insulation resistance

[snowplough]

Hi GUYS,

Can any of you guys tell me what happens to the I.R reading if you increase the c.s.a of a cable,
and if cables run in paralell?

Is it same as resistance where it decreases as the c.s.a increases etc.

Many Thanks

Locket

 

[pushrod]

Increase the csa of cable slight decrease in IR. (might not be very noticeable)
Cables run in parallel will decrease IR.


edit : Insulation resistance will not always mimic resistance. eg increasing the length of a circuit will increase its resistance but will decrease its insulation resistance.

If you are increasing the area of the insulation around the cable you are increasing the area through which current will leak ie decreasing the insulation resistance.

 

[Adam W]

How would an increase in csa decrease IR? Surely if it's the same insulation type it would give a similar reading?
Running cables in parallel would basically halve the reading provided they're installed the same way.

 

[pushrod]

How would an increase in csa decrease IR? Surely if it's the same insulation type it would give a similar reading?
Running cables in parallel would basically halve the reading provided they're installed the same way.

If you increase the csa of a cable then you must be increasing the outer area of the encasing insulation so theoretically you would have more area for the current to leak through. Just going to the next csa up of cable size and the difference would be very small and possibly not even be measurable especially if it was already a >299Ω reading for example.

edit -
1/Rt = 1/R1 + 1R2
is the formula for calculating resistances and insulation resistances in parallel

 

[snowplough]

Hi Pushrod ,
So you are saying that if you increase the thickness of insulation around a condutor say double the insulation, then the insulation resistance will
decrease when you would think it would increase even more, very interesting i need to get my head around that .

Many Thanks for replying

Locket

 

[pushrod]

Hi Pushrod ,
So you are saying that if you increase the thickness of insulation around a condutor say double the insulation, then the insulation resistance will
decrease when you would think it would increase even more, very interesting i need to get my head around that .

Many Thanks for replying

Locket

No, sorry haven't explained it clearly enough . If a cylinder (the copper wire) has a larger diameter then its circumference will increase as well. Therefore it will take more insulation to go around it. Therefore more area of insulation to "leak" the current through and so IR goes down

If you increase the thickness of the insulation on the same size conductor then it is more difficult for the current to get through so the insulation resistance would increase.

 

[snowplough]

Cheers Pushrod,

Your Saying a bigger circumference leaves more leackage current to get through , so I.R decreases unless you then thicken the insulation again.

regards

locket

 

[pushrod]

Cheers Pushrod,

Your Saying a bigger circumference leaves more leackage current to get through , so I.R decreases unless you then thicken the insulation again.

regards

locket

I am. No problem

 

[i=p/u]

10m of 1.5mm and 10m of 6mm which will have higher reading on isulation resistance, 1.5mm because less to loose.

bidoink!!!