Date: Sat, 22 Jan 2022 09:35:41 -0600
Reply-To: Tom Hargrave <thargrav@HIWAAY.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Tom Hargrave <thargrav@HIWAAY.NET>
Subject: Re: Best Wire Selector -- Voltage Drop Charts Mayhem
In-Reply-To: <CY4PR0801MB3731DE2A302699EBF94E0C19A05C9@CY4PR0801MB3731.namprd08.prod.outlook.com>
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There's one other factor that modifies wire size in automotive, and that's
vibration (and stresses all of this causes).
This factor is the reason automotive wiring is often larger than 'needed'
for the amount of current the wires need to carry. Make the wires too small
and wire breakage becomes a problem because of the environment the wires
operate in.
Thanks, Tom Hargrave
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-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Dennis Haynes
Sent: Saturday, January 22, 2022 9:14 AM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Best Wire Selector -- Voltage Drop Charts Mayhem
From: Dennis Haynes
Sent: Saturday, January 22, 2022 10:12 AM
To: Derek Drew <derekdrew@DEREKMAIL.COM>; vanagon@GERRY.VANAGON.COM
Subject: RE: Best Wire Selector -- Voltage Drop Charts Mayhem
Derek,
Sorry about the delay in responding. Answering your question is a bit tough
as there are so many variables. Wires size selection for low voltage
circuits is a bit of a compromise act. Amongst some of the variables include
the temperature rating of the insulation, wire in free air or bundles or in
conduit, and the quality-strand count of the copper. Much primary automotive
wire today is cheap copper clad aluminum.
Marine wiring methods can be a bit overkill and with good insulation and
proper weather shielded terminations there is no reason for tinned wire to
needed. There are marine grade rated wire that is not tinned. Another major
difference in marine use is using the chassis for ground is not common. Most
devices actually get 2 wires to/from the source. This is also common in RVs
with wooden cabinets and furniture.
For simplicity I pretty follow the NEC electric code for wire size based on
ampacity. Rarely will I use anything under 18 AWG just for reliable
terminations and mechanical strength. 14 AWG up to 15 amps, 12 AWG for 20,
10AWG for 30A, and 8 AWG for up to 50A non continuous. By definition we use
continuous load as three hours or more. Battery charging, lighting, and some
other loads can fall into this category. For mixed loads such as feeding a
fuse block diversity can be applied such as your house. You have a 200 A
main but adding up all the branch circuits is much more. Diversity is that
all the circuits will not be loaded at the same time.
So for example you run a fused at 40 A #8 to a distribution fuse box and can
have multiple branch circuits at 20 A each feeding #12 wire.
Over current protection and fuse coordination comes the next step. Point is
as systems become complex and large current some good engineering should be
part of the plan.
Dennis
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