4-prong to 3-prong dryer power adapter??

[EBQ]

So they sell these 4-prong <-> 3-prong adapters for 240V 30-amp dryers (see picture below). I assume they are non-code compliant to use, but from an electrical theory perspective, I have a few questions:



1. Assuming I plug the ground wire into the ground of a 20-amp outlet, the typical 20-amp circuit ground wire is only 12 AWG, but the 30-amp dryer ground requires 10 AWG, so this adapter is insufficient to handle dryer ground fault, am I wrong?
2. What if I split this ground and tie it to the ground wires of two separate 20-amp circuits, would that electrically/theoretically provide a good safety margin for 30-amp return in case of ground fault?
3. This gets me thinking if one bonded the chassis of a dryer and the chassis of a washer (plugged into a 20-amp outlet) sat next to each other (e.g., with a 10 AWG wire), would it accomplish #1 the same? And if one bonded the chassis of the dryer to another 20-amp circuit ground (in addition to the washer chassis), would it accomplish #2 the same?
4. If #2/3 is electrically/theoretically good enough for 30-amp fault currents, other than potential mechanical failures (accidental loosening etc), are there any electrical/theoretical concerns if everything remains in contact?

Thanks!

 

[ptonsparky]

My SEWAG is the 12 would carry an adequate fault current to trip the 30 amp breaker eventually. Most likely even a 14.

Anyone using such an adapter probably doesn't have the dryer wired up correctly anyway.

 

[retirede]

That thing probably costs more than a new 3 wire cord.

 

[Buck Parrish]

Put it on a two pole gfci 30 amp breaker then you will not have to worry about the equipment ground.

 

[kwired]

If starting with three wire receptacle, why not just bond the N-G together for the output? That gives same result had you gone with three wire cord on the appliance in the first place. That external EGC is going to cause undesired neutral currents on whatever it is connected to if the bonding jumper is not removed in the appliance also.

What can more easily create hazards is if trying to make such an adapter but the other way around - four wire receptacle to three wire appliance cord.

 

[EBQ]

If starting with three wire receptacle, why not just bond the N-G together for the output? That gives same result had you gone with three wire cord on the appliance in the first place. That external EGC is going to cause undesired neutral currents on whatever it is connected to if the bonding jumper is not removed in the appliance also.

What can more easily create hazards is if trying to make such an adapter but the other way around - four wire receptacle to three wire appliance cord.

That thing probably costs more than a new 3 wire cord.

My SEWAG is the 12 would carry an adequate fault current to trip the 30 amp breaker eventually. Most likely even a 14.

Anyone using such an adapter probably doesn't have the dryer wired up correctly anyway.

But in a 3-wire configuration, if anything happened to neutral, the chassis would become electrified... this adapter at least allows one to keep neutral and ground separate (not bonding N-G in dryer)? Of course, if it was going to be code non-compliant, one could just break up the N-G bond in the dryer and pigtail a ground from chassis to outlet ground to accomplish the same...

Would bonding the chassis of the dryer and washer be a safer approach in most situations, if there were no other metal parts in the surrounding area on a hardwood upper floor? Any theoretical reason why bonding the two could be bad?

Tying the ground wire to the grounds of two circuits (end in same breaker panel) appears safer than just the ground of one circuit for 30-amp fault current... did I miss anything here?

 

[ptonsparky]

A neutral bond at the dryer has been used pretty successfully for a lot of years. Yes, loosing that bond can cause some grief.

 

[ramsy]

But in a 3-wire configuration, if anything happened to neutral, the chassis would become electrified... this adapter at least allows one to keep neutral and ground separate (not bonding N-G in dryer)? Of course, if it was going to be code non-compliant, one could just break up the N-G bond in the dryer and pigtail a ground from chassis to outlet ground to accomplish the same...

Would bonding the chassis of the dryer and washer be a safer approach in most situations, if there were no other metal parts in the surrounding area on a hardwood upper floor? Any theoretical reason why bonding the two could be bad?

Tying the ground wire to the grounds of two circuits (end in same breaker panel) appears safer than just the ground of one circuit for 30-amp fault current... did I miss anything here?

Losing service neutral is common enough with power failures, and energized frames per NEC 240.140 grandfathered exception, are avoided with re-identified branch-cable Neutral as EGC, for use with 3-wire L-L European 230v appliances, since no local code or equipment listings are violated on either continent.

Short of that, my out-of-state clients that bring electrics with them, are told to use the common gas hookup instead, and let me change the convenience outlet to a Leviton AGTR-2.

 

[kwired]

But in a 3-wire configuration, if anything happened to neutral, the chassis would become electrified... this adapter at least allows one to keep neutral and ground separate (not bonding N-G in dryer)? Of course, if it was going to be code non-compliant, one could just break up the N-G bond in the dryer and pigtail a ground from chassis to outlet ground to accomplish the same...

Would bonding the chassis of the dryer and washer be a safer approach in most situations, if there were no other metal parts in the surrounding area on a hardwood upper floor? Any theoretical reason why bonding the two could be bad?

