Cable dimensioning
- Thread starter Ed91e
- Start date
Airmapper
Inactive Member
14, for strips? Maybe you should specify watts or amp draw to help us understand. 18g is plenty for most LED strips, heck even 20g. Very low draw on those.
I Installed a strip on my awning that runs off USB....
As a general rule it's better to have too large a gauge than too small, but still smaller wire is much easier to work with.
The spots will pull more, calculate the watts they run first. There are a multitude of online calculators for selecting appropriate gauge wire, converting units, and calculating voltage drop. I'm betting you'll be around 14g for them perhaps if it's not too long a run. Plan ahead, if you want to run anything else in the same area, go bigger to accommodate everything.
I Installed a strip on my awning that runs off USB....
As a general rule it's better to have too large a gauge than too small, but still smaller wire is much easier to work with.
The spots will pull more, calculate the watts they run first. There are a multitude of online calculators for selecting appropriate gauge wire, converting units, and calculating voltage drop. I'm betting you'll be around 14g for them perhaps if it's not too long a run. Plan ahead, if you want to run anything else in the same area, go bigger to accommodate everything.
Mattersnots
Adventurer
I agree with Airmapper. Here's a chart that may help.
Ed91e
New member
DaveInDenver
Middle Income Semi-Redneck
What time and temperature assumptions are made for this chart? It appears fairly aggressive to me. My $0.02 is that the NEC-based and similar charts are way too conservative but when you deviate from them you need to be aware of the details.I agree with Airmapper. Here's a chart that may help.
Just a spot example, say a 10 foot run of 16 AWG. This chart suggests this will be fine with 18 or 20 amps. This is likely true of 105 ºC or 125 ºC wire for 60 seconds or less and an ambient of 30 ºC in still air. But if the ambient is warmer, the time is longer or you use 90 ºC insulation (NEC suggests 16 AWG is 18 amps max with 90 ºC insulation) then you start to get into questionable conditions and have to start taking into consideration things like how fast the heat is actually dissipating and whether the wire is bundled.
FWIW, this is one manufacturer's current carrying recommendations: https://www.weicowire.com/image/pdf/CurrentCapacityChart.pdf
OTOH, they recommend 2 AWG for a 25 foot run and 150 or 200 amps. This I agree would be fine even with 90 ºC for up to 4 minutes and NEC actually almost agrees, which suggest 90 ºC 2 AWG is good to 130 amps with up to 3 wires bundled. If you assume some cooling and use 125 ºC insulation a 2 AWG should be fine even higher. I personally use 2 AWG EPDM for my winch wiring assuming a stalled current of 275 amps (I have a really old Warn 2.5 HP motor, so this is probably high) and fuse with a 250 A MRBF.
Point I'm making is this chart appears to be a fine rule of thumb but I'd be careful blindly using it without knowing a bit more. Generally I'd consider using at least 105 ºC insulation or increasing one higher AWG from their recommendation to add margin.
Last edited:
DaveInDenver
Middle Income Semi-Redneck
Blue Sea is based on the ABYC E-11 standard, which has always seemed realistic to me. That rates, for example, an unbundled 8 AWG conductor with 105 ºC for 80 amps DC outside of engine spaces (35 ºC ambient). Inside engine spaces it's derated to 68 amps based on a 50 ºC ambient.
Last edited:
restorationrides
Member
DaveInDenver
Middle Income Semi-Redneck
Blue Sea app is based on good data, minimal risk in following it.
BTW, I assume you mean this: http://circuitwizard.bluesea.com
Last edited:
DaveInDenver
Middle Income Semi-Redneck
Might be useful to mention the term conservative in this context. With a cable you are managing two things primarily, voltage drop and heat or temperature rise. You balance these against cost, weight and ease of working.
It's impossible to be too conservative technically and all things being equal having a cable that is grossly over what you need is only impractical. About the only true negative might be the mechanical strain you put on a terminal that's too small for a wire size. But as a current carrying device bigger is better.
So we're left with voltage drop and temperature rise, which you determine based on expected current and decide based on judgment. When you pick something excessively small it will have too much voltage drop, which is generally more inconvenient than anything, and too much temperature rise. Sometimes voltage is important or can be compensated for, like in the discussion on dual batteries, using a DC-DC charger allows you to run a smaller wire because voltage differences are made unimportant. Without a DC-DC device you would need to use very large wires to minimize voltage drop at high current. With one you know the max current and you run a wire large enough to be safe.
Temperature is where the selection is tricky. Because if you allow a little bit of temp rise you can use a wire that is safe but not more expensive or hard to work than it needs to be. If you pick way too small it will fuse, which means it burns in two. That's actually more inconvenient than strictly dangerous. It's self limiting, it's breaking current like a fuse or breaker.
The real dangerous situation is picking a wire that is marginally small that heats up slowly or only in harsh condition and then only enough to melt through its insulation but not in two. This is how you expose wire, create shorts and arcs, burn things, cause fires. So conservative is judged by how close to the edge you want to run and in that vein the ABYC I think is reasonably safe in the majority of cases. Boats have the same issue we do, space and weight. You want large enough to be safe without bundling a dozen 10 AWG wires that run from front to back of your truck unnecessarily. This is really the point, to be mindful of how you lay out your branch circuits to use time and materials efficiently.
Last edited:
Yes, also see the "Download for Android/iFruit" links at the top, no Internet access needed after it's on your phone.
my bad, I'd read "unrealistic".
