bugs
Well-Known Member
Can multiple smaller diameter wires be used in place of one with a thicker cross section to minimise voltage drop?
Wire Size -Voltage Drop
- Thread starter bugs
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PaulRainbow
Well-Known Member
Yes.
bugs
Well-Known Member
Thank You.
Lon nan Gruagach
Well-Known Member
Yes but.
A bundle of wires wont be rated at the sum of all its parts, there is a small de-rating to factor in when bundling.
A bundle of wires wont be rated at the sum of all its parts, there is a small de-rating to factor in when bundling.
savageseadog
Well-Known Member
Yes, but with the qualification that if a wire or wires were to become disconnected for some reason the current would be carried by the remaining connected wires.
Yngmar
Well-Known Member
macd
Well-Known Member
...which should individually have sufficient ampacity for any likely load (to spell out what I'm sure was your point).
noelex
Well-Known Member
It is not good practice but, yes it can be done. The danger is if one or more of the wires becomes disconnected or develops a high resistance contact the fault is not obvious. The device will still continue to function often not giving much hint that a bad connection exists.
If you are going to do this as Macd and Savageseadog have said at least make sure that each wire has sufficient capacity to carry the full current (it needs to be derated slightly because it is in a bundle).
In this way if a fault develops there is at least no danger of a fire. The wire thickness needed for this is often not very great. Marine wires need to be large not for current carrying capacity but to keep the voltage drop within acceptable limits.
If you are going to do this as Macd and Savageseadog have said at least make sure that each wire has sufficient capacity to carry the full current (it needs to be derated slightly because it is in a bundle).
In this way if a fault develops there is at least no danger of a fire. The wire thickness needed for this is often not very great. Marine wires need to be large not for current carrying capacity but to keep the voltage drop within acceptable limits.
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pvb
Well-Known Member
Doesn't that rather defeat the object?
VicS
Well-Known Member
It may only require a small increase in size, if at all, because if they are of any length and have been sized to minimise volts drop they may be close, to or even greater than, the size needed for safe operation.
Lon nan Gruagach
Well-Known Member
Maybe, maybe not... In low voltage circuits cable size is often determined by volt drop rather than current capacity. To avoid fire risk due to overloaded cables but also use a bundle of thinner wire then each wire should be able to carry the full current while it is only the bundle that prevents significant volt drop. If one wire becomes open circuit then the equipment will suffer brown out while you avoid a potential fire.
David2452
Well-Known Member
Whilst it will do the job (with the caveats mentioned earlier) it is extremely difficult to get a quality crimped termination with any more than two lots of conductor and insulation. Cable is cheap, even the right tinned stuff and 6mm2 is not twice as expensive as two lots of 2.5mm2 so why bother?
noelex
Well-Known Member
Re: Wire Size -Voltage Dro
No
Most of the time, with marine wiring the size of the cable needs to significantly larger than the minimium required to carry the current.
My solar panel wiring is 25mm2 for example Much larger of the minimum needed to carry the 20 or so amps. It is sized to keep the voltage drop within exceptable limits. Something like 6mm2 will carry 20 -30A safely (look up the tables to be sure especially a bundled cable in an engine room) so 4 cables each 6mm2 (giving a total of 24mm2) could be used instead of a single 25mm2 cable, providing the fuse (say 25A) was below each of the wire ratingings. It is not best practice, but it is done.
In the worst case of three of the cables became disconected (or developing a poor connection) the voltage drop would rise so I would get less output from my panels but the single wire would handle the current without melting and creating a fire risk. If a short developed on the battery side the fuse would blow before the wire melted. This is not true if you used more cables of much thinner wire.
However, a single larger wire is better.
No
Most of the time, with marine wiring the size of the cable needs to significantly larger than the minimium required to carry the current.
My solar panel wiring is 25mm2 for example Much larger of the minimum needed to carry the 20 or so amps. It is sized to keep the voltage drop within exceptable limits. Something like 6mm2 will carry 20 -30A safely (look up the tables to be sure especially a bundled cable in an engine room) so 4 cables each 6mm2 (giving a total of 24mm2) could be used instead of a single 25mm2 cable, providing the fuse (say 25A) was below each of the wire ratingings. It is not best practice, but it is done.
In the worst case of three of the cables became disconected (or developing a poor connection) the voltage drop would rise so I would get less output from my panels but the single wire would handle the current without melting and creating a fire risk. If a short developed on the battery side the fuse would blow before the wire melted. This is not true if you used more cables of much thinner wire.
However, a single larger wire is better.
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pvb
Well-Known Member
Re: Wire Size -Voltage Dro
So it seems we're agreed that a single larger cable is preferable.
So it seems we're agreed that a single larger cable is preferable.
lw395
Well-Known Member
Re: Wire Size -Voltage Dro
If you need it to flex.
If you want to spread the heat dissipation around.
If you want to standardise on a certain size connector.
If you happen to have a lot of wire of a certain size already...
Generally yes, but not always!
If you need it to flex.
If you want to spread the heat dissipation around.
If you want to standardise on a certain size connector.
If you happen to have a lot of wire of a certain size already...
thinwater
Well-Known Member
Re: Wire Size -Voltage Dro
I only find the first reason compelling; occasionally a fat wire simply won't bend where it needs to, though this is very rare. I have run into it in panels a few times, as well as pulling wire.
If the voltage drop is low there is little heat.
I wonder what the OP's reasons was. Probably he had the stuff.
I only find the first reason compelling; occasionally a fat wire simply won't bend where it needs to, though this is very rare. I have run into it in panels a few times, as well as pulling wire.
If the voltage drop is low there is little heat.
I wonder what the OP's reasons was. Probably he had the stuff.
syneraida
Well-Known Member
Re: Wire Size -Voltage Dro
The practice of bundling multiple wires is done regularly on medium voltage (11KV) installations on ships, where a lot of amps are generated and where a single cable would be unmanageable.
But with this above exception, I would try and avoid multiple (bundled) wires. Its a good workaround if you are stuck in the middle of nowhere, but otherwise I would try and use a single wire.
Remember surface area is a function of the radius and pi squared, so after a little while a small diameter increase dramatically increases the mm2 and thus your current carrying capacity.
The practice of bundling multiple wires is done regularly on medium voltage (11KV) installations on ships, where a lot of amps are generated and where a single cable would be unmanageable.
But with this above exception, I would try and avoid multiple (bundled) wires. Its a good workaround if you are stuck in the middle of nowhere, but otherwise I would try and use a single wire.
Remember surface area is a function of the radius and pi squared, so after a little while a small diameter increase dramatically increases the mm2 and thus your current carrying capacity.
lw395
Well-Known Member
Re: Wire Size -Voltage Dro
Surface area, which affects dissipation is a function of r, cross section area affects DC resistance is proportional to r squared.
Sometimes you want a higher surface area for more dissipation, for a given resistance.
Meaning that a single round cable is not always best...
I can't imagine this often crops up in yachts, except possibly linking two batteries where one is highly loaded.
E.g. a thruster battery.
Best to do the maths and RTFM in some cases...
Surface area, which affects dissipation is a function of r, cross section area affects DC resistance is proportional to r squared.
Sometimes you want a higher surface area for more dissipation, for a given resistance.
Meaning that a single round cable is not always best...
I can't imagine this often crops up in yachts, except possibly linking two batteries where one is highly loaded.
E.g. a thruster battery.
Best to do the maths and RTFM in some cases...
