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hi everyone jeff cote here with boating

tech talk so we've got a question from a

fellow voter

this voter is wondering about wire sizes

specifically for large loads that are

running intermittently right so a

thruster a starter a winless

winch

those loads are generally not running

for 20 minutes or 10 minutes continuous

right they're sort of sporadic they come

on they're intermittent so the question

from this boater is as follows jeff i've

got a 53 foot sca catch and the bow

thruster draws about 500 amps at 24

volts so that's a lot of amperage at 12

it would be a thousand a thousand amps

just imagine that that's crazy

what is the best and reasonable way to

size a wire the manufacturer of the boat

decided to go 2 watt for 20 feet still

under size but they claim it's ok due to

the loads not being sustained what to do

oh god i love it

really geeky question

it's interesting first of all let's back

up a little bit and let's think about

this issue

you know people and boaters and builders

and you know previous owners and people

in the marine industry are all of us are

incented to save costs we all are right

that's that's what we've been taught by

our parents we've been thought that

through life

we're trying to do more things with less

right that's life

the challenge is is that all too often

wire sizes are

chosen on basically trying to do

the most with the least amount

and that might work for a lot of boaters

that never use their boats think about

it marinas are full of boats that never

leave the dock those boaters have

everything they need on board because

they never use their boat

the board is is simply an as something

in their imagination something they

might get to use

but for the rest of us that are actually

using our boats and like for this

example this owner has a bow thruster

and plans on using his bow thruster

if i was running a bow thruster that had

a 500 amp load at 24 volts and it

doesn't matter if it's 12 500 amps or

500 amps at 24 it's still just 500 amps

would i be running

2 watt wire to that you know what maybe

it works but i would go up on a wire

size i think it's important to

emphasize that minimum does not mean

ideal minimum is what it means it means

that actually the very least you should

do is this

that does not mean that that's what you

should shoot for that means that you

should never do less than that

so when

in times people are saying well actually

i'm going to do less than the minimum

that's where i get a little bit nervous

now it's not going to actually

you know in this instance what could

happen if you undersize a thruster could

be one of the things that could happen

is that windlass under not windlass or

thruster under load is going to be

underpowered right

because voltage

under load and no load is different

so i would have probably done 4 i would

have gone bigger and i always

err on the size of caution

because my philosophy when we're

designing and implementing electrical

systems

is that time is the most valuable thing

we have not necessarily money and you

don't want to do something and have to

do it again there's nothing more

frustrating than doing it once and doing

it a second time so when we size wires

we size batteries we size everything

we never shoot for the least amount we

can do we go a little bit on caution and

go a little bit up and we figure you

know what if we're going to put the time

to put a cable in why not go up the size

yeah sure it might be more capital cost

more money on the wire size but you know

what i don't want my thruster to ever be

under

voltage under load because that's how

thrusters winless starters die

winches they all die not because the

manufacturer doesn't know how to build a

good windlass or a good thruster it's

simply because you know the batteries

are too far away they're already

somewhat depleted you're running the

thruster for longer than you should have

all these exceptions but they do happen

and then eventually your thruster

actually goes to put

and that's frustrating because it's

expensive

so personally even intermittent loads

yes it's a factor in derating a wire

right like when you go through a formula

you you ask literally is this a constant

load or an intermittent load but even

for intermittent loan further thruster

at 500 amps i would have gone a little

bit bigger wire size because i think the

minimum is not ideal and it's a really

good question um and think about that

when you're doing your boat don't go for

the floor

go a little higher than the least amount

you can do so great question thanks for

asking

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