I understand it is bad practice to concatenate extension cables.
Why?
I understand it is bad practice to concatenate extension cables.
Why?
On 2025-06-25, Chris Hogg <[email protected]> wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Because Americans.
They don't have fused plugs, so by daisy-chaining extension leads they
can easily overload the ones closer to the supply and start fires. So
"over there" it's considered a serious problem.
Theoretically*, with the 13A (or less) fuse in all UK plugs, is shouldn't
be possible to overload anything, and the worst that will happen is the
fuse will blow (or you'll trip on the tangle of wires and kill yourself
that way instead).
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Ohms law
On Wed, 25 Jun 2025 13:45:30 +0100, Andy Bennett <[email protected]>
wrote:
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Ohms law
Can you be a bit more explicit?
On 25/06/2025 14:24, Chris Hogg wrote:
On Wed, 25 Jun 2025 13:45:30 +0100, Andy Bennett <[email protected]>
wrote:
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Ohms law
Can you be a bit more explicit?
Sure, V = IR.
NY wrote:
So the longer the cable, the more resistance in the wires and
therefore the more voltage dropped across it.
Fair enough. But it is any worse to daisy-chain two 20-metre extension
cables than to use a 40-metre extension cable?
The 40m extension is more likely to come as 2.5mm^2 cable and the 20m extensions more likely as 1.5mm^2 ... unless from Amazon ...
On 25/06/2025 17:37, Andy Burns wrote:
NY wrote:
So the longer the cable, the more resistance in the wires and
therefore the more voltage dropped across it.
Fair enough. But it is any worse to daisy-chain two 20-metre extension
cables than to use a 40-metre extension cable?
The 40m extension is more likely to come as 2.5mm^2 cable and the 20m extensions more likely as 1.5mm^2 ... unless from Amazon ...
The outside diameters of all three cables that I have are very similar, suggesting that they are all 1.5 mm^2 or all 2.5 mm^2.
I've committed the cardinal sin of daisy-chaining three extension reelsIt will just be lower power, thats all
- 40 and two 20s - to run our garden shredder at the bottom of the
garden close to where I'm stripping branches off fallen or pruned trees,
so I don't have to lug all the branches up to nearer the house and shred
them on the gravel drive.
On 25/06/2025 16:37, mm0fmf wrote:
On 25/06/2025 14:24, Chris Hogg wrote:
On Wed, 25 Jun 2025 13:45:30 +0100, Andy Bennett <[email protected]>
wrote:
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Ohms law
Can you be a bit more explicit?
Sure, V = IR.
So the longer the cable, the more resistance in the wires and
therefore the more voltage dropped across it.
Fair enough. But it is any worse to daisy-chain two 20-metre
extension cables than to use a 40-metre extension cable?
I've committed the cardinal sin of daisy-chaining three extension
reels
- 40 and two 20s - to run our garden shredder at the bottom of the
garden close to where I'm stripping branches off fallen or pruned
trees, so I don't have to lug all the branches up to nearer the house
and shred them on the gravel drive.
So the longer the cable, the more resistance in the wires and therefore
the more voltage dropped across it.
Fair enough. But it is any worse to daisy-chain two 20-metre extension
cables than to use a 40-metre extension cable?
I understand it is bad practice to concatenate extension cables.
Why?
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance.
For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and overheat.
[1] So if something goes wrong (say you partially chop through you hedge trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the adiabatic equation to see what effect extra extension lead resistance
can have)
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance.
For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and >overheat.
[1] So if something goes wrong (say you partially chop through you hedge >trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the >adiabatic equation to see what effect extra extension lead resistance
can have)
On 25/06/2025 12:47, Chris Hogg wrote:
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance.
For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and overheat.
[1] So if something goes wrong (say you partially chop through you hedge trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the adiabatic equation to see what effect extra extension lead resistance
can have)
On 2025-06-26 11:48, John Rumm wrote:
On 25/06/2025 12:47, Chris Hogg wrote:I spent some time playing with extension cables when I had the EV before
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance.
For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and
overheat.
