| Author |
Message |
Watson A.Name - \"Watt Su
Guest
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 Posted:
Sun Feb 13, 2005 8:07 pm Post subject:
Re: How much current safe for 30m extension? |
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<bigcat@meeow.co.uk> wrote in message
news:1108302344.391913.292380@o13g2000cwo.googlegroups.com...
Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | bigcat@meeow.co.uk> wrote in message
news:1108237955.923021.112840@f14g2000cwb.googlegroups.com...
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.
No. These cells are 4V each, 12 in all, each is sealed.
|
If youre going to deal with this you'll need a few clues. You will have
2v cells in pairs, 4v lead acid cells dont exist.
| Quote: | 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. |
thats fine if youve got the money, but since they've been there 9
years, and are found dead but still in service, I was guessing you
havent.
Is it April yet?
| Quote: | 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.
This is *not* how you run a battery backup system! The idea is to
start
out with fully charged batteries, so that when the power fails for a
long period, the voltage of the batteries may drop to 40V or less as
the
cells discharge, keeping the PBX online. If you start at anything
less,
even 36V, you're not going to have any discharge time before the PBX
system crashes. It would be essentially worthless.
|
You misunderstood completely, hopelessly, and idiotically. 48v is a
I think I'm talking to a tree here. **PLONK**
very old standard, and many 48v telecomms systems are now run on 24v.
If your equipment were 24v compatible, as some is, you would only need
half the number of cells.
And if you had no money to replace the battery, odds are you'll have at
least 50% of cells still serviceable.
Even if its not 24v compatible, you would get better backup performance
by removing any dead cells from the chain. Whether you remove them or
not you'll run below voltage.
| Quote: | What capacity at 48v is it on?
The rectifier can put out a hundred amps at 54VDC, to charge the
batteries while the PBX is also running. That must be 6 or so kW
input.
So I would guess that it's 208V at 30A breakers. But with no
batteries,
the load would be more like 3.6kW.
|
3.6kW @ 50v = 72A, so if we take an ultra-vague guess at C/10 charging,
that gives us 700ah capacity @48v. Ouch.
| Quote: | 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
The UPS in the computer room is 150kW, easily capable of handling
another 6 or so kW.
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.
The batteries and rectifier are a "UPS" to protect the PBX against
failure of the commercial power. That's what it's being fed from.
|
Why dont you find someone else to discuss this with.
| 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.
Assuming that it could be pulled 1300 feet. Probably not without
damage.
|
You thread it section by section. Regular access points also allow a
section can be replaced if it fails. The T&E also includes a spare
conductor for backup.
| Quote: | Heavily insulated cable would be needed. Probably double
jacketed.
|
T&E is double insulated, high v rated and cheap - thats why i suggested
it.
| 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.
RF transmission coax is typically copper clad steel wire center
conductor, which would have much greater I^2R loss than pure copper
cable at 50 or 60Hz. That would be unacceptable.
|
obviously it depends what v and i youre running it at, its very much
higher v rated than T&E.
| Quote: | T&E's probably far more practical.
Thanks, but I've never heard of T&E here in the U.S. I don't know
what
that acronym stands for.
|
twin and earth, its our standard house wiring cable, 2 cores double
insulated plus one single, comes in various copper sizes, is very cheap
and can be bought at thousands of outlets... here, anyway. I dont know
what export would cost.
You would need to get some basic concepts sorted out before youre in a
position to imlpement anything.
NT
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Peter A Forbes
Guest
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| Posted:
Sun Feb 13, 2005 8:28 pm Post subject:
Re: How much current safe for 30m extension? |
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On Sun, 13 Feb 2005 12:22:02 -0800, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:
| Quote: | I got one for you. I checked the fuse panel of a really old bldg (well
for the U.S., anyway..) - almost 100 yrs - and it had the ground
fused(!) Now _that's_weird.
|
Was it 3-wire DC originally??
Peter
--
Peter & Rita Forbes
Email: diesel@easynet.co.uk
Web: http://www.oldengine.org/members/diesel |
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John Rumm
Guest
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| Posted:
Sun Feb 13, 2005 9:11 pm Post subject:
Re: How much current safe for 30m extension? |
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Jerry G. wrote:
| Quote: | As long as the maximum current load does not exceed the current rating of
any of the cables that are used in the extension, it will be safe. There
should not be very much loss over a few hundred feet of extension. If there
is a loss, you can then change the extensions for ones that are of a larger
gauge.
|
The other issue to beware of is as the length of wire increases, so does
it fault loop resistance (i.e. path from line to earth / ground). This
will reduce the maximum current that can be passed to earth in the event
of a fault, and hence extend the time between the fault occuring and the
circuit protective device (fuse, circuit breaker etc) opening to
disconnet the power. Obviously if *you* are forming part of this earth
fault loop, the sooner the power goes off the better!
