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[Healeys] Wiring - reformatted

Subject: [Healeys] Wiring - reformatted
From: happolk at cox.net (Hap Polk)
Date: Sat, 5 Feb 2011 21:30:51 -0800
We pretty much beat up the Healey wiring sizing, fusing and connecting
subject, but for those who want even more stuff, take a look at wire sizing
at  http://www.simetric.co.uk/siwire_elect.htm



Fabricators vary as to how much wire load rating safety factor is best. My
personal maximum amperage limits for 150C rated insulated wire at an assumed
for design purposes stress-case 70C under hood temperature are as follows.

Standard Automobile Wire Capacities

Gauge | Max constant amps in open air | Max constant amps enclosed | Max
fuse | Max load @ 50% safety factor | Voltage drop per foot at 70 degrees
Centigrade at max safe load.

AWG 0 | 245 | 172 | 200 | 114 | 0.016

AWG 2 | 181 | 127 | 150 | 84 | 0.015

AWG 4 | 135 | 95 | 100 | 63 | 0.014

AWG 6 | 101 | 71 | 80 | 47 | 0.016

AWG 8 | 73 | 51 | 50 | 34 | 0.018

AWG 10 | 55 | 39 | 40 | 26 | 0.021

AWG 12 | 41 | 29 | 35 | 19 | 0.029

AWG 14 | 32 | 22 | 25 | 15 | 0.036

AWG 16 | 22 | 15 | 15 | 10 | 0.038

AWG 18 | 16 | 11 | 10 | 7 | 0.043

AWG 20 | 11 | 8 | 7.5 | 5 | 0.038

AWG 22 | 7 | 5 | 5 | 3 | 0.039



AWG 20 and 22 are not recommended for car wiring.

Open air = single wire in an air stream

Enclosed = all other conditions



Bill Lawrence kindly suggested checking out the Wiki article about
automobile fuses. That article referenced an OptiFuse site,

http://www.optifuse.com/fusesautoblade_reg.php which gives the following
fuse hold/blow standards.



ATO/ATC Fuse Design Standards  SAE J1284

Time Characteristics

Amp load versus amp rating | hold time min | hold time max

110% | 100 h  min | na

135% | 750 ms  min | 0.5 h max

200% | 150 ms  min | 5 s max

350% | 80 ms min | 250 ms max

600% | 30 ms min | 100 ms max

So, blade fuses in car service survive at 110% of rating, survive short
surges but otherwise cook at 135%, blow at 200%, and almost always blow
within 1 second somewhere around 250%.



A Lucas 35 amp fuse holds at 17.5 amps. Using 17.5 as the Lucass USA
equivalent rating, the Lucas 17.5 amp blows at 200%, and fast blows at
228%, quite similar to the ATO/ATC standard blade fuse.



USA glass ACG BUSS or LittleFuse glass fuse substitutes for Lucas fuses have
somewhat different characteristics with a shorter 110% overload hold time.
Again, per OptiFuse,

FSA/FSA-P Fuses < x 1 < (6.3 x 32mm) 3AG

Fast Acting/Glass Construction

12A-30A    32VAC

Time characteristics

Amp load versus amp rating | hold time

110% | 4 h min

135% | 1 h max

200% | 10s max



So, substitute a Lucas 35 amp with a US ACG 15 or 20 amp. Let your personal
experience be your guide. From the above starting at 15 amps but carrying 20
amps just in case should work but, frankly either should be sufficient to
protect the Healeys wiring from dead short burn risks.



Hap Polk

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