How can I make sure there are no safety issues with my electric tankless water heater?

Question

More of an electrical question. I've got a new tankless electric water heater I installed myself. Being tankless, this uses a lot of power (6 AWG wire with a 70amp breaker 220 monophase). I've got it wired through an AC disconnect near the heater due to the thick cable.

Everything is fine and I'm quite sure I wired it up properly. However, with all that power I just want to be sure on the facts regarding electrocution danger with such a setup. I've got the ground wire properly connected. Not sure if this matters, but the ground wire is in very close proximity (maybe even touching the case) to the wires in the AC disconnect. I have plastic PVC plumbing in the house.

Given this setup, is there any danger that I could ever be electrocuted if this heater were to short out or malfunction or if that ground wire ever touched one of the hot leads? Can water in a plastic pipe even carry that kind of power? Thanks for any information!

Answer 1

First, the heavy current available gives no more rise to electrocution than does 15 amps since it takes only a fraction of an amp travelling through a human body to cause death.  The 220 volts, however, is more than enough power to drive a lethal does of current through dry human skin (your body's first line of defence) -- and therefore your setup deserves caution and respect.

As to the ground touching one of the hot leads YES there is danger if a bare portion of the leads contact each other. The danger, however, is not so much electrocution as it is fire.  If either hot lead touches the ground without proper insulation, you will have a direct short.  The breaker may save you but the leads can get very hot very quickly and damage the insulation, perhaps in a place you cannot see.  

Also note:  the voltage between a hot lead and ground is 110 but the voltage between the two hot leads is 220.

The answer to your question is that, as long as the insulation is well done and set up so that it cannot "chafe through", and your tank is grounded, you are probably quite safe.

And yes, assuming your water has some mineral in it, the water in a 1/2" plastic pipe can certainly carry enough power to be dangerous.