Chassis ground to neutral in Seattle?
March 20, 2020 2:52 PM   Subscribe

I just moved to a home with a 3-prong dryer outlet. My dryer has a four-prong. I read an old ask, did my YouTube research, decided this is something I should be able to swap, and bought a 3-wire cord. However, the manual calls out that in some places the electric code does not allow you to connect cabinet-ground conductor to neutral wire. I can follow dryer instructions but government codes are inscrutable! Does Seattle allow this?
posted by rouftop to Home & Garden (14 answers total)
 
You should call the county or city building department that handles electric inspections. They will know. If it were me I'd want to hear it from the regulating body, not some rando on the interweb.
posted by humboldt32 at 2:58 PM on March 20 [2 favorites]


I recognize that sometimes you can do something that's to code once, and then the code changes, and so the next guy has to upgrade it to get it to code, but...if the house has a 3-prong dryer outlet, and the house is in Seattle, surely that means you're allowed to connect to a 3-prong dryer outlet in Seattle? At least for that pre-existing house?
posted by Huffy Puffy at 3:15 PM on March 20 [1 favorite]


Get a quote to fix the outlet. It might not be all that expensive.
posted by jgreco at 3:42 PM on March 20


I deleted a bit of my question because I thought it wasn't relevant but maybe it is. The dryer has instructions for wiring a 3 prong outlet where the code allows the connection, and then other instructions for wiring a 3 prong outlet where code disallows this connection. The latter requires you to actually run a ground. So I guess there are places where your home can have a 3-prong outlet that you are not allowed to use. I suspect this is not the case in Seattle but I'd still like to do this correctly.
I reached out to the city number but got no answer -- they may not yet have wired things up for WFH calls...?
posted by rouftop at 4:00 PM on March 20


Neutral is not equal to ground, and does carry current. On your dryer outlet, it will be the difference in current between the two hot legs - i.e., if you have lots of 120v stuff on that goes through breakers on one side of the panel, and not much on that goes through breakers on the other side of the panel, the neutral will be charged by that difference of amperage.
Doesn't directly answer your question, but this is why.
posted by rudd135 at 4:30 PM on March 20


First off, this is grandfathered, so you don't need to change the outlet. Electric codes do not cover the appliance, only up to the outlet itself.

However, there's a very small chance of bad things occurring (dryer body becoming a live voltage), which is why it's mandated all newer systems that need a neutral have a separate ground wire. Also, clearly, for many decades all homes were setup this way and most people lived.

So it's up to your risk tolerance.

If it were me? I would wire up the 3-wire cord and verify a low-impedance connection from the neutral to a ground (copper water pipe or the ground of any grounded outlet), then put it in my TODO list to have a separate ground wire run.

Or I'd get a dryer that only needs 240V and ground (no neutral connection) and use that with a 3-wire plug. This is exactly as safe as having a separate ground wire for an appliance that needs neutral.
posted by flimflam at 4:33 PM on March 20


I would say that in a normal universe, (only one receptacle on the circuit, neutral and ground bus bonded,) the 3 prong is just as safe as the 4 prong. The receptacle exists so it isn't a code violation to use it.
posted by Pembquist at 7:07 PM on March 20 [1 favorite]


Seattle building department will be able to answer this with a phone call. You won't have to identify yourself so there isn't any possibility of legal blow back whatever you decide.

Personally for a place I owned I'd upgrade the building wire if at all within possibility and budget. Or switch to a gas dryer if you have gas handy in/near the laundry room.

The receptacle exists so it isn't a code violation to use it.

The receptacle exists because it would still be legal in new installs for pure 240V loads (for example a really big cord connected A/C). Also just because a home improvement store sells something doesn't mean it is legal or even particularly safe to install (shocking i know). They regularly sell (for a particularly egregious, clear cut and common example) accordion drain P Traps that don't have smooth interiors despite them being illegal for use on potable water connected systems. They also routinely sell unlisted (illegal to install) electrical fixtures.

Also, clearly, for many decades all homes were setup this way and most people lived.

