DC Circuit Breaker on a Boat

The arc quenching conditions differ, basically requiring DC breakers to have wider opening gaps and faster times.

At low voltages I like the collection of Poly Switch resettable fuses. These devices do have some complications that require careful thought to use them safely. An annoying aspect is the ambient temperature will significantly alter the tripping current. So you may not wish to use them for your boat.

I would just consider using automotive fuses.

A discussion with the local Boat Chandler would be the perfect starting place.

.. perhaps I already did... Nevertheless, thanks for your invaluable input!

Ebay's got a bunch of marine 12 VDC breakers.

I know... but importing stuff into my country is a nightmare now. I am looking for a B plan!

Regardless of breaker type (thermal or magnetic);

1. Unless the breaker is rated for AC and DC service using an AC breaker would not be a good idea.

2. The breaker must be rated for Marine use.

These requirements are meant to improve reliability, prevent an electrical fire. and to ensure the boat occupant's safety.

You really do not want to risk a fire or a major electrical failure in a boat especially when at sea or away from shore.

Yea the fire department will have a hell of a time getting to you.

BTW the company I work for got a safety violation notice for storing our bottled water in our furnace room. Apparently two pallets of bottled water next to a heat source was considered a fire hazard.

Western Marine has a distributor in Buenos Aires.... If anybody can help they can....otherwise it looks like a boat trip will be necessary....

Argentina

Herby Marina

AvCostanera Norte v Pte Castillo - Edifico Costanera Uno - 1425 Buenos Aires ARGENTINA

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http://www.westernmarine.com/acrobat/bepinstall.pdf

That place has been my first choice ... but they have no breakers in stock right now, so I probably will have to buy industrial switches and protect the line with old fashioned fuses. Spending 20 K in Diesel to sail up to the US for parts does not seem to me as a plausible alternative right now

Yes it's an oppressive regime, we get it....

In Argentina, you use IEC-type circuit breakers, yes?

Most of the major brands of miniature circuit breakers (MCBs) have tested them, and approved them for use in DC circuits. Typically, you can go to 48VDc on one pole, above that you have to put poles in series.

It does pay, however, to check the manufacturer's datasheets as ratings vary and not all MCBs are rated for DC

Thanks for the input. Last evening I sent a inquiry by mail to Siemens Argentina asking which of their breakers can be used on my installation

About your question: yes, the norm is IEC

Nicely summed up Paulusgnom.

Regular MCBs trip at their rated trip current regardless of whether the current is AC or DC and the voltage doesn't matter so long as it isn't exceeded, and in this application it isn't.

So from an electrical protection perspective they will stop your wires from catching fire if they are the right rating for the conductor being protected.

The marine environment though does pose another problem and premature contact/mechanism/terminal corrosion may be an issue. Could be resolved if a suitably IP rated enclosure and glands were used or, if the MCBS are cheap enough, then just routinely replace them as a consumable during maintenance. Or both.

You did not say what the problems were with the original unit.

You might consider a repair job if you are a good DY type of person.....

Usually far cheaper and you will learn a lot!!

Never forget that warm, moist, salty air is bad for many things.....so it must be done exactly right!!

Circuit breakers trip on current not voltage, so quality 24 VDC units possibly made for trucks or bulldozers might still be accurate enough for 12 volts, though have to admit that have never tested such an idea myself..... but ! cannot see a flaw in my thinking, but fully willing to be wrong if there is one...

Get some old ones from a truck breakers yard and test using light bulbs as load, while measuring current through the circuit......would cost very little to test and then to KNOW!! You may even be able to buy new 24 volt DC breakers more easily where you are....

Just a thought or two.....keep us informed please.

Hello Andy, the "old" panel did almost not exist: the boat (new to me) is 40 years old and was owned by a sloppy sailor, so there were bunches of cables crossing the boat in all directions I chopped off for safety, having in mind to start from scrap. Buenos Aires is in front of a large river (my playground) so a salty sea environment is no issue here.

As said before I contacted Siemens for advice, as they manufacture breakers locally. I´ll keep you updated.

You can buy DC breakers or can get an AC MCB with some sort of a reduced DC rating. As has been mentioned the arc they need to break is different. An AC arc breaks 50 or 60 times a second whereas a DC current is constant.

Best way forward, and safest, is HRC fuses which you can get in a holder that is about the same size as an MCB. If you have a fault, and especially on a boat, its better to change a fuse than put out a fire.

Thanks for your input! So far (unless I finally get DC breakers locally, at a decent price) I probably will go for switches + fuses.

PS: last year I rented a motorhome in the UK and drove about 2000 Mi around your country not having had a single day of rain! (probably beginner´s luck), happening to travel trough the beautiful region where you live. My plans for the near future are to rent a narrowboat to make a trip on the inland waters.

I used a standard 230 vac domestic consumer unit for DC wiring on my boat.No problems. But it is a narrowboat and only used locally on UK inland waterways.

Being 12vdc and a long boat, cables are sized for volts-drop, so overload current is not an issue, only if a short circuit occurs. They work OK.

But I do agree that 'micro-gap' breakers without toggle action, OK for ac, might be a problem on dc if a load 'hovers' around the tripping current causing a persistent arc

Hi J Raef! thank you for taking the time of reading all the posts and writing such a comprehensive reply! On my search, Yesterday I found a store that sells DC thermo magnetic breakers from a company called Schneider, but they cost 5 times more than a regular breaker does. As I need about 30 of them, the electrical panel would probably cost more than my boat´s diesel engines! Siemens just sent me a PDF with the spec´s of all low voltage breakers they manufacture, and yes: the ones you mentioned are on this brochure. This weekend I will read this info and then go for a distributor to see how much they cost. The "critical marine situation" you depicted made me laugh because I care a lot to prevent such situations from happening. I hope Scotty can finally get my boat to reach warp speed when the new 12V breakers are installed on it!

Really good infos, I hope the OP can buy them locally.....

EUREKA!

5SY, 5SP Miniature Circuit Breakers

Overview

MCBs are used to protect plants in buildings and for industrial applications. The devices can be used as main switches for the disconnection or isolation of plants.

For industrial applications and in plant engineering, miniature circuit breakers can be supplemented with additional components, such as auxiliary switches, fault signal contacts, shunt trips, undervoltage releases, remote controlled mechanisms and RC units.

The devices are approved for worldwide use according to IEC standards for systems up to 250/440 V AC. 60 V DC per pole is permitted in DC systems.

For North America, we also have additional certification to UL 1077 for use as "supplementary protectors" in systems up to 480Y/277 V AC. For use in ship building, the devices have numerous certifications according to shipping classifications BV, DNV, GL and LRS. For further information, please refer to the section "Configuration".

$ only twice as much as a regular breaker!