Can I Run 20 Amp Tools Off A 30 Amp Outlet? - Page 1
Forum section: electronics / beginners

author: electromateria
author_rank: Regular Contributor
timestamp: May 09, 2022, 10:32:44 pm
content: I have a 35 foot 10/3 extension cable that goes from my dryer outlet to my 250v / 50 AMP stick welder (works great on low setting).My plasma cutter is 125v / 20 amp and my MIG welder is the same. I don't have a 20 amp plug in my house and I'm getting a free 35 foot 10/3 extension cable next weekend so I'll have a second one I could use.My brother in law told me that the dryer circuit carries both 250v and 125v depending which wires I use (that's the reason there are 4 wires instead of 3).My thinking is I'll rewire the cords and plugs on the MIG welder and plasma cutter to ones rated at 30 amps then connect them to the 125v / 30 amp dryer circuit. I'm conflicted on if this is ok or not. Looking for advice to follow, thanks in advance!

author: thm_w
author_rank: Super Contributor
timestamp: May 09, 2022, 10:45:30 pm
content: Depends on if you are asking if its OK as in it will work, or OK it will meet code.The easiest solution is buying the cable with build in 20A breaker:https://www.homedepot.ca/product/ac-works--1ft-30a-4-prong-14-30p-dryer-plug-to-household-outlet-with-20a-breaker/1001632852I don't know if the 30A rewiring will meet code, of course it will work, just be careful and lookup the pinout, measure everything multiple times, etc.

author: electromateria
author_rank: Regular Contributor
timestamp: May 09, 2022, 11:09:58 pm
content: Quote from: thm_w on May 09, 2022, 10:45:30 pmOk as in the device will function without issue and no damage will be caused by improper setup. Why is the code against this kind of setup? If there's good reasoning why I shouldn't do it I'll go the more expensive way I'm really trying to avoid (run 20 amp from breaker).I don't really understand the use of the 20A breaker you linked. It's right at the dryer outlet which is putting out 30 amps, won't that just immediately trip? I thought the machines took the amperage they need. If I run a 10 amp motor off a 15 amp outlet it doesn't need a breaker. What scenario is there an issue that requires a breaker?

author: thm_w
author_rank: Super Contributor
timestamp: May 09, 2022, 11:22:24 pm
content: Quote from: electromateria on May 09, 2022, 11:09:58 pmThe 20A breaker is there to protect the outlet and downstream wiring.If you have a 20A outlet, connecting 20A capable wire, and it is able to pull 30A without tripping a breaker that is bad, as the wiring could burn up causing a fire.If you are rewiring with 30A capable wire, and using 30A outlets, it should be OK.

author: electromateria
author_rank: Regular Contributor
timestamp: May 10, 2022, 12:33:41 am
content: Quote from: thm_w on May 09, 2022, 11:22:24 pmReally appreciate your help! TyvmThe setup will be 30A breaker at the fuse box -> 10/3 to 30A dryer outlet -> 30A plug, 10/3 extension cord wire, 30A receptacle -> 30A plug, 10/3 wired directly into machineMaybe if you'd be so kind you could help me wrap my head around something. In this scenario the machine is rated for 20A but I'm passing 30A to it. In my mind this should cause damage. What is happening to that additional 10A? It just can't pass through? What's the mechanism by which that gets blocked out?

author: themadhippy
author_rank: Super Contributor
timestamp: May 10, 2022, 12:53:14 am
content: your socket can provide UP TO 30A,if your equipment only needs 20A then only 20A will be drawn

author: electromateria
author_rank: Regular Contributor
timestamp: May 10, 2022, 02:17:07 am
content: Quote from: themadhippy on May 10, 2022, 12:53:14 amWhat's the relevant law? I'd like to read up a little on it

author: pqass
author_rank: Super Contributor
timestamp: May 10, 2022, 02:45:40 am
content: Quote from: electromateria on May 10, 2022, 02:17:07 amOhm's law. A load's resistance determins the current drawn at a given voltage.

author: IanB
author_rank: Super Contributor
timestamp: May 10, 2022, 02:47:52 am
content: Quote from: electromateria on May 10, 2022, 02:17:07 amI don't see how this question makes any sense.You have plenty of 15 A outlets in your house, but if you plug a USB phone charger into one of them it doesn't draw 15 A, it draws just what it needs (a few milliamps at most). This is how electricity works. The outlet sets the voltage, the appliance sets the current.

