21EC wiring harness

[fran uteg]

I was checking the tug yesterday after a great run on Lake Hartwell and I noticed that the wiring harness on the port side of the engine was badly chafed by the engine mount. The main cabin supply cable insulation was almost worn through by the front engine mount where it turns to go below the deck. I checked the entire length of the cable bundle and it was also hitting the rear engine mount just in front of the main buss bar. I re-bundled the entire run and anchored it approximately one inch from the engine mounts ........ the 3YM30 "dances" about a quarter inch at idle. This is just an FYI for all the 21EC skippers ........ a direct short of a main cable carrying many amps can be a real light show .......... Fran Uteg ....... Reflactions

 

[SGIDAVE]

I was checking the tug yesterday after a great run on Lake Hartwell and I noticed that the wiring harness on the port side of the engine was badly chafed by the engine mount. The main cabin supply cable insulation was almost worn through by the front engine mount where it turns to go below the deck. I checked the entire length of the cable bundle and it was also hitting the rear engine mount just in front of the main buss bar. I re-bundled the entire run and anchored it approximately one inch from the engine mounts ........ the 3YM30 "dances" about a quarter inch at idle. This is just an FYI for all the 21EC skippers ........ a direct short of a main cable carrying many amps can be a real light show .......... Fran Uteg ....... Reflactions

Hello Fran,

GOOD tip! My wiring shows no wear at this point.

As far as LIGHT SHOW...if the wire to 'house' shorts there would be a little spark then the breaker would trip. If the wire to the bow thruster shorts in that location...probably a large fire since that wire is UNFUSED from the battery/s to the bow where the 150A fuse is located (in the factory supplied wiring). I've modified my boat's wiring to include fusing from the battery as per ABYC recommendations.

Blue Sea makes a MRBF (battery terminal fuse)

or like this for TWO wires coming off the pos terminal

Food for thought. Standard ANL fuses can be configured to accomplish the same thing but will require more space which is unavailable in my tug.

I'm gonna go check my fire extinguisher...

/david

 

[fran uteg]

Excellent point on the thruster main line ........ I will get the breaker installed ....... my German background prompts me to avoid der spittzen und der sparken und der blinden white flashen ........ thanks ....... Fran

 

[fran uteg]

Just a quick follow-up on the Blue Sea fuses ....... the fuse block (single pole $30.00 +/-) is Blue Sea MRBF pn 5191 ........ the fuse ($17.00 +/-) itself is Blue Sea pn 5187 for the 200 amp ...... there are fuses that fit this particular block ranging from 30 amp to 300 amp ...... FYI :idea:

 

[SGIDAVE]

Just a quick follow-up on the Blue Sea fuses ....... the fuse block (single pole $30.00 +/-) is Blue Sea MRBF pn 5191 ........ the fuse ($17.00 +/-) itself is Blue Sea pn 5187 for the 200 amp ...... there are fuses that fit this particular block ranging from 30 amp to 300 amp ...... FYI :idea:

Hello Fran,

Blue SEa products are not cheap, that's for sure...

Check at Genuinedealz.com for the MRBF terminals and fuses. MUCH cheaper...fuses run less than $12 and the MRBF terminal set up is $14.75 for the single. Note that they sell the single MRBF in either 1/4 bolt/nut OR M8 bolt/nut. Given the choice I'd choose the 1/4" since sourcing a SS nut in the SAE 1/4" size is vastly easier than finding an M8. The two sizes LOOK equivalent but they are NOT interchangeable. Different thread pitch.

Look here (https://www.youtube.com/watch?v=y3gzhep8w4A) for a vid of an intentional MRBF tripping. It is very reassuring to know your battery cables won't act like toaster elements when something wears through the insulation to cause a short. The vid is from the guy with the write ups on compass marine/pbase website (http://www.pbase.com/mainecruising/boat_projects)

/david
PS: I have no financial or other interest in the entities mentioned above. I do not know the Compass Marine guy but have become a fan from a recommendation many years ago on Cbrats.com

 

[RProffer]

I don't know if you missed it, but there is a 150 amp fuse for the bow thruster on the R21-EC. It is located under the stbd bunk cushion right next to the on/off switch for the bow thruster, mounted on the aft bulkhead for the bunk. If you leave that switch in the ON position all the time, then that whole circuit is protected by the fuse all the time. An additional fuse/breaker is not required. If you decide to install an additional circuit breaker or fuse, then make sure it is a 150 amp device - not more or less. I don't know too many people who would go to the trouble to lift that bunk cushion to turn the switch on/off every time they want to use the bow thruster.

 

[SGIDAVE]

I don't know if you missed it, but there is a 150 amp fuse for the bow thruster on the R21-EC. It is located under the stbd bunk cushion right next to the on/off switch for the bow thruster, mounted on the aft bulkhead for the bunk. If you leave that switch in the ON position all the time, then that whole circuit is protected by the fuse all the time. An additional fuse/breaker is not required. If you decide to install an additional circuit breaker or fuse, then make sure it is a 150 amp device - not more or less. I don't know too many people who would go to the trouble to lift that bunk cushion to turn the switch on/off every time they want to use the bow thruster.

Hello Rick,

I respectfully disagree with you. There are times when the forward-located ANL fuse WILL NOT protect the circuit.

I'll explain...

ABYC standards require all main DC circuits to be overcurrent protected (fused) within 7 inches of the battery. The starting cable being one exception. The reason for locating the fuse CLOSE to the battery is to protect AS MUCH OF THE CABLE AS POSSIBLE. Protect the cable from overcurrent situation, that is. (ABYC 11.10.1.1.1)

To be clear, the fuse protects the wire...not the devise. Therefore, the fuse is SIZED according to the current carrying capacity of the conductor. But I digress...

A fuse, like the ANL on the 21EC in the forward compartment, protects the portion of wire BETWEEN the fuse and the devise (thruster in this case). But there are times, such as when there is a dead short along the cable BETWEEN the battery and the ANL fuse, then that fuse becomes USELESS, and the overcurrent situation will continue unabated (FIRE being the end result) since the fuse does not see any overcurrent. If you consider this situation, even if the fuse blew, the dead short would persist since it occurred "before" the fuse along the course of the wire. The house/thruster cables chafing as they pass by the vibrating engine on their way forward is what sparked (pun intended 😉 ) this discussion. Shorts can happen on any boat; overcurrent protection (fuses) will prevent disaster/s.

IF the overcurrent (or short) occurs between the fuse and the devise, then, YES, it does protect the "downstream portion" of the circuit. Well, there again, the fuse would blow, and current flow would stop 'after' the fuse (between the fuse and the devise) but the portion of wire BETWEEN THE BATTERY AND THE FUSE would remain energised...and UNPROTECTED (from overcurrent or a short).

The emphasis, and goal of the ABYC standard, is to protect AS MUCH OF the conductor as possible by locating the fuse CLOSE to the battery. HENCE the MRBF discussion above.

I removed the ANL under the stb bunk and replaced it with an MRBF at the battery terminal.

Stay safe my friend...Fuse early and often

/david