3P breaker feeding two single phase resistive loads

[kwired]

So here's the deal- I'm working at a hair salon/day spa recently, running power to a second electric water heater to work in tandem with the existing.

The service is a highleg so I have to move a some circuits around to get two spaces together and keep the 120V loads off the high leg.

Are you telling me that all I needed to do was swap out the breaker on the existing water heater with a three pole, land my hots for both water heaters accordingly and been done before lunch?

the phase common to both heaters will carry 1.73 times current as other phases, you will probably need a feeder supplied by the 3 pole breaker and individual protection for each heater.

 

[kwired]

I need some help wrapping my head around something I saw recently. In a nutshell, there was a 3P breaker (208Y/120 3PH) feeding two separate heat trace circuits. Phase A and B was wired to the first heat trace, and the second heat trace was wired B to C. The question I have is, what is the current on B phase? Looking at these as two independent single phase loads, it looks like you would have the same magnitude entering and leaving B phase for a net result of 0? Is that correct? Are there any issues with this application?

Thanks!

As has been explained the current on B phase would be 17.32 amps if your individual single phase elements were 10 amps.

Now add another 10 amp element from phase A to C and all three phases will draw 17.32 amps.

 

[ActionDave]

the phase common to both heaters will carry 1.73 times current as other phases, you will probably need a feeder supplied by the 3 pole breaker and individual protection for each heater.

Breaker panel is in the same room as the water heaters, so no need for disco.
Common phase could have on B phase of a high leg. Since most of the circuits were 120V it probably would have helped balance the loads.
Still legal?

 

[kwired]

Breaker panel is in the same room as the water heaters, so no need for disco.
Common phase could have on B phase of a high leg. Since most of the circuits were 120V it probably would have helped balance the loads.
Still legal?

your common phase with 4500 watt loads will draw about 33 amps, you will probably still want a 45 amp feeder and two disconnects with overcurrent protection for each heater

 

[hurk27]

Breaker panel is in the same room as the water heaters, so no need for disco.
Common phase could have on B phase of a high leg. Since most of the circuits were 120V it probably would have helped balance the loads.
Still legal?

If the water heaters are 240 volt it would have not mattered if one of your 2 pole breakers landed on the "B" phase, so you could have just used two two poles just the same. would have saved allot of moving breakers around.

With a high leg service I always look at the transformers to see if the center tap one is larger or smaller then the others, so I know which phases I can add single phase loads to, and how much.

 

[ActionDave]

No the idea was to swap a two pole with a three pole and run two water heaters.
Kwired gave a reason that it would not be as simple as that. Thanx.

 

[hurk27]

No the idea was to swap a two pole with a three pole and run two water heaters.
Kwired gave a reason that it would not be as simple as that. Thanx.

A'hhh got ya, yep the 1.732 would have got ya, unless you had a 35 amp 3-pole breaker and ran #8 to the water heaters.