1-Phase 208V Ckt

[Alwayslearningelec]

I know dumb question. If you have a 1 Phase 208v circuit isnt that a single pole breaker? But 208V would require 2 pole breaker...??Thinking about this wrong.

 

[bwat]

208 typically means it's from (at least) two phases, so it'd be 2-pole breaker. 208 is line to line. 120 is line to neutral.


edit to add: when we use 2 phases of a 3 phase system, we often still call it 'single phase' which is partially why it can be a little confusing.

 

[Alwayslearningelec]

Ahhh...that's what I thought. So this should be fed from a 2p breaker which is what I'd assume even though says single phase.

 

[ActionDave]

It's no different that a 240V single phase circuit, you need a two pole breaker for that

 

[Electromatic]

You could use a 1-pole on a high-leg.

 

[texie]

You could use a 1-pole on a high-leg.

Oh, please don't go there. We've had that discussion plenty here.

 

[retirede]

The most basic way to look at this is to remember that all ungrounded conductors must be protected.

 

[Carultch]

I know dumb question. If you have a 1 Phase 208v circuit isnt that a single pole breaker? But 208V would require 2 pole breaker...??Thinking about this wrong.

What it really is, is a connection across two phases of what starts as a 3-phase grid. It is called single phase, because a hypothetical single phase 208V source could supply the same AC voltage waveform that the device requires. In practice, the two phases of a 3-phase grid is where you get 208V single phase power from typical voltage grids that supply buildings. Due to the fact that it comes from two ungrounded conductors, you need a breaker pole for each of them, hence a 2-pole breaker.

You might also have a load that requires both 120V and 208V, such as a clothes drier in an apartment dwelling unit. It uses 208V for the heating element, and 120V for the motor. For historical reasons, this is still called "208V single phase/3-wire", and would be derived from 2 phases for the 208V, and each of the phases-to-neutral would be 120V. I prefer the term "open wye circuit" for such a load, because it is more descriptive of what is really happening.

 

[Carultch]

You could use a 1-pole on a high-leg.

"Good luck" finding a straight-rated 1-pole breaker. Most, if not all, are slash rated, and require 120V nominal to ground. A panel built for 277/480V could theoretically be sufficient for the voltage, but labeling would confuse everyone and I don't know if the NEC allows it. Bottom line is, avoid using high-leg-to-neutral to power anything.