| Author |
Message |
Guest
|
 Posted:
Sat Feb 12, 2005 10:26 pm Post subject:
Re: How much current safe for 30m extension? |
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|
Ian Stirling wrote:
| Quote: | In uk.d-i-y Sammo <noone@no-where.com> wrote:
I am in the UK (so mains voltage is about 230V or 240V).
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.)
It's always going to be safe, as it's got a fuse.
I suppose you mean the wire won't melt. Other safety issues |
come into play - the device at the far end may fail due to voltage
drop. In some cases it could conceivably burn. Hardly safe if that
happens. The job of the fuse is to protect the wire from
overcurrent, but there is a lot more to safety. Psooible need for
RCD, protection from damage, supporting the wire etc all may
come into play.
Ed
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Feb 13, 2005 12:40 am Post subject:
Re: How much current safe for 30m extension? |
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"Palindrâ~»me" <sb382638@hotmail.com.invalid> wrote in message
news:376e05F59cjg9U2@individual.net...
| Quote: | Sammo wrote:
I am in the UK (so mains voltage is about 230V or 240V).
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?
30 metres at 10 amperes isn't going to be a problem - so I
have considered just the longer lengths.
Basically, you have two factors to consider:
The first is how hot the wire will get. Now, provided that
the cable is unwound and in the open air, then its length is
immaterial. If you coil the cable up or cover it in
something that restricts the flow of heat from it, that is a
different matter. However, for an unwound cable, the rated
current, say 10 amperes, is the maximum that is allowed due
to heat constraints. Pass more current than this and the
wire will get too hot. Pass a lot more current than this and
the insulation could fail.
The second is the volt drop. Its resistance is about 0.02
ohms per metre - so a 60 m length will have a resistance of
1.2 ohms and will drop 1.2 volts per ampere. A 120 m length
would drop 2.4 volts per ampere.
|
Presumably, you did the calcs with it in mind that the current runs down
the cable 30M and then back up 30M for a total of 60M of conductor...
| Quote: | Now the equipment at the far end of the cable will have a
specified range of input voltage for which it was designed.
You must simply ensure that it gets the minimum rated
voltage, or higher, at the current it draws. This minimum
voltage will depend on the equipment type.
As a rough guide, losing 12 volts in 240 is probably going
to be fine. So, you could use a 60 metre cable at 10 amperes
or 120 metre cable at 5 amperes.
If your load is happier with a lower minimum voltage, say
220 volts, then you could run the 120m cable at about 8
amperes. However, you would still be limited to 10 amperes
for the 60 metre cable, because 10 amperes is the most the
cable should be used to carry, irrespective of length.
Purely resistive loads, like heaters, aren't terribly fussed
if their voltage is a bit low - so you could happily run a
2kW heater at the end of 120 metres of your cable. If you
have a lamp plugged in at the far end, then it will get
noticeably dimmer when the heater is switched on. This isn't
a safety problem, although it might appear so.
Some loads are very fussy about their minimum voltage but
even those should be happy with 10 amperes taken from your
60 metre cable.
Hope that helps.
Sue
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Feb 13, 2005 12:51 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Bob Eager" <rde42@spamcop.net> wrote in message
news:176uZD2KcidF-pn2-pgQf8dbMMKeL@rikki.tavi.co.uk...
| Quote: | On Sat, 12 Feb 2005 12:46:19 UTC, Ian Stirling
root@mauve.demon.co.uk
wrote:
Or for 60m, 8.4*10^-1 ohms, or .84 ohms.
Plus the resistance on the two connections. Not sure whether the earth
fault loop impedance is still OK...
|
Yeah, true. You 220VAC and 240VAC guys think you got it bad, we have
four times as much of a problem here in 120VAC land. ;-)
Those poor souls that put a hundred feet or so of 18GA (about 1mm sq)
extension cord on their weed wackers soon find that not only does it run
slow, but the motor overheats. So we have extension cords that are 16
or 14 gauge, and can handle the extra current. But people are too cheap
to pay double for the heavy duty extension cord, so they end up eating
their money up in burned out motors.
