Dual supply (240V/120V) grounding and GFCI

[artongue88]

Hello,

Im setting up an electric brewery in which two 5500W elements are driven by a three-prong dryer outlet, and the pumps are driven by a separate 120V, non-GFCI outlet, both on separate breakers in my home's electrical panel.

I have in-line GFCI solutions on both the 240V and 120V sources. I am wondering how to handle grounding everything given that:
- My 240V source is three-prong, 10-30 with hot-hot-neutral
- I am not running any 120V device off of the 240V source
- I am running a separate 120V source with ground to my panel to run my 120V devices

Apologies for the crude drawing, but here is a high level schematic. DC wiring which controls SSRs and relays not shown.

My main question is: since I am not driving any 120V devices off of my 240V source, I should be able to safely use it as ground. Will my inline GFCIs work if I link my 120V ground to my 240V ground, as shown? Or, should I ground my 120V devices to 120V ground, and separately ground my panel, door, and kettles to 240V ground/neutral? I just want to make sure I do not throw off the correct functioning of my inline 120V and 240V GFCIs.

Thanks!

 

[artongue88]

Edit to the last bit: ...I should be able to safely use the 240V neutral line as ground

 

[day_trippr]

fwiw, I doubt there is a legit code that allows "My 240V source is three-prong, 10-30 with hot-hot-neutral ".

And given there isn't a "neutral" in single-phase 240VAC, more likely - assuming the "dryer" references are to an outlet originally used for an actual electric dryer - it's hot-hot-ground already...

Cheers!

 

[jseyfert3]

I'm not familiar with electric brewing setups, but that 240 V outlet is only good for 30 amps, and you have heaters that if both on will draw 44 amps. That outlet is not sufficient.

I'd suggest you have a 50 amp circuit with a 4 prong plug (hot/hot/neutral/ground) installed, and then you could run the 120 volt pumps off that as well. One cord, one outlet, one ground. In general mixing multiple power sources is not best practice.

fwiw, I doubt there is a legit code that allows "My 240V source is three-prong, 10-30 with hot-hot-neutral ".

And given there isn't a "neutral" in single-phase 240VAC, more likely - assuming the "dryer" references are to an outlet originally used for an actual electric dryer - it's hot-hot-ground already...

Cheers!

Electric dryers almost exclusively used hot/hot/neutral with neutral connected to the case of the dryer to act as ground (since it's bonded to ground at the main panel) until code in 1996 changed and required 4-prong outlets (hot/hot/neutral/ground). Existing 3 prong outlets were grandfathered in, but if replaced or new must always be 4 prong now if neutral is needed.

 

[day_trippr]

But, let's be accurate here, there is no neutral in a 240VAC single phase circuit.
Hence you can call that third wire an "elephant", but it's still a ground wire...

Cheers!

 

[jseyfert3]

But, let's be accurate here, there is no neutral in a 240VAC single phase circuit.
Hence you can call that third wire an "elephant", but it's still a ground wire...

Cheers!

I am being accurate. Dryers use 120 volts for the motor and control circuitry, and 240 volts for the heater wire. 3 prong dryer outlets are hot/hot/neutral and are ran with black/black/white or black/red/white (US colors), there is NOT a ground (green) wire, because they are using it as a neutral for the 120 volt pump.

Again, this was only allowed till 1996. The code now requires a proper ground wire for new dryer outlets. This same exception was available for ranges too, except they use 50 amp plugs/circuits, but used 120 volts for lights and controls.

There's even a different type of plug for this. Hot/hot/neutral 30 amp outlets are NEMA 10-30, hot/hot/ground outlets are NEMA 6-30. NEMA connector - Wikipedia

The OP, with a 10-30, if installed to code, will indeed have hot/hot/neutral and should NOT use neutral as ground.

Cheers!

EDIT: Yes, if used as the OP drew it it would indeed be a ground not neutral wire (assuming one main panel, since sub-panels don't bond neutral and ground), but using a neutral (white) wire for ground, or using the neutral pin of a 10-30 for ground would be against code.

In either case it's moot, as there is not enough current in a 30 amp circuit to run two 5500 watt heaters, the OP will need to have at least a 50 amp circuit installed, which if installed to code will have the proper green ground wire and proper NEMA with ground instead of neutral.

Idk how much the 120 pumps pull but if not much a single, 4 wire, 50 amp circuit should be able to power this and have a single source of power and proper, to code grounding. NEMA connectors come in up to 60 amp versions, that may be more applicable than a 50 amp depending on draw of 120 volt pumps.

 

[day_trippr]

Functionally everything you said is correct, except I believe the code supported the third wire as a designated ground - then allowed shipping 120vac motor and clockwork current over it...

Cheers!

 

[artongue88]

Thanks for replies. Note that I have planned for only using one element at a time, due to the 30A limit. This is why I have the selector switch.

It still is not clear to me whether or not I can safely use the white/neutral wire on my 240V source as ground, and whether or not my inline GFCIs as drawn will function correctly if the 120V ground and the 240V "ground" are connected. Any thoughts/alternatives? (Other than paying an electrician to replace my 3-wire setup)

 

[artongue88]

It may also help to know that the house was built in '77 - if that helps clarify the hot-hot-neutral 240V configuration!

 

[day_trippr]

My primary residence was built in '76, and the vacation house my dad and I built was wired in '84.
Both with 3-wire dryer - and oven - drops, which was proper for the era.
Both since rewired with four-conductor because the kitchens/baths/laundries were remodeled which triggered new code requirements...

Cheers!

