DELTA System

[shaw0486]

Hi Everyone,
I just started a job that I have to replace a panelboard that is being fed from a 3 wire center phase grounded straight 240 delta panelboard. I am not extremely familiar with this, however have heard of it. What I am not sure of is do the breakers in the panelboard have to have any special rating other that the normal 120/240?

 

[kwired]

Hi Everyone,
I just started a job that I have to replace a panelboard that is being fed from a 3 wire center phase grounded straight 240 delta panelboard. I am not extremely familiar with this, however have heard of it. What I am not sure of is do the breakers in the panelboard have to have any special rating other that the normal 120/240?

They can not be the normal 120/240 rated breakers. They have to be rated 240 only. Three pole breakers are usually rated straight 240, it is double pole breakers, if you have any, that you will need to watch for this.

 

[acrwc10]

They can not be the normal 120/240 rated breakers. They have to be rated 240 only. Three pole breakers are usually rated straight 240, it is double pole breakers, if you have any, that you will need to watch for this.

Just currious, why can't the breakers be 120/240volt rated? the 240 rating meets the upper end requirements. Aside from there being no 120, what would the code section be?

 

[meternerd]

Hi Everyone,
I just started a job that I have to replace a panelboard that is being fed from a 3 wire center phase grounded straight 240 delta panelboard. I am not extremely familiar with this, however have heard of it. What I am not sure of is do the breakers in the panelboard have to have any special rating other that the normal 120/240?

3 wire delta, regardless of any corner grounding, put out single phase or thee phase 240. Therefore, only double pole or triple pole 240 breakers would be used, since there is no neutral to obtain 120.

 

[tom baker]

A 120/240 breaker is only rated at 120 to ground and won't clear a 240 volt fault. This has long been a requirement in the UL white book and that language was added in perhaps the 2002 NEC. I suspect there are a lot of misapplied slash rated breakers as a delta breaker costs about 10X and few houses carry them.
Take a look at 240.85

 

[kwired]

A 120/240 breaker is only rated at 120 to ground and won't clear a 240 volt fault. This has long been a requirement in the UL white book and that language was added in perhaps the 2002 NEC. I suspect there are a lot of misapplied slash rated breakers as a delta breaker costs about 10X and few houses carry them.
Take a look at 240.85

Won't clear a 240 volt fault? Sure hope it will. Even if system is 120/240, if you have a fault from phase to phase it is supposed to protect from that. I understand the rules of the 120/240 vs 240 rated breakers but have no idea why other than the fact that most of the time the fault is from phase to ground, but it can be phase to phase.

 

[acrwc10]

Sorry Tom for my ignorance on this it's not a situation I run in to too often and I am trying to understand this completely.

I understand a coner grounded Delta, no neutral basically, one of the phases connected to "earth". Now you would only be using two pole or three pole CB's on this panel, wouldn't a phase to ground fault be the same as a phase to phase fault? because the "grounded conductor" is a phase conductor. Or am I miss understanding the system he has in this set up? What I am not clear on is, if a two pole breaker says it is 120/240 rated shouldn't it be fine on a corner grounded delta, but not a "high/stinger leg" 240 system?

I just want to understand completely, so I can explain this to someone else if I have to.