The Offshore Voyaging Reference Site

5 Safety Tips For Working on Boat DC Electrical Systems

One more chapter before we get to the good stuff, this one on safety. I know, even more boring than the two theory chapters you just endured. Still, it’s a short one, so please don’t skip it. I would hate see anyone get hurt.

Just because the battery-supplied systems on cruising boats are low voltage, that does not make them safe, and yet that’s the common view.

Sure, none of the DC voltages on our boats (12, 24 or 48) will hurt us—except possibly the last, and then only in special circumstances (don’t stick a 48-volt wire in your mouth)—but the current (amperage) sure can¹.

So let’s take a look at five ways we can reduce the chances of getting hurt. Particularly relevant since in the first chapter we encouraging you to work on your own system².

¹Actually, it’s always the current that damages people, even in high voltage (shore power) systems, but let’s not split the hair in four.

²If this sounds like an article written to cover my ass and keep our journalism insurance underwriters happy, trust your instincts. Nonetheless, these tips reduce, but do not eliminate, very real risks.

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More Articles From Online Book: Electrical Systems For Cruising Boats:

  1. Why Most New-To-Us Boat Electrical Systems Must Be Rebuilt
  2. One Simple Law That Makes Electrical Systems Easy to Understand
  3. How Batteries Charge (Multiple Charging Sources Too)
  4. 5 Safety Tips For Working on Boat DC Electrical Systems
  5. 7 Checks To Stop Our DC Electrical System From Burning Our Boat
  6. Cruising Boat Electrical System Design, Part 1—Loads and Conservation
  7. Cruising Boat Electrical System Design, Part 2—Thinking About Systems
  8. Cruising Boat Electrical System Design, Part 3—Specifying Optimal Battery Bank Size
  9. Balancing Battery Bank and Solar Array Size
  10. The Danger of Voltage Drops From High Current (Amp) Loads
  11. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 1
  12. Should Your Boat’s DC Electrical System Be 12 or 24 Volt?—Part 2
  13. Battery Bank Separation and Cross-Charging Best Practices
  14. Choosing & Installing Battery Switches
  15. Cross-Bank Battery Charging—Splitters and Relays
  16. Cross-Bank Battery Charging—DC/DC Chargers
  17. 10 Tips To Install An Alternator
  18. Stupid Alternator Regulators Get Smarter…Finally
  19. WakeSpeed WS500—Best Alternator Regulator for Lead Acid¹ and Lithium Batteries
  20. Smart Chargers Are Not That Smart
  21. Replacing Diesel-Generated Electricity With Renewables, Part 1—Loads and Options
  22. Replacing Diesel-Generated Electricity With Renewables, Part 2—Case Studies
  23. Efficient Generator-Based Electrical Systems For Yachts
  24. Battery Bank Size and Generator Run Time, A Case Study
  25. A Simple Way to Decide Between Lithium or Lead-Acid Batteries for a Cruising Boat
  26. Eight Steps to Get Ready For Lithium Batteries
  27. Why Lithium Battery Load Dumps Matter
  28. 8 Tips To Prevent Lithium Battery Black Outs
  29. Building a Seamanlike Lithium Battery System
  30. Lithium Batteries Buyer’s Guide—BMS Requirements
  31. Lithium Batteries Buyer’s Guide—Balancing and Monitoring
  32. Lithium Batteries Buyer’s Guide—Current (Amps) Requirements and Optimal Voltage
  33. Lithium Battery Buyer’s Guide—Fusing
  34. Lithium Buyer’s Guide—Budget: High End System
  35. Lithium Buyer’s Guide—Budget: Economy Options
  36. 10 Reasons Why Hybrid Lithium Lead-Acid Systems are a Bad Idea
  37. 11 Steps To Better Lead Acid Battery Life
  38. How Hard Can We Charge Our Lead-Acid Batteries?
  39. How Lead Acid Batteries Get Wrecked and What To Do About It
  40. Equalizing Batteries, The Reality
  41. Renewable Power
  42. Wind Generators
  43. Solar Power
  44. Watt & Sea Hydrogenerator Buyer’s Guide—Cost Performance
  45. Battery Monitors, Part 1—Which Type Is Right For You?
  46. Battery Monitors, Part 2—Recommended Unit
  47. Battery Monitors, Part 3—Calibration and Use
  48. Battery Containment—Part 1
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Dick Stevenson

