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I'm moving my dryer from one side of the laundry room to the other one, and extending my circuit from the existing outlet box -- the new length of the run (old+new) is roughly 25 feet.

During an on-site consultation, my licensed electrician suggested I use 10/3 Romex** for this, which also happened to match the recommendation of the staff at the hardware store, where I purchased a spool of 20feet of that 10awg cable. I fished that thing through.

I was sifting through my LG dryer's user manual to figure out a detail, and stumbled on this:

If the branch circuit to dryer is 15 ft. (4.5m) or less in length, use UL listed No.-10 AWG wire (copper wire only), or as required by local codes. If over 15 ft (4.5 m), use UL-listed No.-8 AWG wire (copper wire only), or as required by local codes. [elided]

15ft max on 10/3, why so short?

What possibly could be going on here? I looked at the voltage drop table, and it's something like 1.9V at 25' (30Amp circuit, single phase ~240V AC). Is the manufacturer being paranoid, is my electrician being lenient, what?

Here's the output of the [voltage drop calculator] (https://www.cerrowire.com/products/resources/tables-calculators/voltage-drop-calculator/) for this (I think I'm using it with the correct values):

voltage drop

Regarding my local code (I'm in BC, Canada), it does provide equations that can let me pick the right conductor for the job, but I can't use them without the parameters and tolerances of the equipment attached to the circuit -- which LG doesn't give.

Example:

example equation
Click here for full size. (there's a second page of steps to arrive at the answer, which I've omitted)

The specs of the dryer don't reveal much, in terms of max draw, or average power consumption. It just says it needs a 30A circuit, and single phase 230VAC 60Hz, fused at 30A (on both sides of the line).

** 10/3 Romex is a non-metallic sheathed cable with 3 insulated copper conductors (10AWG), and a bare copper. The outlets in my particular case have 4 pins. The dwelling was built in 1990.

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    Does seem weird for such a short distance. Voltage drop should not be much of factor till you start with larger distance(100ft). The only thing that would make any sense is if the electronics inside are that sensitive. Miss the older simple(non electronic) times.
    – crip659
    Commented Jan 13, 2023 at 11:41
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    Well written question. Doesn't make much sense to me, either. I suspect that there was a problem somewhere and LG's lawyers made them include this instruction as a CYA.
    – FreeMan
    Commented Jan 13, 2023 at 12:33

2 Answers 2

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My best guess is that someone who absolutely did not understand the National Electrical Code (NEC) or electrical engineering got confused between the rules for and the reasons behind:

  • Maximum length of cable/wire for connection from receptacle to breaker
  • Maximum length of cord for the cord/plug of an appliance

The only issue I am aware of regarding length of the cable/wire from receptacle to breaker is voltage drop. And, as you have already determined, that is simply not an issue with 10 AWG wire for a 30A circuit in most houses. And if you had a house where that was an issue from the main panel because the house was HUGE, you would almost certainly have a subpanel closer to the laundry room.

However, there are very different rules for cordage. In fact, as I understand it cordage actually should have the same issues with respect to voltage drop (i.e., not an issue at typical distances) and less of a problem with heating (because it is not inside an insulated wall cavity), but there can be other factors. However, a prime rule for cordage is to keep the length to the shortest practical. For a typical dryer, that is 4 to 6 feet. Not long at all, and based on the dryer being right next or right in front of the receptacle, which makes sense as dryers are normally installed in designated laundry rooms or in planned areas elsewhere (kitchen or bathroom). Moving a dryer receptacle is easy compared to the other things in a laundry room - plumbing for the washer. It is perfectly normal to have special rules for long cordage. An extension cord for a large appliance that is suitable at 6' may really have issues if the same cordage was used at 20'. While it does not explain the wire size issue, there is a definite push to keep cords short to avoid tripping hazards, which is a big reason behind spacing of receptacles in living areas (12' so 6' cord is enough for most things) and kitchens (4' so 2' cord is enough for most things).

Combine all of that with a manual writer who is handed a pile of stuff and told "format this nicely", then reviewed by someone for spelling, grammar and formatting but not for electrical accuracy, and this can be the result.

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    Seems like a very reasonable assumption.
    – FreeMan
    Commented Jan 13, 2023 at 13:31
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    A long time ago in a place far away(high school) one of my teachers mentioned that electricity flows on the outside surface of wires, so cordage/stranded wires should be better than solid wires. Think long cordage concerns is that it can get in the way.
    – crip659
    Commented Jan 13, 2023 at 13:37
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    @crip659: Skin Effect. But at 60Hz the effective "skin" depth is over 8mm - so over 16mm diameter. For normal house wiring this never comes into play.
    – brhans
    Commented Jan 13, 2023 at 14:39
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    @crip659 also a stranded wire acts just like a normal wire as far as the skin effect is concerned. It doesn't apply separately to each strand. Commented Jan 13, 2023 at 17:59
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    @manassehkatz-Moving2Codidact I do get derating for continuous loads. There is some disagreement as to whether this applies to a dryer as a continuous load is defined as 3 hours or more. At any rate (pun intended), for decades a dedicated circuit for a clothes drier was 10/3 w/grnd and it worked fine. Commented Jan 13, 2023 at 19:41
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I suspect they might be a bit over-cautious, but they are over-sizing the cable to allow for the current surge when the dryer starts up.

A stalled motor can draw a much higher current than normal. Maybe 10 times its running current. Any motor that is starting up is temporarily stalled until it gets running. How big that current surge is, and how long it lasts, depends on the load on the motor.

A dryer will contain high-power heating elements, and a motor to rotate the drum. If the dryer is full of heavy wet clothes, the motor may be struggle to get the drum rotating.

If the volt drop in that brief period is too high, the motor may take longer than it should to start up. This leads to overheating and damage to the motor. Even if it does manage to start, the damage may accumulate over many drying cycles.

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    That doesn't quite add up. The gas model uses a 120V 15A circuit. I would expect motors and control electronics to be largely the same except for the heating element. Which puts the motor as capable of running on something under 15A @ 120V, probably a lot less than that. But this is an interesting beast - the manual gives instructions for hard-wiring the dryer, which is something I haven't seen in the past, though it can make a lot of sense. Commented Jan 13, 2023 at 20:58
  • Looked at a similar high-end GE dryer and it also allows hard-wire installation but it doesn't specify anything about the circuit beyond 10 AWG, 30A fuse or breaker. Commented Jan 13, 2023 at 21:02
  • re:hardwiring. I suspect that's a cost saving strategy to ship the same product in multiple geopolitical locations. From the user manual: The power cord (pigtail) connection between the wall receptacle and the dryer terminal block IS NOT supplied with the dryer. Type of pigtail and gauge of wire must conform to local codes and with instructions on the following pages. (the printed manual doesn't actually provide these instructions. I looked. maybe online it's different). I wasn't there for the original installation, I imagine the service technician slapped on some 4-prong cord they had.
    – init_js
    Commented Jan 13, 2023 at 21:44
  • The cord/plug is not installed for two reasons: 1 - as has been the case for decades, there are both 3-prong and 4-prong receptacles, so they ship with nothing and let the installer get whichever type and length is needed; 2 (new for this and similar recent models) - they allow for hardwiring as well. Hardwiring does not use the same type of cable as cord/plug. Commented Jan 14, 2023 at 23:37

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