CR4® - The Engineer's Place for News and Discussion®


Previous in Forum: Piping QA/QC   Next in Forum: Kelvin Double Bridge for Resistance Measurement
Close
Close
Close
25 comments
Member

Join Date: Jul 2017
Posts: 8

Current Carrying-Capacity of Cables

07/05/2017 7:23 AM

Dear All,

How to calculate manually the maximum current carrying capacity of single core 10 sqmm cable,without knowing the power (watts)?

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru
Engineering Fields - Electrical Engineering - Been there, done that, still doing it. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 12217
Good Answers: 774
#1

Re: Current carrying capacity of cables

07/05/2017 7:43 AM

There really is not a maximum current carrying capacity for a conductor without specifying many additional attributes; conductor metal/alloy, insulation, heat dissipation, ambient temperature range, cable tension, and many more. This is why local cabling standards with lookup tables are actually based on past incidents and not theoretical calculations. Sometimes a nominal formula for a given set conditions is made but this is still based on past experiences.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#2

Re: Current carrying capacity of cables

07/05/2017 8:14 AM

Easy. Follow the protocols in British Standard 7671.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#3
In reply to #2

Re: Current carrying capacity of cables

07/05/2017 8:33 AM

Anyway, that's an Electrician's job.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Apr 2010
Posts: 5747
Good Answers: 576
#4

Re: Current Carrying Capacity of Cables

07/05/2017 9:23 AM
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13438
Good Answers: 152
#5

Re: Current Carrying Capacity of Cables

07/05/2017 9:39 AM

The simple answer: IF you don't have the local code, you don't.

You did not specify the single core 10 mm2 cable as copper, aluminum, silver, gold, iron, or other metal. It could be anything. BTW, the local code where you are will only apply to domestic or industrial applications where copper is the only allowed conductor in the code.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru

Join Date: Mar 2007
Location: at the beach in Florida
Posts: 19235
Good Answers: 1125
#6

Re: Current Carrying Capacity of Cables

07/05/2017 11:22 AM

..."The ampacity of a conductor depends on:

  • its insulation temperature rating;
  • the electrical resistance of the conductor material;
  • frequency of the current, in the case of alternating current;
  • ability to dissipate heat, which depends on conductor geometry and its surroundings;
  • ambient temperature.

All common electrical conductors have some resistance to the flow of electricity. Electric current flowing through them causes voltage drop and power dissipation, which heats conductors. Copper or aluminum can conduct a large amount of current without damage, but long before conductor damage, insulation would, typically, be damaged by the resultant heat.

Ampacity rating is normally for continuous current, and short periods of overcurrent occur without harm in most cabling systems. The acceptable magnitude and duration of overcurrent is a more complex topic than ampacity."...

https://en.wikipedia.org/wiki/Ampacity

__________________
Life is like riding a bicycle. To keep your balance you must keep moving. A.E.
Register to Reply Score 1 for Good Answer
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 19979
Good Answers: 749
#7

Re: Current Carrying Capacity of Cables

07/05/2017 2:51 PM

This is not ordinarily calculated; it is usually looked up in an appropriate table.

Not everything is calculated, anyway; some things are measured instead.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Power-User

Join Date: Sep 2016
Location: SPAIN
Posts: 163
Good Answers: 7
#8

Re: Current Carrying Capacity of Cables

07/06/2017 12:57 AM

Adding the watts is what got me confused.

Current carrying capacity of a cable depends on the current. You might want to know that adding information about the power is not helpful.

What got me even more confused is that you are measuring the power output of a 10m2 in watts. Considering that current carrying capacity is about 100A, and your load is at least 24V (minimum voltage for power applications in the industrial sector), you would be having at least a few kW. Am I wrong?

__________________
Building the future!
Register to Reply
Member

Join Date: Jul 2017
Posts: 8
#9

Re: Current Carrying Capacity of Cables

07/06/2017 2:34 AM

Hi all,

Am new for cable manufacturing field,clients asking about what is the maximum current carrying capacities for cables for example 10 mm2.here we followed BS,BSEN/IEC standards,i can use BS 7671 for knowing the details,but how its came what are the parameters they used to find out the amps.Is any particular formula they used ,what are the factors they used.I know only resistance of that cable and length of the cable.am confused to clarify this to our clients.

