Preparation for working on 12V High Amp circuits

[j-yelroc]

Hi, my brother-in-law asked me to help him with documentating his electrical system for his 37' French made catamaran with no drawings. The boat is 25 ? years old and has had some rewiring done before he bought it a few months ago. We spent two days this week digging around in the electrical system and I didn't find any safety disconnect means other than disconnecting each battery.

Major Equipment
1 starboard engine, 4 batteries, pumps etc.
1 port engine, 2 batteries (one for refrigerator), 10A charger
1 120V generator on port.
1 12V breaker/switch panel
1 120VAC breaker/switch and shore power/generator switch
Lights, electronics, communications and navigation

I'm a retired electrical engineer and a radio/electronics/computer hobbist for 50+ years but know nothing about practical aspects of boat electrical systems. Being rather uncomfortable around the 12V high amp circuits (70 mm2 conductors) prompts the following questions.

1. Do these boats normally use disconnect switches between batteries and the rest of the 12V systems?

2. Are circuit breakers or fuses used between the batteries and the rest of the 12V systems?

3. Is removing the positive conductors from each of the batteries the usual way to de-energize the high amp circuits for maintenance?

4. We found a switch (DPDT) which apparently connects two battery systems together which had a loose connection on one terminal which had overheated.

Both POS and NEG conductors are switched as verified by measuring different 12V readings on each side of switch and a small voltage (< 0.2V) between positive terminals when it was open.

5. The switch is labeled "Servitudes", a possible definition being "to bind" ?? What would be the English label?

I will appreciate any comments and information to help keep us (and the boat) safe while trying to document the system.

Many thanks!

[Chief Engineer]

On a 25 year old boat there is probaly a lot that has been added/subracted.

First....get rid of all wire that goes no where.

Second....take digital pictures

Third....take lotsa notes and label everything.....

Keep coming back to this board for advice...

[MidLandOne]

I go with Chief Engineer on that as there are so many imponderables.

As a safe start though and in answer to one of your questions, to completely isolate the DC systems, even if an isolating switch is found, disconnect the batteries as it is common for some equipment (eg radios, alternators) to be connected direct to the batteries bypassing any isolating switch.

[David M]

There are high amp breakers available in case one of your primary wires shorts out. Disconnecting your batteries from your DC system is normally done with high capacity battery switches.

[btrayfors]

Disconnect the batteries.

The standards for DC wiring of boats are codified in the ABYC Standards. They are voluminous. The different sections are available online (do a Google search).

There are many other authoritative sources. One of the very best is Nigel Calder's Mechanical and Electrical Manual...it's the bible for lots of folks in the boating world.

Here's a teaser re: the ABYC DC standards... http://www.cruisersforum.com/gallery...649&original=1

One other thought... it's often a lot easier when tackling a project like this to completely gut the wiring and design the new system from scratch. Often, it is the case that this will go MUCH faster and better than trying to deal with what's there already. Figuring out the wiring on a French boat which is 25 years old and which previous owners have modified/added to over time sounds like a masochistic experience.

For most of us -- even those who are fluent in French as I am -- the logic is still daunting.

Hint #1: Know how to lock the door on some French-built cars? You pull the locking mechanism UP.

Hint #2: Know how to start some French-built cars after you've inserted the key into the steering column? You turn the key TOWARD you!

Disclaimer: this is NOT knocking the French. I like 'em and respect 'em and especially value their contributions in the yachting world. But, they're just wired differently than some of us! And, alas, so are their boats :-)

Bill

[Roy M]

I'm working on a French catamaran, for a customer. French physics and electrical theory is the same as ours, only the dialect is different.

First, ensure there is a battery ON/OFF switch between the battery and the electrical panel. Add an overload fuse before the switch (Google Blue Seas). A lot of French boats use remote relay boxes to distribute circuits. These suck, but unless you want to rewire the boat, trace them out and understand their logic.

Make all new additions compliant with US standards (AYBC, for example). Use standard US electrical panels, breakers, high capacity fuses, etc., wired directly to the output of the battery switch. Then, eventually, trash the French system and incorporate its circuits into a US standard.


Cruise the Blue Sea webpage for ideas.

[j-yelroc]

Thanks to each of you for your comments. I wish I had taken more and better notes when we were there last time.

My brother-in-law (BIL) has the Mechanical & Electrical Manual book by Nigel Calder which is recommended in the "Homework" postings. Lots of reading ahead.

Bill, would you translate the following for me please:

"Servitudes" - label under the DPDT switch with the loose overheated lug connection.

Following labels on a circuit breaker (?):

Circuit Breaker is:
Merlin Gerin
Multi 9
C60N
C20
400V AC
6000 (with box around it)
IP 55
AC 400V

Attached labels on circuit breaker:
"Alim. avant C.B. "
"Pompe de cale BD"
"Pompe de cale TD"

I think pompe may be pump.

Thanks

Jess

[Chief Engineer]

ZE wire colors may be deeferant zan ze Etats Unie

[btrayfors]

"Bill, would you translate the following for me please:

"Servitudes" - label under the DPDT switch with the loose overheated lug connection.

