A few Electrical Questions Please?

[Dougal]

1) Where or when should 'slow blow' fuses be used in place of standard or 'fast blow' items?
2) Apart from max ratings, are there any specific reasons for using one fuse type over another? I mean for example the use of either Midi, Mega, ANL or Trips ?
3) Can current wiring be accurately measured to check for correct sizes for each situation?

 

[AngusMcDoon]

1) Where or when should 'slow blow' fuses be used in place of standard or 'fast blow' items?
2) Apart from max ratings, are there any specific reasons for using one fuse type over another? I mean for example the use of either Midi, Mega, ANL or Trips ?
3) Can current wiring be accurately measured to check for correct sizes for each situation?

1) Where the circuit supplies a device that takes a large initial surge current. Fridge, for example.
2) Not that I know.
3) Only by stripping the insulation off and measuring the core diameter with a caliper.

 

[Dougal]

1) Where the circuit supplies a device that takes a large initial surge current. Fridge, for example.
2) Not that I know.
3) Only by stripping the insulation off and measuring the core diameter with a caliper.

Re number3. I have gauges aboard. No doubt then, there's a table that that will tell me actual sizes vs wire spec?

 

[nigelmercier]

Sometimes the size is marked on the cable. If not, as AngusMcDoon says, strip the insulation and measure the diameter of filament in the core (d) and count the filaments .

The wire size is n x π x (d/2)² or for a quick approximation, 0.8 x n x d²

 

[Lon nan Gruagach]

Sometimes the size is marked on the cable. If not, as AngusMcDoon says, strip the insulation and measure the diameter of filament in the core (d) and count the filaments .

The wire size is n x π x (d/2)² or for a quick approximation, 0.8 x n x d²

You really know how to have fun...

 

[VicS]

Sometimes the size is marked on the cable. If not, as AngusMcDoon says, strip the insulation and measure the diameter of filament in the core (d) and count the filaments .

The wire size is n x π x (d/2)² or for a quick approximation, 0.8 x n x d²

You really know how to have fun...

Or without sitting there like a stuffed idiot trying to count the strands 0.196 x D² x π where D is the overall diameter of the conductors.,

 

[nigelmercier]

Or without sitting there like a stuffed idiot trying to count the strands 0.196 x D² x π where D is the overall diameter of the conductors.,

Yes, that would be easier with more than 30 strands, and something I didn't know, thank you.

[Later] Hmmm... My formula of 0.8 x n x d² comes from the fact that π/(2²) is 0.785
0.196 x 4 is 0.784, but there is still a π multiplier. I assumed the 0.196 took account of the tessellation, and the 1/(2²)
Confused, or is this a coincidence?

 

[<152587>]

1) Where or when should 'slow blow' fuses be used in place of standard or 'fast blow' items?
2) Apart from max ratings, are there any specific reasons for using one fuse type over another? I mean for example the use of either Midi, Mega, ANL or Trips ?
3) Can current wiring be accurately measured to check for correct sizes for each situation?

2) it is a matter of horses for courses, for instance the post size on a midi fuse is smaller than a mega or an ANL so the correct size of cable matched to the post dia. Another consideration is ignition protection, ANL fuses are encased in ceramic with a mica window providing containment of the link combustion in event of blow. Some cartridge fuses were sand filled for ignition protection.

trips provide a method of a relative quick reset compared to finding the spanner and spare fuse. I usually specify trips on critical gear where speed is of the essence to recover control of the vessel

 

[VicS]

Yes, that would be easier with more than 30 strands, and something I didn't know, thank you.

[Later] Hmmm... My formula of 0.8 x n x d² comes from the fact that π/(2²) is 0.785
0.196 x 4 is 0.784, but there is still a π multiplier. I assumed the 0.196 took account of the tessellation, and the 1/(2²)
Confused, or is this a coincidence?

just a coincidence i think.

 

[Dougal]

Great stuff - thanks guys. I love this forum;-) You are, as ever, a font of errrrr..... ;-)
Seriously, thanks. much appreciated