And then when they get tired of doing that, they go out and buy a weed
wacker with the gas engine. This is on the end of a long pole, so the
engine is right up next to their face, so they go deaf from all the
engine noise. And they put the weed wacker in the garage, where the gas
from the tank runs out and catches on fire!
|
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Feb 13, 2005 1:08 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Sammo" <noone@no-where.com> wrote in message
news:95FB7BA1F25441A7D4@130.133.1.4...
| Quote: | 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. 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.
| Quote: | 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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Palindr☻me
Guest
|
| Posted:
Sun Feb 13, 2005 1:52 am Post subject:
Re: How much current safe for 30m extension? |
|
|
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
<snip>
| Quote: | Presumably, you did the calcs with it in mind that the current runs down
the cable 30M and then back up 30M for a total of 60M of conductor...
|
Kind of you to put it that way but it was a case of application of
WNTL*. :). Otherwise known as SMAFN**
--
Sue
*Write Now Think Later
**Saturday Morning after Friday Night |
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Guest
|
| Posted:
Sun Feb 13, 2005 1:52 am Post subject:
Re: How much current safe for 30m extension? |
|
|
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | "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
|
the first logical thought is repair them rather than replace. Lead
acids are often repairable.
Quick repair, doesnt always work:
rinse muck out of cells
fill with new acid
charge, monitor acid conc and adjust as required
This wont fix all cells by any means, but many it will. Those it wont
in some cases may only need replacement plates and acid, which can be
made much cheaper than buying new batts.
Also they can often be run happily at 24v, if not in all cases. If
yours could, it may be that your present cells would do that as is.
What capacity at 48v is it on?
| Quote: | 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.
|
i've no ida how that fits into this
| Quote: | 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. But should I expect to
have
a max loss of 5% at max current, or what?
|
well how much current are you shifting??
And why cant you power your pbx from whatever power source it uses now?
You havent given us nearly enough information.
| Quote: | I think I came up with 4GA
cable, but at 480VAC, I'm guessing that it would have to be special
insulated underground cable.
|
standard uk T&E should do that, but shuold be insulation tested to the
required v first. Costs around £12 a 100m reel, depending on copper
size.
| Quote: | 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.
|
rf transmission co-ax is rated pretty high... and its concentric. T&E's
probably far more practical.
| Quote: | I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
rated at 10 Amps.
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?
|
10A
NT |
|
| Back to top |
|
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Guest
|
| Posted:
Sun Feb 13, 2005 1:52 am Post subject:
Re: How much current safe for 30m extension? |
|
|
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | "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
|
the first logical thought is repair them rather than replace. Lead
acids are often repairable.
Quick repair, doesnt always work:
rinse muck out of cells
fill with new acid
charge, monitor acid conc and adjust as required
This wont fix all cells by any means, but many it will. Those it wont
in some cases may only need replacement plates and acid, which can be
made much cheaper than buying new batts.
Also they can often be run happily at 24v, if not in all cases. If
yours could, it may be that your present cells would do that as is.
What capacity at 48v is it on?
| Quote: | 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.
|
i've no ida how that fits into this
| Quote: | 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. But should I expect to
have
a max loss of 5% at max current, or what?
|
well how much current are you shifting??
And why cant you power your pbx from whatever power source it uses now?
You havent given us nearly enough information.
| Quote: | I think I came up with 4GA
cable, but at 480VAC, I'm guessing that it would have to be special
insulated underground cable.
|
standard uk T&E should do that, but shuold be insulation tested to the
required v first. Costs around £12 a 100m reel, depending on copper
size.
| Quote: | 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.
|
rf transmission co-ax is rated pretty high... and its concentric. T&E's
probably far more practical.
| Quote: | I have a reel of main extension cable made of 3-core 1.0 mm^2 wire
rated at 10 Amps.
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?
|
10A
NT |
|
| Back to top |
|
|
Guest
|
| Posted:
Sun Feb 13, 2005 2:27 am Post subject:
Re: How much current safe for 30m extension? |
|
|
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | "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
| Quote: | 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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John Rumm
Guest
|
| Posted:
Sun Feb 13, 2005 4:12 am Post subject:
Re: How much current safe for 30m extension? |
|
|
ehsjr@bellatlantic.net wrote:
| Quote: | 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 ?
|
For that money you coud buy the PBX a UPS all of its very own!
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/ |
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Mike
Guest
|
| Posted:
Sun Feb 13, 2005 4:56 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:110sjq6kis36k05@corp.supernews.com...
| Quote: | And then when they get tired of doing that, they go out and buy a weed
wacker with the gas engine.
|
One question to somebody presumably residing in the western colonies.