 

[artongue88]

That's cool and all, but doesnt help me much >.<

Looking for solutions for properly grounding my setup and correctly utilizing the in-line GFCIs

 

[jseyfert3]

What is the current draw on the 120 volt pumps?

 

[jseyfert3]

The short answer is no, nothing with the grounds will affect GFCI operation. Grounds are intended to, well, ground metal that could potentially become energized due to a fault. The idea with ground is if a hot wire touches grounded metal, there is a short circuit and the current flow trips the breaker, cutting power and de-energizing the hot metal.

GFCI is different. It watches the difference in current between hot and neutral. These have to match if the circuit is working properly. If current is leaking outside the circuit, say a heater failed and you have your hand in the water and you're touching a grounded surface so the current is leaking through YOU, then the current returning to neutral no longer matches current coming out of hot and the GFCI trips.

As you have it drawn for grounding is how I would do it, IF I was doing seperate power sources. I can't say I recommend that course of action though. The only course of action I recommend is having a 4 wire 240 volt outlet (hot/hot/neutral/ground), and this single outlet would provide power to both the 240 volt heaters and the 120 volt pumps.

Hope that helps!

 

[day_trippr]

I agree, I would run a four wire drop with a proper circuit (and life) protector and be done with it...

Cheers!

 

[Bobby_M]

Regarding the slight disagreement I just watched... NEMA 10-30 is absolutely Hot, Hot, Neutral. The 3rd conductor is insulated. If it went to a subpanel, it would terminate on the neutral buss, not the ground. The NEMA standard is clear about it.

In the OP's planned usage, since the neutral line back through the feeder circuit is not going to be carrying current, it is effectively being used as a 3 wire 240v, Hot, Hot, Ground.

Tying the grounds together from two different sources will not trip the GFCIs.

 

[day_trippr]

I sit corrected

Cheers!

 

[Drmax]

Hello,

Im setting up an electric brewery in which two 5500W elements are driven by a three-prong dryer outlet, and the pumps are driven by a separate 120V, non-GFCI outlet, both on separate breakers in my home's electrical panel.

I have in-line GFCI solutions on both the 240V and 120V sources. I am wondering how to handle grounding everything given that:
- My 240V source is three-prong, 10-30 with hot-hot-neutral
- I am not running any 120V device off of the 240V source
- I am running a separate 120V source with ground to my panel to run my 120V devices

Apologies for the crude drawing, but here is a high level schematic. DC wiring which controls SSRs and relays not shown.
View attachment 701413
My main question is: since I am not driving any 120V devices off of my 240V source, I should be able to safely use it as ground. Will my inline GFCIs work if I link my 120V ground to my 240V ground, as shown? Or, should I ground my 120V devices to 120V ground, and separately ground my panel, door, and kettles to 240V ground/neutral? I just want to make sure I do not throw off the correct functioning of my inline 120V and 240V GFCIs.

Thanks!

i am a licensed electrician. You should change over the 3 prong outlet with a 4 wire circuit and 4 prong plug.

 

[artongue88]

I am renting and this is unfortunately not an option - what alternative would you advise?

 

[jseyfert3]

I suspect there is no alternatives (besides not building), if you are renting. Unless you happen to have a landlord who is also a homebrewer. Or if you have a garage, tell them you need a 60 amp, 4 wire outlet for the Tesla you're going to buy.

You might put a label on the door that says something like "DANGER: Multiple power sources." That's what I've seen done at my work when we have something powered by more than one power source. This is just a reminder to you, or anyone else who may look at/work on it in the future, that there is more than one power source to disconnect before you open it and start poking around inside thinking it's dead. These give you an idea of what I mean: warning multiple power sources - Google Search

 

[Gruel]

Hot/hot/neutral, really? Those first electricians that emigrated to the US and wrote the original code must have left the old country for a reason

 

[day_trippr]

Right?
As a practicing EE for over four decades rationalizing some of the electrical codes makes my brain hurt...

Cheers!

 

[Bobby_M]

Well in fairness, the first electrical power in most homes had exposed conductors strung up the wall through non conductive standoffs. It got safer from there but there was the compromise to not require a full gutting of installed wiring. Those 3 wire dryer circuits are grandfathered in.

 

[day_trippr]

lol! Low bar

fwiw, I grew up in a town full of revolutionary-era homes, had a few HS gf's living in them, and have seen some things that would freak out a modern-era inspector. Tube 'n' knobs all over the place - including within reach (though I was 6'5" tall at the time - which also conveyed all kinds of potential for a brain-damaging conflict with the ceiling beam heights sized for the comparative midgets of that era. But I digress...)

Doesn't change anything. Modern electrical codes can still seem borderline rational at times...

Cheers!

 

[Skeptonomicon]

Warning! Danger! I am very concerned with this setup. The safety depends on the type of GFCI you have on the 240V, and I could not get enough data on the model you chose. If This GFCI is designed for hot/hot/neutral, and you have a leak from the heater to the water, and you touch the water and the pot at the same time, you become the conductor. The current through your body will return through the neutral of the 240. The 240 will still see a balance between the 3 conductors and will not trip. You will not have erroneous trips of the GFCI, but you will have effectively bypassed it. It might as well not even be used.

 

[Ihop2many]

I am also concerned about the safety of this setup. Ground for the 120V equipment is coming from a different point to that of the 240V equipment. If the electrical installation is defined as being in one building without crossing a boundary to an outbuilding we know that the neutral and ground should be bonded at, and only at, the service entrance but how far away is that in terms of DC resistance? Grounds coming from different termination points could cause voltage differences between them resulting in an unsafe condition.