ECN Electrical Forum - Discussion Forums for Electricians, Inspectors and Related Professionals
ECN Shout Chat
ShoutChat
Recent Posts
100 Definitions: Accessible 2023
by gfretwell - 07/22/24 09:03 PM
Chinese motors rated 220 v 50 hertz
by sabrown - 07/22/24 04:29 PM
240V only in a home and NEC?
by emolatur - 07/18/24 01:05 PM
2023 CEU Course
by gfretwell - 07/17/24 01:08 AM
Is this really a thing
by dsk - 07/16/24 01:23 PM
Recent Gallery Topics:
This is a new one
This is a new one
by timmp, September 24
Few pics I found
Few pics I found
by timmp, August 15
Who's Online Now
1 members (Scott35), 264 guests, and 22 robots.
Key: Admin, Global Mod, Mod
Previous Thread
Next Thread
Print Thread
Rate Thread
Page 1 of 4 1 2 3 4
#122077 09/21/05 09:37 PM
Joined: Aug 2001
Posts: 7,520
P
pauluk Offline OP
Member
Here we have a graphic demonstration from the U.K. of the damage which can result from running a heavy load on a coiled extension cord.

Quote
I came across this extension lead in work, I was borrowing it from another department. They kept it coiled on a cable reel. When I collected the extension cable it looked fine, when I began to uncoil it; it still looked fine, until I had removed the first set of turns, the whole outer coil, then I noticed a problem. The inner coils wouldn't unwind, they had melted into an amorphous blob of plastic and copper. Clearly someone had run this extension lead at close to full load when it was coiled. The cable heated up but as the cable was coiled the heat couldn't dissipate fast enough and the cable just kept getting hotter, until it melted.

I forced off some of the second layer of coils so that I could see exactly the extent of the damage.


[Linked Image]

[Linked Image]

Joined: Mar 2005
Posts: 1,803
Member
This is a cardboard drum of cable, as supplied by the manufacturer, and adapted to make up an extension reel!!? - Unless the Chinese re-exported this from The New Guinea Rain Forest Economic Electric Co Inc. The mind boggles at what crass idiocies businesses will get up to to save a few pounds!

Alan


Wood work but can't!
Joined: Jun 2005
Posts: 821
S
Member
^^
Not mention the money the company wasted! LOL.

I have never seen anything like this before, thats for sure...

Joined: Aug 2001
Posts: 466
Likes: 1
J
Member
Of course it is a cardboard roll. If they used a metal reel everything steel would have been flying thru the air and landing on the magnetized coil.

Joined: Sep 2001
Posts: 806
N
Member
I've replaced a few of those overhead retractable cord reels used in garages, etc. Exactly the same failure mode when someone plugs in a heavy load without unreeling the entire length of cable.

Joined: Dec 2001
Posts: 2,498
T
Member
Help!
Guess that's why all real extension cord reels here now have a thermal cutout!

Mine is bit hefty though... sometimes it trips on the load of a standard 18W flourescent wand the second you plug it in, out in cold weather... a hefty kick on the reel or stomping it onto the ground usually helps...

Joined: Jan 2005
Posts: 155
D
Member
My son learned a valuable lesson after he plugged in a heatgun into the outlet on my retractable trouble light drop cord while working in the garage. I discovered it the next time that I tried to extend it to work on the car. That may be why most retractable trouble lights (if not all) sold today don't have outlets on them today.
It's one of those thngs you forget about and them after it happens "dah" I should have known better.

Joined: Aug 2001
Posts: 7,520
P
pauluk Offline OP
Member
Quote
If they used a metal reel everything steel would have been flying thru the air and landing on the magnetized coil.

With opposing AC currents in adjacent conductors? [Linked Image]

The center of this is actually metal. As Alan pointed out, this reel is the type that our equivalent of Romex comes on -- A central metal cylinder with cardboard disks fitted each end.

Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Member
I have an extension cord mounted on a reel, with receptacles in the end cap. I find it very useful, and a great way to transport and store the cord.
While mine is home-built, it anticipated the commercial manufacture and sale of a similar product- though theirs' is a lighter-duty version.

The commercial product is, I believe, UL listed. My cord does not show any signs of heat damage.

I would be very interested in learning the details of this melt-down. What wire size? How many amps? Over how long a time?

With the neutral accompanying the hot wire within the cord, I have trouble thinking "induction heating" occurred. Rather, I think that heat built up as if the wire was within thermal insulation.....and only reached melt-down because of overloading.

Anyone willing to set up a test?

Joined: Dec 2001
Posts: 2,498
T
Member
I assume 1,5 sq mm wire and a significant overload. Commercially manufactured ones for 230V usually have a label "1500W max. when rolled up, 3500W completely unwound", that means 6.5 and 16A. So a 16A load might already be able to do that.