What's a "weed wacker" ? |
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Spehro Pefhany
Guest
|
| Posted:
Sun Feb 13, 2005 5:23 am Post subject:
Re: How much current safe for 30m extension? |
|
|
On Sat, 12 Feb 2005 22:56:43 -0000, the renowned "Mike"
<nospam@bt.com> wrote:
| Quote: |
"Watson A.Name - "Watt Sun, the Dark Remover"" <NOSPAM@dslextreme.com> wrote
in message news:110sjq6kis36k05@corp.supernews.com...
And then when they get tired of doing that, they go out and buy a weed
wacker with the gas engine.
One question to somebody presumably residing in the western colonies.
What's a "weed wacker" ?
|
It's (I think) a trade name that has become a generic term for a gas
or electric (with or without cord) powered lawn trimmer/edger:
http://www.amazon.com/gp/product/images/B00004DTNC/ref=dp_product-image-only_0/103-1119717-3922242?%5Fencoding=UTF8&n=228013
They cut by flailing around the end bit of a spool of thick filament
of extruded nylon, and are thus unlikely to cause serious injury. When
the nylon wears down or breaks off you typically dispense a bit more
by thumping the business end (as it spins) onto a spare bit of grass.
We have one with a cute little gasoline engine. I assume it's a trade
name because when I inquired about one in a B&D outlet store, the
clerk pretended not to know what I was talking about.
Is that what you'd call a "Strimmer"?
Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com |
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Owain
Guest
|
| Posted:
Sun Feb 13, 2005 5:24 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Peter A Forbes" wrote
| >Those poor souls that put a hundred feet or so of 18GA (about 1mm sq)
| >extension cord on their weed wackers
It's a different language isn't it :-)
| >soon find that not only does it run slow, but the motor overheats.
| >So we have extension cords that are 16 or 14 gauge, and can
| > handle the extra current. But people are too cheap to pay double
| > for the heavy duty extension cord, so they end up eating
| >their money up in burned out motors.
| Why use anything as small as 1mm sq cable???
If it's in Wall-mart, they'll buy it.
Owain |
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sun Feb 13, 2005 6:10 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Peter Bennett" <peterbb@somewhere.invalid> wrote in message
news:42jt01h7q5dpasoeufg6gfa0d7mu1qmkcl@news.supernews.com...
| Quote: | On Sat, 12 Feb 2005 17:17:16 -0800, "Watson A.Name - \"Watt Sun, the
Dark Remover\"" <NOSPAM@dslextreme.com> wrote:
No. These cells are 4V each, 12 in all, each is sealed. Well,
except
for the one cell that's split open because of internal pressure. :-(
They must be replaced, not repaired. This is a phone system, where
it
has to be online during emergencies. Batteries that are working
fine,
but over 5 years old are considered unacceptable and must be
replaced.
I don't know of any 4 volt rechargeable cell chemistry.
I expect that your "4 volt cells" are actually two cell lead-acid
batteries, with each cell good for 2.1 volts.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca |
|
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Paul Miller
Guest
|
| Posted:
Sun Feb 13, 2005 6:10 am Post subject:
Re: How much current safe for 30m extension? |
|
|
"Sammo" <noone@no-where.com> wrote in message
news:95FB7BA1F25441A7D4@130.133.1.4...
| Quote: | I am in the UK (so mains voltage is about 230V or 240V).
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)
|
I would say 2.5kw at 30M and around 2Kw at 60M. Its not gonna make
much difference(resistive load) if the cable is protected by the correct
fuse in the plug.
The big problem is going to be earth loop impedance, I know it sounds
trivial
because it will work fine, but you did quote a PSC figure of 120A......must
be
a TT instalation. Please make sure you have a RCD on this circuit..
Regards,
Paul Miller iEng MIIE (elec) |
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Peter Bennett
Guest
|
| Posted:
Sun Feb 13, 2005 6:10 am Post subject:
Re: How much current safe for 30m extension? |
|
|
On Sat, 12 Feb 2005 11:08:03 -0800, "Watson A.Name - \"Watt Sun, the
Dark Remover\"" <NOSPAM@dslextreme.com> wrote:
| Quote: |
"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. 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.
|
If you're going to use transformers at each end of the link, you can
make one of them tapped, so you can select an appropriate tap to
compensate for the voltage loss in the cable.
--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca |
|
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