No idea. May be "slave" of some sort, since servitude in French means same thing as in English.


Following labels on a circuit breaker (?):

Circuit Breaker is:
Merlin Gerin
Multi 9
C60N
C20
400V AC
6000 (with box around it)
IP 55
AC 400V

The Merlin Gerin Multi 9 circuit breakers are described here: http://www.stevenengineering.com/Tec...IT960N120N.pdf

Attached labels on circuit breaker:
"Alim. avant C.B. " Probably, "Feed to the circuit breaker"
"Pompe de cale BD" Bilge pump BD probably Starboard (Fr. "babord")
"Pompe de cale TD" Bilge pump TD probably Port ( Fr. "tribord")

Don't ask why you'd have a starboard bilge pump and a port bilge pump. C'est tres francais, mon amis :-)

I think pompe may be pump. Yes, it is.

By the way, there's a helpful English-French list of sailing terms which you can find here:

English-French Sailing Dictionary

Good luck,

Bill

[j-yelroc]

Thanks Bill. The boat is a catamaran so one bilge pump for each hull I guess. Earlier I thought I saw a "Sailing Technical Terms" link on here but later could not find it.

That French-English Dictionary will probably come in handy. Thanks

Ya Chief Engineer, ze colours heir are mostly black, nyet zo deeferant zan ze Etats Unie. Danka!

Jess

[MidLandOne]

No French electrical type has come along yet to explain "servitudes" so I will have a less informed go -

In general French engineering terms my understanding is that "servitudes" normally means similar to "ancillary services" so I would hazard a guess that the switch is the main breaker between the batteries and the main switchboard. If there isn't a switchboard (heaven forbid ) I would suspect that it is between the batteries and a bus providing individually fused (hopefully ) circuits to the various uses on the boat (eg lighting, instruments, etc).

But you mention that it appears to parallel two banks of batteries ("slaving" one to the other??) so maybe it does that as well but I would suspect that both banks (being a catamaran) are perhaps paralleled all the time and the switch provides overall isolation in the manner above. Why I say that rather than the switch being a paralleling switch is "servitudes", plural, is a noun whereas I would expect a paralleling switch to be named with a verb.

Hopefully a more informed explanation from the French will turn up in time or its usage for "anciliary services" will jolt suggestions from others.

[MidLandOne]

Originally Posted by MidLandOne

But you mention that it appears to parallel two banks of batteries ("slaving" one to the other??) so maybe it does that as well but I would suspect that both banks (being a catamaran) are perhaps paralleled all the time and the switch provides overall isolation in the manner above...

... or the switch allows selection of one bank or the other. Keep in mind that it is best (necessary in my view) practice for the main isolator to switch both the positive and negative. For this kind of detail only an inspection can determine it.

[hellosailor]

j-y:
25 years ago it was arguably normla to just "wire up" the batteries to the main switch and breaker panel. Today that is recognized as a safety failure, and new construction would use a primary fuse installed at/on the postive post of each battery terminal, or as close to it as possible. That fuse should be of a type, or in a hole, so that it cannot explode if it fails dramatically.
Some radio manufacturers will also require fusing the negative lead in the same manner, in order to prevent ground loops from destroying radios, i.e. if the primary ground is interrupted and the radio "becomes" the ground link. That's more of a matter of personal decision, but it has real merits.

Breakers are strongly not recommended as battery primary fuses. This is because typical breakers are only rated for 3000 amps in a surge, and typical "car" batteries can easily exceed that in a dead short, so the breaker welds shut and fails in the worst possible way. Other breakers are available rated 5000+ amps, but they will cost you over $100 a piece--making fuses very reasonable for this job.

I'm not sure what "servitudes" is intended to be, I would guess "Spares" or "Auxiliary" would be the more common English label, for a terminal or breaker used for assorted and sundry circuits, as opposed to cabin lights, anchor light, navigation lights, radio/electronics, and other dedicated purposes.

You can easily go crazy installing too many breakers/fuses, but personally I like to ask "If this circuit blew out, could I afford to lose everything on it?" and if the answer is No, then install separate circuits instead. For instance: Wind/depth/speed instruments togther, and even perhaps the GPS with them, but VHF all by itself.

[j-yelroc]

MidLandOne - Thanks for more insight to Servitudes. Based on the brief measurements of voltage we made my inclination is to consider it similar to a Tie Breaker in US AC systems except that it is a "Tie Switch" rather than a breaker. The tie breaker connects together like phases two ac buses of the same voltage. The neutral is not included.

I'm thinking maybe it ties the port and starboard batteries together. As you suggest we will probably need to discharge one or the other sets of batteries and compare the readings with those taken at the batteries rather than tracing the wires which would be more difficult since virtually all are similar size and color and behind panels and bulkheads.

Is there a French term for Tie Breaker or Tie Switch or similar meaning?

Thanks for your comments.

[j-yelroc]

Thanks h-s:

I agree with the protection near the batteries and think we will work toward that end. We have a noisy hum in the VHF and tried a dedicated battery for power and it cleared it up. We Will plan on running power direct from a battery with fuses in both pos and neg leads. Also need to be careful with any other control circuits attached to VHF.