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection anyway
of course, to negate the problem)
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/
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John Rumm
Guest
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| Posted:
Sun Feb 13, 2005 9:17 pm Post subject:
Re: How much current safe for 30m extension? |
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Paul Miller wrote:
| Quote: | 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..
|
If you do the sums for 1mm sq cable that is the PSC you get *without*
including the supply impedance - it only gets worse in reality.
(not sure what significance the supply being TT would have on PSC mind you)
--
Cheers,
John.
/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/ |
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Andy Wade
Guest
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| Posted:
Sun Feb 13, 2005 10:31 pm Post subject:
Re: How much current safe for 30m extension? |
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Dave Plowman (News) wrote:
| Quote: | Dunno where you'd get 4mm flex,
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RS for one, see stock no. 250-1410.
| Quote: | but you'd never get it to fit a 13 amp plug. 2.5mm is the limit, and
not all plugs will have a cord grip suitable.
|
Actually 1.25 mm^2 is the limit - in the sense that it's the largest
size that BS 1363 requires a plug to accept. Nevertheless _most_ plugs
will accept 1.5 mm^2 without too much difficulty and _some_ will accept
2.5 mm^2.
--
Andy |
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Sun Feb 13, 2005 11:40 pm Post subject:
Re: How much current safe for 30m extension? |
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"John Rumm" <see.my.signature@nowhere.null> wrote in message
news:420f6e03$0$96635$ed2e19e4@ptn-nntp-reader04.plus.net...
| Quote: | Jerry G. wrote:
As long as the maximum current load does not exceed the current
rating of
any of the cables that are used in the extension, it will be safe.
There
should not be very much loss over a few hundred feet of extension.
If there
is a loss, you can then change the extensions for ones that are of a
larger
gauge.
The other issue to beware of is as the length of wire increases, so
does
it fault loop resistance (i.e. path from line to earth / ground). This
will reduce the maximum current that can be passed to earth in the
event
of a fault, and hence extend the time between the fault occuring and
the
circuit protective device (fuse, circuit breaker etc) opening to
disconnet the power. Obviously if *you* are forming part of this earth
fault loop, the sooner the power goes off the better!
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection anyway
of course, to negate the problem)
|
I just got thru working with some equipment that we inherited that had
the fuse in the plug. In this case, the luser that had replaced the
fuse used 32V auto fuses instead of the proper 125V or 250V rating. I'm
glad I caught that problem. But fuses in plugs are rare, usually the
only thing between the breaker panel and the equipment is the 15A
breaker built into the power strip.
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Sun Feb 13, 2005 11:49 pm Post subject:
Re: How much current safe for 30m extension? |
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"Andy Wade" <spambucket@ajwade.clara.co.uk> wrote in message
news:420f812d$0$8751$db0fefd9@news.zen.co.uk...
| Quote: | Dave Plowman (News) wrote:
Dunno where you'd get 4mm flex,
RS for one, see stock no. 250-1410.
but you'd never get it to fit a 13 amp plug. 2.5mm is the limit, and
not all plugs will have a cord grip suitable.
Actually 1.25 mm^2 is the limit - in the sense that it's the largest
size that BS 1363 requires a plug to accept. Nevertheless _most_
plugs
will accept 1.5 mm^2 without too much difficulty and _some_ will
accept
2.5 mm^2.
|
I don't know about the UK, but in the U.S. most decent plugs come with
three large headed screws that have a square washer under them, with one
edge of the washer hanging over the edge of the brass pin, so it retains
the copper wire. So if you can unscrew the screw 3/16" (5mm) and get
the copper strands in there and screw it down, then it would hold almost
that big a conductor. Of course getting it all thru the hole in the
cord grip is another matter..
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Guest
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| Posted:
Sun Feb 13, 2005 11:51 pm Post subject:
Re: How much current safe for 30m extension? |
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good, itll save me the temptation to reply in future |
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Bob Eager
Guest
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| Posted:
Sun Feb 13, 2005 11:59 pm Post subject:
Re: How much current safe for 30m extension? |
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On Sun, 13 Feb 2005 17:49:42 UTC, "Watson A.Name - \"Watt Sun, the Dark
Remover\"" <NOSPAM@dslextreme.com> wrote:
| Quote: | I don't know about the UK, but in the U.S. most decent plugs come with
three large headed screws that have a square washer under them, with one
edge of the washer hanging over the edge of the brass pin, so it retains
the copper wire. So if you can unscrew the screw 3/16" (5mm) and get
the copper strands in there and screw it down, then it would hold almost
that big a conductor. Of course getting it all thru the hole in the
cord grip is another matter..
|
Some earlier plugs were like that. These days, there is a hole in the
end of the pin, and a grubscrew into a threaded hole at right angles
that clamps the wire. Remember the wire is thinner over here.
