How much current safe for 30m extension?

[Tim (Remove NOSPAM.]

Hell, if you have any more grass than that the size of a postage stamp here in the UK, we buy a petrol driven "weed wacker", the electric ones, even at

230v are worse than useless!

Tim..

[Dave Plowman (News)]

Dunno where you'd get 4mm flex, 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.

[bigcat]

thinking

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.

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?

You misunderstood completely, hopelessly, and idiotically. 48v is a 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.

batteries,

3=2E6kW @ 50v =3D 72A, so if we take an ultra-vague guess at C/10 charging, that gives us 700ah capacity @48v. Ouch.

Why dont you find someone else to discuss this with.

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.

T&E is double insulated, high v rated and cheap - thats why i suggested it.

obviously it depends what v and i youre running it at, its very much higher v rated than T&E.

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

[Watson A.Name - "Watt Sun, th]

thinking

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.

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?

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.

batteries,

3.6kW @ 50v = 72A, so if we take an ultra-vague guess at C/10 charging, that gives us 700ah capacity @48v. Ouch.

Why dont you find someone else to discuss this with.

copper

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.

T&E is double insulated, high v rated and cheap - thats why i suggested it.

obviously it depends what v and i youre running it at, its very much higher v rated than T&E.

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

[John Rumm]

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)

[John Rumm]

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)

[Andy Wade]

RS for one, see stock no. 250-1410.

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.

[Dave Plowman (News)]

Right. Didn't know chapter and verse.

Our location sparks use 2.5mm TRS for most uses - and as many things may have to plug into a house supply at some point, use 13 amp adaptor leads to feed theirs. Think the 13 amp plugs they use are Duraplugs

[Watson A.Name - "Watt Sun, th]

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.

[Watson A.Name - "Watt Sun, th]

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..

[bigcat]

good, itll save me the temptation to reply in future

[Bob Eager]

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.

[Stefek Zaba]

A terminogical inexactitude, to a degree. The earthing derangements will make naff-all difference to the PSC for an L-N fault, but will clearly affect the current which'll flow for an L-to-E (or, since the distinction is crucial here, actually an L-to-protective-conductor) fault. It's precisely becuase the impedance of a local earth rod can't be expected to be low enough to get a hefty enough fault current to flow that UK regs [note trimming of followups :-] require a 100mA RCD on all TT installs.

As you know anyway ;-)

[Andrew Chesters]

Spehro Pefhany wrote: SNIP

Yep!

[Andrew Chesters]

SNIP

_FUSE?_ 1/2 of their plugs don't even have an earth!!

[Stefek Zaba]

Aye - and their stores [sic] will happily sell you an adaptor to let you plug those weird-ass 3pin plugs with that pinko-liberal ground pin into an honest red-blooded real man's 2-pin outlet...

[Watson A.Name - "Watt Sun, th]

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.

[Peter A Forbes]

Was it 3-wire DC originally??

Peter

-- Peter & Rita Forbes Email: [e-mail] Web:

[VWWall]

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.

[Andrew Chesters]

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!