Can someone check my wiring maths please?

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IanFiTheDwarf said:
PFC's have naff all to do with it. i hope you are not an electrician, I am and have been an auto electrician as well and a plant engineer, avionics engineer and an authorizing engineer for electrical installations.

house and industrial wiring has a whole load of calculations to be done to determine if an installation (cable, fuse ect) is safe. when it comes to wiring in cars a lot of assumptions are made and all the calculations have been done and factored into the ratings of the cable and fuses already so a 10A cable must be protected by a 10A or less fuse and that is that. if your car was to catch fire after you did some wiring and you had some 10A cable protected by a 25A fuse do you think your insurance will pay out?
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PFC has everything to do with it... otherwise we would be wiring ring mains in 70mm cable to deal with fault currents wouldn't we!
Take a look at the wiring loom in your car and tell me how many 2.5mm and above cables you can find - other than main battery connections and starter motor!

I ain't getting into a dick measuring contest though, so we'll leave the OP to make his own mind up shall we...
 
lerk said:
PFC has everything to do with it... otherwise we would be wiring ring mains in 70mm cable to deal with fault currents wouldn't we!
Take a look at the wiring loom in your car and tell me how many 2.5mm and above cables you can find - other than main battery connections and starter motor!

I ain't getting into a dick measuring contest though, so we'll leave the OP to make his own mind up shall we...
Click to expand...

that's just running loads nothing to do with fault conditions which is what your fuse is for.

Power factor only rears its head with inductive loads in ac circuits so no concern in a car and not much concern in the home either as most inductive loads are fairly small.

As long as your cable is rated above the fuse and the fuse above the load then alls well. In domestic wiring you have volt drops in the cables due to length and de-rating due to insulation and disconnect times to worry about but not in a car.
 
PFC = Prospective Fault Current... why would I be talking about Power Factor Correction on a DC Circuit???? :doh:

The PFC for a ring main is hundreds of Amps so by your reckoning we need to fit the 70mm or above cable as it will see the fault current for a few milliseconds, in practice this is not necessary as current ratings for cables are for constant draw of that current.
 
lerk said:
PFC = Prospective Fault Current... why would I be talking about Power Factor Correction on a DC Circuit???? :doh:

The PFC for a ring main is hundreds of Amps so by your reckoning we need to fit the 70mm or above cable as it will see the fault current for a few milliseconds, in practice this is not necessary as current ratings for cables are for constant draw of that current.
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no you have misunderstood me, i agree with you here.
 
so shirley you can then say that any fault current on the cable will be high enough to ensure that the fuse will blow before any damage occurs to the lower rated cable???
 
lerk said:
so shirley you can then say that any fault current on the cable will be high enough to ensure that the fuse will blow before any damage occurs to the lower rated cable???
Click to expand...


in domestic wiring yes but in a car i dought it. 10A cable and 25A fuse is a long way apart and blade fuses are ****e
 
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