I finally had honey nut Cheerios for breakfast ... been at least a year or 2 ... I missed them

 

The 3-wire dryer circuit did not have a ground. Just two hots and a grounded conductor. You were allowed (required) to bond the dryer frame to the grounded conductor. Nothing was ever terminated on the MSP ground bar (if it even had one, back then they often did not).

So your old MSP which is now a sub panel and needs to have the neutral/grounds separated and you can't do that for the dryer circuit. You understand all this (because you stated so).

You have determined that it's not enough of a safety hazard to go to the expense to install a new dryer circuit (or you got a failed inspection because of it) and you are looking for validation for this perspective. This is how I interpreted your post.

Anyway, to your question. I'm not educated enough to support your determination. I can understand your line of thinking, but remember, "I'm just a dumb contractor", and "the book" (NEC) says it's a no go, no fly, fail.

So, sorry I couldn't help but, how close was I?

 

I see you why you would come that conclusion. Im actually genuinely curious. I know what we re supposed to do, just seeing if I fully understand the why. I appreciate your thoughts on the matter

 

It'd be better to land it on the neutral bus rather than the ground bus. The reason is if the ground wire gets disconnected anywhere between the panel and the neutral-ground bond, and the dryer is running or trying to run, everything grounded will be 120 volts above the actual ground.

If it's landed on the neutral bus, the only thing that could get energized is the dryer frame.

But the actual reality is it needs to be 4 wire.

 

Right, you'll have an energized panel enclosure looking for a return path. That does add another potential hazard

 

One could extend the dryer circuit into the new main panel and forgo replacing the whole run. If you oversize the feeder conduit between the new main and the old main you can pull the dryer circuit upstream.

 

Thats a good point

 

The 3-wire can come from a subpanel if the grounded conductor is insulated. What can't come from a sub is SE cable with a bare neutral. Reasoning is they don't want the bare conductor to come in contact with metal objects along the path and into the panel.

I was granted permission by the inspector on a generator install where the main panel was converted to a subpanel, to tape the bare conductor white everywhere it was exposed. This was a 3-wire feed for a range. Not code, but safer than leaving to exposed.

 

The 3-wire can come from a subpanel if the grounded conductor is insulated.

As best as I remember, the requirement for being allowed to install a 3-wire to a dryer is that the circuit originates in the service panel. I don't believe it was ever code compliant to install a 3-wire dryer circuit from a subpanel.

 

If I am not mistaken, that exception for existing 3 wire ranges and dryers is wiped out completely in the 2020 NEC. if your area is subject to 2020 or later then just Forgetaboutit....................

 

I understand shock hazard on the shell of the dryer on a 3 wire set up.

What's the hazard?

 

In the 3 wire configuraton, if you had a loose or lost neutral upstream in the MSP or meter the shell of the dryer could have potential

 

they used the same reasoning that they used when they added the grounding prong to a 120V receptacle
separate the neutral and ground so that the ground is seldom to never used and therefor more likely to allow a higher fault current which will trip the breaker sooner
3 wire dryers were initially all 240V components and did not need a neutral
4 wire dryers have 240V and 120V components and need a neutral

the correct way to change a main panel to a subpanel is to add an EGC to it's feeder, unbond the neutral bar, add a bonded ground bar and move all the EGC's to it
if you do none of that .... the shock hazard does not suddenly change because of adding a disco somewhere before the previously main panel

 

3 wire dryers were initially all 240V components and did not need a neutral

I believe this is inaccurate. If you have a source for this information, would you share it please? Thanks

 

I Have a question about 3 vs 4 wire dryer recptacles. I understand the new 4 wire standard on new construction and the need to update a 3 wire setup when doing a service change with a meter main, making the MSP a subpanel. As I understand it, old 3 wire setups were spec'ed for MSP termination only. I understand shock hazard on the shell of the dryer on a 3 wire set up. My question is: When you install a meter main and seperate grounds and neutrals in the newly created subpanel, if you were to leave an existing 3 wire setup and land the bare ground on the subpanel neutral bar, are you substantially increasing the shock hazard ? My understanding is no not really, the potential hazard is the same, but you now have a situation in the subpanel where you technically dont have a proper place for the bare ground without violating 250. Not arguing for skirting this requirement, just curious.

