wire length help

[K8MHZ]

I was going to suggest the voltage drop method until I thought it all the way through.

Such as:

Find the biggest load your circuit breaker can handle and connect the spool in question in series with the load. Now, powering it up should show enough voltage drop do to the math. I forgot to take into consideration that the spool will act like a coil and the impedance won't be purely resistive, and the fact that the spool would turn into a large electromagnet, pulling tools and sharp metal objects toward it at a fairly respectable velocity.

 

[kwired]

I was going to suggest the voltage drop method until I thought it all the way through.

Such as:

Find the biggest load your circuit breaker can handle and connect the spool in question in series with the load. Now, powering it up should show enough voltage drop do to the math. I forgot to take into consideration that the spool will act like a coil and the impedance won't be purely resistive, and the fact that the spool would turn into a large electromagnet, pulling tools and sharp metal objects toward it at a fairly respectable velocity.

It needs an iron core before it will have any significant inductance. If you have a reel with thru bolts holding it together... then I guess you do have some core.

 

[ptonsparky]

I was going to suggest the voltage drop method until I thought it all the way through.

Such as:

Find the biggest load your circuit breaker can handle and connect the spool in question in series with the load. Now, powering it up should show enough voltage drop do to the math. I forgot to take into consideration that the spool will act like a coil and the impedance won't be purely resistive, and the fact that the spool would turn into a large electromagnet, pulling tools and sharp metal objects toward it at a fairly respectable velocity.

Only if you use DC, otherwise the tools don't know of they are coming or going and lay there vibrating with indecision. Or maybe anticipation.

 

[kwired]

I measure 14 and 12 NM and UF cable on 1000 foot reels all the time with digital ohm meter and thermomoter. I have a wire paramater calculator I found online a long time ago. all I need is conductor resistance (to .01 ohms) and temperature and it will calculate length. For best results make sure wire and meter have been in an ambient long enough that everything is same temperature - like overnight in the shop. It is not 100% accurate but it is usually closer than other guesstimate methods. If I wanted to spend more $$ for a very accurate meter that even is accurate in the .001, or .0001 ohm ranges then it may be right on.

I have weighed wire before but never seem to come up very consistant - of course a good scale helps but also costs $$. If you don't know what the reel weighed when full and how much was on it you will not be as accurate either. Comparing to another full reel only works if identical - as in produced at about same time in the same place.

 

[handy10]

Questions on suggested methods:

1. Does not the resistance measurement method require access to both ends of the wire?

2. In the weight method, is not the weight of the empty spool required? Perhaps that can be neglected, but perhaps not.

 

[kwired]

Questions on suggested methods:

1. Does not the resistance measurement method require access to both ends of the wire?

2. In the weight method, is not the weight of the empty spool required? Perhaps that can be neglected, but perhaps not.

Yes to both.

Inside end of conductors or cables on reels is usually brought through a hole in the reel so it is accessible for measuring

 

[tkb]

You could always look to see if the cable is marked with footage marks every foot.
Read the marking on both ends and subtract. Easy as that.

 

[ptonsparky]

Sshhhh.

 

[Cow]

I never see wire marked with footages, only LV cable. It would make sense to do it, one reason, the guys in the supply house could check their measurements when they are doing cuts off a master reel. You'd think the supply houses would be pushing for the wire manufacturers to include footages on ALL wire? Maybe it's not that big of a deal, but I know guys in the field would love it.

 

[kwired]

I never see wire marked with footages, only LV cable. It would make sense to do it, one reason, the guys in the supply house could check their measurements when they are doing cuts off a master reel. You'd think the supply houses would be pushing for the wire manufacturers to include footages on ALL wire? Maybe it's not that big of a deal, but I know guys in the field would love it.

If there is not enough of tail from the inner end of the reel exposed you don't know what the last inside number is. Conductors/cables that do have measurement marks don't necessarily always start at zero (I think).

 

[ptonsparky]

My help noticed last summer that some of the quad URD we were using had footage marks every 3' (I think). Other than that I know communication cable and similar have marks. Not so on single conductors.