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Topic Title: Undersized cables
Topic Summary: Atlas Kablo
Created On: 03 October 2017 01:21 PM
Status: Read Only
Linear : Threading : Single : Branch
 Undersized cables   - rogerbryant - 03 October 2017 01:21 PM  
 Undersized cables   - KFH - 03 October 2017 02:29 PM  
 Undersized cables   - AJJewsbury - 03 October 2017 02:30 PM  
 Undersized cables   - broadgage - 03 October 2017 04:03 PM  
 Undersized cables   - Zoomup - 08 October 2017 09:14 AM  
 Undersized cables   - broadgage - 08 October 2017 09:33 AM  
 Undersized cables   - sparkingchip - 03 October 2017 03:55 PM  
 Undersized cables   - sparkingchip - 03 October 2017 04:04 PM  
 Undersized cables   - davezawadi - 04 October 2017 10:49 AM  
 Undersized cables   - mikejumper - 04 October 2017 02:06 PM  
 Undersized cables   - Zoomup - 08 October 2017 09:18 AM  
 Undersized cables   - davidwalker2 - 04 October 2017 04:26 PM  
 Undersized cables   - Zoomup - 08 October 2017 09:19 AM  
 Undersized cables   - davidwalker2 - 04 October 2017 04:30 PM  
 Undersized cables   - AJJewsbury - 04 October 2017 04:46 PM  
 Undersized cables   - rogerbryant - 05 October 2017 06:55 AM  
 Undersized cables   - broadgage - 05 October 2017 09:40 AM  
 Undersized cables   - broadgage - 05 October 2017 11:06 AM  
 Undersized cables   - Zoomup - 08 October 2017 09:21 AM  
 Undersized cables   - Zoomup - 08 October 2017 09:25 AM  
 Undersized cables   - AJJewsbury - 08 October 2017 09:42 AM  
 Undersized cables   - Zoomup - 08 October 2017 09:58 AM  
 Undersized cables   - Zoomup - 08 October 2017 09:48 AM  
 Undersized cables   - AJJewsbury - 08 October 2017 10:14 AM  
 Undersized cables   - sparkingchip - 08 October 2017 10:45 AM  
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 03 October 2017 04:03 PM
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broadgage

Posts: 2389
Joined: 07 August 2007

IIRC the reduced conductor size will not be a problem in the majority of cases, most cables in domestic use are indeed lightly loaded if compared to their nominal rating.

For example domestic lighting is commonly wired in 1.0mm on a 6 amp MCB. If the allegedly 1.0mm cable is in fact 0.8mm, then that is still good for 6 amps.

Domestic small power is commonly wired in 2.5mm, as either a 20 amp radial or a 32 amp ring final. If the alleged 2.5mm is actually 2.0mm, then that should be good for over 20 amps.

So MOST installations should be fine, but the worry is the small percentage that are already marginal and could be pushed "over the edge"
Consider for example two ring finals bundled together and both slightly overloaded to 35 amps. The 32 amp OCPD will pass 35 amps almost forever, and four cables bundled together and each carrying 17 or 18 amps will get very warm and perhaps dangerously hot.
Even worse would be a circuit that is ALREADY wrongly installed, but goes from a "bit rough but probably ok in practice" to "dangerous" as a result of undersized cable.
For example it is regrettably common to use 2.5mm twin with earth on a 32 amp MCB to supply a cooker or electric shower.
Incorrect in most cases, but generally OK in practice. If however the cable was only 2.0mm then an already poor choice could become actually dangerous.
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