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HARESHNN
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Join Date: Oct 2011
Posts: 1

Power Cable

10/29/2011 5:25 AM

Dear users,

Can anybody tell me what type of power cable I should use if I have to run a 75 HP pump undersea.

Thanks
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redfred
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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
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#1

Re: Power Cable

10/29/2011 8:03 AM

I recommend that you hire an electrician to do this installation. 75 HP is a significant amount of power and salt water has so many ways that it will corrode any exposed metal that you need someone familiar with local wiring codes. They will also be able to see the myriad of other details that your not telling us like length of run under water, couplings, flexing requirement of cable, etc. There will also likely be a safety and liability factor here that only a licensed individual can properly address with authority. Any advice you get from a public web page (CR4 included) will have no authority on how to safely power an undersea pump.

Now if you don't understand why your electrician wishes to do something a certain way, then we can gladly help you understand the reasoning or standard rule they are following.

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Snave
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Join Date: Oct 2007
Location: S. California, USA
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#6
In reply to #1

Re: Power Cable

10/30/2011 2:22 PM

You did not say how long the cable run would be. Under sea could be a few feet or thousands of feet. If it is a long run, voltage drop rather than heating will set the wire gauge. The current carrying capacity of wire is normally sized to keep cool and within the temperature rating of the insulation. For a submerged cable, the sea water will do a good job of dissipating the heat.

If it is a long run, you may consider adding transformers at both ends of the transmission line so that voltage on the cable is high and the current low so that the size of the conductors in this very expensive undersea cable can be reduce.
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lyn
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Join Date: Oct 2008
Posts: 42355
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#2

Re: Power Cable

10/29/2011 10:19 AM

75 HP roughly equals 100kW. That's a lot of power to hook up. Hire an electrician who is experienced with large, underwater motors.

Otherwise, you will have problems.
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pnaban
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Join Date: Jun 2010
Location: srilanka
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#4
In reply to #2

Re: Power Cable

10/29/2011 11:34 PM

75hp is approximately >50kW. If you write to supplier of pump they will supply with suitable cable

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msamad
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Join Date: Feb 2009
Location: Houston, USA
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#3

Re: Power Cable

10/29/2011 12:17 PM

Cable type:

Subsea cables must be resistant to corrosion and abrasion caused by sea currents, waves as well as human and vegetation attack. It also must be capable of offering a maximum of efficiency over long distances. Since subsea cable installation is safety critical, very expensive and long length, you should engage experts in your project. Here is some link that may help:

http://www.drakamog.com/pdf/subsea-brochure.pdf

http://www05.abb.com/global/scot/scot245.nsf/veritydisplay/b659d8705a55706ec1257287002a6ef8/$file/subsea%20power%20cables.pdf

Cable size:

There are many factors need to be considered for the cable selection. See this thread for details:

http://cr4.globalspec.com/thread/57342/Cable-Selection-as-per-Theory-Calculation. Here is a rough calculation for the cable size (per NEC):

Per NEC table 430.52, the full load current for 75 HP (56 KW), 460V motor = 96 A

For continuous duty motor, required ampacity is 96 x 1.25 = 120 A.

You need a cable of size of with minimum amapcity 120 A.

Per NEC table 310.16, the cable size for 120 A minimum at 75⁰ C (167⁰ F) for 30⁰ C (86⁰ F) ambient temperature is 1 AWG. Since there are other factors as described in the above thread required to be considered, it is safe to select the next higher size cable 1/0 AWG (ampacity 150 A).

This is again a rough calculation; however the subsea cable is generally of long length and the distance is one of the dominating factors that may lead you to go for the higher size cable.

- MS

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Bazzer Englander
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Join Date: Aug 2007
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#5

Re: Power Cable

10/30/2011 9:24 AM

Get a long shaft pump so all the electrics are out of the water.

Bazzer

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sriram1988
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Join Date: Sep 2011
Posts: 47
Good Answers: 2
#7

Re: Power Cable

10/30/2011 11:10 PM

Mr.MsaMad said correctly that various factors are to be considered in choosing the cable.If you want immediate answers you can try this tool with caution.

This is only for cable sizing NOT for cable type selection.

http://www.cablesizer.com

Always consult can experience electrical engineer for these works.
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Rockyscience
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Join Date: Sep 2011
Location: Near the New Madrid Fault. USA
Posts: 269
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#8

Re: Power Cable

10/31/2011 3:24 PM

Hi, If it is more than 36 feet below the surface a hydraulic motor may be cheaper..

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brich
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Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
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#9

Re: Power Cable

11/28/2011 12:35 AM

would you be thinking about an ESP (electrical submersible pump)?

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Bazzer Englander (1); brich (1); lyn (1); msamad (1); pnaban (1); redfred (1); Rockyscience (1); Snave (1); sriram1988 (1)

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