[1] So if something goes wrong (say you partially chop through you hedge
trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the
adiabatic equation to see what effect extra extension lead resistance
can have)
the proper charger. The variability between different 13A plugs and
sockets was quite marked, some staying quite cool and others getting worryingly warm for something you need to leave running unattended for
hours. I was testing using an old 3kW fan heater. I was surprised also
at how much warmer a cable would get just coiled on the floor, not even
wound on a reel.
I ended up making my own lead with chunky 2.5 mm^2 cable, which is a bit
of a squeeze in some plugs, an old MK plug of the type where you wind
the conductor around a post and then clamp down with a nut, and a single plastic trailing 13A socket where I was lucky first time. Plugged into a
new RCD-protected wall socket that all ran cool.
The 2.5 cable also stayed reasonably cool when lightly coiled on the
floor rather than stretched out.
The only non-ideal element was the 13A plug moulded on to the charger
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
On 26 Jun 2025 at 13:59:43 BST, nib wrote:
On 2025-06-26 11:48, John Rumm wrote:
On 25/06/2025 12:47, Chris Hogg wrote:I spent some time playing with extension cables when I had the EV before
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance. >>> For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and >>> overheat.
[1] So if something goes wrong (say you partially chop through you hedge >>> trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the
adiabatic equation to see what effect extra extension lead resistance
can have)
the proper charger. The variability between different 13A plugs and
sockets was quite marked, some staying quite cool and others getting
worryingly warm for something you need to leave running unattended for
hours. I was testing using an old 3kW fan heater. I was surprised also
at how much warmer a cable would get just coiled on the floor, not even
wound on a reel.
I ended up making my own lead with chunky 2.5 mm^2 cable, which is a bit
of a squeeze in some plugs, an old MK plug of the type where you wind
the conductor around a post and then clamp down with a nut, and a single
plastic trailing 13A socket where I was lucky first time. Plugged into a
new RCD-protected wall socket that all ran cool.
The 2.5 cable also stayed reasonably cool when lightly coiled on the
floor rather than stretched out.
The only non-ideal element was the 13A plug moulded on to the charger
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
Isn't a warm plug - especially a moulded plug - equally likely to be a poor/loose connection at the socket?
The only non-ideal element was the 13A plug moulded on to the charger
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
On 26 Jun 2025 at 13:59:43 BST, nib wrote:
On 2025-06-26 11:48, John Rumm wrote:
On 25/06/2025 12:47, Chris Hogg wrote:I spent some time playing with extension cables when I had the EV before
I understand it is bad practice to concatenate extension cables.
Why?
The main concern is that inclusion of extra plug/socket connections
combined with the extra cable resistance could result in raising the
earth loop impedance to a point were you could no longer rely on it
being low enough to clear a fault quickly[1].
There is a secondary concern that many extension cable makers will spec
the thinnest flex that they can get away with taking into account the
length. Using several may result in excessive voltage drop at the point
of use - especially for higher power loads. For mainly resistive loads
this may just result in lower performance / less power at the appliance. >>> For something like a mower with an induction motor, it could result in
motor damage since it can draw more current that it was designed to, and >>> overheat.
[1] So if something goes wrong (say you partially chop through you hedge >>> trimmer cable, and end up with it snared in the blade and shorted) the
fault current that flows needs to be large enough to blow the fuse
before the cable melts or catches fire. (you can play about with the
adiabatic equation to see what effect extra extension lead resistance
can have)
the proper charger. The variability between different 13A plugs and
sockets was quite marked, some staying quite cool and others getting
worryingly warm for something you need to leave running unattended for
hours. I was testing using an old 3kW fan heater. I was surprised also
at how much warmer a cable would get just coiled on the floor, not even
wound on a reel.
I ended up making my own lead with chunky 2.5 mm^2 cable, which is a bit
of a squeeze in some plugs, an old MK plug of the type where you wind
the conductor around a post and then clamp down with a nut, and a single
plastic trailing 13A socket where I was lucky first time. Plugged into a
new RCD-protected wall socket that all ran cool.
The 2.5 cable also stayed reasonably cool when lightly coiled on the
floor rather than stretched out.
