Tankless Water Heaters: Safety Certifications?

I'm an electrical engineer whose job requires me to design and submit 240/277VAC power control products to Underwriters Laboratories for safety approval. To do my job I have to maintain constant vigilance on where the current goes when stuff gets hooked up wrong or wires accidentally break after the installer leaves the job site.

I recently repaired a UL-listed under-counter tankless water heater at my church. I noticed that the heating element (a coiled nichrome wire) is immersed in the cold water stream without the benefit of any insulating sheathing around the wire.

How do heaters of this architecture manage to get safety certification? The guys at safety certification agencies are usually junkyard dogs about current flowing into the green safety ground wire. They generally disallow intentional ground current, saying the green safety wire is intended for rare fault events involving component failure or mis-wiring.

If a tankless water heater is powered from a branch circuit that is neutral referenced (for example, 120VAC) there must be significant amount of current flowing constantly from the exposed nichrome wire, through the warmed water, and into the grounded inlet/outlet brass fittings. Loss of green safety ground at a tankless heater would make the nearby faucet electrically live if plastic plumbing pipe is used upstream from the heater.

Would appreciate any feedback from other posters on this.

Hello Jim, Welcome to Terry's Forums.

You might want to post this over on the electrical Forum also.

That is a very good question.

I would hope that it is on a Ground Fault interrupt.

Have a Great Day.

DonL

Thanks for the feedback, Don. The suggestion about posting to the electrical forum is a good one.

A ground fault interrupter probably wouldn't work with a tankless water heater of the kind I describe. The continuous and intentional current leakage into the grounding wire would trip the GFI as soon as the heater turns ON.

Hello Jim and all,

I would have thought that a ground Fault would be a requirement too meet electrical code.

But then Churches may be exempt.

If it does trip a Ground Fault interrupt, then I think it may not be safe. Should be working off the Neutral.

When they went to Plastic Pipes it sure changed the safety factor.

Around here they ground to the Natural Gas line, It is still Iron. (Even tho it is not a good idea.)

I hope You get your answer. There are a lot of knowledgeable persons on this Forum.


Enjoy Your Weekend.


DonL