Neutral to Ground Connection in Dryer

[Meterman Eng]

I am new to the trade (please forgive if I misuse terms, as corrected I will use the right terms) and have a question about the neutral connection of a basic appliancy (a 240V dryer). I think this still is debated...

The dryer receptacle is 4 terminal: 240Vac (+120V to neutral, and -120V to neutral). One terminal is ground.

The appliance is wired with the neutral bonded to the ground (it is labelled on the machine). This puts the neutral return path in parallel with the effective-ground-fault-current path. As such, any neutral current will split between the neutral conductor and the grounding conductor (so if it were protected by GFCI breaker, it would most likely trip).

As I learn the NEC more, it seems that electricians rightfully seperate the neutral and the ground paths, but tie them together at the service point.

What are people's thoughts and comments about this? It seems like it would be better to remove the jumper (inside the machine) that connects neutral to ground, then connect ground to ground and neutral to neutral, removing the parallel path for return current.

 

[augie47]

For many years electric dryers (and ranges) were allowed to use a a grounded conductor as both neutral and equipment ground. The Code now, of course, requires separation. The dryer manufacturer's that I have seen all have the set up you observed for connectiion to the older 3 wire system with the ability to convert to the newer 4 wire.
IF your supply is 4 wire you need to separate the neutral and equipment ground in the appliance,.

 

[JFletcher]

The neutral to ground bond inside the dryer is for the installation of 3 wire plugs to fit existing installs. Read the directions of the machine, it will tell you to remove that jumper if a 4 wire cord is used.

 

[iwire]

When you have four wire receptacle with two ungrounded, one grounded and one grounding conductor the bond at the appliance must (should be) lifted.


The bond is there because many older installations exist that only have three wire receptacles supplied with two ungrounded and one grounded conductor with the grounded conductor serving double duty as the grounding means so the bond is needed.

 

[Meterman Eng]

Got It

Got It

Well, that makes sense! Thank you all very much.

 

[Meterman Eng]

What is typical?

What is typical?

What do you all typically see installed, a 4-wire or 3-wire receptacle?
If machines were mostly isolated neutral-to-ground, I would think everyone is installing 4-wire receptacles.

 

[kwired]

I once had a service call in a mobile home (which is supposed to be served with separate neutral and grounding conductors). Troubles started the moment they unplugged the dryer. I found the feeder neutral to the home was lost, and the bonding jumper in the dryer was still installed. So the bonding jumper was carrying the neutral for the entire home, and of course the grounded/grounding conductors to the dryer and the feeder equipment ground conductor, until they unplugged the dryer.

 

[iwire]

What do you all typically see installed, a 4-wire or 3-wire receptacle?
If machines were mostly isolated neutral-to-ground, I would think everyone is installing 4-wire receptacles.

No one is currently installing 3 wire receptacles for 120/240 electric dryers or ranges. That is no longer allowed by the NEC. However a great many are already in place as they where installed when the code allowed it.

Here is what the NEC currently states. see the exception.

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.

(1) The supply circuit is 120/240-volt, single-phase, 3-wire;
or 208Y/120-volt derived from a 3-phase, 4-wire, wyeconnected
system.

(2) The grounded conductor is not smaller than 10 AWG
copper or 8 AWG aluminum.

(3) The grounded conductor is insulated, or the grounded
conductor is uninsulated and part of a Type SE serviceentrance
cable and the branch circuit originates at the
service equipment.

(4) Grounding contacts of receptacles furnished as part of
the equipment are bonded to the equipment.

 

[Meterman Eng]

Got it, Thanks

Got it, Thanks

Thanks for the answer. I am just learning the NEC.

 

[JFletcher]

What do you all typically see installed, a 4-wire or 3-wire receptacle?
If machines were mostly isolated neutral-to-ground, I would think everyone is installing 4-wire receptacles.

4 wire receptacles for dryers and ovens have been required since like the 96 NEC, but there are millions of existing 3 wire receptacles that are getting new appliances, so they come internally bonded from the mfg to be able to do both installs.

We do occasionally replace the big surface mount 3 prong tombstone receptacles for dryers and ovens due to rodent damage, but other than that it's all 4 wire receptacles in 2 gang boxes.

 

[kwired]

4 wire receptacles for dryers and ovens have been required since like the 96 NEC, but there are millions of existing 3 wire receptacles that are getting new appliances, so they come internally bonded from the mfg to be able to do both installs.

We do occasionally replace the big surface mount 3 prong tombstone receptacles for dryers and ovens due to rodent damage, but other than that it's all 4 wire receptacles in 2 gang boxes.

What kind of rodents do you have that are damaging the receptacles? The ones here would prefer the NM cable feeding the receptacle or the appliance cord.

 

[JFletcher]

What kind of rodents do you have that are damaging the receptacles? The ones here would prefer the NM cable feeding the receptacle or the appliance cord.

Their urine gets in the contacts causing corrosion, high impedance plug/receptacle connection, overheat and failure. Earlier this year we saw 2 ovens within days of each other with the same failure from this.

 

[kwired]

Their urine gets in the contacts causing corrosion, high impedance plug/receptacle connection, overheat and failure. Earlier this year we saw 2 ovens within days of each other with the same failure from this.

I guess I can see that. I also think they have more potential health problems though then they have electrical problems.

 

[JFletcher]

I guess I can see that. I also think they have more potential health problems though then they have electrical problems.

These receptacles were mounted to the floor, contacts face up vs on the wall. After replacement, we relocated them to the wall and caulked around the SE cable poking up thru the subfloor. The bossman is deathly afraid of mice; he saw the droppings when we moved the oven and was like "you can handle this, right?".

 

[Meterman Eng]

but there are millions of existing 3 wire receptacles that are getting new appliances, so they come internally bonded from the mfg to be able to do both installs.

And plus it is safer to connect the neutral to ground inside the appliances when shipped (but for the people that did not read their instructions when changing 3-wire to 4-wire :ashamed1.

Makes sense. Thanks!