How far can I run an extension cable?

[stan250]

Hi folks,
I'm building a greenhouse out of timber and need to run a temporary power extension cable.
Will be using a small compressor and a circular saw.
Its about 60m from the nearest socket: is this too far to be safe?
I have an rcd on the fusebox. Whats the worst that can happen if its too far?
thanks.

[watson]

If its too far...you run out of grunt.
That means that at high current usage, the voltage drop along the cable may be too much to deliver sufficient power to run heavy duty devices like a welder or similar.
I reckon you'd be OK with those two tools as they are intermittent use as well.
The other thing to remember is to uncoil all of the extension chord.

[chrisp]

For the compressor, rather than run a long electrical cable, place it near the power point and run a long air line.

[murray44]

And remember, a 20m extension lead won't go 25m :D

[Smurf]

For a normal extension lead you'll end up losing a bit over 20 Volts running a 10 Amp load over that distance. So you'll end up with a bit under 220V, rather than 240V if the load is 10 Amps. If the load is lower, the loss of voltage will be reduced accordingly.

That's not ideal, but in practice you'll get away with it as long as the voltage at the outlet where you plug the lead in isn't unusually low. Just be careful with the motors - make sure you don't labour the saw motor since you could end up overheating it if the voltage is down.

Shouldn't be a problem in practice. :)

[Moondog55]

For a normal extension lead you'll end up losing a bit over 20 Volts running a 10 Amp load over that distance. So you'll end up with a bit under 220V, rather than 240V if the load is 10 Amps. If the load is lower, the loss of voltage will be reduced accordingly.

That's not ideal, but in practice you'll get away with it as long as the voltage at the outlet where you plug the lead in isn't unusually low. Just be careful with the motors - make sure you don't labour the saw motor since you could end up overheating it if the voltage is down.

Shouldn't be a problem in practice. :)
is this assuming a standard extension lead? not all extensions use HD wire so I assume this figure is based on the resistance of 2.5mm*2 flex?/

I had a long flex melt once at this sort of distance
http://www.renovateforum.com/f195/difference-between-flex-cable-92779/

[stan250]

And remember, a 20m extension lead won't go 25m :D


You are, perhaps, taking the piss, mon ami?

[Moondog55]

You are, perhaps, taking the piss, mon ami?

Who? What ?? US???

[Smurf]

is this assuming a standard extension lead? not all extensions use HD wire so I assume this figure is based on the resistance of 2.5mm*2 flex?/

I had a long flex melt once at this sort of distance
http://www.renovateforum.com/f195/difference-between-flex-cable-92779/
I didn't get the books out, but it's based on 1.0mm2 cable (ie a 10A lead) at voltage from of 37mV / AM.

That's from memory and sounds about right in practice.

[Moondog55]

OK then I would suggest for that length of flex to use 15A rated 2.5mm*2 only and minimize the voltage drop and heating of the wire.
I like to play things safe

[2x4]

An extension lead with 2.5mm conductors is good for 60mtrs.



.

[stan250]

An extension lead with 2.5mm conductors is good for 60mtrs.



.

oops.... I recently bought another 50m on top of what I already had so now I have about 100m of 10amp.

[applied]

oops.... I recently bought another 50m on top of what I already had so now I have about 100m of 10amp.

better pickup a few spare plugtops for when they melt in the wall outlet.:2tsup:
where in SA are you?

[Moondog55]

This may be a dumb question; but are you allowed to run parallel flex to a single plug? two runs of 1mm*2 would halve the resistance and double the current capacity ( the proper flex/cable for the job is always better but often those long extensions are so cheap when on sale that it may be cheaper to double up.

[applied]

This may be a dumb question; but are you allowed to run parallel flex to a single plug? two runs of 1mm*2 would halve the resistance and double the current capacity ( the proper flex/cable for the job is always better but often those long extensions are so cheap when on sale that it may be cheaper to double up.

You cannot parralel conductors of this size.

[Moondog55]

You cannot parralel conductors of this size.

