Ungrounded vs. grounded in the developing world
I would like to share my experience with ungrounded, small, battery based systems in the developing world and get input from others. When I say small I mean under 1kW PV, max inverter size 1200VA. These systems are 12 or 24V DC with AC at 220V. No DC or AC ground. Always mounted on a metallic pole mount with no additional equipment ground. I previously worked in the US and upon arrival in Peru was quite concerned that few small offgrid systems were being grounded, but there is ample evidence that these systems are working just fine.
After working here for two years, I haven’t seen any issues that I can directly link to the fact that these types of systems are ungrounded - no issues with lighting (other than a direct strike to a pole mount, but everyone was fine), no issues with transient overvoltages, no electrical accidents, and no problems with the system functioning improperly due to being ungrounded. This is not to say that I am completely convinced that this is the right way to be doing things, thus I would like to discuss the logic that I see behind not grounding a system and hear the opinions of others on the subject.
Reasons to not ground a system in this context:
· In rural Peru it would be extremely rare to see metallic conduit or boxes – everything is run in plastic. Therefore an equipment grounding system wouldn’t be effective.
· If a system is ungrounded, it requires a short between both wires in a circuit to have a fault, rather than just one wire to ground. Thus, it is extremely difficult for a user to be shocked in the case of a fault – unless they were completing the circuit between the two legs – as there is no return path through ground.
· The inverter itself is current limited and relatively sensitive to shorts. If there is a short between the two legs, the inverter should quickly identify it and shut down.
· It keeps costs down.
Any input on the following would be much appreciated:
1. Setting aside electrical codes, what
reasons technically can you think of for grounding a system like this on either the AC or DC side?
2. Are there any other advantages to not grounding a system that you are aware of?
3. Once again setting aside electrical codes, with a small inverter – which cannot supply sufficient current to exceed the ampacity of the wiring on any circuit on the AC side – is it necessary to install OCPDs on each AC output circuit? In my thinking, an inverter will automatically shutdown in the case of a short or in the case of any electrical accident as quickly or almost as quickly as an OCPD with a delay.
4. I have read quite a few discussions regarding lightning and grounding module frames. I am not trying to reignite this discussion, but it seems like with with a metallic pole mount sunk into the ground that it should not necessarily be a significant lightning attraction, but nor would it or a proper grounding system likely protect the other system equipment in the case of a direct strike. Therefore a ground rode and grounding system for the pole mount likely doesn't have any a advantages. Thoughts?
Thanks for your input!