Total Noobie Question: Using a heavier cable in the middle safe? - Page 1
Forum section: electronics / beginners

author: The009
author_rank: Newbie
timestamp: October 22, 2020, 11:18:51 pm
content: Hello All,Here is an issue I currently have.I have a load that is currently on a 18AWG cable that has a connector in the middle. The cable is to short and I need to make it longer.I have tons of 16AWG laying around, would it be safe to splice a segment of 16AWG in between the two 18AWG Segments?The cable can not just be replaced from the PSU or the Load just made longer with a extension bitThank you for any help.EDIT: PS I am sorry if this belongs in the power category, I was torn between which one it should go in.Voltage: ~36vLoad: Constant ~300wExtension Length: ~5ftPSU is Sealed and can't be accessed to replace the starter cableLoad is Sealed and can't be accessed to replace end cable.Regards,The009

author: vk6zgo
author_rank: Super Contributor
timestamp: October 23, 2020, 02:41:25 am
content: Not a problem electrically, but I haven't dealt with AWG wire for "many moons",------- how much thicker is 16AWG?I am only thinking in terms of it being heavier & perhaps might put more mechanical stress on the connections in the device.My guess is that it won't be a problem, but sometimes it is the "not very technical" things which can be .

author: Ground_Loop
author_rank: Frequent Contributor
timestamp: October 23, 2020, 03:15:04 am
content: The 16AWG extension will be fine.

author: james_s
author_rank: Super Contributor
timestamp: October 23, 2020, 03:15:54 am
content: Not tremendously larger, it's common to see at least as much variation in outer jacket thickness.There are charts for converting AWG to mm^2.https://www.multicable.com/resources/reference-data/cross-reference-awg-to-mm2/As for the OP's question, the weakest link must be strong enough to carry the maximum load, electrically speaking the weakest link should always be the fuse or circuit breaker. It is never a problem other than for mechanical or cosmetic reasons to use a thicker wire. Likewise you could use a section of heavy rope or chain to extend a thinner and weaker rope or chain without issues. The capacity of the system is still determined by the weakest part.

author: bob91343
author_rank: Super Contributor
timestamp: October 23, 2020, 03:27:18 am
content: Every three AWG steps results in half (or double) the resistance per foot. Since this is only two steps, the difference is almost negligible. Still, if you are increasing cable length, it's best to add as little resistance as possible, so using 16 AWG is a good idea.16 AWG is about 0.004 Ohms per foot if memory serves.

author: ogden
author_rank: Super Contributor
timestamp: October 23, 2020, 04:05:09 am
content: As already said - it will work. You may consider to shorten remaining 18AWG "tails" down to convenient for installation lenghts, so main run of the cable is 16AWG.

author: Berni
author_rank: Super Contributor
timestamp: October 23, 2020, 04:21:49 am
content: If anything AWG16 is more appropriate for the job since a longer cable has more resistance and will loose more voltage along the way, so having a thicker cable compensates for that. This is pretty common in 12V systems where loosing a few volts along the way is definitely not acceptable so long cable runs are overrated to reduce resistance.Tho this being 300W at 36V = 8.3A and AWG18 is 8mOhm per foot, so the loss is only about 0.3V along 5ft of it. So voltage drop really is not a problem. You could proabobly get away just fine even with AWG20 wire even, tho it might be a little warm.

author: ledtester
author_rank: Super Contributor
timestamp: October 23, 2020, 04:53:14 am
content: Quote from: Berni on October 23, 2020, 04:21:49 amThe 5 ft extension is the 16AWG wire. The OP didn't say how long the 18AWG wires are.(Also the voltage drop is going to be twice 0.3V if you count the return path - still not really a problem for 36V.)I do agree that if the OP has "tons" of 16AWG wire I would just use that for the entire run - given that the run is at least 5 ft and the current is > 8A.

author: The009
author_rank: Newbie
timestamp: October 23, 2020, 05:08:28 am
content: Thank you all for answering the question.I used to run network cable like no other and make RJ45 junctions of all sorts practically in my sleep.But I have never used larger cable in the middle on anything more then lousy hobby stuff like Arduino. My brain said it was safe but me being a programmer and not a professional electrician was thinking anything that can go wrong will go wrong.When I was younger I was told NEVER use a different size wire on one run as your job-site wont pass inspection. I learned to do mains on housing and that is all I was ever taught.Then in the entertainment industry doing stage stuff, those cables always went largest to smallest ( which made sense )So while my brain said yeah it has to be safe, everything I was taught when younger was 'Don't do it man that is not code'.Quick Edit:As it was mentioned a couple times.The original cable is only about 1 foot long to begin with

author: wizard69
author_rank: Super Contributor
timestamp: October 24, 2020, 08:21:39 pm
content: Quote from: The009 on October 23, 2020, 05:08:28 amGood answers here but you really need to understand context.QuoteElectrical systems (home and industrial wiring) are regulated via codes to keep thing simple and safe at the lower end of the industry. For example the NEC requires specific minimal wire sizes for 15 and 20 amp circuits for all cases of insulation and installation methods. This doesn't mean you can't go larger and in some cases you should (minimization of voltage drop), just that you can' go smaller even if the engineering calculations might allow it.QuoteThis is absolutely correct. It prevents the accidental application of the wrong size breaker if for example somebody was to tack on some 14 ga wire to a 12 ga run. The original intent might have been to run a 15 amp breaker on 12 ga due to a long run, somebody coming up 30 years later might say hey I got 12 ga wire let me bump up the breaker immediately creating a fire hazard. The danger that the code trys to eliminate is running too much current through a given wire.QuoteWell there are lots of things to consider here, but the code always wins.First; going bigger (higher capacity wire) is not a concern. Remember the NEC is all about fire and personal safety, if you implemented a wire of smaller capacity you would instantly have a problem.Second I'm not clear as to what you are wiring up here but it sounds like some sort of power supply, remotely connected to another device. This has to be done safely but there is allowance to properly engineer the wiring which the manufactures have most likely done.Third the code does provide for a number of very specific cases where you cam go to a smaller wire on a branch circuit. For example light fixtures can have much smaller wire than the 14 ga or 12 ga found in lighting circuits. The wires have to remain in the junction box the fixture is mounted on though. But beyond very specific case you can never drop in gauge size without protection of some sort. Another example, frankly related to another posts, is creating branch circuits from wire splitting blocks. You can split a large conductor, in a panel box, to smaller ones to feed branch circuit breakers if you meet all requirements. The norm though is to never permit going to another size conductor on a branch circuit.QuoteAs long as you use the original manufactures plugs and sockets you should not have a problem. I've seen far to many cases where people cut off the manufactures socket & plug, then end up using a NEMA spec'ed socket outside of its designated usage. While this might not create a fire hazard it can create a other issues. If the plug and sockets the manufacture uses are hard to source you probably should consider a new solution outside of the NEMA or other standardized plug and socket solutions.