Is that a practical or legal thing?/


I am aware that if you have conductors of the same size but different lengths the major current will try and run down the path of least resistance :ie: the shorter conductor, but I have a mate who is a Sparkie who told me that when he started his apprenticeship it was a common practice to run dual TPE if the correct size was not available

[chrisp]

Is that a practical or legal thing?/


I am aware that if you have conductors of the same size but different lengths the major current will try and run down the path of least resistance :ie: the shorter conductor, but I have a mate who is a Sparkie who told me that when he started his apprenticeship it was a common practice to run dual TPE if the correct size was not available

It is an AS/NZS-3000 thing. Essentially it is a regulation thing. The standard defines a flexible cord (no more than 5 conductors, etc.)

In practice, you could double them up. Ideally, the length/type/route would need to be the same to help ensure equal current sharing.

[pedantic=ON]
Just to correct a common fallacy, current doesn't 'take the path of least resistance', it takes all paths proportional to the inverse of the resistance. The 'path of least resistance' will have more current than a path with higher resistance - but they'll both have current flowing.
[pedantic=OFF]

Aside for the practicality of running two cords together, there is the issue of how to terminate the two sets of conductors into the plug and socket.

Anyone even thinking of doing this should carefully consider the plug and socket arrangement. Please don't go adding a second cord/plug to the appliance to allow it to the powered from two separate extension cords. Why? consider what would happen if only one plug was connected - to other would have live exposed pins. :o

[Moondog55]

I love the "pedantic button" can we all please have one.
Yes I am aware of that but I was using common terminology as a shorthand, I have some flex here that consists of 6 conductors, 3 with standard colour coding, Brown + Green/Yellow + Blue, but also Red + White + Black; I do not know what it was used for or where it came from but it is 1mm*2 conductors, I was thinking that if I used it paralleled I would have a flex that could safely handle more current, better not then Hey??

[chrisp]

I have some flex here that consists of 6 conductors, 3 with standard colour coding, Brown + Green/Yellow + Blue, but also Red + White + Black; I do not know what it was used for or where it came from but it is 1mm*2 conductors, I was thinking that if I used it paralleled I would have a flex that could safely handle more current, better not then Hey??

It could be worth a try - if it is all the same size, it certainly will be the same 'length' and 'route'.

I'd be more concerned with trying to run two separate runs of 3-core, but 6-core would probably work well.

BTW, only do it for yourself - don't sell/give/loan it to anyone else. :)

[Bedford]

I think Chrisp has given the safest and best advice in this situation,and I think some of this is heading into dangerous territory.

I have attached some operating instructions from a small compressor.

I suspect this is partly because the Chinese have perfected the art of thinness, and I know these compressors will start ok from an empty tank when using an extension lead, but when the motor tries to restart at the cut in pressure, it will mostly sit there grunting without actually starting.



For the compressor, rather than run a long electrical cable, place it near the power point and run a long air line.

[applied]

im sure there are AS/NZS 3199:2007 rules that prevent these size conductors being parraleld
sub sections 5.3.1 cord type, 7.2.4 compliance, 7.3 attachment of insulated cores, 7.4 and 7.5 attachment of conductors but what you do is upto you i suppose.

[Moondog55]

OK, but I like to know the reasoning behind the rules, can you tell my why??

I mean 2.5mm^2 isn't particularly big wire, I use bigger for speakers for instance.

[chrisp]

OK, but I like to know the reasoning behind the rules, can you tell my why??

I mean 2.5mm^2 isn't particularly big wire, I use bigger for speakers for instance.

The 'rule' is in AS/NZS3000. The scope of AS/NZS3000 is 'electrical installations'. From AS/NZS3000:
1.4.47 Electrical installation
Electrical equipment installed for the purposes of conveyance, control, measurement or use of electricity, where electricity is or is to be supplied for consumption. It includes electrical equipment supplied from a distributor’s system or a private generating system.
NOTES:


An electrical installation usually commences at the point of supply and finishes at a point (in wiring) but does not include portable or stationary electrical equipment connected by plug and socket-outlet (other than where a socket-outlet is used to connect sections of the fixed installation).

Or, to simplify, the 'rule' in AS/NZS3000 is not applicable beyond the power-point.

Technically, there is no practical reason as to why you can't parallel up the conductors. Indeed there are many cases where parallel conductors work better than a single conductor.

[Moondog55]

Any ideas what the 6 conductor flex would have been made for originally??

I have just remembered that I bought it a Dick Smiths just after Woolworths bought the company, I thought it was something else, but I remember it was about $0.55 a meter

[chrisp]

Any ideas what the 6 conductor flex would have been made for originally??