Tying the ground wire to the grounds of two circuits (end in same breaker panel) appears safer than just the ground of one circuit for 30-amp fault current... did I miss anything here?

Same happens with a three wire cord on the dryer and plug it into the three wire receptacle and something happens to the neutral. They finally got away from allowing three wire in 1996 NEC after it been that way for ~50 years, but did put in allowances for existing three wire installs to be permitted to remain.

My point is if the three wire receptacle is permitted to remain then this adapter is kind of pointless, just put a three wire cord on the appliance and let it remain as the exceptions permit, or put in a 4 wire circuit, cord and receptacle.

2020 NEC that dryer receptacle needs GFCI protection in most cases, GFCI's don't play well with frames of equipment bonded to the neutral, unless it does remain fully isolated from other grounding paths.

 

[EBQ]

Same happens with a three wire cord on the dryer and plug it into the three wire receptacle and something happens to the neutral. They finally got away from allowing three wire in 1996 NEC after it been that way for ~50 years, but did put in allowances for existing three wire installs to be permitted to remain.

My point is if the three wire receptacle is permitted to remain then this adapter is kind of pointless, just put a three wire cord on the appliance and let it remain as the exceptions permit, or put in a 4 wire circuit, cord and receptacle.

2020 NEC that dryer receptacle needs GFCI protection in most cases, GFCI's don't play well with frames of equipment bonded to the neutral, unless it does remain fully isolated from other grounding paths.

so, isn't it in fact safer to use this adapter with a 4-wire configuration for the dryer, allowing N and G to be separated? I know 3-wire is grandfathered in per code, but for personal safety in practice, if the ground wire is fastened securely, this enables a 4-wire setup..

 

[ramsy]

so, isn't it in fact safer to use this adapter with a 4-wire configuration for the dryer, allowing N and G to be separated? I know 3-wire is grandfathered in per code, but for personal safety in practice, if the ground wire is fastened securely, this enables a 4-wire setup..

You are asking contractors to approve un-listed adapters that violate equipment UL listings and 110.3B code requirements.

You challenge the current adopted code standards with Micky-Mouse adaptors, and expect installers to assume all liability when such miss-used or untested design questions skip NRTL listing requirements.

You're design point may be valid, but not legal to install until approved by your AHJ.

 

[Hv&Lv]

Most of the dryers I worked on the manufacturers bond wasn’t ever removed in the first place…

 

[EBQ]

You are asking contractors to approve un-listed adapters that violate equipment UL listings and 110.3B code requirements.

You challenge the current adopted code standards with Micky-Mouse adaptors, and expect installers to approve this untested design question that skips NRTL listing requirements.

You're design point may be valid, but not legal to install until approved by your AHJ.

I am just trying to understand the physics and any pitfalls I wasn't aware of. I know it's not allowed by code, just trying to dig deeper what the concerns might be other than accidental disconnect of the ground wire. These are sold at home depot, Amazon, etc, and by the number of reviews, it appears a good number of people are using them without actually understanding how they work.

 

[EBQ]

Most of the dryers I worked on the manufacturers bond wasn’t ever removed in the first place…

In this case, if the dryer chassis touched the washer chassis (forming an electrical connection), wouldn't the dryer's 120V current then split between the dryer neutral and the washer ground wires, turning the washer ground wire live?

 

[retirede]

In this case, if the dryer chassis touched the washer chassis (forming an electrical connection), wouldn't the dryer's 120V current then split between the dryer neutral and the washer ground wires, turning the washer ground wire live?

Ground wires don’t “turn live.” In your theoretical scenario, the washing machine circuit’s EGC could carry some neutral current, but that in itself won’t create a hazard without some other aberration. The neutral current on a dryer is pretty small to begin with.


As others have stated, a 3 wire circuit to a dryer had been the norm for many years and the world didn’t end.

 

[LarryFine]

This device is for a DIYer who finds changing a dryer cord too daunting.

 

[EBQ]

Ground wires don’t “turn live.” In your theoretical scenario, the washing machine circuit’s EGC could carry some neutral current, but that in itself won’t create a hazard without some other aberration. The neutral current on a dryer is pretty small to begin with.


As others have stated, a 3 wire circuit to a dryer had been the norm for many years and the world didn’t end.

Thanks, this clarified what the neutral in a dryer is used for that I read about but didn't think about. So, this would only be a problem if there was a short in the dryer.

 

[drcampbell]

I always wondered why they didn't just install a 240-volt motor and eliminate the need for the fourth wire. It's certainly not because the volume of electric dryers being manufactured is too small to justify it. Anybody have the inside scoop?

 

[LarryFine]

I always wondered why they didn't just install a 240-volt motor and eliminate the need for the fourth wire. It's certainly not because the volume of electric dryers being manufactured is too small to justify it. Anybody have the inside scoop?

Popularity of 3-wire 120/208v services in apartment buildings.

Only the heater element uses line 2, making the dryer "universal".

 

[kwired]

Popularity of 3-wire 120/208v services in apartment buildings.

Only the heater element uses line 2, making the dryer "universal".

Manufacturer could also use same motor and control timer on a gas dryer.