ME needs EE help

[trennick]

Being an ME, I need some EE help. Can I reliably run one of those new tankless water heaters (essentially a big resistor), which draws 30A at 240Vac, from a 240Vac, 30A, 3 phase supply? Or will I be constantly tripping power?

Thanks,
Tim

 

[itsmoked]

Probably.. A few more details would be helpful. Is the 3Ph supply nothing special like a generator? Is the waterheater 3ph? You didn't specify.

 

[trennick]

The supply is from our company's electrical distribution, so I suspect it's ultimately the local utility company. I think the heater is single phase. - Tim

 

[davidbeach]

The NEC requires that the overcurrent protection for a water heater be sized at 125% of the water heater rating, so no, you can not feed a water heater that draws 30A from a 30A circuit. The phasing and voltage of the supply circuit will need to match the water heater.

 

[trennick]

Thank you for your help. I'll consider alternatives. - Tim

 

[rbulsara]

If the question is can a single phase load be served from a 3 phase supply, the answer is yes. To meet Code you will require a 40A, 2 pole breaker for a 30A, 240V rated heater.

I cant imagine your supply capacity is limited to 30A.

 

[dpc]

Not sure about your application, but experience has shown that these babies are capable of producing some very noticeable lamp flicker when they kick in due to voltage dip. Don't say I didn't warn you