Could be anything. It sounds like it might be some type of industrial/control cable. For example, an industrial control such as a over-head crane control panel.

[Moondog55]

Agreed if those used 240Volt, I thought that only 240V + ( i:e: mains voltages ) used the green and yellow striped safety earth colouring

[applied]

would have to be controll wiring but if you bought it from dicksmiths its probably trailer light wiring.

does it have a KVA rating and a V rating printed or imbossed in it if not its probaby selv wire of the the type that has no fire retarding propertys and bursts into flames on overload like figure 8 does.

in commercial and industrial it is not uncommon to use up to 20 conductor cables in lighting fixtures incorporating several fluroesent loads.

[Moondog55]

Rated 450/700V embossed every meter, but no other markings, fiber cored and tissue wrapped and outer sheath is over 13mm diameter.
It most definitely isn't trailer wiring ( wrong colour coding and far too heavy duty ) I am familiar with auto stuff and this is 1.25mm^2 conductor.

Seems a shame not to use it as I have a 15M length

[Master Splinter]

[pedantic=ON]



<pedantic> Correct intarwebs usage is to wrap the text in pedant tags as shown here. <pedantic/>

[applied]

Copper cables worth about $2.20 so it's probably worth a pint at the pub at lunchtime other than that 15mtrs is pretty useless.

[chrisp]

<pedantic> Correct intarwebs usage is to wrap the text in pedant tags as shown here. <pedantic/>

An interesting point.

From my Boolean logic days, a "bar" above a variable or expression was used to indicate the inverse or "NOT" of that variable or expression. My understanding is that the "/" preceding a variable or expression is the ASCII-ised version of a bar.

I could be pedantic and note that "<pedantic/>" reads as "pedantic not"

:)

Me thinks we need a set of pedantic delimiter smilies.

[jago]

Oh NO the code monkeys are at it!

[watson]

An interesting point.

From my Boolean logic days, a "bar" above a variable or expression was used to indicate the inverse or "NOT" of that variable or expression. My understanding is that the "/" preceding a variable or expression is the ASCII-ised version of a bar.

I could be pedantic and note that "<pedantic/>" reads as "pedantic not"

:)

Me thinks we need a set of pedantic delimiter smilies.

The only ones I can find in the spares cupboard spell pedantic as "pedarist" :o

[jago]

I blame the Greeks!

[chrisp]

look what has been found:

:pedon:

blah blah ...

:pedoff:

Thank you Mr Watson!

[Moondog55]

Love it,,, LOL LOL :rofl:

[Moondog55]

Copper cables worth about $2.20 so it's probably worth a pint at the pub at lunchtime other than that 15mtrs is pretty useless.

15 meters as a domestic extension is borderline but definitely usable, which is why I have been asking all these D*** questions:2tsup:

[Vernonv]

Technically, there is no practical reason as to why you can't parallel up the conductors. Indeed. There is a situation however that could arise where one of the parallel conductors fails and the other conductor will be required to take the full load.

[Moondog55]

In all my years of building high power speakers, I have never seen that happen, but it could.

Speakers carry massive current but at relatively low voltage ( 12 -> 70 V )

[applied]

hey moondog the only real problem with it is the earthing conductor must be green and not anyother colour if you parralel the active and neutral the earth would need to be the same size so you would have to use another colour with earth too whitch is where it becomes illegal not dangerious.

i would suggest if you have your heart set on it go price the plugtops you will most likely find that it is almost as expensive as a short extension cord rated at ten amps whitch would hold up under load over that distance by the time you make it.

would be good for caravans thou.

now that i have rained on your parade for a few days check out the cord i have been using in the garden for months i thought of you today while i was puting up a fence so i took this photo.

http://www.facebook.com/photo.php?pid=103594&l=650a1d7559&id=100001360862696

short answer is just do it and tell noone you will know thou and maybe solder the conductors?

[elkangorito]

In all my years of building high power speakers, I have never seen that happen, but it could.

Speakers carry massive current but at relatively low voltage ( 12 -> 70 V )

Sorry Moondog but speakers do not 'carry massive current', unless you wish to deafen the neighbourhood with sound (thousands of real watts [RMS]).

The reason why some speaker cables are so large is all to do with 'skin effect'. At high frequencies, the current in conductors tends to travel on the outside of the conductor.

