Very Thin Wiring Inside AC Household Appliances - Page 1
Forum section: electronics / general

author: jonovid
author_rank: Super Contributor
timestamp: November 09, 2024, 01:16:24 pm
content: I occasionally get to teardown old AC mains household appliancesin particular Chinese manufactured microwave ovens & washing machines.expecting to find 7 or 10 amp mains level wiring. but its a lot thinner then that.only when I went to re-use some mains appliance wiring for its insulated spade connectors in a AC mains project did I question if this is the right wiring gauge for the job?having all the appearance of 2amp hook-up wire. has anyone noticed this also?

author: Siwastaja
author_rank: Super Contributor
timestamp: November 09, 2024, 01:25:58 pm
content: If you compare loose wires inside equipment to gauges you would use when wiring up the home, there are two main differences:1) Long wires (as used in home wiring) reduce short-circuit current by introducing resistance because of their length; short-circuit current is important for fuses to blow in time; therefore thicker gauges are required than from heating alone; 2) Home wiring can be inside the walls, possibly in wooden structures and passing through thermal insulation. Even if not, they would have another layer of insulation. So less heat escapes, and again thicker gauge is required.So thinner gauge can work legally and safely inside equipment. Plus, inside grounded or otherwise double insulated equipment thinner wire insulation can be possibly used making the wire appear thinner than its real gauge is.

author: wraper
author_rank: Unknown
timestamp: November 09, 2024, 01:29:59 pm
content: 1.5mm2or 16AWG is completely enough for full 16A load. You need thicker wire in the walls due to voltage loss under load over much larger lengths. Also with better cooling with wire being basically in free air rather than in the tube with other loaded wires you can push quite a bit more current.

author: Someone
author_rank: Super Contributor
timestamp: November 09, 2024, 09:05:00 pm
content: Quote from: jonovid on November 09, 2024, 01:16:24 pmWhy expect 10A rated wire? what's the fuse on the appliance?

author: jonovid
author_rank: Super Contributor
timestamp: November 10, 2024, 02:53:46 am
content: Quote from: Someone on November 09, 2024, 09:05:00 pmmicrowave oventhe appliance fuse is 250V 12A as also stated on the input pcbthe wire diameter 0.9mm but with insulation 1.5mm .

author: Someone
author_rank: Super Contributor
timestamp: November 10, 2024, 03:03:09 am
content: Quote from: jonovid on November 10, 2024, 02:53:46 amSo everything is likely working as intended, 0.9mm diameter with 12A has low enough heating to operate continuously (with appropriate insulation and not being buried inside something extremely hot). 0.75mm2(1.0mm diameter) is completely normal here for domestic/consumer 10A appliance cabling like the ubiquitous mains to IEC C13.

author: wraper
author_rank: Unknown
timestamp: November 10, 2024, 03:03:54 am
content: ^More than enough cross section. Most likely it's rated for <1500W, such cross section would work for twice of that continuously (with some moderate heating), and survive even continuous current required for blowing the fuse.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 10, 2024, 04:12:36 am
content: Those appliances are intermittent loads, in particular the washing machine would only draw maximum current for the 15 or so seconds it takes to accelerate up to spinning speed.

author: TimFox
author_rank: Super Contributor
timestamp: November 10, 2024, 04:34:18 am
content: Here is a wire manufacturer's table of "AWM" wire, used for appliance wiring (inside appliances, not building wiring):https://www.champcable.com/wp-content/uploads/2016/08/48.-EXAR-150-UL3271-R1.pdf22 AWG stranded wire (7 strands of #30) is rated for 14 A.Note that 14 AWG (41/30) is rated for 46 A, but 14 AWG solid wire in buildings (#14 and #12 are typical in home wiring) is rated for only 15 A.

author: Analog Kid
author_rank: Super Contributor
timestamp: November 10, 2024, 05:14:45 am
content: Quote from: TimFox on November 10, 2024, 04:34:18 amPuzzled here: I've done lots of electrical wiring using #14 (& #12), but what is "14 AWG (41/30)"? Stranded?46A? that's got to be some kind of heavy conductor.

author: TimFox
author_rank: Super Contributor
timestamp: November 10, 2024, 03:11:34 pm
content: Yes: 41 strands of AWG 30. This is a standard way to specify stranded wire, and appliance wiring normally uses stranded wire.

author: ejeffrey
author_rank: Super Contributor
timestamp: November 11, 2024, 02:40:01 am
content: The rating doesn't depend much on solid vs stranded. The difference is just how it is used. Fixed wiring needs to handle long runs either bundled in a conduit or inside an insulated wall cavity, and it needs to handle the very high surge currents from inrush without fusing. This we use awg 12 for 20 amp circuits in the US. Chassis wiring that is not in a bundle and in free air has much better cooling and is generally rated several times higher. Very short jumpers with significant cooling from conduction to the ends can be run even higher.Here is a table with one set of guidelines for current capacity:https://www.powerstream.com/Wire_Size.htmThose guidelines are conservative estimates for typical use cases. If you are pushing limits or have unusual situations there is no substitute for more careful analysis.

author: Russ_A
author_rank: Contributor
timestamp: November 13, 2024, 03:45:14 pm
content: I know I'm probably repeating what's above but this is what I can come up with:1. Voltage drop2. Heating of wires in walls and conduits and other confined spaces3. The wires need to withstand pulling and whatever other stresses they're subjected to during installation and house construction4. Being able to conduct very high short-circuit currents, and other faults, without melting insulation or causing a fireWires in appliances generally aren't subject to any of these issues.

author: tom66
author_rank: Super Contributor
timestamp: November 13, 2024, 05:17:31 pm
content: A microwave oven pulls about 1500W (if 1000W power output), so if that's 115V input then maybe 13 amps. You can do 13 amps on 0.75mm^2 cable if it's singly insulated. An appliance fuse should be able to interrupt that fine too preventing any continuous overcurrent.For even lower power appliances, it's acceptable to have even thinner cable, provided a fuse provides protection... e.g. a lot of UK appliances have 13A fuses in the plug but maybe a 2-3A fuse on the power board, so the IEC flex has to be rated to 13A (because that could be used with anything) but the internal cabling in the appliance could be rated at much less.