DC Grounding

[dtdarrah7]

Grounding & Bonding for a 24V DC Hydroponics Setup - Needed Input​

Hello all,

I am designing an electrical system for my Senior Design Project, which powers a hydroponics setup, and I’d appreciate some guidance on grounding and bonding.

System Overview:​

• Power Source: 120V AC to 24V DC charger (Victron Blue Smart IP22, 24V 16A x2 in parallel) acting as a power supply and battery charger (includes backflow prevention).
• DC Bus:Powered by the charger, distributing power to three circuits:
  1. 24V 100Ah LiFePO₄ battery (backup power source).
  2. 24V DC to 120V AC inverter (powers two sump pumps, controlled via hi-low sensors).
  3. 24V DC to 5V DC buck converter (powers a Raspberry Pi for monitoring).
• Operation: Runs on building power under normal conditions; if power is lost, the system islands and supplies loads via the battery + inverter.

Grounding & Bonding Questions:​

1. DC Panel (Metallic Enclosure): Should the chassis be bonded to the building grounding system?
2. Battery Negative Terminal: Does it need to be bonded to the building ground, or should it remain floating?
3. Inverter Grounding Terminal: Does this need to be bonded to the building grounding system?
4. Hydroponics Water Tanks: Since the water has high electrolytic content, should I install grounding electrodes in the tanks?

My Thoughts So Far:​

• I believe the DC panel chassis should be bonded to the building ground for touch potential safety.
• I am reconsidering bonding the battery negative to building ground, as my DC panel is metallic, and I want to create a path back to the source for my OCP to work.
• NEC compliance is a priority, but since my system is below 60V DC, I’m trying to determine the best approach for grounding while maintaining safe operation.

I would love to hear your input on this! Any NEC references or best practices would be greatly appreciated.

Thanks!

 

[jaggedben]

The DC panel chassis should be bonded; this can be done through the conduit or cable from the AC-to-DC charger. This is equipment grounding, not system grounding.

I would *not* bond the battery negative, at least not without further investigation. DC systems below 60V are not required to have system grounding. Read the AC-to-DC charger manual, it may contain specific instructions on this. There is a possibility that it already effectively grounds the system negative, or (less likely) that it would be dangerous to do so. Since it's not code required I wouldn't do it unless equipment documentation told me to.

I'm more concerned about grounding for your inverter. That system is supposed to be grounded but possibly that cannot be done safely without it being separately derived from the AC side of the charger. Is all this equipment designed to work together or are you cobbling it together yourself? There are potential saftey issues here depending on the internal design of the charger and inverter. If they are designed by a single manufacturer to work together, read the manuals.

I would not put grounding electrodes inside water tanks, you'll just get corrosion I think.