Actually, this is a total 'rip-off' for everyone because the frequency is not high enough to worry about (audible frequencies) unless you have ears like a dog & your sound system is of a 'normal' size (less than about 50 Watts RMS per channel).

The people who know about this simply buy normal 'figure 8' speaker cable....& their listening enjoyment is superb (unless they have ears like a dog).

40 Watts RMS per channel is enough to blow the doors & windows out of your house.

[applied]

40 Watts RMS per channel is enough to blow the doors & windows out of your house.

Maybe where you are but we use those fancy square rocks so you can huff and
you can puff but it won't blow my house down

[Moondog55]

Well I consider 75 Amps massive, and thousands of watts is about right, you have to remember that I did not say this was for home use, although my home stereo is conservatively rated at about 1200 watts I usually only use about 12 or 15 of them.

[Pedantic button ON] Talking about RMS is wrong it is only power that should be discussed I can give you the links if you want [Pedantic button OFF]

Ant the main reason we use big cable is to handle the voltage drop on long runs, although 4mm^2 is about the limit for convenience.

At home I use 3 core 2.5mm^2 with the earth and neutral wires soldered together for the return, but as I bi-amp and use multiple subwoofers the current isn't all taken by one cable.

[Master Splinter]

The reason why some speaker cables are so large is all to do with 'skin effect'.


<pedantic> The reason why some speaker cables are so large is that it provides Monster Cable (TM) with a unique selling proposition so that they can convince people to pay $80 -$200 for an interconnect that functions just the same as the $5 one from Deal Extreme (especially when it comes to digital signal cables).

We'll ignore the comparison that showed that people could not tell the difference between Monster Cable and old coathangers (http://consumerist.com/2008/03/do-coat-hangers-sound-as-good-monster-cables.html).

Right, that's kicked Monster Cable (TM)'s groin again. Job done. </pedantic>

<pedantic> <ironic> Yes, I was wrong with my pedantic tag syntax....it should actually be /pedantic </ironic>, <lame_excuse> but I typed that before my morning coffee and I had /brainfunction. </lame_excuse> </pedantic>

<sarcasm> If anyone wants to point out that I have nested my tags incorrectly, feel free to post... </sarcasm>

<untagged_text> Just to be different, I haven't tagged this text. </untagged_text>

[chrisp]

<sarcasm> If anyone wants to point out that I have nested my tags incorrectly, feel free to post... </sarcasm>

<tag_check> They're all good! </tag_check>

:)

[Cecile]

This is one of the funniest threads I've read in a very long time.

Oh, and I was going to try to make a scrolling marquee tag with < hysterical >< /hysterical > but the scrolling marquee tag didn't work and it's not nearly as funny as you guys anyway

[Master Splinter]

<henny_youngman> Thank you. We'll be here all week. Try the veal. </henny_youngman>

[elkangorito]

My comments in blue.


Well I consider 75 Amps massive, and thousands of watts is about right, you have to remember that I did not say this was for home use, although my home stereo is conservatively rated at about 1200 watts I usually only use about 12 or 15 of them.

I assumed a 'normal' stereo system & not an industrial strength 'blow the brains out of people' type of system.

[Pedantic button ON] Talking about RMS is wrong it is only power that should be discussed I can give you the links if you want [Pedantic button OFF]

Feel free to discuss RMS & 'power' with me at any time. :)

Ant the main reason we use big cable is to handle the voltage drop on long runs, although 4mm^2 is about the limit for convenience.

Considering that you are not talking about domestic stereo systems but systems that use thousands of watts, voltage drop would certainly be a major consideration.

At home I use 3 core 2.5mm^2 with the earth and neutral wires soldered together for the return, but as I bi-amp and use multiple subwoofers the current isn't all taken by one cable.

I must reiterate that 40 watts RMS per channel is enough to blow the doors & windows out of your house....unless you like 'live concert volume' whereby you could not hear me if I shouted into your ear from about 10cm away.

With regard to the extension lead, as a temporary measure only, I would parallel some cores together to do the job.
Since this is a temporary measure, a more permanent solution must be designed in which flexible cable is not used.

[Moondog55]

Maybe we should move discussion of system power to the home theater part of the forum.

I have friends with stereos that develop 5 watts and they are happy, but those systems do not develop concert levels of sound and I like to listen to classical music at live levels.