| Author |
Message |
Sammo
Guest
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 Posted:
Sat Feb 12, 2005 6:09 pm Post subject:
How much current safe for 30m extension? |
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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)
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Dave Plowman (News)
Guest
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| Posted:
Sat Feb 12, 2005 6:09 pm Post subject:
Re: How much current safe for 30m extension? |
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In article <176uZD2KcidF-pn2-pgQf8dbMMKeL@rikki.tavi.co.uk>,
Bob Eager <rde42@spamcop.net> wrote:
| Quote: | 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...
|
IIRC, 1mm flex will just about make the test at 30 metres.
We use a multi-core cable to feed a floor monitor on location filming
which has mains, video and audio. And that's about it's length. Of course
if you extend it everything still 'works'. And I don't have anything to do
with the H&S regs testing. ;-)
--
*Wrinkled was not one of the things I wanted to be when I grew up
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound. |
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Dave Plowman (News)
Guest
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| Posted:
Sat Feb 12, 2005 6:09 pm Post subject:
Re: How much current safe for 30m extension? |
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In article <376fo9F59cjg9U3@individual.net>,
Palindr☻me <sb382638@hotmail.com.invalid> wrote:
| Quote: | OOPs! Yes, I forgot it was twin flex.
|
3 core, actually. ;-)
--
*Happiness is seeing your mother-in-law on a milk carton
Dave Plowman dave@davenoise.co.uk London SW
To e-mail, change noise into sound.
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Ian Stirling
Guest
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| Posted:
Sat Feb 12, 2005 6:46 pm Post subject:
Re: How much current safe for 30m extension? |
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In uk.d-i-y Sammo <noone@no-where.com> wrote:
| 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.)
|
It's always going to be safe, as it's got a fuse.
Ok...
Copper has a resistivity of 0.7*10^-8 ohms/meter.
Or, for a 1mm^2 wire, 0.7*10^-2 ohms/meter.
Or for 2 wires, 1.4*10^-2 ohms.
Or for 60m, 8.4*10^-1 ohms, or .84 ohms.
At 10A, 8.4V, or heating by 84W.
If at the plug end is 240V, at the socket end will be 232V, which is
(232^2/240^2)= .93444444444444444444
So, you lose 7% of the power for a heater, for example. |
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Ian Stirling
Guest
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| Posted:
Sat Feb 12, 2005 6:54 pm Post subject:
Re: How much current safe for 30m extension? |
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In uk.d-i-y Ian Stirling <root@mauve.demon.co.uk> 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.
Ok...
Copper has a resistivity of 0.7*10^-8 ohms/meter.
|
Doh, 1.7.
| Quote: |
Or, for a 1mm^2 wire, 0.7*10^-2 ohms/meter.
1.7*10^-2
Or for 2 wires, 1.4*10^-2 ohms.
3.4*10^-2 |
| Quote: | Or for 60m, 8.4*10^-1 ohms, or .84 ohms.
|
2 ohms.
At 10A, 20V, or the cable heating by 200W.
If at the plug end is 240V, at the socket end will be 220V, which is
(220^2/240^2)= .84027777777777777777
So, you lose 16% of the power for a heater, for example. |
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Peter A Forbes
Guest
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| Posted:
Sat Feb 12, 2005 7:08 pm Post subject:
Re: How much current safe for 30m extension? |
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On Sat, 12 Feb 2005 10:51:00 -0800, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:
| Quote: |
"Bob Eager" <rde42@spamcop.net> wrote in message
news:176uZD2KcidF-pn2-pgQf8dbMMKeL@rikki.tavi.co.uk...
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!
--
Bob Eager
|
Why use anything as small as 1mm sq cable???
For 30metres I'd want to see 2.5mm sq at least, if not 4mm sq.
If not for the volt drop or lack of, for the mechanical strength and resistance
to damage.
Peter
--
Peter & Rita Forbes
Email: diesel@easynet.co.uk
Web: http://www.oldengine.org/members/diesel |
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Palindr☻me
Guest
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| Posted:
Sat Feb 12, 2005 7:17 pm Post subject:
Re: How much current safe for 30m extension? |
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Sammo wrote:
| 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?
|
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.
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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Bob Eager
Guest
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| Posted:
Sat Feb 12, 2005 7:18 pm Post subject:
Re: How much current safe for 30m extension? |
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|
On Sat, 12 Feb 2005 12:46:19 UTC, Ian Stirling <root@mauve.demon.co.uk>
wrote:
| Quote: | 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...
