Safely getting 110 volts from a 3 wire 220 volt conductor

[Bird76Mojo]

I'll try to keep this short.

Have a hot water heater already wired with 3 conductor cable. Two hots and a ground.

I already have 110v heat tape installed and insulated. I need to power it.

Any advice on using step-down transformers in this case? It is regularly done on large industrial equipment to power Windows PC's and 110v lighting. The transformer creates the neutral?


Thoughts? Experience in this area? Anyone?

 

[Curious Hound]

Not advised. And here is why.

1. You're adding load to the original circuit, which was (hopefully) sized properly for the load of the water heater only.

2. Yes, adding a transformer would get you the 120volts. But, you would need to add more than the transformer. Fuses or circuit breaker for the 120volt load side, suitable enclosure, and what about switching to turn it on and off? The original wiring and breaker would need to be upsized to account for the new load. In the industrial systems you mention, everything is properly sized and engineered to do that from the beginning, including all necessary controls and safeties.

3. Somebody is likely to recommend using the ground as a neutral and deriving 120 volts that way. This is bad. It is against code and unsafe. You would be running current on the uninsulated ground conductor. Plus, you would no longer have a dedicated safety ground. Do NOT do it.

I would strongly recommend running a new circuit for your heat tape. Or, add it into an existing 120volt circuit that has little or no load on it, such as a guest bedroom receptacle circuit.

 

[rubydist]

You get 120V by using one of the hot wires and the neutral. Whether that is a good idea on that circuit or not depends on the existing loading and how much you are going to add with the heat tape as Eric described above.

 

[Curious Hound]

You get 120V by using one of the hot wires and the neutral. Whether that is a good idea on that circuit or not depends on the existing loading and how much you are going to add with the heat tape as Eric described above.

He already said his cable doesn't have a neutral.

 

[lil_Blue_Ford]

Not advised. And here is why.

1. You're adding load to the original circuit, which was (hopefully) sized properly for the load of the water heater only.

2. Yes, adding a transformer would get you the 120volts. But, you would need to add more than the transformer. Fuses or circuit breaker for the 120volt load side, suitable enclosure, and what about switching to turn it on and off? The original wiring and breaker would need to be upsized to account for the new load. In the industrial systems you mention, everything is properly sized and engineered to do that from the beginning, including all necessary controls and safeties.

3. Somebody is likely to recommend using the ground as a neutral and deriving 120 volts that way. This is bad. It is against code and unsafe. You would be running current on the uninsulated ground conductor. Plus, you would no longer have a dedicated safety ground. Do NOT do it.

I would strongly recommend running a new circuit for your heat tape. Or, add it into an existing 120volt circuit that has little or no load on it, such as a guest bedroom receptacle circuit.

This.

Why people have such a casual disregard for the dangers of electricity and why it should be done correctly is beyond me. You can die or burn things to the ground by doing it wrong. Don’t do it wrong, if it’s beyond your abilities, find someone who does the work.

 

[Li'l Work Truck]

I am not an electrician. This suggestion may not be appropriate, and so it's mostly a question for @Curious Hound. Would the use of a light bulb socket to 110v 2-prong adapter work for this situation?

 

[Bird76Mojo]

The heat tape will be consuming a massive 84 watts.

This is done all the time in well pump house applications.

I cannot find fault with this installation:

 

[rumblecloud]

well then....

 

[pentode]

Setting aside the totally valid safely considerations, wouldn't a breaker and a bit of Romex be cheaper than a transformer anyway?

 

[Curious Hound]

I am not an electrician. This suggestion may not be appropriate, and so it's mostly a question for @Curious Hound. Would the use of a light bulb socket to 110v 2-prong adapter work for this situation?

Not entirely sure what you are recommending. But the answer is definitely "NO".

 

[Curious Hound]

The heat tape will be consuming a massive 84 watts.

This is done all the time in well pump house applications.

I cannot find fault with this installation:

That will work. Check local codes for legality. At 84 watts, you are not significantly increasing circuit load. Follow ALL the steps he showed. The same 2 amp fuses will work for you. I, personally do not like Wago connectors. I would make those shared ground connections a different way. But that is just personal preference based on my 44 year career.

Personally, I would go the cheaper route and just run a 120v circuit to it. The reason people do this or similar things for their well-house installations is because the well-house is usually a great distance from the power source and running a separate circuit would be more expensive.

 

[pentode]

Yep, if it's a well house type application, copper gets expensive quick, that's true. I was just thinking about how expensive transformers are now.

 

[Bird76Mojo]

That will work. Check local codes for legality. At 84 watts, you are not significantly increasing circuit load. Follow ALL the steps he showed. The same 2 amp fuses will work for you. I, personally do not like Wago connectors. I would make those shared ground connections a different way. But that is just personal preference based on my 44 year career.

Personally, I would go the cheaper route and just run a 120v circuit to it. The reason people do this or similar things for their well-house installations is because the well-house is usually a great distance from the power source and running a separate circuit would be more expensive.

I use the Wago connectors at work all the time, mainly because our PM's require a lot of disconnections and the Wago's make that fast and easy. Plus I do a lot of work while the circuits are live and untwisting wires that had a wire nut on them often leads to shorting a wire to ground. This is primarily on very low amperage draw devices and circuits.

I believe I have a line on a cheap transformer. More affordable than a run of Romex anyway. Plus the ease of installation is a major factor here compared to fishing a new circuit.

Thank you for the advice.