And the code changed because enough people didn't.

This is one of the quirky differences between the NEC and CEC. In Canada 4 wire receptacles have been required for at least 40 years, maybe all the way back to the 60s when bonded receptacles first became required for standard receptacles. And in Canada you can't convert a newer dryer to three prong. It's fine to continue using a three prong dryer (or range) if it has been in place since before the rule change but if you buy a new dryer you have to upgrade the receptacle.
posted by Mitheral at 7:47 PM on March 20


I would just make the 3-wire conversion on your dryer. It's the same outlet the owner before you used for their dryer and likely used for decades. The NEC changed to a 4-wire plug in 1996 but the 3-wire is grandfathered for existing outlets.

Just make sure you make the cabinet ground connection to neutral. Read the dryer manual carefully. Some use a wire to make the bonding connection. Some have a bus bar that connects neutral and chassis ground terminals.

The neutral wire is connected to the same bus bar on the panel as all of the other grounds from your standard typical grounded outlets. It is a dedicated circuit so that the only current in the neutral wire is the small amount used by the electronic control panel in your dryer. So it is effectively the same as a ground. The only thing that a fourth dedicated ground wire provides is redundancy for a bit more safety.

See the exception in the national code below. Your outlet should meet all of these requirements for the exception.

National Electric Code 250.140 Frames of Ranges and Clothes Dryers

Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.
The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.
The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.
Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

posted by JackFlash at 9:11 PM on March 20 [2 favorites]


It is a dedicated circuit so that the only current in the neutral wire is the small amount used by the electronic control panel in your dryer. So it is effectively the same as a ground.

Little nitpick: The motor turning the drum is 120V. A 1/4hp motor only draws a couple amps but it is still a lot more than a small amount used by a timer put on the bond conductor.
posted by Mitheral at 9:42 PM on March 20


Right. And don't forget the light bulb!

Anyway, its a few amps in a 10 gauge wire so the voltage drop is effectively zero.
posted by JackFlash at 9:58 PM on March 20


I would have the receptacle upgraded. Building codes are there for a purpose. I am not an electrical engineer, but I trust that the folks who write codes are, and there must be a reason for the code to specify circuits and equipment.

My first house had a few not quite up to code improvements from previous owners. They were easy to overlook until I sold the house. The seller had a house inspection, and I ended up hiring an electrician, on short notice (which adds to the cost) to correct things the inspector found. They were technically grandfathered in, but I wanted to sell quickly so I had the work done.

If it’s possible you may end up needing to have the receptacle upgraded, you may as well do it now when you can shop around, and get a little peace of mind for your expenditure.
posted by coldhotel at 7:22 AM on March 22


I would have the receptacle upgraded.

If the cable is exposed all the way to the panel, this would be pretty easy to do. But if the cable is routed through finished walls, it can require some demolition and repair to fish a new cable 10/3 with ground, which could be rather expensive.

The current receptacle is perfectly safe as long as the neutral is secured at the panel and the receptacle. It has been that way for decades and wires generally don't just spontaneously disconnect themselves.

I might think twice if the cable is aluminum, but that is easy to check by removing the cover to the receptacle. In that case I would consider the expense of running a new cable or at least using an approved Al/Cu pigtail.
posted by JackFlash at 9:23 AM on March 22 [1 favorite]


The receptacle exists because it would still be legal in new installs for pure 240V loads (for example a really big cord connected A/C). Also just because a home improvement store sells something doesn't mean it is legal or even particularly safe to install (shocking i know). They regularly sell (for a particularly egregious, clear cut and common example) accordion drain P Traps that don't have smooth interiors despite them being illegal for use on potable water connected systems. They also routinely sell unlisted (illegal to install) electrical fixtures.

I think you misread me. By "the receptacle exists" I mean the receptacle that is in the owners house exists not that they are available for sale, I should have said "is an existing receptacle". It is legal to use because the code says it is legal to use see Jack Flashes post.
posted by Pembquist at 3:47 PM on March 28


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