Switching from 3 prong to 4 prong dryer plug

[NoGoodAtScreenNames]

Hi folks.

I’ve recently become aware that when my new dryer was delivered and installed (i.e hooked up the cord and plugged it in) they used the existing 3 prong 240 volt plug which apparently is no longer to code.

I’m somewhat comfortable swapping out like for like things but this seems a little more complicated. I’m going to have an electrician do the work here but I do like being able to speak intelligently with them and ask the right questions to make sure they do a good job.


I was hoping that there would be 4 wire service to the outlet (2 hots a neutral and a ground). As I worried the cord only has 3 wires. I opened the sub panel next to the outlet and I’m a little confused as to what’s going on.

First there are two breakers in there that move independently instead of being attached like a double pole breaker should be. I assume that’s not to code.

I expected a wire coming in from the main panel and then another wire going to the outlet coming out. instead there is a 4 wired cord coming in and then two other 3 wired cords going out. One which must go to the outlet. Nothing else is on this circuit that I’m aware of.

Am I thinking of this correctly and was this an old school method of providing 240 volt service?

 

[AlbergSteve]

Assuming the top of the box is the supply coming from the panel, there are two hots and a ground. At the bottom of the box the white nmd has its neutral bonded to ground. While technically this will work, I'm pretty sure (in Canada anyway) neutral can only be bonded at the service entrance, ie. main panel. Pretty sure you cannot use a ground as a current carrying conductor. The electricians may have to run a neutral back to the main panel.
It may have been old school when old dryers didn't need 120v leg to run electronics.

 

[NoGoodAtScreenNames]

Assuming the top of the box is the supply coming from the panel, there are two hots and a ground. At the bottom of the box the white nmd has its neutral bonded to ground. While technically this will work, I'm pretty sure (in Canada anyway) neutral can only be bonded at the service entrance, ie. main panel. Pretty sure you cannot use a ground as a current carrying conductor. The electricians may have to run a neutral back to the main panel.
It may have been old school when old dryers didn't need 120v leg to run electronics.

Thanks. I didn’t open up the main breaker box to see what the supply wire is but you are probably right that one of the top is the supply. That leaves the question of what the newer white romex wire from the bottom is doing. Is that from a different circuit back at the main breaker.

I guess I’m having a hard time picturing why there are three wires coming into the sub panel. In my mind it’s a wire from the main breaker to the sub panel and then another from the sub panel to the outlet. What am I missing?

 

[peakbagger]

If you look in the main panel there are 4 wires in play. On a 240 VAC panel there are the two "hots" coming from the utility, a neutral coming from the utility meter(always white) and a ground (bare or in some cases green). At one and only one point in the system, usually the main panel, the house neutral is tied to ground. When the main panel is installed the neutral bus bar is usually electrically isolated from the panel frame and the ground bus but its usually supplied with a screw or device that can be installed by the electrician to bond the two together. This is only done once in any house usually at the main panel where the utility comes in. In some cases like trailers or apartments, the "main panel" is actually a subpanel and the neutral will stay separate from the ground but there will still be two bus bars in the subpanel.

The intent with an up to date electrical system is that the ground wire never carries current in the house, while the neutral does. Technically a 240 VAC circuit has no need for a neutral as the current runs from one hot to the other and that was how your outlet was wired. What has happened is many dryers and ovens may have a need for a small amount of 120VAC to run the controls or possibly a light. In older equipment, one of the hots would be tapped and tied to the ground to get 120VAC. It worked but violated the intent that there would be no current running through a ground. So this is why the new 240VAC appliances are set up for 4 wire plugs so there is a neutral available if one is needed.

My guess is this box was added after the original wiring to add an additional 240VAC circuit that needed a neutral. They took an existing cable running between a main panel and an existing 240VAC load that had been wired with 2 hots and a ground. They cut that cable and ran the two ends into the box. The grounds were connected to the common bus bar that may or may not be bonded to the steel case while the hots were effectively spliced using the screw down terminals that feeds the newer breakers. The new 240 VAC circuit coming up from the bottom needed a seperate neutral so they just tied both the ground and the neutrai to the ground bus bar on top. This violates the no ground will carry current rule.

In your case the white romex is being bonded to ground in this box, that is not to code. There should be four wires, two hots, a neutral and ground running to the main panel from this box. If there is another circuit being tapped off the outlet there could be two bus bars in the box but the neutral bus bar would be electrically isolated from the panel frame.

In addition to the lack of neutral its highly likely that the cable connections to the breaker were not rated for multiple conductors. Generally a screw down terminal like what is shown is designed for only one conductor. I also cannot tell if the hot wires up top are aluminum or copper. Its very rare to find an aluminum screw down connector rated for two conductors. What happens over time is when the circuit is energized is the connections heat up and cool down, which also means they expand and contract. Aluminum expands and contracts more than copper so the two conductors move around in the connector and eventually the connection gets loose which further increases resistance in the connection ultimately possibly leading to fire. Aluminum also corrodes faster than copper especiall in exposed connectors, this further increases the potential heating an cooling.

