Tech Net Library


Electricity and Electronics - Short Topics

Breakers and Fuses

Breakers and fuses are the primary devices used to prevent fire and other damage due to excess current flow. These devices will open an electrical circuit when the current exceeds a specified limit.

Most common uses are:
1. To prevent damage or fire due to overheating of conductors. In this case, it is important to note that the fuse or breaker should be near or at the source of the power. A fuse at the load end of a conductor will do no good if the conductor is somehow shorted to ground or other return path.

2. To limit or prevent damage to electrical devices sourcing or receiving electric power. In this case it doesn't matter where the fuse is.

Safety Tips:
1. Locate the fuse or breaker as close as possible to the source of power. It is common for supply cables of electronic devices like VHF radios to have a fuse near the radio end of the cable. This fuse is intended to protect the radio. The source end of the cable must also be protected to prevent the cable from bursting into flames if there is a short circuit along the cable.

2. Make sure that all conductors connected to a circuit are sized appropriately for the protection device. A common hazard is to tap off an existing circuit to power a device like a lamp or fan. More than once, I have seen fans supplied with 22 gauge wire connected to circuits protected with a 20 amp breaker.

Two fuses are better than one.
ABYC calls for the fuse to be within 7" of the power source with the exception of the starter circuit.

High Power DC Motors

This would include things like the windlass and watermaker, etc.

Tip: Check brushes once in awhile. If they are worn and touch the commutator, the commutator may be seriously damaged. A ten dollar fix becomes a high dollar fix. Replacement brushes are recommended.

Query: What's the main cause of brush wear?
Arcing. It literally erodes the brushes. Usually the positive one wears fast. Not allowing the motor to stop before changing directions wears them down extremely fast.


Since almost everything onboard is contaminated with salt, its important to use non-acid flux when soldering.
The use of heat sinks is a subtlety. Use too much and it removes heat from the solder.
Use a wet shoe lace as a heat sink. (Salty Paws)

Query: Would rosin core flux work?
It doesn't work well in the long term, but it looks and works good when first applied. It eventually turns crumbly.
Solder made for electrical connections works best.
Yes, look for electrical solder specifically.

Miscellaneous Tips

30 amp/12 volt relays can be found at auto parts stores. Pick up a handful to keep on board. (Dyad)

To demagnetize the core of a solenoid, give it a sharp rap. Modify the AC current by reversing the polarity.

If you need a long jumper wire for testing AC circuits, buy a cheap extension cord. Cut the female end off, then plug into a standard wall outlet. (Bees Knees)

GTO cable can be made by stripping the ground braid from standard RG8 coax.

Dip It Whip It can be used on ends of wire to keep them from fraying. (Shining Star)

Water Intrusion / Damage of Electronics
When Electronic Gadgets Go Swimming. I Fished it Out. Now What Can I Do?
1. First, remove the battery.
2. Use distilled water to remove any salt.
3. Rubbing alcohol will evaporate water intrusion on electronics. It can also help remove salts.
4. Allow plenty of time to air dry.