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Old 06-02-2015, 15:40   #31
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Re: Upgrading windlass wiring

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Originally Posted by James S View Post
I don't see a problem with multiple conductors.
If the lengths of the conductors are not exactly the same, the resistance will not be the same and the current flow will be unequal.

Also, if one of the conductors fails or the connection fails or becomes loose or corroded, the entire current will attempt to flow in the other conductor and since the overcurrent protection was sized for the expected capacity of the two conductors in parallel it will not blow or trip and you have a fire hazard.

Doing it right means replacing the too small conductor with a single conductor of the required size. The old conductor can be used to pull the replacement into place.
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Old 07-02-2015, 09:56   #32
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Re: Upgrading Windlass Wiring

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Originally Posted by janders View Post
The manufacturer calls for a 135A breaker/fuse on the circuit but if I'm running parallel conductors of 1/0AWG and 4AWG, I don't really know how to size those fuses.
Two good ways of doing this.

a) Protect both wires with a single fuse, located upstream of the point where the wire "splits" and very close (inches; ABYC is quite specific for a reason) to the energy source (battery or a bus that is fed by a wire that is protected by something else). Rating of the fuse should be not greater than the ampacity of the lighter wire.

Only downside is that you cannot use much of the ampacity of the wires; in DC typically this is only an issue in very short runs where ampacity dominates. I would follow this route for a windlass.

b) Protect each wire with its own fuse, rated not greater than ampacity of the respective. This is not very "neat" in that you can think the circuit is not hot when it is (eg when you take one fuse out). We engineers do not like this option for a number of reasons but it is mentioned only for completeness. I would only do this if draw of the windlass was greater than ampacity of the original (lighter) wire, which would be unusual on a "normal" boat.

***

Make sure you know where your drop comes form. IME windlass cables tend to have quite a bit of drop from bad crimps that got corroded. You fix the crimp and solve the problem. I have found it useful to compare actual measured drop along the cable with the theoretical Ohm's law value (voltage drop = draw measured with clamp times resistance from a table that shows ohms per foot times length in feet).
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Old 07-02-2015, 10:03   #33
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Re: Upgrading windlass wiring

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Originally Posted by rwidman View Post
If the lengths of the conductors are not exactly the same, the resistance will not be the same and the current flow will be unequal.
That is true but not a problem. Sam thing happens if the cross sections are not the same.

Quote:
Originally Posted by rwidman View Post
Also, if one of the conductors fails or the connection fails or becomes loose or corroded, the entire current will attempt to flow in the other conductor and since the overcurrent protection was sized for the expected capacity of the two conductors in parallel it will not blow or trip and you have a fire hazard.
You presume the electrician did not know her/his stuff. If both wires are protected by a single fuse then the rating of the fuse should be no greater than ampacity of the lighter of the two wires. No problem then.

It is true that thsi approach does not lket you use teh whole ampacity of each wire, but ampacity is not a driver of wire size in long DC runs. Drop drives sizing typically in this situation.

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Originally Posted by rwidman View Post
Doing it right means replacing the too small conductor with a single conductor of the required size. The old conductor can be used to pull the replacement into place.
Agree in many cases but not so sure for windlasses and DC side of large inverters. If you wire big inverters you will come across the instructions from Victron that wisely tell you to use two wires in some cases where a single wire would be impractical (too stiff).
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Old 07-02-2015, 10:58   #34
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Re: Upgrading Windlass Wiring

Good thread, I am following this one.
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