--
Bob Eager
begin a new life...dump Windows! |
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Owain
Guest
|
| Posted:
Sat Feb 12, 2005 7:44 pm Post subject:
Re: How much current safe for 30m extension? |
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|
"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.
The 10A rating will be for the flex *fully* unwound. If you use the cable
wound on the reel it will have a lower rating. All cables have resistance,
and get warm as current passes through them. With the cable unwound, that
warmth can dissipate safely. If the cable is wound up (or otherwise
enclosed) that heat cannot dissipate and the cable will get warmer and
warmer ... possibly to the point it melts and/or starts a fire.
As an aside, using flex rated at 10A to wire extension leads with 13A
sockets is unwise, as the cable probably insufficiently protected by a 13A
fuse. A 1.25mm or, for longer lengths, 1.5mm, flex would be better.
| Is the reduction in current/power carrying capability significant?
There is no reduction in the current carrying capacity of the flex due to
length. The resistance in the cable causes voltage drop, which varies with
current drawn and length of cable. Voltage drop is a factor in determining
whether a larger cable size is needed for a given load. Whether it is
acceptable or not depends on your application.
| If so, then is there a rough guideline figure for available
| current/power which I can use?
Voltage drop should normally not exceed 4--6% from the origin of the
installation.
| 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?
This would be very unwise. A 60m extension lead strongly suggests there is
a need for suitable fixed wiring to be provided. The earth fault loop
impedance will be high and the circuit protective arrangements are likely to
be insufficient. This is quite apart from issues such as physical protection
and suitability of the flex.
Is this some elaborate scheme to get round Part P?
Owain |
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Palindr☻me
Guest
|
| Posted:
Sat Feb 12, 2005 7:47 pm Post subject:
Re: How much current safe for 30m extension? |
|
|
Palindr☻me wrote:
| 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.
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.
|
OOPs! Yes, I forgot it was twin flex.
Ignore my last post - I clearly shouldn't have got up so
eary this morning...and will now correct that error. Well,
it was a good party last night, from what I remember.
--
Sue |
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Ian Stirling
Guest
|
| Posted:
Sat Feb 12, 2005 7:59 pm Post subject:
Re: How much current safe for 30m extension? |
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|
In uk.d-i-y Bob Eager <rde42@spamcop.net> wrote:
| 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...
|
I took that into account. (but misremembered the resistivity of copper)
See other post for correction. |
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Interfacebus.com
Guest
|
| Posted:
Sat Feb 12, 2005 8:02 pm Post subject:
Re: How much current safe for 30m extension? |
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|
The other consideration would be the length of time it would take to
disconnect from the power source.
I don't know the requirement ~ time required to disconnect from the source
(60m) or disconnect from the extention (30m).
Additional link:
http://www.interfacebus.com/Reference_Cable_AWG_Sizes.html
"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) |
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Ian Stirling
Guest
|
| Posted:
Sat Feb 12, 2005 8:22 pm Post subject:
Re: How much current safe for 30m extension? |
|
|
In uk.d-i-y Owain <owain41276@stirlingcity.coo.uk> wrote:
| 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
snip
Voltage drop should normally not exceed 4--6% from the origin of the
installation.
This is some 9% at rated load. (60m0
| 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?
This would be very unwise. A 60m extension lead strongly suggests there is
a need for suitable fixed wiring to be provided. The earth fault loop
impedance will be high and the circuit protective arrangements are likely to
be insufficient. This is quite apart from issues such as physical protection
and suitability of the flex.
|
Short current is some 120A, plenty to blow a 10A fuse quite prombtly. |
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John Rumm
Guest
|
| Posted:
Sat Feb 12, 2005 8:56 pm Post subject:
Re: How much current safe for 30m extension? |
|
|
Ian Stirling wrote:
| Quote: | Short current is some 120A, plenty to blow a 10A fuse quite prombtly.
|
You are assuming that the supply impeadance is zero however. If you
factor that in, then you drop the PSC a bit...
(Still ought to be plenty to blow a 13A fuse in under a second though)
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/ |
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Andrew Chesters
Guest
|
| Posted:
Sat Feb 12, 2005 9:35 pm Post subject:
Re: How much current safe for 30m extension? |
|
|
Sammo wrote:
| 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)
|
Others have discussed the current & voltage side of your post. However,
something else to concider is where you are doing this. At 30-60m my
guess is that you would be outdoors? If so, you should be using an
earth leakage circuit breaker (RCD)to supply your extensions. This
could be installed in your CU, built in to the supply socket or a
plugtop type. |
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