be 'returned' to the inverter on either on the EGC or the other circuit conductors. Unless there is a ground fault on the DC side, source circuit current would be balanced.
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
This rule has always confused me. If an inverter's conductor back to the service experiences a fault to ground, the inverter will shut down and the fault will look just like any other ground fault to the GFP in the MDP. What is the rule trying to accomplish?
Inverter shut down for that event because the system voltage drops below nominal. When the fault occurs on a branch, such as when PV taps into utility on the utility side of loads, the voltage doesn't drop until the supply sags... so it will depend on supply stiffness and level of fault current. GFP is set up to detect a ground fault well below where the supply voltage sags.
Thanks for your responses. I have resolved this by using a GFP breaker on the solar side to feed into the main gear. Square D makes a GFP breaker that is rated for back feed. The only thing I am worried about is that the GE GFP main has not been tested for back feed, although I was assured by tech support that it will still work.
- Status