Hi John,
Great reminders.
When working on the batteries with a wrench long enough to bridge the gap between terminals, I tape the non-working end of the wrench. I have been tempted, on occasion, to buy a shorty wrench set (or a few dedicated shorty wrenches) for just this reason also. One rarely needs the extra length for its ability to provide torque.
My best, Dick Stevenson, s/v Alchemy

Arne Mogstad

Buy yourself a couple of electrically insulated spanners. They are a MAHOOSIVE piece of mind when doing that! And not very expensive, you just need one or two. And the same goes for screwdrivers. I have a set of the most common ones that are fully insulated except for the tip. Here’s a selection from Tengtools (just random brand) as an example

Marc Dacey

I got a Knipex “toothless” channel lock wrench a couple of years ago and the handles are insulated. I seem to find a use for it every day as it doesn’t mar metals but isnlarge enough to provide reasonable leverage.

Dick Stevenson

Hi John,
I wired my inverter to include an on/off switch in the positive lead from the battery bank: this not only limits the territory for DC to roam, but precludes the chance that a more dangerous AC connection might be discovered lurking in that maze of wiring.
My best, Dick Stevenson, s/v Alchemy

Alan Bradley

Good point, Dick. It’s been on my list since being suggested by my electrical guru, an advisor on the ABYC electrical standards group. I’d better hop to it!

Marc Dacey

After learning this is SOP on, I think, Jeanneaus, I put a positive side on/off switch in also. I use it not just for typical jobs, but when I service the bank periodically.

Dick Stevenson

Hi John and all,
At the beginning of the season, I had occasion to reach deep in to an area not visited in many a year and came out with an impressive slice on the back of my wrist from a cut-off (but still protruding) electrical tie.
I am forever impressed with how I go through electrical ties when doing wiring (and for securing in other projects as well) and one of my favorite tools, always ready-at-hand when working with electrical ties, is a pair of flush cutting diagonal cutters (Xcelite 170M). With a snip the tie is flush cut leaving no sharp ends to catch you (or a later workers) unawares.
My best, Dick Stevenson, s/v Alchemy

Stein Varjord

Hi Dick,
Good point! This is indeed an “electrical” work safety issue. I’ve spilled significant amounts of red stuff after cutting myself on these sharp ends. They can be as small knifes. Protruding screws are on the same team of mostly non lethal, but abundant danger zones where electric wires live.

Rob Gill

A larger size stainless toenail-clipper, the type with the black plastic “catcher” at the sides to retain the little plastic cutoffs works well. Simply cut off the tie close to the end with the clippers held on an angle or using pliers for larger ties.

Then clip the sharp end remaining with your nail clipper as you would a finger nail. Puts a perfect radius on the corners.


Very much looking forward to your in depth article on rewiring your J109.

Gino Del Guercio

Wedding rings are dangerous in lots of situations on sail boats. When I started cruising full time I swapped mine out for a silicone ring. They come in lots of different styles.

Steven Hodder

Years ago while doing safety training in the navy, they showed us LOTS of pictures of “degloved” fingers to get the point across. To this day, I only wear my wedding ring on special occasions, like my anniversary.

Drew Frye

My maternal grandfather had a nasty scar from a high amperage short across his wedding ring. They cut it off and he never wore one again. The scar was still bad 50 years later.

My first boss had 9 fingers, the result of a de-gloving injury climbing down a ladder (it caught it on the grip tread as he jumped down the last rung).

I had two minor catches (both on threads exposed past nuts) with mine the first month after I was married. That was the end of that.

P D Squire

Thanks guys. I’m replacing my keel-lift winch this weekend. I’ll disconnect the battery and tape over at least one terminal while we work on it. My sons will be helping with the project so you can tell your insurer that the safety lesson will cross two generations.