The only non-ideal element was the 13A plug moulded on to the charger
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
Isn't a warm plug - especially a moulded plug - equally likely to be a poor/loose connection at the socket?
Isn't a warm plug - especially a moulded plug - equally likely to be a poor/loose connection at the socket?
I spent some time playing with extension cables when I had the EV beforeI remember my parents' three-bar electric fire began to emit "a funny
the proper charger. The variability between different 13A plugs and
sockets was quite marked, some staying quite cool and others getting worryingly warm for something you need to leave running unattended for
hours. I was testing using an old 3kW fan heater. I was surprised also
at how much warmer a cable would get just coiled on the floor, not even
wound on a reel.
The only non-ideal element was the 13A plug moulded on to the charger
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
On 26/06/2025 13:59, nib wrote:
I spent some time playing with extension cables when I had the EV
before the proper charger. The variability between different 13A plugs
and sockets was quite marked, some staying quite cool and others
getting worryingly warm for something you need to leave running
unattended for hours. I was testing using an old 3kW fan heater. I was
surprised also at how much warmer a cable would get just coiled on the
floor, not even wound on a reel.
The only non-ideal element was the 13A plug moulded on to the chargerI remember my parents' three-bar electric fire began to emit "a funny
which would always get warm, especially around the L pin, though pin,
fuse and fuse holder looked clean.
smell" when it was on three bars for a while. I investigated with my multimeter.
There was no measurable resistance between the live wire in the plug and
one end of the heating element, nor between the neutral wire and the
other end of the element.
I noticed that the live pin was getting too hot to touch, and this
happened in a variety of sockets, so it *probably* wasn't high
resistance contact between socket and pin. It turned out to be poor
contact between the live-wire side of the fuse and the fuse itself,
between spring clip and circular barrel of fuse - I measured about 5
ohms which is 13^2 * 5 = 845W being dissipated in that bad junction. :-(
I spent some time playing with extension cables when I had the EV before
the proper charger. The variability between different 13A plugs and
sockets was quite marked, some staying quite cool and others getting worryingly warm for something you need to leave running unattended for
hours. I was testing using an old 3kW fan heater. I was surprised also
at how much warmer a cable would get just coiled on the floor, not even
wound on a reel.
On 26/06/2025 15:55, NY wrote:
On 26/06/2025 13:59, nib wrote:
I spent some time playing with extension cables when I had the EV
before the proper charger. The variability between different 13A
plugs and sockets was quite marked, some staying quite cool and
others getting worryingly warm for something you need to leave
running unattended for hours. I was testing using an old 3kW fan
heater. I was surprised also at how much warmer a cable would get
just coiled on the floor, not even wound on a reel.
The only non-ideal element was the 13A plug moulded on to theI remember my parents' three-bar electric fire began to emit "a
charger which would always get warm, especially around the L pin,
though pin, fuse and fuse holder looked clean.
funny smell" when it was on three bars for a while. I investigated
with my multimeter.
There was no measurable resistance between the live wire in the
plug and one end of the heating element, nor between the neutral
wire and the other end of the element.
I noticed that the live pin was getting too hot to touch, and this
happened in a variety of sockets, so it *probably* wasn't high
resistance contact between socket and pin. It turned out to be poor
contact between the live-wire side of the fuse and the fuse itself,
between spring clip and circular barrel of fuse - I measured about
5 ohms which is 13^2 * 5 = 845W being dissipated in that bad
junction. :-(
Hardly. In the case you are postulating, the volt-drop across the
fuse-end would be 65 volts so the load would receive about 165 volts.
What sort of 13A-socket-compatible load would draw 13 amps at 165
volts?
Interesting anecdote - shame about the dodgy digits ;}}
I once had a Netgear powerline adapter (a.k.a. mains wifi extender)
which wouldn't work properly if one of the two adapters was plugged
into a short trailing mains socket.
On Sat, 28 Jun 2025 16:07:48 +0100
Pamela <[email protected]> wrote:
I once had a Netgear powerline adapter (a.k.a. mains wifi extender)
which wouldn't work properly if one of the two adapters was plugged
into a short trailing mains socket.