author: Zero999
author_rank: Super Contributor
timestamp: May 10, 2022, 09:58:33 am
content: This is a common question which crops up. I don't know why. It's always been something I thought was obvious because the voltage and resistance of the load is what determines the current. I've considered it to be similar to asking "I have a jack capable of lifting 2000kg. Can I use it to lift a 200kg engine?" To be clear: I'm not attacking the original poster and others who ask it, but the quality of education they've received.

author: BeBuLamar
author_rank: Super Contributor
timestamp: May 10, 2022, 11:18:12 am
content: You should be able to run a 20A tool on a 30A outlet without any problem. If not how can you use a 1A device on a 15A outlet?

author: tooki
author_rank: Super Contributor
timestamp: May 10, 2022, 03:04:29 pm
content: Quote from: Zero999 on May 10, 2022, 09:58:33 amIs ohm’s law a part of any primary education?The average joe has no clue what voltage, current, and power mean, so they use the terms kinda interchangeably, knowing simply to match the numbers.

author: TimFox
author_rank: Super Contributor
timestamp: May 10, 2022, 04:19:48 pm
content: In the US, I was taught Ohm's Law formally in my 8th-grade electricity shop class, when I was 13 years old.They probably just teach coding now.

author: IanB
author_rank: Super Contributor
timestamp: May 10, 2022, 04:26:02 pm
content: Surely we know by observation that a table lamp takes less power to run than a space heater, yet both are plugged into the same receptacle?

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2022, 04:47:50 pm
content: The receptacle is rated for the maximum current it can carry, the circuit breaker in the panel should be sized to protect the wire. You can put a 30A plug on any device that draws 30 amps or less and it will be just fine. The standard household outlet in North America is 15A, you surely have lots of devices that plug into those while drawing much less than 15 amps. The rating is the maximum that it can safely supply, whatever you plug in will draw whatever it needs, if the need exceeds what the circuit can supply then the breaker will trip.A 4 wire dryer receptacle has a ground, a neutral and a pair of live wires that are each 120V to neutral or 240V between them.

author: Zero999
author_rank: Super Contributor
timestamp: May 10, 2022, 04:48:14 pm
content: Quote from: tooki on May 10, 2022, 03:04:29 pmYes. We were all taught Ohm's law at school, at GCSE science level, which was between the ages of 14 and 16. It also made an appearance in other subjects: design and technology and home economics. Typical questions consisted of estimating how long a battery will power a device for and calculating the power consumption and cost of running a mains appliance.

author: electromateria
author_rank: Regular Contributor
timestamp: May 10, 2022, 05:39:43 pm
content: Quote from: IanB on May 10, 2022, 02:47:52 amI kind of recognized that was happening, but don't understand why. I'll put some research into ohms law.Quote from: Zero999 on May 10, 2022, 09:58:33 amMy high school education was kind of similar to a minimum security prison sentenceI had physical science classes in grade 9-10 but it was taught by the most boring, monotone teacher on earth with zero passion for his job. I mostly just ignored everything and still passed, I regret that now of courseQuote from: BeBuLamar on May 10, 2022, 11:18:12 amYeah, just needed to make sure I wasn't overlooking anything. Don't want to destroy expensive equipment.Quote from: TimFox on May 10, 2022, 04:19:48 pmDon't underestimate how easy it is to get through high school. I never failed a test and never studied for any exam except the finals + I skipped school all the time and was pretty faded for any classes after lunch break lol.-Appreciate the advice fellas, I'm confident to move forwards now

author: IanB
author_rank: Super Contributor
timestamp: May 10, 2022, 06:13:39 pm
content: Quote from: electromateria on May 10, 2022, 05:39:43 pmIt's a bit like taking money out of the bank. You can choose how much to withdraw, as long as it is less than your available balance.

author: james_s
author_rank: Super Contributor
timestamp: May 10, 2022, 09:11:26 pm
content: Quote from: electromateria on May 10, 2022, 05:39:43 pmOhms law is one of the very first and most fundamental concepts to learn if you are doing anything with electricity or electronics. It is a very simple equation V = I * R which can be rearranged into two permutations in order to solve for whichever of the three values you don't have.Unfortunately the often used water analogy doesn't quite work to describe electricity. The lower the resistance of a load, the more electricity it will allow the flow through it. If the resistance is too low, it will allow too much flow and the circuit will be overloaded. The important thing to remember is that the load is what determines the amount of flow, and in the case of a simple resistive load like a heating element or incandescent light bulb the flow is determined by the resistance of the filament or element.