Wire Gauge Charts vs Calculators

[MisterSandals]

I've been using the big colorful wire gauge chart from Blue Sea.

Part 1: Choosing the Correct Wire Size for a DC Circuit - Blue Sea Systems

Engineering high quality marine electrical components for safety, reliability and performance

www.bluesea.com

This has been at odds with online calculators that others have been using.

Here is the latest scenario:
25 amps
130 feet (both ways, 65' from array to SCC)
84 volts

The Blue Sea chart says 4 awg for 10% voltage drop, 0 awg for 3% voltage drop
Even using 65', this shows 6 awg so don't think it has to do with round trip, but its closer.

Bos'ns' Corner - Wire Size Calculator Says 8 awg for 2.5% voltage drop


Voltage Drop Calculator Says 8 awg for 2.04% voltage drop

What say you?
Bonus question: why the difference?

 

[John Frum]

The bluesea circuit wizard android app says 8 awg as well.
Shux.

 

[Supervstech]

Tin plating improves the corrosion resistance of the wire, but increases the amperage resistance of the wire.
ABYC insists on fine stranded tin plated wire. Also, they don’t count the round trip distance, just the aggregate distance from the bank.
The two combined equal the result.

 

[Dzl]

ABYC insists on fine stranded tin plated wire.

To my knowledge neither ABYC guidelines nor the UL 1426 which they reference actually requires tinned copper wire (but in practice most is). They do require stranded copper, along with some other stipulations. (edit: actually someone correct me if I'm wrong, I'm doubting myself now, what I can say is that I can't find any reference to "tin" or "tinned" in the 2008 ABYC guidelines)(edit 2: i found the source that says no ABYC/USCG requirement for tinned copper wire)

This also wouldn't explain the discrepancy since both the Bay Marine and Blue Sea calculators are marine calculators they would be based on ABYC data, and if I'm understanding @MisterSandals correctly, blue sea even disagrees with itself depending on which resource you use (app, chart, or circuit wizard).

Also, they don’t count the round trip distance, just the aggregate distance from the bank.
The two combined equal the result.

Can you break this down a little more, I'm not quite getting what you are saying, what do you mean by aggregate distance?

 

[Forbisher]

This voltage drop calculator has a lot of variables.

Best Wire Size Voltage Drop Calculator

Voltage Drop Calculator This is a calculator for the estimation of the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current. Please note this calculator assumes the circuit is operate in a normal...

diysolarforum.com

Does anyone know of other calculators?

 

[Dzl]

@MisterSandals Just saw that we are talking about a non-standard voltage (84V), the blue sea chart and the blue sea circuit wizard won't give accurate results, the chart is a 12V chart, the circuit wizard is 12, 24, 32V.

Its a frustration of mine that Blue Sea doesn't explicitly state that on the chart itself.

As I understand it voltage drop will be:
Vdrop = current x ohms per foot x total length in feet

So if we assume like Blue Sea does that the circuit is 12V, using your numbers we get:
4 AWG Vdrop = 25A x 0.00024 x 130 ft = 0.78V / 12V = 6.50% voltage drop
6 AWG Vdrop = 25A x 0.00040 x 130ft = 1.30 V / 12V = 10.8% voltage drop


So Blue Sea is actually correct, its just that they are correct at 12V, not 84V
The same math at the circuit voltage of 84V would return the same figures, BUT as a % of system voltage it would be much lower (0.9% and 1.5% for 4 and 6 gauge wire)

(wire resistance was derived from West Marine's chart which lists ohms per 1000').

 

[Dzl]

Does anyone know of other calculators?

Personally I use the Blue Sea Circuit Wizard for standard marine voltages (12v and 24v), and the Bay Marine calculator for standard or non-standard voltages. For two reasons (1) I like these calculators, (2) for simplicity I decided to choose a standard and stick to it, I decided on ABYC, so it makes sense for me to stick with marine calculators.

 

[Supervstech]

@MisterSandals Just saw that we are talking about a non-standard voltage (84V), the blue sea chart and the blue sea circuit wizard won't give accurate results, the chart is a 12V chart, the circuit wizard is 12, 24, 32V.

Its a frustration of mine that Blue Sea doesn't explicitly state that on the chart itself.

As I understand it voltage drop will be:
Vdrop = current x ohms per foot x total length in feet

So if we assume like Blue Sea does that the circuit is 12V, using your numbers we get:
4 AWG Vdrop = 25A x 0.00024 x 130 ft = 0.78V / 12V = 6.50% voltage drop
6 AWG Vdrop = 25A x 0.00040 x 130ft = 1.30 V / 12V = 10.8% voltage drop


So Blue Sea is actually correct, its just that they are correct at 12V, not 84V
The same math at the circuit voltage of 84V would return the same figures, BUT as a % of system voltage it would be much lower (0.9% and 1.5% for 4 and 6 gauge wire)

(wire resistance was derived from West Marine's chart which lists ohms per 1000').

Current is amps... not volts.

 

[Supervstech]

To my knowledge neither ABYC guidelines nor the UL 1426 which they reference actually requires tinned copper wire (but in practice most is). They do require stranded copper, along with some other stipulations. (edit: actually someone correct me if I'm wrong, I'm doubting myself now, what I can say is that I can't find any reference to "tin" or "tinned" in the 2008 ABYC guidelines)(edit 2: i found the source that says no ABYC/USCG requirement for tinned copper wire)

This also wouldn't explain the discrepancy since both the Bay Marine and Blue Sea calculators are marine calculators they would be based on ABYC data, and if I'm understanding @MisterSandals correctly, blue sea even disagrees with itself depending on which resource you use (app, chart, or circuit wizard).