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#10
In reply to #9

Re: Current Carrying Capacity of Cables

07/06/2017 3:05 AM

The standard, like many others, is based upon current (sorry for the pun) best practice, which is based upon experience. Any formulae therein are after the facts, and not before them.

It is not the role of the cable manufacturer to select the right size cable for the Client's needs; it is the role of the Qualified Electrician actually doing the installation to do this. After all, the Electrician can see the job and will be certifying a correctly installed and tested installation, and not the cable manufacturer!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Power-User

Join Date: Sep 2016
Location: SPAIN
Posts: 163
Good Answers: 7
#13
In reply to #9

Re: Current Carrying Capacity of Cables

07/06/2017 7:33 AM

Let's make this easier. Can you provide a datasheet of the cable? Or maybe your reference, as a manufacturer?

__________________
Building the future!
Register to Reply
Member

Join Date: Jul 2017
Posts: 8
#14
In reply to #13

Re: Current Carrying Capacity of Cables

07/06/2017 8:26 AM

Hi,

Cable data :1Core x 10 mm2 stranded copper conductor ,pvc insulation 70 degree,Conductor DC resistance 1.83 ohm/km,length of the cable-1 km.Now this 10 mm2 pvc insulated copper cable can carry how many amps?installed in free air,ambient temperature 45 degree Celsius. This parameters is enough ?

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#19
In reply to #14

Re: Current Carrying Capacity of Cables

07/07/2017 3:48 AM

That information is insufficient to use as the input to the protocols in British Standard 7671 and achieve compliance.

The missing information is the method of installation, the style of over-current protection device and its characteristics, the permissible voltage drop on the circuit and the length of the run. All of these things are in the domain of the qualified Electrician who selects and installs it. The cable supplier (still) cannot be expected to know these things, as they are installation-specific.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Member

Join Date: Jul 2017
Posts: 8
#15
In reply to #13

Re: Current Carrying Capacity of Cables

07/06/2017 8:28 AM

Hi,

Cable data :1Core x 10 mm2 stranded copper conductor ,pvc insulation 70 degree,Conductor DC resistance 1.83 ohm/km,length of the cable-1 km.Now this 10 mm2 pvc insulated copper cable can carry how many amps?installed in free air,ambient temperature 45 degree Celsius. This parameters is enough ?

Register to Reply
Power-User

Join Date: Sep 2016
Location: SPAIN
Posts: 163
Good Answers: 7
#16
In reply to #15

Re: Current Carrying Capacity of Cables

07/06/2017 9:08 AM

According to this, you would get 73A in Normal Conditions. If you do not know how to use derating coefficients, say about 50%, about 40A.

I hope the forum does not punish me for teaching you how to google "Current carrying capacity cable".

__________________
Building the future!
Register to Reply Score 1 for Good Answer
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#22
In reply to #16

Re: Current Carrying Capacity of Cables

07/07/2017 4:34 AM

Caution: that is not the cable supplier's job. It is the installing Electrician's job.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Power-User

Join Date: Sep 2016
Location: SPAIN
Posts: 163
Good Answers: 7
#24
In reply to #22

Re: Current Carrying Capacity of Cables

07/07/2017 5:25 AM

I think this is just a business talk between sales department of the supplier and purchasing department of the client, both non technical.

Maybe the product is stored in a warehouse, codified in a database, and whenever it needs to be used, performance will be evaluated. After all, multiple wires in parallel can be used in case only one does not have enough current carrying capacity.

I seriously doubt a salesman will be making any electrical installation.

__________________
Building the future!
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#25
In reply to #24

Re: Current Carrying Capacity of Cables

07/07/2017 5:39 AM

<...doubt....> hope, more like!

The Original Poster needs to consider this: in the event of an incident involving the cable, who gets sued or prosecuted - the Seller or the Installer (rhetorical question - NNTR)?

  • If there is evidence that the Seller recommended the cable size that caused the incident and the Installer followed that recommendation, then the Seller is liable. So it is in the Seller's interests to defer the question to the Installer on liability grounds.
  • If the Installer can warrant, using installation test records, that the installation complied with local codes when it was completed then neither the Seller nor the Installer is liable.

