Thank you Jan and Nigel. I’m just trying to figure out what the recommendations/requirements are and the derations had me confused. Thank you for clearing that up and for your helpful website.

Nigel, your boat owners mechanical and electrical manual was the first how to book that I purchased when my first boat. I have the second edition, and I see the fourth is now current. I guess I’ll need to upgrade.

Thanks again guys

Hi Aaron,
You have a very sharp eye! I had adjusted the Wire Size Calculator to the new edition of the standards but the ampacity tables were still the old version. Now they are updated as well and should be in alignment with the calculator.
Please let us know if you find any other inconsistencies!
Best
Jan

Aaron,

The DC derating at more than two current carrying conductors (e.g., three or more) is in the latest version of the E-11 standard which was published in July 2025 and comes into force in July 2026. We are using this.

Nigel

However, when I use your calculator, it does not seem to derate DC wires when there are two in a bundle. It only derates for 3 or more. Is this because the PDF refers to an older set of guidelines?

Just curious. Thanks.

Robert,

These additional Blue Seas derating factors are related to continuous currents and temperature issues when using 105C conductors attached to devices (e.g., fuses) which likely have been rated at a lower temperature. They are based on testing done by a brilliant Blue Seas engineer, Wayne Kelsoe, to whom we all owe a debt of gratitude.

We address these issues in the text, but you are correct have not built this into the wire sizer which adheres to ABYC and ISO wire sizing.

The bottom line as always is we should err on the conservative side, especially with any circuit which is likely to be energized for continuous periods of time!

Nigel

Totally understand. Maybe just adding a note to hit enter after changing any entries or add an enter (refresh) button (equivalent to touching the screen). Might be easier than changing programming? Or add some text to the instructions?

I noticed when comparing to the Blue Sea Systems Circuit wizard that they also have additional derating factors (not per ABYC). From their site: “These factors are not considered in the ABYC Standards for wire sizing and they are not required to be entered in the Circuit Wizard to determine a wire size that meets ABYC requirements.

However, Blue Sea Systems’ engineers have identified Additional derating factors from experience in the field and experimentally in our laboratory as factors that can significantly influence the proper wire size required in a circuit. Some of these factors are under consideration by ABYC for future inclusion in the Standards.”

I know you are following approved ABYC or ISO standards but thought I would just mention in the case where someone uses that calculator and compares to yours with different results.

Robert,
Thanks for digging into this. This is actually how I programmed this thing. It waits for an input from the User and once the input is completed (i.e. you press enter or leave the input field) it calculates the output.
However, I do agree with you that this may be counterintuitive and misleading if you can read the input in the field but the output is still the old one, because internally the tool does not know yet that you are done (i.e. you have not pressed enter or touched the screen somewhere else).
I will look into ways to improve this, by having the calculator constantly listening for changes in the fields. But I am not sure if this is technically feasible. In any case, this may take a while as my todo-list is pretty full right now.
But I will keep this in mind and see what I can do!
Jan

Jan, I’ve been playing with the calculator to see what makes the result refresh when either the Cable run or Electrical load values are changed. It seems to update to the correct wire calculation when I tap on any portion of the screen – even on the background outside the calculator. Or if I hit the enter key. Without that stimulus the previous result remains. Hope that helps?

I have replicated the same issue on two different IPads, 1 PC and on my cell phone (iPhone).

Disregard my last comment about the ampacity since I didn’t tap on the result given from the wire size mode. When I do that it does automatically update the correct wire size in the ampacity mode. I had opened the ampacity mode icon instead of the wire size result. My bad.