Can you break this down a little more, I'm not quite getting what you are saying, what do you mean by aggregate distance?

I am not saying it is the ABCY standard, I am saying it is specifically stated in the instructions for the chart referenced above.
Fine strand,
Tin plated conductors, and simple distance from battery.
This is why THAT CHART is different from other calculators.

 

[MisterSandals]

So Blue Sea is actually correct, its just that they are correct at 12V, not 84V

This is what i am accepting as the the consensus.
I searched for wire gauge recommendations on this forum and what i found is that they pretty much ignored voltage (or assumptions were made behind the scenes).

I learned something today. I wish i learned this on the day i learned about the round trip.

 

[PHoganDive]

The 3% allowable drop will be different depending on voltage, higher voltage can tolerate more voltage drop and stay under 3%.

 

[Supervstech]

This is what i am accepting as the the consensus.
I searched for wire gauge recommendations on this forum and what i found is that they pretty much ignored voltage (or assumptions were made behind the scenes).

I learned something today. I wish i learned this on the day i learned about the round trip.

A higher voltage will affect the volts lost... but it wont affect the amperage chart.

 

[Dzl]

Current is amps... not volts.

What are you referring to? Where did I confuse the two?

I am not saying it is the ABCY standard

Well you did say "ABYC insists on fine stranded tin plated wire." Its probably worth correcting your post if that's not what you meant to prevent confusion.

A higher voltage will affect the volts lost... but it wont affect the amperage chart.

Just to make sure we are all on the same page, I agree that voltage doesn't effect the amperage chart, but the chart @MisterSandals referenced was not an ampacity chart, it takes into consideration voltage drop, and the discrepancies he noticed were based on voltage drop as a % of system voltage.

 

[Dzl]

I searched for wire gauge recommendations on this forum and what i found is that they pretty much ignored voltage (or assumptions were made behind the scenes).

I learned something today. I wish i learned this on the day i learned about the round trip.

I feel your pain man, It took me a long while to understand this bit too, most people seem to not know or not explicitly acknowledge it, even reputable sources like Blue Sea don't make it cleaer (I think they do it to make a complicated subject slightly simpler, and because using 12V (the lowest common marine voltage) means their recommendations will never be unsafe or undersized--but still...) It wasn't until I dug into the actual ABYC code, and that I started to think about it, and I think it was FilterGuy and BiduleOhm that helped me understand the math (in an unrelated thread).

The actual ABYC table differentiates by voltage:



I added screenshots of the ABYC tables for voltage and ampacity to the resources section

 

[Durangö]

Hi everyone!

Take a look in the following page, at Solar Cable Gauge Calculator section, think it is a good one.

solar powered calculators, solar panel calculator | Renogy

Renogy's Solar Power Calculator Tool can quickly help to estimate your solar power requirements, calculate the size and cost of an off-grid solar system needed.

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[tictag]

I understand that these reference tables can be useful but they do seem to just create confusion, especially if each table is calculated based on differing assumptions.

Personal preference: just do the maths, this really isn't rocket science.

As @Dzl says above, V(drop) = I x R (Ohm's Law),
where, R can be found in lookup tables such as this one.

and %V(drop) = 100 x V(drop) / V(supply)

No tables required and good for every cable size, every voltage in almost every situation.

 

[Forbisher]

I understand that these reference tables can be useful but they do seem to just create confusion,

No tables required and good for every cable size, every voltage in almost every situation.

Why do the math when a calculator mentioned in this thread can do the job with no tables required?

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

 

[Dzl]

Why do the math when a calculator mentioned in this thread can do the job with no tables required?

Voltage Drop Calculator

This free voltage drop calculator estimates the voltage drop of an electrical circuit based on the wire size, distance, and anticipated load current.

www.calculator.net

My 2c

I use calculators most of the time, but there is a simplicity and security in just doing the math. Its simple math, and it teaches you that its a simple concept. It wasn't until someone showed me how the math worked that I finally felt I had an intuitive understanding of voltage drop/wire sizing and could start answering some of the less straightforward questions I had had bouncing around my head.

Calculators make things easier, but they can also create some confusion, as some have minor differences, overcomplicate or oversimplify, or have unstated or barely stated assumptions, or just perpetuate pre-existing confusion. As an example, I think the whole confusion over round trip vs one-way distance is largely the result of calculators.

That said, I use calculators probably 90% of the time

 

[MisterSandals]

I think the whole confusion over round trip vs one-way distance is largely the result of calculators.

Uh, so is that table for one way or round trip?

I understand the resistance is per 1000m, so i am guessing round trip.

 

[Dzl]

Uh, so is that table for one way or round trip?

I understand the resistance is per 1000m, so i am guessing round trip.

Are you talking about the bluesea table you posted or the ABYC table I posted?

I believe (and I'm sure as soon as I say this, I'll realize I'm wrong, or find an exception) every reputable marine table or calculator uses total distance (round trip).


In my opinion, roundtrip vs one-way is an unnecessary and sometimes confusing distinction (probably inflicted upon us by the automitive industry and chassis-return), I think that all the one-way calculators deserve to die a fiery death for the unnecessary confusion they have inflicted upon us.

For me at least, it made it much simpler to stop thinking about in terms of one way or round trip, and think about it just simply as 'total feet of wire.' Its all the math cares about, and at least for me its much clearer.