From the Seller's perspective, any query on cable capacity is unanswerable on the basis of liability as the conditions of use are beyond the Seller's control.

Which is where this thread needs to keep going.

<unsubscribes>

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13438
Good Answers: 152
#18
In reply to #15

Re: Current Carrying Capacity of Cables

07/06/2017 1:51 PM

The current your cable can carry is the current that the resistance of the cable (per Km) can handle before it overheats (70 °C or slightly higher) and the insulation fails, as the PVC is the limiting factor. Current will be in amperes.

Power in = current x current x 1.83Ω/km x length (km)

Power out = variable depending on location in conduit, in air, etc.

This is where the applicable standards come into force. These have established by experience how much power a wire can dissipate without overheating and shorting out, or becoming a fire hazard.

If the wire is located buried in metal conduit, the power dissipation possible is higher.

If the wire were somehow enclosed in wood or other heat insulating material, overheating will occur at a much lower heat dissipation.

The code deals with all the likely situations and leaves a window of safety such that fires and shorting out are to be avoided by following the code.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Anonymous Poster #1
#20
In reply to #15

Re: Current Carrying Capacity of Cables

07/07/2017 4:12 AM
Register to Reply
Guru

Join Date: Aug 2010
Location: Melbourne, Australia
Posts: 684
Good Answers: 21
#11

Re: Current Carrying Capacity of Cables

07/06/2017 4:32 AM

look at

https://www.powerstream.com/Wire_Size.htm

Register to Reply
Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1531
Good Answers: 35
#12

Re: Current Carrying Capacity of Cables

07/06/2017 5:00 AM

As others have rightly said, it is the ability to withstand heat that usually governs the maximum current a cable can carry. Having a 50 foot long narrowboat with a 12 volt DC supply, I find the volts drop matters long before the maximum current carrying capacity of a cable takes effect.

__________________
When arguing, remember mud-slinging = lost ground.
Register to Reply
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 13438
Good Answers: 152
#17

Re: Current Carrying Capacity of Cables

07/06/2017 9:30 AM

P=I2R, so one does not ever have to calculate the watts. The resistivity of the copper is a known, and then it is known even better, by the National Electric Code of the United States of America telling you precisely what wire goes with the current carrying demand of a circuit, the length of wire run, etc.

CABLE SIZER

Go ye forth, my son, and learn much from the leaders of our forefathers whom discovered the power electrique' and how to prosper while using it. Do not abuse the power you have been given, or God will let the smoke issue forth from your body, like a billowing volcano, or like the voluminous crap from an over-consuming camel.

Do not let the goat near your electrical cabinets, enclosures, or MCC's, and remember to have a professional (wizard) calculate the energies involved in those cabinets, and advise you about the safe way to approach the cabinet when energized, that it does not become the Ark of the Cabinet.

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26693
Good Answers: 700
#21

Re: Current Carrying Capacity of Cables

07/07/2017 4:15 AM

With all those wonderful links and an active duplicate thread policy, it is now possible to have a CR4 sandpit that is completely free of the monotony of any more cable sizing threads. Phew!

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Guru

Join Date: Jan 2006
Location: Tamworth, UK.
Posts: 1531
Good Answers: 35
#23

Re: Current Carrying Capacity of Cables

07/07/2017 5:23 AM

I imagine manufacturers of electric heater elements know about max current, in their case it is well into the amps range that causes the wire to glow red hot continuously without melting.

Similarly, manufacturers of HRC cartridge fuses must have a good idea of how to exceed the maximum current to ensure they melt quickly at the rated current.

I don't know the formula, but I guess it will include a factor/coefficient of transient time.

__________________
When arguing, remember mud-slinging = lost ground.
Register to Reply
Register to Reply 25 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

Anonymous Poster (1); horace40 (2); Ivanov327950 (4); James Stewart (3); kavin011 (3); PWSlack (7); redfred (1); Rixter (1); SolarEagle (1); Tornado (1); WAWAUS (1)

Previous in Forum: Piping QA/QC   Next in Forum: Kelvin Double Bridge for Resistance Measurement

Advertisement