230V L-G supply for a 240V load

[mull982]

Had a situation the other day where a new A/C unit was installed that required 240V power. The only source that we had avaliable was a 230V L-G transformer (European Equipment). The question was brought up weather or not we could use this 230V transformer to feed this 240V A/C unit. The A/C connection diagram did not show a neutral being used as part of the input connection and just required the two legs of 240V. It did show a ground connection on the input connection.

At first we thought about just using the 230V source to the A/C unit because there was no neutral needed. But then after seeing electronics in the unit I thought that maybe these electronics were designed to have a 120V L-G reference and if we brought in the 230V L-G source then they would not have this.

We called the A/C rep and he insisted that we must have the two seperate legs of 120V L-G brought to the unit to give the 240V. I questioned him on why this was since they did not have a neutral but he was not very clear in his answer. I can only assume that there were components inside that referened to ground. Is this a correct assumption?

If there were no electronics or anything inside that referenced to ground such as a motor, or heater, then would it have been o.k. to connect the 230V L-G supply to this unit and have it operate fine ( ignoring the slight volage difference).

 

[LarryFine]

If the load has no neutral connection, your supply should work. The load shouldn't care whether one line is grounded.

 

[qcroanoke]

Had a situation the other day where a new A/C unit was installed that required 240V power. The only source that we had avaliable was a 230V L-G transformer (European Equipment). The question was brought up weather or not we could use this 230V transformer to feed this 240V A/C unit. The A/C connection diagram did not show a neutral being used as part of the input connection and just required the two legs of 240V. It did show a ground connection on the input connection.

At first we thought about just using the 230V source to the A/C unit because there was no neutral needed. But then after seeing electronics in the unit I thought that maybe these electronics were designed to have a 120V L-G reference and if we brought in the 230V L-G source then they would not have this.

We called the A/C rep and he insisted that we must have the two seperate legs of 120V L-G brought to the unit to give the 240V. I questioned him on why this was since they did not have a neutral but he was not very clear in his answer. I can only assume that there were components inside that referened to ground. Is this a correct assumption?

If there were no electronics or anything inside that referenced to ground such as a motor, or heater, then would it have been o.k. to connect the 230V L-G supply to this unit and have it operate fine ( ignoring the slight volage difference).

We have connected 240 volt A.C.H units to 220/380 systems and they worked fine.
But we pulled a phase and a neutral to the units and connected them to the input
breaker. Phase on one side and neutral on the other.
I'm not sure if yours would work with a phase and ground only.

 

[Besoeker]

Had a situation the other day where a new A/C unit was installed that required 240V power. The only source that we had avaliable was a 230V L-G transformer (European Equipment).

If it's European transformer, it's likely a single phase 230V. Whether one end or the other of the 230V is grounded would depend on external connections.

It's likely to be rated for 50Hz but it should still work fine on 60Hz and the small difference in voltage probably won't matter to the A/C.

 

[winnie]

In theory it should work fine, and as has been noted, people have done this in the past with no problems.

_However_ you can be pretty certain that this unit was designed and evaluated for safety with the assumption of a 120/240V center grounded supply. You may have a system that would work fine but simply has not been evaluated by UL or other testing lab for safety in this use.

Also, with no neutral is brought to the unit, then you can be comfortable that it doesn't require a 120V power supply, however some components _may_ use the EGC as a ground reference. In particular, you would need to watch out for any L-G filtering or transient voltage suppression. I don't have any experience with AC units, but a VSD that I worked with had specific instructions for disabling various TVSS components if the drive was used with anything other than a center grounded source.

-Jon

 

[mull982]

The transformer was indeed a 230V unit with one side grounded. I was almost certain that without a neutral connection this would work fine, but the tech insisted that we have a center grounded source. I could not get an answer why.

It could have been due to safety testing reasons, or due to compnents referencing to the EGC as Winnie stated.

 

[Besoeker]

The transformer was indeed a 230V unit with one side grounded..

Where was it grounded?
And how?

 

[mull982]

Where was it grounded?
And how?

Actually truth be told, I'm not even sure that it was grounded since I did not see the transformer grounded anywhere. However we read on side of the secondary at 230V to ground and the other side 0V to ground, so I'm assuming it was somehow grounded or the capacitive coupling kept the voltages to normal.

But for the sake of this conversation it appeard to be grounded on one side of the secondary.

 

[LarryFine]

The only possible issue I can imagine would be with electronic ignition, but, since the appliance has no neutral, and the unit will be grounded (it will be, won't it? ), it still shouldn't matter.

I mention it because I've seen ranges with 120v-powered igniters that keep sparking if the hot and neutral are reversed. It must have something to do with a flame-sensing feature.

 

[Besoeker]

Actually truth be told, I'm not even sure that it was grounded since I did not see the transformer grounded anywhere. However we read on side of the secondary at 230V to ground and the other side 0V to ground.

The 0V and 230V are just the start and finish of the windings. It has no relevance to potential to ground.

 

[brian john]

Just connected a $1,000,000.00 + particle analyzer that way and NO ISSUES.

 

[mull982]

The 0V and 230V are just the start and finish of the windings. It has no relevance to potential to ground.

So if ungrounded then these would have been the reference voltages to ground determined by the winding. If it was grounded it should have been grounded on the 0V potential side.

It sounds like there would have been no issues connecting it in this method (except possilby L-EGC references as mentioned.) I do not know why the manufacturer was insistant on this. To satisfy the manufacturer we went ahead and purchased a new 480-120/240 transformer.

 

[Besoeker]

So if ungrounded then these would have been the reference voltages to ground determined by the winding.

The winding would have no reference to ground unless you externally grounded it. And you could ground either end.

 

[LarryFine]

Just connected a $1,000,000.00 + particle analyzer . . .

Can I come work with you??? You have all the fun!

 

[brian john]

Can I come work with you??? You have all the fun!

Last year for the same people we hooked up a machine that makes REAL diamonds. Supposedly a jeweler cannot tell the difference

 

[dbuckley]

If this AC unit is designed for American electricity then it will expect the potential to ground to be no greater that 120V, and will have been built, tested and certified that way.

So then connecing it to a power source with 240V potential to ground violates all of that stuff. It may well work, but that is a different issue.