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I want to run a couple of 110 volt plugs from a box that has 240 volts. I understand that I can't just use one of the two hots and wire both the neutral and ground to the 240V neutral.

My question is, what about if I use a second, new ground rod to create a ground, and then just use one of the 240V hot wires and it's neutral return? Is that safe/legal?

THANKS! Dave

  • Not sure if by "box" you mean a receptacle box or a breaker panel. If you are talking about pulling a 120v leg off of another circuit, such as a range or clothes dryer that's not remotely close to being code legal. I also don't understand about the new ground rod? If in a breaker panel, it's easy, but I don't think that's where you are talking about. – George Anderson Apr 25 at 15:46
  • Thanks for the quick response, George. I'd like to add a 120V GFCI outlet fed from my 240V 3 wire 2 phase pool heater cutoff switch box. My thinking was that I can easily drive a new ground rod into the earth near that box to provide a true ground for the 120V outlet, and use one of the hot wires and the neutral from the 3 wire 240V pool heater line. – mnvelocitypilot Apr 25 at 15:50
  • I understand that it may not be code, but my thinking is that it'd be safe, since the ground would be a true ground an would not be providing a return for the 120V GFCI outlet – mnvelocitypilot Apr 25 at 15:51
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    Very sorry, but I won't comment on something that might work but isn't code legal. – George Anderson Apr 25 at 15:58
  • Is the feed to that pool heater box run using a cable, or as individual wires in conduit? – ThreePhaseEel Apr 25 at 16:29
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Ground rods are no substitute for ground wires

Because at the risk of stating the obvious, dirt doesn't conduct electricity very well.

Further, electricity wants to get back to source, not earth. Natural electricity like lightning and ESD, their source is the earth. They are extremely high voltage, and so the poor conductance of dirt isn't really a problem for them.

However human-generated electricity is extremely low voltage (by Nature's standards, anyway) and it simply will not move effectively through dirt. That's why ground wires must be fitted as well. The purpose of the safety ground wire is to return (to source; i.e. the ground bar back at the main panel via its equipotential bond) any fault current due to malfunctioning equipment etc.

That is excessively important for water areas like a pool.

Electrical drownings happen every day, and are especially horrifying because it also kills rescuers - until about the second or third arrives and realizes "oh, something is killing rescuers, don't dive in". Every time, the problem is traced back to a faulty or just obsolete installation like yours. And the firemen shake their head and go "I can't believe anyone allowed / continued this in service this way".

Neutral is not ground

Some people think it is, because they see them tied back at the panel. Some particularly awful installers even put the neutral and ground wire on the same screw in the neutral bar, making it seem particularly pointless. No, it's serious business. Location is everything. Why does a classic torque wrench have the big beam and the separate little stick? The big bar bends, the little bar doesn't. That doesn't begin to describe what ground is all about.

But make sure the pool pump's "neutral" is actually neutral, and not safety ground. Neutral is a white wire. If the wiring was done with SE cable (ancient and unlikely) and it has braided bare wires around 2 black conductors, that also is neutral. Any other bare wire is ground.

Do not tie ground to neutral anywhere except the main panel.

Get that pool pump on a GFCI breaker. Now.

I know you're thinking "GFCI is a 120V receptacle" and "GFCI breaker" seems like "Ford cupcake". But first, never use the LOAD lines except for one purpose. And the one purpose is that any GFCI device can protect other outlets downline. That's what GFCI breakers do - they protect the entire downline - the entire circuit. It must be a GFCI breaker because it's 240V. And yeah, that's an expensive beast.

At this point, the pool pump is rendered safe, even though it doesn't have a ground wire. Any leakage current will snap the GFCI. (mind you if it's leaking already, that means the trip will be instant, but on the upside it may have saved a life).

At that point, you will be able to do your plan - attach a 3-prong PLAIN receptacle to pool pump hot and neutral, connect the ground wire to nothing, and label the receptacle like this:

 GFCI Protected
 No Equipment Ground
 Reset at breaker

Yeah, it's perfectly legal to have a grounded recep with no ground, if it's labeled just like that (third line optional).

There are some other rules about putting 15/20A 120V receptacles on circuits like this, but I'm not too worried about them because they're not 5-alarm shocking safety issues. They include

  • can't put receptacles on a circuit where hardwired loads account for 50% of breaker trip (put the pool pump on a NEMA 6 receptacle tee hee!)
  • can only put common 15A/120V receps on a 15A or 20A breaker

You can solve both of these by fitting a subpanel here. However go ahead and feed the subpanel from the GFCI breaker. That way you are better protected and only need one of them.

You can retrofit ground if you really want to

It's perfectly possible to retrofit a ground wire to the circuit. However I wouldn't make that a priority, since the GFCI breaker back in the panel will do all your heavy lifting for you. With a ground wire, you improve the odds of preventing an electrical drowning, with a GFCI breaker you pretty much set the odds to zero.

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  • Wow - thank you, Harper - Reinstate Monica! That's a GREAT answer - I really needed that background to understand the issue(s). Thank you so much! – mnvelocitypilot Apr 25 at 19:16
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Your approach will provide 120v power to your outlets, but it is not code/safe and violates several NEC principles.

  1. Grounds(non-conductive) an neutrals(grounded conductor) should not be connected anywhere except at the main panel. Sub-panels and junction boxes must separate these paths.
  2. It's unlikely that you dual breaker or fuse will protect the circuit.
  3. Multiple grounding rods must be bonded (directly connected). Separate grounds create different potentials i.e. electricity.

You have options of a sub-panel or a spit breaker at the the panel, but these may not work for your purpose. See Using half of a 240v dual-phase circuit as a 120v single-phase circuit (US)

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  • Thanks, Clifford - VERY helpful. I understand the issue with the potential ground loop created by two ground rods. What I was planning was to take one of the two 240 hot lines into a separate box with a 15 amp breaker, which then feeds a third box containing the 120V GFCI. The 10 gauge wire feeding the pool heater, which is protected by a 50A breaker. So, my thinking is/was, if the heater is on and drawing 40 amps, and I draw more than 10A via the 120V GFCI, I trip the 50A breaker. If the pool heater is off and I draw more than 15A from the GFCI outlet, I trip the 15A breaker. – mnvelocitypilot Apr 25 at 16:15
  • So, in theory, I'm protected. BUT, to do this, I'd have to run the 120V GFCI outlet ground and neutral BOTH to the 240V neutral.... making a connection between neutral and ground outside of the main panel (dangerous and wrong). That – mnvelocitypilot Apr 25 at 16:16
  • That's why I had the idea of a second ground rod. – mnvelocitypilot Apr 25 at 16:16
  • The 15A breaker in a sub-panel as described works fine. I don't understand why you have to GFIC ground to a neutral. Keep it separate. – Clifford Eby Apr 26 at 2:52
  • Use of 10ga wire in a 50A circuit is a problem. Should be 8ga minimum. – Clifford Eby Apr 26 at 2:53

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