Introduction – Real Site Hook
During routine inspection of a battery room, technicians found one grounding strip loose at the main busbar connection. The copper strip showed minor blackening. The M8 bolt had rotated slightly. Contact resistance measured higher than expected.
Bolt used: mild steel zinc plated M8 bolt
Washer used: flat washer only
Torque applied: not recorded
This is a common battery earthing issue.
Grounding joints are often overlooked because they carry no visible load.
But they carry fault current.
If earthing bolt loosens, electrical safety is compromised.
Why Proper Earthing Bolt Setup Matters
Battery rooms contain:
- • High DC voltage
- • High fault current
- • Sensitive electronics
- • Metal racks and enclosures
Grounding strips ensure:
- • Fault current path
- • Touch voltage safety
- • Equipment protection
- • Compliance with safety standards
Loose connection increases resistance.
Increased resistance creates heat.
Heat at grounding point is dangerous.
Case Study: Improper M8 Grounding Bolt Installation
Site findings:
- • Zinc plated M8 bolt used
- • Flat washer only
- • No serrated washer
- • Surface paint not removed fully
- • Torque applied below 15 Nm
After 1 year:
- • Oxidation at interface
- • Increased contact resistance
- • Loose grounding strip
The failure was not bolt diameter.
It was improper installation method.
Correct M8 Grounding Bolt Setup
Recommended configuration:
- • M8 SS304 Bolt
- • Serrated washer (internal tooth or external tooth)
- • Copper grounding strip
- • Flat washer
- • M8 hex nut
- • Spring washer (optional depending on design)
You can review specifications for our
👉 M8 SS304 Grounding Bolt for Battery Rooms
For improved contact use:
👉 M8 Serrated Washer for Electrical Bonding
For corrosion resistance use:
👉 SS304 Hex Nut for Earthing Applications
Serrated washer ensures metal-to-metal contact by penetrating surface coating.
Why SS304 Bolt Is Preferred for Earthing
Advantages:
- • Corrosion resistance
- • Stable electrical conductivity
- • Compatible with copper strips
- • Prevents rust-induced resistance
Zinc plated bolts may corrode in humid battery rooms.
Corrosion increases resistance over time.
Torque Recommendation for M8 Grounding Bolt
| Bolt Grade | Recommended Torque |
| M8 Grade 8.8 | 22–25 Nm |
| M8 SS304 | 18–22 Nm |
Proper torque ensures:
- • Adequate contact pressure
- • Low contact resistance
- • Long-term stability
Under-torque causes loosening.
Over-torque may deform copper strip.
Contact Resistance Logic
Electrical contact resistance depends on:
- • Contact pressure
- • Surface cleanliness
- • Oxide layer thickness
- • Material compatibility
Higher preload reduces micro-gaps.
Serrated washer breaks oxide layer and improves conductivity.
Typical Electrical Load Scenario
In fault condition:
- • DC system may carry several kilo-amperes briefly
- • Grounding joint must withstand thermal rise
Loose joint increases I²R heating.
Heat can:
- • Damage insulation
- • Cause local melting
- • Trigger fire risk
Earthing fasteners are safety components, not optional hardware.
Inspection Checklist for Battery Room Grounding
✔ Verify bolt material (SS304 recommended)
✔ Ensure serrated washer installed
✔ Remove paint at contact surface
✔ Check torque annually
✔ Measure contact resistance
✔ Replace corroded fasteners
Grounding inspection must be part of battery maintenance schedule.
FAQ
Q1: Why does battery earthing issue occur even with correct bolt size?
Because improper washer selection and low torque reduce electrical contact quality.
Q2: Is SS304 bolt good for grounding?
Yes. SS304 provides corrosion resistance and stable long-term performance.
Q3: Why use serrated washer in grounding?
Serrated washer penetrates oxide layer and improves metal-to-metal bonding.
Q4: What torque is recommended for M8 grounding bolt?
Typically 18–22 Nm for stainless bolt in grounding applications.
Q5: Can zinc plated bolts be used for earthing?
They can be used, but corrosion may increase resistance over time in humid environments.
Q6: How often should grounding joints be inspected?
At least annually or as per electrical safety compliance guidelines.
Conclusion
A battery earthing issue usually begins with a loose or corroded M8 grounding bolt.
Upgrade your grounding setup using:
- • M8 SS304 bolt
- • Serrated washer
- • Proper torque
- • Clean contact surface
Ensures electrical safety and fault current reliability.
Need proper earthing fastener specification for your battery room?
Contact our engineering team for safety-focused recommendations.
References
IEC 60364 – Electrical installations safety
IEEE 80 – Grounding safety guidelines
ISO 3506 – Stainless steel fastener properties
NEC grounding practices