Joined: Aug 2001
Posts: 7,520
P
pauluk Offline OP
Member
I'm afraid I have no more details about this mishap. I'm not sure of the source now either -- I stashed the pics and notes on my disk a while ago.

Judging by the original author's description, it sounds as though he would have no knowledge of the precise circumstances either..

As T-R suggested, I would think it's 1.5 sq mm conductors (that's between 15 and 16 AWG).

It looks like the blue version of \"Arctic flex.\"



[This message has been edited by pauluk (edited 09-24-2005).]

Joined: Dec 2004
Posts: 161
G
Member
This might have happened because it was still on the reel; extension cables, with their paltry length, just can't wind on that many coils, bought by the drum: no limit!

So probably a company DIYer or even a qualified engineer did this!

Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Member
OK, guys, here's the results of today's experiment.

I used an (nominal rating) 1800 watt space heater as my load. This heater does have temperature settings; I set it on the maximum. Since the day was rather nice (65 degrees F), the heater would not operate at full bore.

For a cord, I wound about 80 ft. of #12 SJEOW (about 2.3mm dia for stranded) around a cable reel.
The reel was 4" diameter at the smallest, and about 5" long. The core was cardboard tube, while the ends were plastic. I had 4 or 5 layers of cable when done.

I placed a thermocouple in the middle of the length, atop the first layer...approximating the location of the char in these pics.


After an hour of running, the thermocouple registered 110 degrees F; I weasured a draw of 11.4 amps. This draw did not vary for the few minutes I measured it.

I did note that one of the molded-on plugs of the cord supplying this set-up was noticeably warm to the touch. The test spool did not seem warm; I did not uncoil the cord.


I would conclude that overheating on a coil is NOT a concern. I would like to repeat this test again some time, with a load closer to 20 amps, and under conditions that would eliminate any cycling that the heater may do; I won't see those conditions until the holigay season.

Joined: May 2003
Posts: 1,158
Member
" I won't see those conditions until the holigay season."


Is this a New thing for Reno [Linked Image]
What will the marketers think of next

Joined: Apr 2005
Posts: 73
D
Member
Wasn't the char under the top layer? Woundn't it have been better to place T/C under top layer? Even in your experiment, if you had checked again in 2 hours, What would the temperature have been? I am also curious to know why heat build up occurred in appoximately the center wraps going end to end.
Larry

Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Member
I placed only one thermocouple; I had no special reason for placing it there, except that that approximates the location of the scorch in the first pic.

The temp climbed to 90 degrees pretty quickly after I started the test. After about 45 minutes, it was at 108. An hour later, 110. While I did not graph this out, it does appear that the temp had pretty well stabilised.


"Everyone has opinions...but data makes yours stand apart." This test was just an attempt to get some data. I wouldn't want to make a general concusion until I have a little more.
But...it sure looks like the theory that coiling the cord causes some magical super-heating of the cord is on it's way to the dust bin.
Can multiple layers of cord act as an insulator? Sure....we just don't know if this is a problem that needs addressing. Yet...

Joined: Aug 2001
Posts: 7,520
P
pauluk Offline OP
Member
Quote
So probably a company DIYer or even a qualified engineer did this!

It does almost look as if somebody may have just bought a reel of Arctic flex and fitted a plug and trailing socket, leaving it coiled up on the original drum.

Assuming this was fitted with normal BS1363 connectors, the highest-rated appliance one would expect to have been connected would have been about 3kW, drawing around 12.5 amps on our 240V supplies.

Of course, if somebody had shoved an adapter or power strip on this extension and then connected multiple loads, the current could have been more. The 13A cartridge fuses in our plugs will carry a substantial overcurrent for quite a long time.

Joined: Dec 2004
Posts: 161
G
Member
I see no reason to believe it was 1.5mm2 flex. Smaller 0.75mm2 blue arctic flex is readily available in the UK:
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=152382&N=401

Joined: Aug 2001
Posts: 7,520
P
pauluk Offline OP
Member
It looks a little large in overall diameter for 0.75mm compared to the reel, but I'll admit it's hard to judge in the photo, so it could be.

Even if it were the intermediate 1.0 sq. mm size it wouldn't be too hard to overload.

1.0 sq. mm = #17 approx.

0.75 sq. mm is between #18 and #19 AWG.


Edited to add:

The following link is to a conversion chart in the Technical reference area for those not familiar with European cable sizes:
https://www.electrical-contractor.net/ubb/Forum15/HTML/000087.html



[This message has been edited by pauluk (edited 09-26-2005).]

Joined: Sep 2005
Posts: 1
S
Junior Member
Pauluk

I just had a customer last week asking why it was important to unwind the cord from a reel. What a great example.

