- In a previous video,
we reviewed these fantastic retractable cable reels
from Marcaddy and one of the questions
that came up following that video was related
to the power ratings of extension leads.
You'll see there's a difference
between the power rating when they're fully uncoiled
and when they're coiled up.
So in today's video,
we're gonna ignore the manufacturer's instructions
on this cable reel and fully load it with it fully wound up.
Now, I bought this extension lead
from a well-known online retailer
and we can see when it's fully uncoiled
at 10 meters cable length,
it has a power rating of 13 amps or 3,120 watts.
Flip it over and we'll see when it's fully coiled up.
So no cable coming out of it is five amps
and 1,200 watts as a power rating.
So we found something that's gonna take a lot
of power for a long time.
And that's an electric vehicle,
which is where a lot of people are buying extension leads.
And we're gonna see what happens when we put
around 3,000 watts on for a long time
with this fully coiled.
So I'm gonna plug the granny lead
as it's called into the EV.
And on the end here we've got a charger
that'll charge at three kilowatts.
And a lot of people use an extension lead
because the leads that come with them are quite short.
Plug that in there, plug this into the mains
and let's get the charging started.
And I'm gonna plug this in here.
I've put the extension lead in the shade there
so it's not not gonna be affected by the sun.
We don't wanna be unnecessarily overloading it
with the heat from the sun.
Interestingly, all extension leads have a thermal cutout
on it, which we've kept in circuit so far.
And we'll just see how long that actually takes
to trip out as well.
So we'll just start it here.
It's 10:45.
See how long that takes to pop out.
I've also got the thermal camera out as well
because really it's heat that is the issue here
because of the resistance of the cable itself
that generates a power loss, which is trapped
inside the cable reel itself because the cables are wound
and wound and wound on top of it.
So each layer of cable is insulating itself
from the free air
and that should cause this reel to heat up.
But how much will it heat up
and how long will it take for that thermal trip to operate?
Now, we can actually calculate the power loss
inside that extension lead using that equation P
equals I squared R.
So we know the current flowing in the extension lead
from the mount showing on the display for the charger.
It's about 12.51 amps.
And we've measured the resistance of the conductors
inside the extension lead using the multifunction tester.
And that comes out at 0.37 of an ohm.
Now, let's take that current 12.51 squared.
That's 156-ish multiplied by that 0.37 ohms.
And we end up with 57.9 watts.
Now, that's essentially having a small heater trapped
inside the middle of our cable reel
but we've yet to see actually what happens
as a result of that.
Now it's 11:15 or about 30 minutes
since we started the car charging and reassuringly,
the thermal trip has just cut out.
So the car has now stopped charging and if I put my finger
in the side of the reel underneath into some
of those inner layers of the PVC cable now is red hot.
So it's reassuring that that's happened.
However, is that really enough for this trial?
What would happen if we removed the thermal cutout?
So it's now 11:22, I've removed the thermal cutout
and the car's back on charge.
We may be some time.
So interesting, when you take a closer look
at the thermal trip inside the extension lead,
I can see it's got some safety certification marks there,
the CE mark that we find on everything.
And it seems to be rated
at 56 degrees C plus or minus five degree C,
which would make sense because obviously, PVC cables used
inside that extension reel are usually rated to 70 degree C.
(clicking sound)
So we're back in the workshop with our extension leads.
We left the car on charge for over six hours,
which obviously takes a long time for these cars
to charge up when you're charging from an extension lead.
Interestingly, if we look on the thermal camera,
we saw we started off at about 34 degrees measured
on the surface.
That got up to about 60 degrees
at the time the thermal trip cut out,
which correlates similar
to that 56 plus or minus five degree C written on there.
When we took it out and carried it on for hours and hours,
this got pretty toasty.
Measured 90 degrees on the front surface.
But interestingly, when we turned it over
onto the back surface, which again was trapped
near the ground, less airflow probably in there,
122 degrees C.
So let's have a look at what happened to the reel.
Well, at the moment it seems okay.
So this is a 10 meter lead.
Ah, okay.
So we're about, let's say three or four meters in
and we can't pull any more off.
So I think it's time to take this to bits.
So dismantle the reel and we can now see
that the cable has really started to stick to each other
and carry on peeling that.
It is a bit of a sticky mess.
(host grunting) (cables pulling)
And I guess I wonder how long this would've carried on
until we'd ended up with a complete meltdown situation.
Oh, there we go.
Starting to see the innards as that splits open.
You can see there, we're almost getting to the stage,
we can see some proper burning.
We're nearly in.
I guess another few hours of that,
we would've been in a fire situation.
So I think this cable reel nightmare
has proven why extension leads do indeed
have two power ratings.
One for when they're coiled
and one for when they're uncoiled.
The thermal trip is there to protect
against this meltdown situation
but should be seen as a last resort,
not something you should seek to use on a daily basis.
It also further shows when when you're designing
an electrical installation, we often hear talk
about grouping factors when there are lots
of cables grouped together, clipped along a wall
in trunking or within conduit.
And why you need to apply that
because those cables together can heat each other up
because they're essentially
in a similar situation where the heat is trapped
in that bundle of cables
and could create a challenging situation like this.
And we'll leave a link here for the video we made
about the Marcaddy retractable cable reels.
And interestingly, there's even a special version
for EV charging.