What are the issues of powering an inline tankless heater with 240V when it is rated for 277V?

 

the real problem would be higher amperage and can the heater handle this higher amps. probably not!

>What are the issues of powering an inline tankless heater
>with 240V when it is rated for 277V?

 

There won't be higher amperage; to get the same power, yes you would need more amperage. But a heater will only have a given resistance, therefore less voltage means less current and less power.

You'll be fine, it just won't get quite as hot.

 

Doesn't work like that. Resistive loads draw LESS current at lower voltage, with the result that the power delivered is actually proportional to the square of the voltage, so at 240V, your 277V heater will only deliver 75% of rated KW (or so -- resistance heaters aren't known for extremely accurate resistance in the first place; figure +/- 10% or so)

So, assuming your hot water load is such that you can get by with no more than 75% of the rated KW, it should work fine, assuming there are no controls that are extra sensitive to their supply voltage, and assuming there are no varistors between any of the current legs and ground. (Feeding the heater with two 240V hot legs, they'll be at 120, 139, or 208V to ground, depending on the service configuration and which phases you pick, where the 277V would almost certainly be 277V to ground on one leg, with the other a neutral)

The concerning portion of the post isn't that, it's viewing the question as "two-phase" vs. three phase. If the heater wants two current-carrying wires (as 277V nominal implies), it's still single-phase, even if fed from a three-phase distribution. (And the correct term, even though there are two ungrounded conductors, is single-phase, not two-phase, though there actually is such a thing as two-phase)

 

>The concerning portion of the post isn't that, it's viewing
Just FYI, in many parts of the world the term "2 phase" is used to describe two-out-of-three phases. Here in North America, where we actually do still have true "2 phase" power systems in use, that would be confusing so we use the term "single phase" to mean two-out-of-three phases.

>the question as "two-phase" vs. three phase. If the heater
>wants two current-carrying wires (as 277V nominal implies),
>it's still single-phase, even if fed from a three-phase
>distribution. (And the correct term, even though there are
>two ungrounded conductors, is single-phase, not two-phase,
>though there actually is such a thing as two-phase)

 

It's two lines, one phase. There is no such thing as two phase.

To understand the difference between line and phase, look at the difference between line-to-line and phase voltage/current in a 3-phase power system.

 

> It's two lines, one phase. There is no such thing as two phase.

Yes, there is such a thing. At one time around the turn of the last century when electricity was first being distributed, 2 phase was actually the norm. Tesla / Westinghouse used a two phase system in Niagara and it is still in place there and in the nearby environs. Many furniture manufacturing plants built in the Philadelphia area at that time were also initially two phase system, but most have now finally upgraded to 3 phase. It's all ancient, and no utility actually generates two phase power any longer, so the old grandfathered systems still in use must use a special transformer called a Scott Tee to derive it.

https://en.wikipedia.org/wiki/Two-phase_electric_power

 

I stand corrected! I was not aware of a two phase generator with 90-degree separation; there would be no real way to get two phases from normal 1- or 3-phase power.

Most people consider two hot lines coming from a center-tapped (single phase) transformer two phase, when that would really be split-phase.