My guess is if you call in an electrician they will run a new 4 wire cable to the original 240VAC load and then run a new 4 wire 240 VAC circuit with breaker to the white romex circuit. At a minimum to make a bad thing less worse, turn off the power and clean up any aluminum wiring connectors and coat them with Noalox anti corrosion paste and retorque the screws. Even better is get properly rated 3 port AlumiCon aluminum rated splices and directly splice the two hots on the top of the panel using the AlumiCons and then run two wires down to the circuit breaker. This is just making a bad thing better and doesnt resolve the lack of separate neutral.

BTW folks who add garage subpanels frequently go cheap and only pull three cables to the subpanel and then bond the ground to neutral. This saves the cost of one conductor. As far as I know this is not to code.

There is also another concept of protecting a home from lightning strikes that factors in on why you keep the ground seperate from the the neutral with its own rules and recomendations. That is whole other discussion for another day.

 

[NoGoodAtScreenNames]

Thanks Peakbagger. I wasn’t thinking about this running to another 240v outlet or appliance. It wouldn’t make sense to run a line up here though. There’s no other 240v outlet and every 240v appliance has a separate dedicated breaker. I wonder if this goes to a dead end somewhere. This wouldn’t surprise me based on the DIY hack electrical stuff I’ve found elsewhere in the house. I’ll see if I can figure that out and leave it to the electrician to untangle the mess.

 

[NoGoodAtScreenNames]

So I think you were right. If I trip the breaker(s) the power to the dryer outlet remains on, so the Romex from the bottom must be the branch. No idea where that goes though... so I put the breakers in the off position and we’ll see if I ever notice losing power somewhere.

 

[peakbagger]

Electricians have circuit tracers they can use to chase hidden wires. The hook up a transmitter on one end of the wire and the wire acts like a radio antenna. They thed walk around with receiver and follow the beep.

My last house was a pre WW2 house. I didnt own it for long but found enough odd wiring that I was starting from scratch. My incoming power feed was a 60 AMP fusebox with a bunch of rag tag electrical boxes hanging off it. I found a few wire connections that were just wires twisted together and wrapped with electrical tape. I ran new wires from a new main panel and then located a junction box under the outlets in the main floor and then fished new wires up to the existing outlets.

 

[zrock]

Well now that is unsettling a 220 line feeding something your are unsure were... got a shop or anything close by? they may have split the wire as well and fed 2 110 plugs... Wonder if the same idiot wired my place..LOL Looking through my panel one day and found a 60 amp breaker and wondered what it fed.. Well after digging around i found it fed the whole addition... after checking code the wire size was right and the number of outlets was within range.. Poped in a 15amp braker and now i pop the breaker as i should when i fire up the air compressor..LOL

 

[AlbergSteve]

BTW folks who add garage subpanels frequently go cheap and only pull three cables to the subpanel and then bond the ground to neutral. This saves the cost of one conductor. As far as I know this is not to code.

Yeah, definitely not to code.

 

[Medic21]

Is that aluminum service wire to the panel? That is also not allowed from a panel to a sub panel inside the house.

here the dryer is a 30amp and no requirement for a disconnect. 10/3 with ground from the main panel off a 30amp breaker and get rid of the disconnect if you can. Much simpler and easier.

 

[fbelec]

as i see it the aluminum cable is probably a #6 good for 50 amps. the second aluminum wire is feeding either a electric stove or a central air cond compressor. the white romex is #10 but the white wire should not be hooked to anything since there is no neutral in the box. they use the 30 amp breaker in the picture to fuse the dryer line to the correct amperage. now some bad news. the plug in the picture looks like it is ready to go. the left side prong looks like it is starting to turn black. the other no no is the screw lugs that have the aluminum wire are only supposed to have one wire under each lug so what ever the second aluminum wire is has to go. if the second aluminum wire is to a stove take those wires out of that box and put them in a junction box with aluminum rated burndy connectors and run a new separate line from the main panel to the dryer. if that is done you can replace the dryer outlet with a 4 prong plug and change the cord on the dryer to 4 prong and you are done. on a second note if you are near the lowell area and in need of a electrician pm me. i am a master in mass only.

 

[NoGoodAtScreenNames]

as i see it the aluminum cable is probably a #6 good for 50 amps. the second aluminum wire is feeding either a electric stove or a central air cond compressor. the white romex is #10 but the white wire should not be hooked to anything since there is no neutral in the box. they use the 30 amp breaker in the picture to fuse the dryer line to the correct amperage. now some bad news. the plug in the picture looks like it is ready to go. the left side prong looks like it is starting to turn black. the other no no is the screw lugs that have the aluminum wire are only supposed to have one wire under each lug so what ever the second aluminum wire is has to go. if the second aluminum wire is to a stove take those wires out of that box and put them in a junction box with aluminum rated burndy connectors and run a new separate line from the main panel to the dryer. if that is done you can replace the dryer outlet with a 4 prong plug and change the cord on the dryer to 4 prong and you are done. on a second note if you are near the lowell area and in need of a electrician pm me. i am a master in mass only.

