Need input on the use of B phase to power single phase load on delta service

[Electric-Light]

I'm aware that the voltage of any conductor must not surpass the lowest rating of a breaker to satisfy the NEC in countries adopting that set of codes, but that aside, I am wondering if equipment are meant to handle it. I know that computers are fine as the world spec power supplies are designed to take it all with no regard to grounding polarity but what about other 208-240v stuff?


Using some fairly common examples in the US, there are corner ground 240v with A phase grounded giving 240v between A-B and B-C.

A-B and A-C provides single ended power just like European domestic power and American 277v lighting power.
B-C provides 240v to ground on either sides and between lines and requires a double pole breaker.

French non-directional type items should be ok on all and almost all European items should be fine on the A-B, A-C setup, but what about American 208/240v items such as water heater, A/C condensing units, etc? Are they UL rated for any parts of internal components having a potential of over 120v to the ground? Is the 240:24v transformer that feeds the living quarters rated to have 208 or 240v of potential between windings?

What about the effect on the TVSS used in BLDC drivers? Minisplits, ECMs (motor) utilize them. I understand that if the TVSS parts were all designed to accept 240v to ground, it would not provide effective common mode suppression on a system that is only 120v to the ground.

What about the legality? The shock of a 240v L-N system is just like that of 277v.

Another one we have is this kind:

A-C gets you 240v just like residential power with 120v to the ground. A-B or B-C however gets you 120v on one side and 208v to ground on the other.

 

[don_resqcapt19]

The corner grounded system is fine for any line to line loads with a voltage rating that matches that of the equipment. You can use any combination of the phases to supply the line to line loads. The same applies to the 4 wire high leg system for line to line loads. The only issue with the high leg system is if you have any line to neutral loads. If there are line to neutral loads you must make sure they are not supplied by the high leg.

 

[Electric-Light]

The corner grounded system is fine for any line to line loads with a voltage rating that matches that of the equipment. You can use any combination of the phases to supply the line to line loads. The same applies to the 4 wire high leg system for line to line loads. The only issue with the high leg system is if you have any line to neutral loads. If there are line to neutral loads you must make sure they are not supplied by the high leg.

What about the 240v potential to ground? For example, are heating elements for water heaters designed and rated for sustained use at 240v from sheath to element?

 

[tshea]

On corner grounded systems--we have 240-3ph-3w grounded B here--you will have A-B 240, A-C 240 and B-C 240.
A-B-C also is 240 giving you 240-3ph.
With a voltmeter if you measure A-ground, and C-ground you will see 240V
B-ground will show as 0 volts!
I have explained this to many machine techs over the years.

As for your water heater 240 is 240.

SqD makes a $pecial breaker for use with 240 grounded B systems--It is a QO2XXB breaker where XX is the ampere rating, ie 25, 30, etc

 

[GoldDigger]

What about the 240v potential to ground? For example, are heating elements for water heaters designed and rated for sustained use at 240v from sheath to element?

It depends on the design of the equipment and hopefully is covered in the specs or installation instructions.
You are more likely, IMHO, to have problems with capacitive leakage to shell or insulation breakdown in smaller 240 volt devices such as commercial coffee urns than in larger appliances like water heaters which are permanently installed. But that is really just a SWAG.
You definitely have to avoid slash rated breakers, switches, receptacles, etc.

Sent from my XT1080 using Tapatalk

 

[Tom Jones]

Breakers used on the "wild leg" must be 240v rated and not 120/240 "slash rated" ones. More money.

Around here, the poco usually puts in only one wing pot, for open delta, so if you put 1ph loads on the wild leg you have a 50% chance of landing on the open side of the delta.

I have heard of cases where 120/240 items such as a cooking range were hooked up to one of the higher sides of the delta, but care has to be taken that the controls or anything that needs 120 is hooked to the lower side and not the side that gives 208.

Usually, however, the tx bank is sized with the assumption that all 1ph loads will be hooked to the center tapped pot.