To me it has great value as a learning tool, learn and play with the variables, gives you a feel for where you can skimp and where not.
restorationrides
Member
- Not to hijack the thread but since we have people reading these threads of all experience and education, I just want to add a note about all of these reference wiring tables and standards (NEMA, ABYC, SAE, etc.)....
For each wire size selection, the wire length you should be using for your calculation is for both the POSITIVE and NEGATIVE wire segments ADDED TOGETHER in length. So if your proposed POSITIVE wire run is 6 feet long and your proposed NEGATIVE wire run is 4 feet long (to complete that circuit), it's a total of 10 ft of wire (not 6 ft).
Be sure to use the correct voltage combined with the expected amperage over the total circuit distance to find your wire gauge.
And as very well explained by some of the other writers here, consideration should be made for the temperature in the environment that your wiring is going to live in.
By example...for really cool looking wiring installations (like when I built a custom wood traditional-looking hotrod ski boat with an exposed supercharged 1st Gen Chrysler Hemi, I ran all of the exposed wiring in PVC tubing which gave it a great finished look, but which could trap heat and create a problem (due to lack of ventilation, and the poor thermal conductivity of most Plastics).
So in that case, I made sure my wiring was oversized to keep everything running cool. (And yes, all the wires were tinned, and of commercial marine grade, and terminated with soldered tinned lugs).
BTW, as pointed out indirectly before by someone else, there are pretty dramatic differences between low-cost wiring and the more expensive high performance grades. You will notice that cheap wiring has larger strand diameters with fewer strands. More expensive grades will have smaller strand diameters with substantially more strands.
Both wires will have similar outside insulated diameters, but look dramatically different inside. Also, the more expensive wire will be of higher grade alloy and more resistant to corrosion and fatigue failure. Also, the more expensive wire will use a higher grade of insulator jacket compared to the cheaper grade.
NOTE:
There are several things I can think of that are impacted here.
FIRST: If we accpt that electrical current runs on the surface of wires, then we want a greater surface area to carry our current. The more expensive wire has a greater surface area so carries the current more efficiently.
SECOND: the finer stranding of the more expensive wire makes for much easier positioning and routing of your wire as it lays down nicely and makes turns much easier.
THIRD: The more expensive wire is more tolerant of inadvertent nicking (as someone said "skive marks"), surface damage, and degredation due to corrosion - as there are so many more strands distributing the electrical load.
FOURTH: I don't think anybody's seriously producing low-grade wire with tinned strands and high-quality jacketing. So I think a pretty safe bet is if you go with tinned wire, you're going to get a bundle of good features...
Regards,
RestorationRides
Sent from my Z981 using Tapatalk
For each wire size selection, the wire length you should be using for your calculation is for both the POSITIVE and NEGATIVE wire segments ADDED TOGETHER in length. So if your proposed POSITIVE wire run is 6 feet long and your proposed NEGATIVE wire run is 4 feet long (to complete that circuit), it's a total of 10 ft of wire (not 6 ft).
Be sure to use the correct voltage combined with the expected amperage over the total circuit distance to find your wire gauge.
And as very well explained by some of the other writers here, consideration should be made for the temperature in the environment that your wiring is going to live in.
By example...for really cool looking wiring installations (like when I built a custom wood traditional-looking hotrod ski boat with an exposed supercharged 1st Gen Chrysler Hemi, I ran all of the exposed wiring in PVC tubing which gave it a great finished look, but which could trap heat and create a problem (due to lack of ventilation, and the poor thermal conductivity of most Plastics).
So in that case, I made sure my wiring was oversized to keep everything running cool. (And yes, all the wires were tinned, and of commercial marine grade, and terminated with soldered tinned lugs).
BTW, as pointed out indirectly before by someone else, there are pretty dramatic differences between low-cost wiring and the more expensive high performance grades. You will notice that cheap wiring has larger strand diameters with fewer strands. More expensive grades will have smaller strand diameters with substantially more strands.
Both wires will have similar outside insulated diameters, but look dramatically different inside. Also, the more expensive wire will be of higher grade alloy and more resistant to corrosion and fatigue failure. Also, the more expensive wire will use a higher grade of insulator jacket compared to the cheaper grade.
NOTE:
There are several things I can think of that are impacted here.
FIRST: If we accpt that electrical current runs on the surface of wires, then we want a greater surface area to carry our current. The more expensive wire has a greater surface area so carries the current more efficiently.
SECOND: the finer stranding of the more expensive wire makes for much easier positioning and routing of your wire as it lays down nicely and makes turns much easier.
THIRD: The more expensive wire is more tolerant of inadvertent nicking (as someone said "skive marks"), surface damage, and degredation due to corrosion - as there are so many more strands distributing the electrical load.
FOURTH: I don't think anybody's seriously producing low-grade wire with tinned strands and high-quality jacketing. So I think a pretty safe bet is if you go with tinned wire, you're going to get a bundle of good features...
Regards,
RestorationRides
Sent from my Z981 using Tapatalk
I only use UL1426-certified tinned "boat cable", matching designed-for-purpose crimper tools and top marine quality terminator fittings and other hardware.
UL may be a US standard, I'm sure there are Euro or ISO equivalents.
Neither electrics nor LPG are areas to save money on by purchasing generic stuff based on price, even need to watch for counterfeits in this era of Chinese imports taking over.
Best to use trusted suppliers only.
UL may be a US standard, I'm sure there are Euro or ISO equivalents.
Neither electrics nor LPG are areas to save money on by purchasing generic stuff based on price, even need to watch for counterfeits in this era of Chinese imports taking over.
Best to use trusted suppliers only.