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Discuss Cable getting warm in the Industrial Electrician Talk area at ElectriciansForums.net

S

sivoodoo

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Hi all,

The cable supplying an immersion heater is getting warm when in opperation. In opperation for 2 hours per day. Cable warms up in a few mins.

Seperate radial on 16A MCB.

Cable length approx: 18 meters.

Can not work out cable CSA without callipers, it looks like 2.5mm (will measure tomorrow).:confused:

Switched of breaker at CU untill I find the problem.

Am I correct in asuming the cable is too small, hence the heat?

Any ideas?

Thanks

Si
 
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B

beaver74

  • Thread Starter Thread Starter
  • #2
sound good to me

what route does it take from consumer unit i.e though insulation
is it hot at either end could be signs of a loose conection
 
W

WarrenG

  • Thread Starter Thread Starter
  • #3
2.5mm sounds Ok with a 16amp Mcb. I take it the cable is supplying a FCU with heat resistant flex to immersion?
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #4
NO it is not supplied with the thermal flex,

same T&E from crappy looking 13A timer as feed, and no FCU either.

Warm at both ends.

Not verified cable size yet, could be 1.5mm?? need to find this out, not easy, digital calipers would help perhaps?

Cable is bunched with many other T&Es for half its journey (all other cables ambient temp), clipped direct then covered in plaster (less than 50mm).

Cheers guys,

Si.
 
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M

mdshunk

  • Thread Starter Thread Starter
  • #5
Warm can mean lots of things. The use of that word is pretty much meaningless.

What are the measured Z's? What is the measured insulation resistance? Does the conductor gauge agree with the measured amp draw?

The mind always goes to loose or resistive connections, and next to a low-level short, when one talks about cables overheating.
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #6
Yes I agree, need to test, will do soon as I am able, just thinking the obvious cable size too small and jumping to conclusions!
 

jeremy

-
Mentor
Arms
If you have access to a clamp metre try measuring the load on the cable, but if it was me i would as a matter of course change the cable to heat resist 3 core 2.5mm as that is what is going to have to be fitted eventually? 1.5 would do but from a local isolation switch to immersion there's not much of a cable run and why not go one up just in case there's a prob with the appliance in future. Better to have a blown MCB than a small fire.
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #8
When using a clamp meter, i take it I just clamp the phase? is this correct?

What kind of reading do i set it too, and what result am i looking for?

The twin and earth from the CU is 1.5mm, the run is four stories, a lot of cable, all burried. Will be ripping out the cable later today and replacing with 2.55mm and heat resistant flex from 20A dp switch next to the immersion.
Thanks.
 
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WarrenG

  • Thread Starter Thread Starter
  • #9
Clamp or Tongue test the Phase conductor on setting (A) for amps (live current test) and meter should show you what load the circuit is pulling in amps.

I personally use the Fluke T5 600V tongue tester, but a clamp meter will do the same job.

Warren.
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #10
Thanks for that, will let you know the results

Current is pulling 13.21A
its a 3kw element.
Cable is 1.5mm
 
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W

WarrenG

  • Thread Starter Thread Starter
  • #11
Thanks for that, will let you know the results

Current is pulling 13.21A
its a 3kw element.
Cable is 1.5mm
Immersions really should be on a 2.5mm cable feeding a FCU for functional switching and then possibably a DP Switch for local isolation for maintenance.

From here you could feed the immersion with some heat resistance flex.

As Beaver74 said there are cabling factors you have to consider when the cable is being run through different areas of the building (such as being run under insulation in the loft, burried in plaster, clipped direct for example)which all has an effect on the cable rating.

I would suggest that you would need to uprate the cable (even though it is carring the load at the moment but don't you know it!) to 2.5mm. If not I think the isulation of the 1.5mm cable wont last.

Fit some functional / isolation points and supply the immersion heater with heat resistance flex.

The flex is usually used to connect the Immersion heater inside the Immersion heating cubard (where it generally gets a bit warm) feed from a local isolation point outside.

That should sort it. :)

Warren
 
S

sivoodoo

  • Thread Starter Thread Starter
  • #12
Thanks Warren, the immersion has a timer at present, will i then have to
a) Run in new 2.5mm cable
b) fit an FCU, (where is the best place to put FCU as there wont be any space in the cupboard after the 20A dp switch and the timer are fitted.
Thanks
 
W

WarrenG

  • Thread Starter Thread Starter
  • #13
S

sivoodoo

  • Thread Starter Thread Starter
  • #14
cheers Warren, so the FCU can go anywhere then..
 
W

WarrenG

  • Thread Starter Thread Starter
  • #15
A typical old domestic would have possibly have one fitted in the kitchen area and one outside the bathroom.

Don't forget that an immersion heater is expensive to run 24hrs a day so many people who still use these will switch them on for several hours to heat the bath water for example or use a timer to arrange this for them.

I do think there is anything in the regs to say that you cannot place a FCU in the cuboard with the Immersion (for local Isolation), but if the Immersion is in the bathroom you will need to take into consideration the moisture (i.e. a IP rated switch etc??) and the actual heat from the Immersion heater?

So don't quote me on this, but personally I would have control outside the Immersion Heater cuboard.
 
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