Re: How much current safe for 30m extension?

ehsjr_at_bellatlantic.net
Date: 02/12/05 

Date: Sat, 12 Feb 2005 20:27:29 GMT

Watson A.Name - "Watt Sun, the Dark Remover" wrote:

>"Sammo" <noone@no-where.com> wrote in message
>news:95FB7BA1F25441A7D4@130.133.1.4...
>
>
>>I am in the UK (so mains voltage is about 230V or 240V).
>>
>>
>
>I'm in the U.S. and this gives me a flashback on what I was thinking
>about trying a few months ago. We have a PBX at work that's on 48V
>batteries, but the batteries are 9 yrs old and need replacing. They
>cost a bundle so I thought it would be possible to run a power cable
>underground to the big UPS we have in our computer room. Problem is
>that the PBX's rectifier takes 30A max at 120VAC, or about 3.6kW. And
>the distance between is about 1300 feet or about 400m.
>
>I would guess that the UPS output should go into a transformer and come
>out 480VAC, so the cable losses would be minimized. Then another transf
>on the PBX end to bring it back to 120VAC.
>
Hmmm... if you do it, just connect the PBX directly to the
480 volts. Just think how much faster the phone calls will
be at 480 vs 48! :-)

I think installing a half mile of # 4 might be "politically" cost
prohibitive, regardless of the technical merits. And I doubt
it would be a good financial solution. How many times
can you replace the batteries for the cost of digging a
1/4 mile trench, and installing conduit, cable, fittings,
transformers, etc ?

Ed

> But should I expect to have
>a max loss of 5% at max current, or what? I think I came up with 4GA
>cable, but at 480VAC, I'm guessing that it would have to be special
>insulated underground cable.
>
>Someday I'll have to ask one of the electricians that work on our HV
>stuff. We have 4160VAC underground around campus but that's all
>specialized switchgear, etc.
>
>
>
>>I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
>>rated at 10 Amps. So the nominal power rating would be about 2,400
>>Watts. (Link to tech reference for the cable is below.)
>>
>>Presumably the current carrying capacity or power delivery
>>capability of the unwound 30m length unwound is going to be a bit
>>less than 10 Amps/2,400 Watts due to losses along the length of the
>>cable itself.
>>
>>Is the reduction in current/power carrying capability significant?
>>If so, then is there a rough guideline figure for available
>>current/power which I can use?
>>
>>If I take *two* of these 30m reels then I can join them with the
>>standard UK 13 Amp plug and socket supplied on the reels. This gives
>>me an overall length of 60m. Taking into account losses, what would
>>be the current carrying or power delivery carrying capability of the
>>60m length if all the 60m cable is unwound?
>>
>>Thanks for any info.
>>Sammo
>>
>>
>>Technical reference for the cable is HAR type H05VV-F3 x 1.00 mm2 -
>>(details at http://tinyurl.com/7y5xx)
>>
>>
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