What should gauge really mean for stranded cables? - Page 1
Forum section: electronics / testgear

author: SharpEars
author_rank: Unknown
timestamp: December 29, 2014, 07:00:26 pm
content: According to Wikipedia:QuoteAfter cutting apart numerous power and extension cords, it seems that power/extension cord manufacturers feel otherwise. They want, for cost saving (and customer scamming) purposes, gauge to reflect the actual diameter and cross-sectional area of the stranded cable. What this means is that a "12 gauge" stranded power cable performs like (i.e., has the resistance characteristics of) a 14 gauge solid copper cable of the same length, because a true 12 gauge stranded wire must be thicker than a solid copper wire of equivalent gauge in order to have comparable resistance characteristics.The manufactures then go on to dupe their ignorant customers a second time, by making the ground wire two gauge units higher than the (already non-conforming) hot/neutral conductors. Granted, the ground wire should not conduct any electricity in a properly functioning circuit, but then the manufacturers extend the lie further by marking the cable as 12/3, 14/3 or 16/3, even though the ground wire has a higher gauge than the other two wires.Let's face it, copper is expensive and any steps that (these unscrupulous) manufacturers can take to conserve it adds up to pure profit.The vast majority of customers aren't even aware of this scam, because they simply judge cables by their outer girth which includes the sheath. They do so by comparing the thickness of one cable with another, but if both are scams what good does that do on an absolute scale?In order to properly test cable, one needs to measure wire resistance with a milliohmeter or a milliohm capable multimeter that most people lack. Even using a wire gauge meter is not enough, because it may show the stranded cord diameter as conforming, when in reality it is not since it should be thicker than the stated gauge, at least to abide by Wikipedia's (common sense expected) definition of what gauge means for stranded wire.

author: Zero999
author_rank: Super Contributor
timestamp: December 29, 2014, 07:20:14 pm
content: Wikipedia is correct.Providing you buy cable from a reputable manufacturer, there shouldn't be a problem. Another possibility is the cores aren't perfectly circular, so can be packed more densely, with less of an air gap than perfectly round wire.

author: SharpEars
author_rank: Unknown
timestamp: December 29, 2014, 07:24:43 pm
content: Quote from: Hero999 on December 29, 2014, 07:20:14 pmNo matter how the cores of a stranded cable get packed, wound or extruded, they must by definition (and physics) result in a total wire diameter that is strictly larger than the diameter of a solid cable (of equivalent resistance). There will always be air/space gaps between the individual strands regardless of their geometry.Every single power cable/extension cord I have tested (at least among cord with marked gauges from 14/3 to 10/3) perpetuates this scam. I have yet to find a cable/cord that doesn't.

author: robrenz
author_rank: Super Contributor
timestamp: December 29, 2014, 07:25:20 pm
content: Measure the diameter of the individual strands and then count how many there are.Look up on this gauge tableto see what effective gage wire you have.

author: SharpEars
author_rank: Unknown
timestamp: December 29, 2014, 07:28:39 pm
content: Quote from: robrenz on December 29, 2014, 07:25:20 pmThanks robrenz, the values in this table state my argument objectively!

author: SharpEars
author_rank: Unknown
timestamp: December 29, 2014, 07:32:31 pm
content: By the way, how do these scammers get their UL/cUL listing? Does UL use a wooden ruler with 1/4" marks to (imprecisely) measure cable gauge or what?For example,UL Standard 62is forFlexible Cords and Cables. However, I don't know what it means for a power cord to comply with this standard, since UL forces one to pay almost a thousand dollars to view it.I now know that a product saying that it is UL listedmeans absolutely nothingto me as a consumer, since there is no way for me to view what the UL standard says about the product.

author: tautech
author_rank: Super Contributor
timestamp: December 29, 2014, 07:35:26 pm
content: In our part of the world we haven't had gauge # in all stranded cable types for 40 years.It's been mm2and IMO there is much less confusion this way.Even single conductor is classed this way now, but often specs are stated both in gauge & metric cross-section.

author: SharpEars
author_rank: Unknown
timestamp: December 29, 2014, 07:44:18 pm
content: Quote from: tautech on December 29, 2014, 07:35:26 pmWhether AWG or mm2is used, specs for stranded cable should be stated in terms of a solid conductor of equivalent resistance and not as actual specs for the stranded cable itself.

author: electr_peter
author_rank: Unknown
timestamp: December 29, 2014, 08:12:35 pm
content: Topics about poor quality cables are becoming more and more frequent recently.Cable properties is one of the areas manufacturer can blatantly lie, becausecable properties are not primary interest of typical consumerit is not obvious from the external looks and markingsit is relatively hard to test (for typical consumer)Metal costs being the big partof cable cost, results are predictable - more and more manufacturers fake product markings.If you want to have proper cable, either make it yourself or buy from reputable source. Personally, I do not trust mm2 markings on cable until I check. I have not encountered smaller earth cable yet, though.

author: robrenz
author_rank: Super Contributor
timestamp: December 29, 2014, 08:14:10 pm
content: If you look at that chart you will see thatalmostall of the stranded variations are lower resistance than solid.There is no trickery involved in the stranded specification. IMO the few that areslightlyhigher resistance are a consequence of standard bundle counts on the very high strand count versions.

author: tautech
author_rank: Super Contributor
timestamp: December 29, 2014, 08:15:09 pm
content: Quote from: SharpEars on December 29, 2014, 07:44:18 pmI acknowledge your point, but consider this: if the Standards in a country or some adopted international Standard specify the max current a particular mm2conductor can carry then adopt that.IMO it's more important that any country's Standard be rigidly adhered to and that should be the issue. Does it comply with the appropriate Standard?If it's mains related it should, end of story.Here there has been a down rating of our TPS cabling ~ 20 years ago, maybe to accomodate the point revealed in you OP. IIRC it was ~20%.A good sparkie mate tells me from time to time how the wiring Standards are being constantlyas they should be IMO.It is expensive to purchase decent extension cables here now especially 2.5mm2(12g) and even hard to find them. The comsumer market now dictates, not the trade where this stuff is more commonly used.

author: Monkeh
author_rank: Super Contributor
timestamp: December 29, 2014, 08:39:45 pm
content: Quote from: SharpEars on December 29, 2014, 07:44:18 pmA 2.5mm² stranded cable will be the same resistance as a 2.5mm² solid conductor.

author: AlfBaz
author_rank: Super Contributor
timestamp: December 29, 2014, 10:41:46 pm
content: Here (aus) a 2.5mm² stranded wire is also called 7/067 which means it has 7 strands each with a diameter of 0.67mm. The 2.5mm² is usually nominal. This, however, is not flex and not used in extension leads. A quick google reveals flex 2.5mm² is 50/025

author: Monkeh
author_rank: Super Contributor
timestamp: December 29, 2014, 10:43:01 pm
content: Quote from: AlfBaz on December 29, 2014, 10:41:46 pm2.468mm². Plenty close enough.

author: AlfBaz
author_rank: Super Contributor
timestamp: December 29, 2014, 10:44:57 pm
content: Quote from: Monkeh on December 29, 2014, 10:43:01 pmAgreed

author: Someone
author_rank: Super Contributor
timestamp: December 29, 2014, 11:37:48 pm
content: Quote from: SharpEars on December 29, 2014, 07:00:26 pmThis is why Australia and other countries introduced appliance testing (PAT testing etc) for products in service. The importer takes on the responsibility of ensuring the product is fit for service, but customers still don't understand that when they buy from overseas they become the importer.http://en.wikipedia.org/wiki/Portable_appliance_testing