Previous in Forum: "Photonic Fence" Laser Wall Mosquito Defense   Next in Forum: Power Consumption of Geyser
Close
Close
Close
11 comments
Rate Comments: Nested
Participant

Join Date: Jul 2013
Posts: 2

3 Phase Power Supply Cable

07/15/2013 6:42 AM

Hi

I am looking to install a 4 core SWA (Steel Wire Armoured )cable which is to carry in excess of 400 amps. Due to the physical size of the cable I wondered if I could run single cores with double insulation, which would make it alot easier to handle

The cable is to be layed in a duct for some of the run and in a sand bed for the rest.

I have been advised that I cannot run singles but cannot find anything in the IEE regulations 17th edition.

The application is being installed in the UK.

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21017
Good Answers: 795
#1

Re: 3 Phase power supply cable

07/15/2013 6:49 AM

Does BS 7671 say anything about it?

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Participant

Join Date: Jul 2013
Posts: 2
#2
In reply to #1

Re: 3 Phase power supply cable

07/15/2013 6:52 AM

Hi

Thanks for replying BS7671 is the 17th edition that I have been reading and I cannot find anything in it.

Regards

James Brown

Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21017
Good Answers: 795
#3
In reply to #2

Re: 3 Phase power supply cable

07/15/2013 7:04 AM

I'm surprised that there wouldn't be anything. There might be some criteria for arrangement and spacing between separate cables, as well as moisture resistance in the sand bed. Some capacitance issues could also apply.

__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#11
In reply to #2

Re: 3 Phase power supply cable

07/16/2013 7:26 AM

Read again. I've got the page in front of me.

__________________
The reports of my death are greatly exaggerated.
Register to Reply
Guru

Join Date: Oct 2012
Location: 100 miles North from the World Center
Posts: 879
Good Answers: 42
#4

Re: 3 Phase power supply cable

07/15/2013 8:43 AM

In my opinion both BS 5467 and BS6724 recommend AWA (Non magnetic Aluminium wire for single cores cable].Only for 2 and more cores SWA.

It is not recommended to run a single-core cable in a steel conduit also, since the eddy current induced in the conduit will heat the conduit and will raise the cable temperature in turn.

__________________
Julius
Register to Reply
Guru

Join Date: Feb 2010
Posts: 1013
Good Answers: 36
#9
In reply to #4

Re: 3 Phase power supply cable

07/16/2013 5:19 AM

He will be runing the 3 single cores together in the metallic conduit, therefore the currents will cancel each other regarding the eddy currents.

Register to Reply
Guru
United States - Member - New Member

Join Date: Jun 2008
Location: Alabama
Posts: 1604
Good Answers: 63
#5

Re: 3 Phase Power Supply Cable

07/15/2013 1:07 PM

You should not run single cables in steel conduit but if you install all 3 phase and neutral in the conduit you will not have the problem mentioned in post#4

Register to Reply
Commentator

Join Date: May 2013
Posts: 86
Good Answers: 2
#6

Re: 3 Phase Power Supply Cable

07/15/2013 1:59 PM

Alternately you can use 2 runs of smaller size SWA cable to Manage the installation difficulties. You will have to apply corrective derating factors which you will find in a good manual or from cable manufacturer. You cannot use unarmoured cables directly buried in sand bed, but have to provide some mechanical protection like cable duct etc against inadvertent damage. You can of course run all 3 phase unarmoured wires and neutral in the same metal cable tray if required. This input is subject to conforming to your local codes with usual disclaimers.

Register to Reply
Power-User

Join Date: May 2010
Posts: 146
Good Answers: 2
#7

Re: 3 Phase Power Supply Cable

07/16/2013 12:29 AM

300mm2 cable is suitable to carry 400 A, but again it depends the voltage drop due to the length. In that case you have to calculate the voltage drop and select 2 runs of cable.

Register to Reply
Guru
Engineering Fields - Mechanical Engineering - New Member

Join Date: May 2008
Location: CHENNAI, TAMIL NADU, INDIA.
Posts: 1851
Good Answers: 65
#8

Re: 3 Phase Power Supply Cable

07/16/2013 5:15 AM

Dear Mr.JamesBrown,

If you run single core (instead of 3 core) Inductance problem is to be tackled, that is why 3 core - which will annel the Inductance - is used.

You can think of 2 runs or 3 runs of 3 core (or 3.5 core if Neutral is required) for deciding the cable size of each run, which needs de-rating factor etc. is to be accounted.

DHAYANANDHAN.S

Register to Reply
Guru

Join Date: Oct 2012
Location: 100 miles North from the World Center
Posts: 879
Good Answers: 42
#10

Re: 3 Phase Power Supply Cable

07/16/2013 6:02 AM

As I already said: no such thing SWA[Steel Wire Armoured] single core cable but only AWA[Aluminum Wire Armoured] single core cable and no interdiction -except as mentioned above-to use it in a duct or directly buried.

Some problems will arise as: armour losses-by eddy current and by circulating current if the armour is grounded[earthed] at both ends.If it is grounded in a single point another problem will be the build-up induced voltage. In a three-phase cable it is not such a problem.

__________________
Julius
Register to Reply
Register to Reply 11 comments
Copy to Clipboard

Users who posted comments:

7anoter4 (2); Alanvaderi (1); dhayanandhan (1); James Brown (1); LAA_Lucke (1); Pattabhiraman (1); TonyS (1); Tornado (2); wareagle (1)

Previous in Forum: "Photonic Fence" Laser Wall Mosquito Defense   Next in Forum: Power Consumption of Geyser

Advertisement