The mystery wire is the Romex. I didn’t take a picture, but when I took the faceplate off of the dryer outlet it’s connected to the heavy aluminum wire. All of my appliances have their own dedicated circuit breaker at the main box. I suspect the Romex leads to a dead end junction box somewhere. I’ve had the breaker turned off for a while now and haven’t noticed anything not working yet. Maybe splicing in was an abandoned project to add an outlet or appliance somewhere else.

We are in the permitting stage of a solar installation, so this will get added to the bucket list of items they will do. They already need to swap out the main panel which is over loaded with the double mini breakers. Based on some of the other half assed DIY electrical jobs I’ve found here I’m sure there’s going to be more surprises.

 

[peakbagger]

If they are putting in new panel make sure they put in 200 amp panel with 250 amp bus bars and 200 Amp main breaker. A 200 Amp panel can only have 40 amps of PV attached to it. A 250 AMP bus panel can have considerably more. The cost for the extra bus rating is supposedly minimal (I havent priced one up).

Get ready for figurative shock, the new panel has to have arc fault breakers (not cheap) for many of the loads. At least Uncle Sam gets to kick in 26% if the panel was required to install a solar system.

 

[NoGoodAtScreenNames]

If they are putting in new panel make sure they put in 200 amp panel with 250 amp bus bars and 200 Amp main breaker. A 200 Amp panel can only have 40 amps of PV attached to it. A 250 AMP bus panel can have considerably more. The cost for the extra bus rating is supposedly minimal (I havent priced one up).

Get ready for figurative shock, the new panel has to have arc fault breakers (not cheap) for many of the loads. At least Uncle Sam gets to kick in 26% if the panel was required to install a solar system.

I’ll have to ask about the rating of the main panel. We are not going to 200 amp service. We have underground service and digging would be prohibitively expensive. They quoted it for me, but warned it was going to be pretty nuts... it was pretty nuts.

They explained the panel upgrade as replacing the box with something that had a lot more space for breakers and would consolidate a sub panel that is sitting right next to it now that’s not to code because it’s behind a water heater. Cost of the panel upgrade is $1,500 prior to the tax incentive. They say they do all the misc electrical work outside of the solar on a discounted basis. I assume it’s still a 100 amp box and not a 200 box with only a 100 amp feed (if such a thing exists).

 

[peakbagger]

Bummer, I am surprised they are not going with line side tap and get rid of the 20% limit for solar.

 

[NoGoodAtScreenNames]

Bummer, I am surprised they are not going with line side tap and get rid of the 20% limit for solar.

What is a line side tap? Seeing as I don’t understand all this, I may be explaining it wrong.

From the schematics they’ve sent me. We go

1. panels on roof
2. Inverter in basement
3. 2 lines to Smart meter on exterior
4. 240 Volt / 60 amp disconnect
5. Another similar disconnect in the basement
6. 2 lines to 100 amp main panel
7. 2 lines to bidirectional utility meter on exterior of house and back out to the grid.

Take all my descriptions here with a grain of salt.

 

[peakbagger]

A line side tap hooks into a new junction box between the meter and the main panel. It is less expensive than installing a main panel. It would have a 60 Amp breaker . I dont understand what a smart meter versus bidirectional meter does unless the Smart meter is a production meter. Most inverters these days have built in reporting so there is no need for a production meter. If you needed one it would be between the inverter and the 60 AMP breaker.

Generally a main panel can be backfed no more than 20% of the bus bar rating. A 100 amp panel will typically only allow a 20amp PV system connected which is a fairly small system (around 4000 Watts). My guess is they are putting in new panel with a higher rated bus bar with a 100 Amp breaker to cover the PV system.

Some contractor were doing line side taps in the utility panels and pissed off some utilities. Normally the tap needs to be in its own box.

 

[NoGoodAtScreenNames]

Upon further review there is a line side tap on the blueprint layout in the proposal. A 20 amp limit wouldn’t be good.

 

[peakbagger]

Nothing wrong with a line side tap as long as its done in seperate box. .

 

[NoGoodAtScreenNames]

I know everyone has been anxiously waiting for an update on how this turned out...

Electricians said it looks like the Romex was probably run to an old AC unit that is at beat case connected to a junction box in a random wall somewhere. Without knocking out some drywall they couldn’t be sure exactly where / how it ends

They ran a new dedicated 4 wire Romex for the dryer. They kept the sub panel connected to the main panel with its own 30 amp double pole breaker and turned off. At some point I may run a new Romex from the sun panel a few feet over to the garage for a Level 2 EV charger.

Thanks to everyone who helped out. I definitely had a better grasp on it to make sure I was clear on how I needed to change it to make it safe.

 

[peakbagger]

Nice to see you cleaned up a potential fire, thanks for the update.