A quick question about current carrying capacity tables

[Chri5]

Can somebody tell me what the r x and z values mean in the volt drop columns for the bigger cables in table 4D1A of the regs. I never use anything this big so I've never had to worry about it.

Also is there a table giving the resistance of different cable sizes per meter. I can't see it if there is.

Cheers

 

[kerching]

r = resistance

x = reactance

z = sq root [r ssquared + x squared]

x has capacitive and inductive components and these are amongst other things a function of frequency or the reciprocal of same sort of looks like 2: crbvcurbvubruvbruvb fl and 1/ [ 2: crbvcurbvubruvbruvb fC ]

how I wish I could do formulae and not have to do it longhand............ :coat

edit....actually looking at that it seems wrong but it is late so I will leave it................ :coat

 

[Technician]

Following on from Kerching; It is a method of "factoring in" the power

factor (Cos phi) for larger conductor sizes. Used in large installations.

Look in the OSG Old reference Table 9A page 166.

All resistances per metre run for single conductors and as (R1 + R2)

calculations are there. That is all you need; all that about r x and

z is waaaaay outside your scope.

HTH

 

[Chri5]

Thanks for that the both of you. I think I'll take technicians advice on the r x and z values for now :Salute

 

[Technician]

Chri5...that is one of the most useful tables you or I would

ever use. I have found it invaluable for estimating reads in

circuits to make assessment of what (R1 + R2) might be.

I have taken a few basic measurements, calculated an

estimated read, taken one and then found the faults and bad

installation practices that led to the high read. Following

repairs, I had the actual read to within 10% of my estimated

one.

Best of Luck.

 

[Sidewinder]

Technician,

Speak for yourself, but some of us do need to consider reactance in our work!

However, it is doubtful that you will ever get the correct values from your client, equipment supplier etc.!

R1 & R2 measurements are made with d.c. so the reactance values are negligible, it is only when you do a Zs reading, or the cable is operating will these really come into play.

 

[Technician]

Sidewinder...Knew you would come in with that!

:slap

 

[Chri5]

Thanks for that. I always turn to the regs book first for some reason but I need to start making more use of the osg. It's all in there if you look.

 

[Technician]

Canoeboy...that's interesting...If the capacitance increases with

conductor length, how might that affect the assessment of

conductor size, if at all?

I have met a couple of guys who did aircraft work and because of

the 400 Hz supplies, their conductor calculations were VERY

different from ours.