I would like to use this picture on our website as an example of what can happen.

A good example like this may just keep someone else form making a disastrous mistake.

Thanks


Steven Border
www.budgetlighting.com
Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Member
Sborder, the entire point of my experiment was to see if there was justification for that "rule." We have NOT established there is any hazard in leaving the cord coiled up.
Indeed, many industrial locations (and auto garages) have ceiling-mounted cord reels.

Joined: Jul 2004
Posts: 145
C
Member
I think Pauluk got it when he showed the comparison between cable sizes, US commercial grade cords are *much* heavier than the UK equivalent.

A pro-grade 2.5mm cord reel (2.5mm being approximately 13 Guage) would be fine wound up even at 13 amps I would think, maybe even 16.

This cable, apparently wasn't.

I have certainly seen grossly undersized cords used coiled, for long periods, with no apparent ill effect, and then something like this comes along and makes you go 'hmm'.

I don't think 'magical' superheating is likely at all, but it may make something marginal, go just the other side of that margin.

Joined: Feb 2004
Posts: 1,438
Member
Ahhh this is reminiscent of a garage I went into where someone was complaining a strip of plugmold had stopped working... with an air compressor and all sorts or goodies loading it up... It traced out to be running on 16/3 orange cord coiled up in the rafters 20+ feet off the floor, the coil looked about like this

Joined: Nov 2000
Posts: 2,148
R
Member
I have had to repair cord on reels on fire and rescue trucks because of this type of damage. In those cases the reels were 250' of 12-3 and the load 500 to 1000 watts. Often times the outer jacket was melted together about 2/3s of the way into the reel if it had been used with only 75' to 100' unrolled. Note that part of the problem on those reels was the metal rods in the center.
Don


Don(resqcapt19)
Joined: Oct 2004
Posts: 806
Member
Some time ago whilst browsing the site here I ran into a thread/post where an EC had a coil of 12/2 NM melt down when he used it as an extension cord. If I find it I'll edit this with the link....

I think with the right conditions of coil wrap it is possible for a choke or inductor-like effect to cause excessive heating, with enough build-up to cause damage. As reno pointed out, there are many cord reels in use and statistically, how many have failed in this way? Probably not a lot.

And as rescapt19 mentioned, I'm sure a metal core/rod would act to increase heating effects.


Stupid should be painful.
Joined: Dec 2001
Posts: 2,498
T
Member
There must have been a significant number of failures, otherwise the Industry would never even consider putting in thermal cutouts as a standard!

Joined: Jun 2003
Posts: 1,143
D
Member
A few months ago the son of a H.O. I was doing a service & panel upgrade for showed me his cord - he'd been running an air compressor via a 100' 14/3 extension cord.

Quite melty in parts... explained the theory of "electron flow" as best I could.

Joined: Mar 2005
Posts: 1,803
Member
Errr. Is that a steel tube in that drum?....

Alan


Wood work but can't!
Joined: Oct 2004
Posts: 806
Member
Quote
The core was cardboard tube, while the ends were plastic. I had 4 or 5 layers of cable when done.

reno, I think that was why you didn't see much of a temperature rise in your experiment. So far all the other posts seem to indicate the problem arises when there's metal of any kind in the center core. Would you be willing to try again with a metal cored reel and post the results? [Linked Image]

I'm still looking for that other thread, I'll find it eventually....


Stupid should be painful.
Joined: Oct 2004
Posts: 265
D
Member
For a control, also roll out your cord so that you can see the temperature rise compared to a cord used in its "intended" state.

Joined: Jan 2005
Posts: 5,460
Likes: 3
Cat Servant
Member
Those are both excellent sugestions....but, again, I'll have to wait a bit for conditions to be right for a more demanding test. Or, perhaps I'll rig up another load, one without an internal thermostat.
Either way, I will keep you posted. And, should anyone else beat me to it- my feelings won't be hurt at all!

Joined: Dec 2001
Posts: 2,498
T
Member
Too bad I don't have thermocouples or other means to check the temperature inside the reel. Otherwise I'd offer to do a test with a solid 2000W heater without thermostat.

Joined: Jan 2014
Posts: 1
G
New Member
I'd be interested in obtaining a photograph like this for a safety alert I'm publishing. We've had a few serious incidents related to this kind of thing. Tried to PM the poster but no response. If anyone else has anything similar, maybe you could post it or PM me. It might save somone some day.

Joined: Apr 2002
Posts: 7,390
Likes: 7
Member
Glowlight:

Welcome to ECN forums, from one of the 'Jersey Guys'!!

Pauluk has not been active here for a while, so he may not have received your PM.





John
Page 1 of 4 1 2 3 4

Link Copied to Clipboard
Powered by UBB.threads™ PHP Forum Software 7.7.5