Where to get a low amperage power cord? - Page 1
Forum section: electronics / projects

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 01:35:31 pm
content: Hi,I have an old piece of equipment (a Heathkit nixie DMM) that needs a new power cord. The old cord is 3 conductors, flat, and low current - probably AWG 20 or smaller. It's just 0.28" wide. It needs to go through a 1/2" hole in the case with a strain relief bushing.Are cords like this still available? I've been unable to find a place to buy one.Thanks,Bob

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 14, 2018, 03:02:14 pm
content: It's probably best to just use 18/3 round computer power cord and switch the bushing out to something like this:https://www.digikey.com/product-detail/en/essentra-components/PGSB-12/RPC4631-ND/3814439https://www.digikey.com/product-detail/en/essentra-components/PGSB-11/RPC3154-ND/3814438

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 03:06:08 pm
content: Are those strain reliefs? It's not clear to me whether they're clamping the cord.

author: reboots
author_rank: Regular Contributor
timestamp: May 14, 2018, 04:00:33 pm
content: You could use a cable gland to hold the cord securely and provide strain relief. PG-7 threads will fit a 1/2" hole.https://www.digikey.com/product-detail/en/essentra-components/CG-PG7-2-BK/RPC1898-ND/3811769If you want to get fancy, there are cable glands with an integrated flexible strain relief:https://www.alliedelec.com/lapp-group-s2307/70123460/

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 04:10:42 pm
content: You might want to review this other discussion:https://www.eevblog.com/forum/beginners/prevent-cable-from-being-pulled-through-hole/

author: Monkeh
author_rank: Super Contributor
timestamp: May 14, 2018, 04:28:38 pm
content: Quote from: reboots on May 14, 2018, 04:00:33 pmGlands are not clamps.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: May 14, 2018, 07:44:25 pm
content: Quote from: rea5245 on May 14, 2018, 01:35:31 pmBob, those are not really safe anymore, in the old days, that sort of thing was done, but made a few fires, etc. I recommend adding the IEC 60320 (https://en.wikipedia.org/wiki/IEC_60320) connector pair if you have the room. This will allow you to choose a cord from almost any discarded piece of modern equipment.Hope this helps...

author: glarsson
author_rank: Frequent Contributor
timestamp: May 14, 2018, 08:08:36 pm
content: Quote from: rea5245 on May 14, 2018, 01:35:31 pmIs it legal? The power cord must be capable to handle the short circuit current until the fuse blows in the equipment or in the distribution panel. In the UK you can have less capable power cords if you fit a low current fuse in the plug.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 08:48:43 pm
content: Quote from: glarsson on May 14, 2018, 08:08:36 pmThe meter has a 1/4 amp fuse.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 08:51:46 pm
content: Quote from: tpowell1830 on May 14, 2018, 07:44:25 pmAlas, the Heathkit does not have room for that: no room to enlarge the hole in the case and no room for the connector inside the case.

author: Fsck
author_rank: Super Contributor
timestamp: May 14, 2018, 09:41:04 pm
content: What about lamp cord? Should be thin enough.

author: glarsson
author_rank: Frequent Contributor
timestamp: May 14, 2018, 09:47:10 pm
content: Quote from: rea5245 on May 14, 2018, 08:48:43 pmWhy did you remove "or in the distribution panel"? The cord must be able to handle a short before the 1/4A fuse, e.g. due to improper cord feed through the enclosure.

author: GerryBags
author_rank: Frequent Contributor
timestamp: May 14, 2018, 09:49:11 pm
content: How about using the retro fabric covered 3-core that Mr. Carlson uses?https://www.aliexpress.com/item/3x0-75MM-Vintage-knitted-black-p-v-cloth-retro-copper-conductor-electrical-wire-pendant-light-lamps/32232743210.html

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 09:52:45 pm
content: Lamp cord doesn't have a ground wire.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 09:53:55 pm
content: Quote from: glarsson on May 14, 2018, 09:47:10 pmBecause I wasn't paying close enough attention. Sorry.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 09:56:54 pm
content: Quote from: glarsson on May 14, 2018, 09:47:10 pmBut wait a minute ... there are plenty of 10A power cords available, and they plug into 15A receptacles. So don't they violate that rule?

author: Myrv
author_rank: Contributor
timestamp: May 14, 2018, 10:03:18 pm
content: Quote from: glarsson on May 14, 2018, 09:47:10 pmProbably because your initial statement wasQuote from: glarssonTheorthere implies to me the cord has to rated to the lower of the equipment fuse or the panel fuse. So stating the equipment has a 1/4 amp fuse is valid as this is all the cord needs to be rated to (assuming this fuse is on the power input) .If this wasn't the case about 90% of the electrical devices in my home would be illegal.

