Using the existing neutral as a PE grounding conductor on a NEMA 10-30 outlet

Question

I was redirected here from the electric engineering exchange with a more specific question out of this earlier post:

https://electronics.stackexchange.com/questions/340136/is-it-possible-to-run-an-antminer-s9-on-a-250v-nema-10-30

I have a NEMA 10-30 split phase 250V dryer outlet that I want to temporarily utilize to run high power server equipment:

https://shop.bitmain.com/productDetail.htm?pid=00020170920224132179WEIOvhXx06D6

I probed the outlet and got the following voltages: LINE1 to NEUTRAL: 125V LINE2 to NEUTRAL: 125V LINE1 to LINE2: 250V

The power supply requires three wires.

My question is, if I created a custom plug that would adapt the computer power supply type input to a NEMA 10-30, assuming the leakage current on the power supply is <1.5MA, wouldn't the existing neutral wire act as a PE grounding conductor? It was suggested on my other thread that I should switch to a grounding NEMA 6-15 outlet. However, I do not see any physical difference whatsoever between what I currently have and what was recommended, because if I installed the NEMA 6-15 outlet it would require me to use the existing neutral as a grounding conductor, or install a new grounding conductor leaving the current neutral unused.

I understand that in the case of an appliance like my dryer, which uses 125V for the lights and the timer and then dumps the current into the neutral, that this is indeed not up to code because there is a lack of grounding conductor. However in the case of the power supply I am now looking to run, it does not utilize split phase power so as far as I can tell close to zero current would be running through what is considered the neutral, which for all intents and purposes would make it a PE grounding conductor.

Is this merely a question of code/semantics or do I actually need to run ANOTHER wire from the panel to use as a grounding conductor? If I did this, it would simply be connected to nothing on the outlet end, because I need a 3 wire plug. There is nothing else on this branch, only the single 10-30 receptacle on a two pole breaker.

Also, is there any code problem with plugging a 7A computer server into a 30A receptacle? What if I used something like the TrippLite 30A PDU that has multiple outlets, then plug the server into the PDU?

Thank you for any help! Please let me know if I am incorrect in my assumptions.

EDIT: This plug is on a sub panel. Also, with the breaker to the outlet OFF, I am reading around 4V AC from either hot to the neutral. Does this indicate a fault somewhere or is this normal?

Answer 1

We can start with this:

As installed, the grounded conductor for your dryer receptacle is white or gray and cannot be re-identified as an equipment grounding conductor according to the National Electrical Code.

250.119 Identification of Equipment Grounding Conductors. Unless required elsewhere in this Code, equipment grounding conductors shall be permitted to be bare, covered, or insulated. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes except as permitted in this section. Conductors with insulation or individual covering that is green, green with one or more yellow stripes, or otherwise identified as permitted by this section shall not be used for ungrounded or grounded circuit conductors.

Then there is using something for which it was not intended. The Code does not allow that.

Article 110.3(B) Installation and Use. Listed or labeled equipment shall be installed and used in accordance with any instructions included in the listing or labeling.

The receptacle you have was designed and intended for the third prong to be a grounded conductor not an equipment grounding conductor.

406.4(C) Methods of Grounding. The equipment grounding conductor contacts of receptacles and cord connectors shall be grounded by connection to the equipment grounding conductor of the circuit supplying the receptacle or cord connector.

So, if your equipment requires grounding, which it apparently does, you cannot connect a cord connector to the grounded conductor of the circuit supplying the dryer receptacle.

There are other reasons not to do this that I don't have the inclination to list here.

Just run the correct wire and install a proper receptacle for your equipment and sleep soundly.

Good luck!