I'm certainly not condoning it... just saying, I'm still waiting to follow the electrician (Or an appliance installer) who has updated a 3-wire dryer receptacle either to a 4-wire outlet with a new run of four conductor wire, or leave the 3-wire outlet and run a ground to the housing of the dryer.

 

In the Hampton Roads area of Va., back in the 70's, we were allowed to install a 10/3 w/out a ground to the dryer but were not allowed to install a 10/2 w/ground to the dryer. You would fail every time.

We were however allowed to install an 8/3 SE cable to the dryer receptacle.

Something to do with the cable design/rating. A technicality that I never bought into. But my thoughts don't count.

 

Finally the 2023 code got something right. Whenever I would make an old service panel into a feeder panel, I would tape the bare SE neutral on the range white and keep it towards the back of the panel hoping the inspector wouldn't question me. Part 5

N 250.140(B) Grounded Conductor Connections. For existing branch-circuit installations only, if an equipment grounding conductor is not present in the outlet or junction box the frame of the appliance shall be permitted to be connected to the grounded conductor if all the conditions in the following list items (1), (2), and (3) are met and the grounded conductor complies with either list item (4) or (5):

(5) The grounded conductor is part of a Type SE service-entrance cable that originates in equipment other than a service. The grounded conductor shall be insulated or field covered within the supply enclosure with listed insulating material, such as tape or sleeving to prevent contact of the uninsulated conductor with any normally non-current-carrying metal parts.

 

In the 4 wire configuration, if you have a loose or lost EGC, the dryer could have potential.

Only if you also have a ground fault.

 

If you have a true 10/3 wo ground and not a 10/2 w ground going to the dryer, and you wanted to make it 4 prong, would 250.130(c) apply and you could just add a ground?

 

If you have a true 10/3 wo ground and not a 10/2 w ground going to the dryer, and you wanted to make it 4 prong, would 250.130(c) apply and you could just add a ground?

Provided it was an existing circuit, yes.

 

No, not really. The ground is sposed to be in the same cable pipe or raceway, no exception for this to booger a wire on. No solution is as good as running a new wire.

 

But isn't this exception exactly for this?

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:

(1) Any accessible point on the grounding electrode system as described in 250.50 ​

(2) Any accessible point on the grounding electrode conductor ​

(3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates ​

(4) An equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates ​

(5) For grounded systems, the grounded service conductor within the service equipment enclosure ​

(6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure. ​

 

It'd be better to land it on the neutral bus rather than the ground bus. The reason is if the ground wire gets disconnected anywhere between the panel and the neutral-ground bond, and the dryer is running or trying to run, everything grounded will be 120 volts above the actual ground.

 

It'd be better to land it on the neutral bus rather than the ground bus.

Would you ever land a neutral conductor on a ground bus?

 

No, not really. The ground is sposed to be in the same cable pipe or raceway, no exception for this to booger a wire on. No solution is as good as running a new wire.

Except that is exactly what the section he posted is for...

It'd be better to land it on the neutral bus rather than the ground bus. The reason is if the ground wire gets disconnected anywhere between the panel and the neutral-ground bond, and the dryer is running or trying to run, everything grounded will be 120 volts above the actual ground.

Can only do that if it is fed from a service enclosure.

 

Whoops, guess I misread.

 

@Dennis Alwon

 

So why was I summoned. Usually one uses the the mod symbol,..... a big M across the sky but ........This thread is from aug 2023 so I am not sure what you want from me...

 

It appears the cmp doesn't think it is a terrible thing because they have made it compliant to install a meter main and hook up the original panel with a 3 wire as long as the outside panel had a disconnect that stated not a service disconnect.

When you mention a bare ground/neutral that may be a problem as that was never allowed unless the cable was a se cable and originated at the service panel. Why that was allowed I don't know.