Correct cable sizing?

flyers

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Join Date
Sep 2006
Location
Amk
Posts
295
Hi guys,

I'm trying to learn the electrical wiring in a panel, I'd like to ask anyone here has a good link for me read up on how to calculate the correct cable sizing like for example: 415V AC, 3 phase, 65Amp?


Thanks.
 
I have used both #4 and #6.

I would use #4 more for continuous duty, in a tight location. Various charts show 85-105 amps depending on insulation and installation.

I have used #6 in a "free air" application often, 'specially in intermittent or light duty. Many charts show 60-65 amps, and a range of50-70, again, depending on insulation and installation.

I gnerally go by the NEC (National Electric Code) charts, and past experience.

There are plenty of charts around, 'specially on Google..

I found a site with a wire size calculator, and it said to use "#14 Minimum"! "NOT HARDLY!!!

Here's a "LINK" to an outstanding site for "ALL THINGS" related to "Industrial Electrical and Maintenance". b With a "SPECIAL THANKS" to Ron for his tremendous efforts in putting the site up and maintaining it!
 
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hi 2 all

as far as i know

v=I(R COS THETA +X SIN THETHA)= IZ
I LOAD CURRENT
THETHA POWER FACTOR
R AND X U WILL GET FROM TABLE 9 NEC

THIS WILL BE MAXIMUM ALLOWABLE VOLTAGE DROP

MOST CONSULTANCTY ALLOW 5 PERCENT DROP

IF VOLTAGE DROP IS MORE THAN 5 OR 3 PERCENT SELECT THE NEXT AVAILABLE CABLE SIZE


REGARDS

JOS
 
The classic texts for electricians are a series of books by a guy named "Stallcup." Look him up on Amazon; if you're going to be doing wiring design very often, get his books on electrical design and electrical calculations. They're a good starting point for industrial wiring.
 
Wow, just realized, I do not have a anything on wire sizes. I know what my next project will be.

The thing about wiring is there are variables i.e. is the wire copper or aluminum, wire length, number of conductors in conduit etc etc. It could be AWG 4, 6, or 8 depending on.....

Whatever I provide will probably be applicable to NEC regulations which should pretty much be same as Canada and European for the most part. What you need to do is find out what regulations are followed in your country and obtain the wiring tables.
 
see if this is any use to you.remember this is Australian standards so current carrying capacity may vary from counrty to country.
 
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Cable size depends on installation as well as current, here is an extract from our design spreadsheets. This for tri-rated equipment wire that we generally use in our panels.

For field wiring we use AMTEK to calculate cable sizes.
 
JohnW said:
Cable size depends on installation as well as current, here is an extract from our design spreadsheets. This for tri-rated equipment wire that we generally use in our panels.

For field wiring we use AMTEK to calculate cable sizes.

HI john, i'm new to this sizing calculation all, may I ask the number in K2 column, 1 - 9, 12, 16 & 20? Is that the number mentioned by CaseyK in the early of the post? Thx..
 
The numbers 1 - 9 etc are the number of cables laid side-by-side. K2 is the derating constant for a single layer of cable. The values in the boxes are the maximum current for that size cable in that configuration.

The full set of tables goes up to I think 5 layers of 20 cables which would be typical of control cabling in trunking in a panel for instance.

These tables are generally for our own use in panel design and have been calculated by myself, so don't take them as gospel. I will try and post the formula tomorrow.
 
What/ are there national standards for your location?

See http://www.plctalk.net/qanda/showthread.php?t=29627 where sizing is done per NEC in the USA. If I were doing this for a continious duty application, 3 wires in conduit, no temperature derating, 90C wire, 65A x 125% = 81.25A so per NEC Table 310.16 I would use #4 (good up to 95A) . For free air, Table 310.17 leads to #6 (good up to 105A)
 
To size any electrical feed you first need to know the external earth loop impedance and the prospective fault current at the source you intend to feed from.

In most installations nowadays voltdrop is a bigger factor in sizing a cable than Ib. Therefore you also should know what percentage voltdrop has been allowed in the cabling to the source you are going feed your panel from!

Regards

Paul.
 

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