One for the sparkies

**Blknight.aus** · 6th October 2020, 08:17 PM

Originally Posted by Gav 110

I’m not sure of the requirements for auto electricians, but 5% of 240 volts is 12 volts and 5% of 12 volts is 0.6 volts
Maybe someone else can elaborate on the auto side of electrimagicians

I personally get annoyed with drop of more than about .2v end to end at nominated load. anything more than 1V between supply and end appliance at nominal load I'll fail and I'll start asking questions at the .5v mark

Bare in mind that in this instance, end to end is not from supply to end use its from major point to major point. for example

battery to primary fuse box
primary fuse box to aux fuse panel
Aux fuse panel to connection point to end appliance

All of those I'd accept upto .2v drop at each stage (regardless of how many connections or meters of run)

but in this example

battery to primary fuse box
primary fuse box to aux fuse panel
Aux fuse panel to trailer connector
Trailer connector to trailer fuse panel
Fuse panel to trailer battery charge controller

if you had .2v at every leg of the system you'd be at 1v of drop

But remember I'm also only aiming at the nominal loading, If in the last example you nominally wanted to charge the battery at 10A but your charge controller was a 30A unit (assuming everything was capable of handling it) if the controller was pulling 25A and you had 1V of drop Id probably consider that acceptable so long as when the initial in rush of starting the charger had leveled out or the charge rate was down to 10A then the drop would want to be under .5V

Of course in a design spec like that I'd be having a good long hard look at why you'd want that configuration (in this instance there was a solar system build in the trailer, the 10a feed from the vehicle was only intended to keep already charged batteries topped up which was when I learned that yes, over a long enough run min spec 10A cable will allow a full short to occur and not blow a 10A fuse)

**Vern** · 6th October 2020, 08:48 PM

If you worked on .5v drop allowance in the real electrical world, you would go broke!

**Gav 110** · 6th October 2020, 10:08 PM

Originally Posted by Vern

If you worked on .5v drop allowance in the real electrical world, you would go broke!

Is there not an Australian Standard for auto electrical work
Or is it just not policed as much as a 240/415 electrician????

**superquag** · 7th October 2020, 01:07 AM

Originally Posted by scarry

No,it is very rarely used anymore,at least in Qld.

After all these years some have actually worked out the small cost saving using the stuff is negated by the problems with using it.

Most,if not all building wiring is multi stranded,but still not suitable for automotive use.

Older places,single stranded is still found,and it is an absolute PITA to work with.

I always found doing a 'Double Fold' is easier with single-solid, - no sneaky sharp strands spearing holes in you fingers!

**RANDLOVER** · 7th October 2020, 02:01 AM

Originally Posted by Blknight.aus

not so, once you get to a certain point the wire itself becomes a current limiting device by turning into a heater, its entirely possible with cheap enough wiring to go full short and not blow out a standard automotive fuse, especially if the wire run is long enough.

Protection Coordination of Circuit Breakers - GSES

I suspect the scenario described above is pro'ly due to a poor earth, so the full short circuit current wasn't able to flow and rupture the fuse. Although in a 12 volt automotive system the battery may not be able to produce a fault current for long enough to operate a fuse that is only mildly overloaded, not so in a HV generator system that can produce massive currents.

People also confuse overload, over current and short circuit, from the above graph it can be seen that a mild overload can be permitted for up to 4 hours, but as the overload value increases the trip time shortens.

**scarry** · 7th October 2020, 06:39 AM

Originally Posted by superquag

I always found doing a 'Double Fold' is easier with single-solid, - no sneaky sharp strands spearing holes in you fingers!

Until it snaps off,then there is no more length on the wire because it was cut off too short to start with by another sparkie during the original install.
Happens all the time.

Multistrand is the go,and the only cable used on mechanical services gear.

**Homestar** · 7th October 2020, 08:53 AM

Originally Posted by RANDLOVER

Protection Coordination of Circuit Breakers - GSES

I suspect the scenario described above is pro'ly due to a poor earth, so the full short circuit current wasn't able to flow and rupture the fuse. Although in a 12 volt automotive system the battery may not be able to produce a fault current for long enough to operate a fuse that is only mildly overloaded, not so in a HV generator system that can produce massive currents.

People also confuse overload, over current and short circuit, from the above graph it can be seen that a mild overload can be permitted for up to 4 hours, but as the overload value increases the trip time shortens.

Yes - High resistance in the earth is often overlooked and very few Electricians consider fault currents or fault loop impedance when calculating cable size and breakers either. In the home environment it's always just been 'Stick in some 2.5 and a 20 amp breaker' and in the commercial & industrial field it isn't much better at times from what I experience even in large installations of a few thousand amps - this conversation only really comes up when I'm speaking to Engineers and Inspectors - although explaining fault current paths in generators to some Inspectors is like pulling teeth. Driving an earth stake in certain situations can actually increase fault trip times as well with gens, but this is also poorly understood by most even though it is covered in the Regs.

**theelms66** · 7th October 2020, 09:17 AM

Originally Posted by Gav 110

Is there not an Australian Standard for auto electrical work
Or is it just not policed as much as a 240/415 electrician????

Seriously! You think they would police brakes before electrical.

**Old Farang** · 7th October 2020, 12:51 PM

Originally Posted by scarry

Until it snaps off,then there is no more length on the wire because it was cut off too short to start with by another sparkie during the original install.
Happens all the time.

Multistrand is the go,and the only cable used on mechanical services gear.

In another life I had a contractors licence in WA and used to do Government work. If any installation work was required it was laid down in the work order that stranded cable had to be used.

**Gav 110** · 7th October 2020, 07:30 PM

Originally Posted by theelms66

Seriously! You think they would police brakes before electrical.

Undersized wires create fires
Use your gears to slow down if your brakes don’t work (had to do it many times in my younger years)
It’s a lot harder to put a fire out under the dash whilst driving (been there too)

Thread: One for the sparkies

Thread Tools

Tags for this Thread

Bookmarks

Bookmarks

Posting Permissions