That's not an electrical power or resistance issue, it's because the
signal being transmitted has a very high frequency which does not
travel well in power cables, and particularly not through plugs and
sockets. I have a pair of powerline devices which work through the
particular extension cable I used to use at one end, but the
instructions simply say not to use them at all.
Transmission will depend on lots of things about the house wiring, the
shape of the cabling, how many spurs, and other things. All the things
that need to be done carefully in high frequency transmission lines are completely wrong in electrical wiring. It's a wonder they work at all.
On 2025-06-25, Chris Hogg <[email protected]> wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Because Americans.
They don't have fused plugs, so by daisy-chaining extension leads they
can easily overload the ones closer to the supply and start fires. So
"over there" it's considered a serious problem.
Theoretically*, with the 13A (or less) fuse in all UK plugs, is shouldn't
be possible to overload anything, and the worst that will happen is the
fuse will blow (or you'll trip on the tangle of wires and kill yourself
that way instead).
* I'm not convinced that poundland-specials could cope with a sustained
load of whatever-it-takes to blow a 13A fuse.
So, although it's not as bad as American media would have you believe,
you still need to be careful. 20 wall-warts taking less than 20W max
each is fine, A kettle, 3-bar electric fire, and toaster may be pushing
it, even on a single extension lead.
On Sat, 28 Jun 2025 16:07:48 +0100
Pamela <[email protected]> wrote:
I once had a Netgear powerline adapter (a.k.a. mains wifi extender)
which wouldn't work properly if one of the two adapters was plugged
into a short trailing mains socket.
That's not an electrical power or resistance issue, it's because the
signal being transmitted has a very high frequency which does not
travel well in power cables, and particularly not through plugs and
sockets. I have a pair of powerline devices which work through the
particular extension cable I used to use at one end, but the
instructions simply say not to use them at all.
Transmission will depend on lots of things about the house wiring, the
shape of the cabling, how many spurs, and other things. All the things
that need to be done carefully in high frequency transmission lines are completely wrong in electrical wiring. It's a wonder they work at all.
On 2025-06-25, Chris Hogg <[email protected]> wrote:
I understand it is bad practice to concatenate extension cables.
Why?
Because Americans.
They don't have fused plugs, so by daisy-chaining extension leads they
can easily overload the ones closer to the supply and start fires. So
"over there" it's considered a serious problem.
Theoretically*, with the 13A (or less) fuse in all UK plugs, is shouldn't
be possible to overload anything, and the worst that will happen is the
fuse will blow (or you'll trip on the tangle of wires and kill yourself
that way instead).
* I'm not convinced that poundland-specials could cope with a sustained
load of whatever-it-takes to blow a 13A fuse.
So, although it's not as bad as American media would have you believe,
you still need to be careful. 20 wall-warts taking less than 20W max
each is fine, A kettle, 3-bar electric fire, and toaster may be pushing
it, even on a single extension lead.
On 26/06/2025 13:59, nib wrote:leave running unattended for hours. I was testing using an old 3kW fan heater. I was surprised also at how much warmer a cable would get just coiled on the floor, not even wound on a reel.
I spent some time playing with extension cables when I had the EV before the proper charger. The variability between different 13A plugs and sockets was quite marked, some staying quite cool and others getting worryingly warm for something you need to
fuse itself, between spring clip and circular barrel of fuse - I measured about 5 ohms which is 13^2 * 5 = 845W being dissipated in that bad junction. :-(The only non-ideal element was the 13A plug moulded on to the charger which would always get warm, especially around the L pin, though pin, fuse and fuse holder looked clean.I remember my parents' three-bar electric fire began to emit "a funny smell" when it was on three bars for a while. I investigated with my multimeter.
There was no measurable resistance between the live wire in the plug and one end of the heating element, nor between the neutral wire and the other end of the element.
I noticed that the live pin was getting too hot to touch, and this happened in a variety of sockets, so it *probably* wasn't high resistance contact between socket and pin. It turned out to be poor contact between the live-wire side of the fuse and the
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