author: glarsson
author_rank: Frequent Contributor
timestamp: May 14, 2018, 10:07:45 pm
content: Quote from: rea5245 on May 14, 2018, 09:56:54 pmThe rules most likely varies depending on where you are.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 10:19:51 pm
content: Quote from: glarsson on May 14, 2018, 10:07:45 pmWell, those cords are available where I am, in the US. Are they available where you are? I think they are frequently used with laptop power bricks.

author: glarsson
author_rank: Frequent Contributor
timestamp: May 14, 2018, 10:44:06 pm
content: Quote from: rea5245 on May 14, 2018, 10:19:51 pmWhat are "those cords"? 10A? That is the common type here (we have 230V). Copper areas are 0.75, 1.0 and 1.5 square mm. You can get smaller than 0.75, and CCA, by buying something cheap on eBay, but those should be taken to the recycling station.

author: rea5245
author_rank: Frequent Contributor
timestamp: May 14, 2018, 11:09:32 pm
content: Quote from: glarsson on May 14, 2018, 10:44:06 pmHere's a 10A, 125V power cord on Amazon:https://tinyurl.com/yaqf2and. It's 18 AWG which would be 0.823 square mm.

author: Gregg
author_rank: Super Contributor
timestamp: May 15, 2018, 02:51:56 am
content: How about one like this? If you are in the US and want to pay postage, I'll send it to you. Genuine made in USA real copper 18 ga new old stock. You could easily fasten the molded flange with a little ingenuity.

author: reboots
author_rank: Regular Contributor
timestamp: May 16, 2018, 08:11:54 pm
content: Quote from: Monkeh on May 14, 2018, 04:28:38 pmAre you saying cable glands aren't suitable for strain relief, or aren't suitable for fastening a cable to an enclosure? Either would contradict the manufacturer's literature I've found. Can you provide more detail?

author: rhb
author_rank: Super Contributor
timestamp: May 17, 2018, 02:10:25 am
content: Get an IEC cable that will fit the hole and cut off the IEC connector. If there is not room for a grommet or cable clamp, get a thin strip of metal flashing and wrap that around the cord where it passes through the case . Secure it with a large cable tie on the inside and another cable tie on the outside, center the cable and slather hot melt glue in the gap and on the zip ties.. Pay attention to the condition of the cable and redo it if it gets to looking dodgy.BTW the bushings used at the end of flexible conduit held in place with hot melt glue will do a fine job as a grommet and eliminate the need for the metal flashing overwrap.Also the flat 3 wire cable is commonly available as a lightweight household extension cord, at least in the US.

author: Monkeh
author_rank: Super Contributor
timestamp: May 17, 2018, 02:15:47 am
content: Quote from: reboots on May 16, 2018, 08:11:54 pmPlain glands are not suited as clamps or strain relief. That's why they make these:Take a normal PVC cable, clamp it in a gland with moderate torque (remember, it's for sealing, not for grabbing the cable). Now pull on it firmly. It will slide at some point.

author: Bratster
author_rank: Frequent Contributor
timestamp: May 17, 2018, 02:19:11 am
content: Quote from: rea5245 on May 14, 2018, 09:56:54 pmI only have anecdotal evidence to support this, but I have not seen a legitimate power cord that uses smaller than 18 gauge wire. 18awg is good for 10amps and I guess somebody determined that that was the smallest allowable wire gauge that could still Trip a 20 amp breaker with no problems.Even though basically all the outlets in most homes in the US are rated for 15 amps a lot of the times they're on 20 amp circuits. Unless it's only one Outlet, in which case it has to be 20 amps rated.The only power cords that I have seen that are a thinner gauge either have a plug with a permanently molded In fuse, are Christmas lights which either have a permanent or a replaceable fuse in the plug, or cheap crap from China that should be thrown away immediatelySent from my Moto x4 using Tapatalk

author: rea5245
author_rank: Frequent Contributor
timestamp: May 17, 2018, 12:16:50 pm
content: Thank you to all who replied.I have found that the Hillman Group's 58237 strain relief bushing can hold a round, 10A cord and still fit into a 0.5" hole, so that's what I'm using.Thanks,Bob

author: CopperCone
author_rank: Super Contributor
timestamp: May 17, 2018, 05:01:23 pm
content: I took apart a power tool recently they had a cable gland that was followed up by a metal strip that was clamping the cable downAn odd combination i can think of is water tight conduit seals.

author: Monkeh
author_rank: Super Contributor
timestamp: May 17, 2018, 05:14:00 pm
content: Quote from: CopperCone on May 17, 2018, 05:01:23 pmBecause a cable flapping around like that is going to get tugged on. The gland will let the cable out eventually, as well as transfer movement of the cores to the terminations, the clamp won't.