And of course, nearly all of our plugs have fuses in them. A 15A breaker
is not too good at protecting a 5A flexible cable to an appliance.
--
Bob Eager
begin a new life...dump Windows! |
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raden
Guest
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| Posted:
Mon Feb 14, 2005 12:20 am Post subject:
Re: How much current safe for 30m extension? |
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In message <110tflss7qq5804@corp.supernews.com>, "Watson A.Name - \"Watt
Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> writes
| Quote: |
"raden" <raden@kateda.org> wrote in message
news:Iv0Z3IeHyqDCFwIg@ntlworld.com...
In message <110taejtbujdh40@corp.supernews.com>, "Watson A.Name -
\"Watt
Sun, the Dark Remover\"" <NOSPAM@dslextreme.com> writes
T&E's probably far more practical.
Thanks, but I've never heard of T&E here in the U.S. I don't know
what
that acronym stands for.
Twin and earth
... colonials !
Yeah, we call it ground here stateside. And it's Romex.
And it's AC line in every schematic I've seen from the American mfgrs
the likes of HP, Tek, etc., not "mains". Mains are those wires up on
top of the power pole.
Separated by a common language, as they say |
--
geoff |
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Andrew Chesters
Guest
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| Posted:
Mon Feb 14, 2005 1:14 am Post subject:
Re: How much current safe for 30m extension? |
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Spehro Pefhany wrote:
SNIP
| Quote: |
Is that what you'd call a "Strimmer"?
Best regards,
Spehro Pefhany
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Yep! |
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Andrew Chesters
Guest
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| Posted:
Mon Feb 14, 2005 1:20 am Post subject:
Re: How much current safe for 30m extension? |
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John Rumm wrote:
SNIP
| Quote: |
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection anyway
of course, to negate the problem)
_FUSE?_ 1/2 of their plugs don't even have an earth!! |
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Watson A.Name - \"Watt Su
Guest
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| Posted:
Mon Feb 14, 2005 2:22 am Post subject:
Re: How much current safe for 30m extension? |
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"Andrew Chesters" <andrew.dontspam.chesters@ntlworld.com> wrote in
message news:379nadF5bcs60U1@individual.net...
| Quote: | John Rumm wrote:
SNIP
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection
anyway
of course, to negate the problem)
_FUSE?_ 1/2 of their plugs don't even have an earth!!
|
Yeah, but everything's gone cordless nowadays, even the weed wackers.
So who cares? ;-)
I think the appliances that have a plug with only two prongs have to be
double insulated, and meet stringent leakage specs.
I got one for you. I checked the fuse panel of a really old bldg (well
for the U.S., anyway..) - almost 100 yrs - and it had the ground
fused(!) Now _that's_weird. |
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VWWall
Guest
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| Posted:
Mon Feb 14, 2005 2:46 am Post subject:
Re: How much current safe for 30m extension? |
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Andrew Chesters wrote:
| Quote: | John Rumm wrote:
SNIP
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection anyway
of course, to negate the problem)
_FUSE?_ 1/2 of their plugs don't even have an earth!!
|
The standard 120V receptical has the two parallel blades polarized. The
"neutral" blade is wider than the "hot one", so even a proper two-blade
plug gives some protection to exposed components, like the shell on
thraded lamps. However there are still many table lamps with equal size
blades which can be inserted either way. Many small appliances and
tools are "double insulated", and these do not require a ground,
(earth), wire plug.
Years ago, as a broacast radio engineer, I had to set up remote
locations. If the "hum level" was too high the standard proceedure was
to reverse the plug on the amplifer. Almost all the new equpment has
three-prong grounded plugs.
--
Virg Wall, P.E. |
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Andrew Chesters
Guest
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| Posted:
Mon Feb 14, 2005 3:03 am Post subject:
Re: How much current safe for 30m extension? |
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VWWall wrote:
| Quote: | Andrew Chesters wrote:
John Rumm wrote:
SNIP
Out of interest, are US style plugs fitted with fuses?
(An extension lead running outside ought to have RCD protection
anyway of course, to negate the problem)
_FUSE?_ 1/2 of their plugs don't even have an earth!!
The standard 120V receptical has the two parallel blades polarized. The
"neutral" blade is wider than the "hot one", so even a proper two-blade
plug gives some protection to exposed components, like the shell on
thraded lamps. However there are still many table lamps with equal size
blades which can be inserted either way. Many small appliances and
tools are "double insulated", and these do not require a ground,
(earth), wire plug.
Years ago, as a broacast radio engineer, I had to set up remote
locations. If the "hum level" was too high the standard proceedure was
to reverse the plug on the amplifer. Almost all the new equpment has
three-prong grounded plugs.
I have to concede that my knowlege of colonial wiring pracice is |
somewhat out of date. My family was part of the UK "Brain Drain", a
period of history where engineers (my father, not me) from here got _1st
class_ berths on liners taking them to the new world! |
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