Came a cross an unusual situation. A hotel with a 480V service was supposed to have PTAC air conditioners rated for 277V.
Apparently they came as 208-230/1/60. The solution that was used was transformers with 480Y primary and 416/240 secondary.
All the air conditioners are then powered via single pole 240V breakers. A hot with a neutral.
Small fan coils etc, can be ordered as 277V, but usually they come with their own little transformers.
Anyone ever come across this, equipment fed with a 240 hot and a neutral?
There are potentially two problems with the described arrangement. The single-pole breaker must have at least a 240V rating. A breaker labeled 120/240V is unacceptable in this case. Also, verify that the air conditioners are intended {listed} for operation at more than 150V to ground.
According to 240.22, you are permitted to open a grounded conductor, as long as all ungrounded conductors are opened simultaneously. Can you physically install 2-pole breakers?
Could these be British/European breakers rated for 240V by any chance?
I see that you're in the Cayman Islands, so I wonder whether someone was under the British influence when they decided to install the xfmr with a 240/415V secondary.
Bjarney- I have been aware of the 240V only rating on breakers. I have been stuck on some jobs with 240 open delta and had to put some 2 pole single phase loads using the high leg. Square D has an "H" suffix for that I think.
I will admit I have never seen a 240V single pole breaker before. I wrote down some numbers and will back check the ratings.It is GE stuff.
I will look into the 150V to ground issue, but I have never seen that sort of rating ever in air condtioning unit specs. The compressor and fan motor manufacturers would most likely be the ones to answer that.
Redsy, no cannot install 2-pole breakers.You want the neutral to trip at the same time?
Pauluk - There is a British Influence here, but the only time I have seen 416 is for some telecommunication equipment here. Rectifiers came from the UK, and 416 was within tolerance of the 380V the British rectifers were designed for.
The original drawings show that the building was to be 1200A @ 208/120, however the service was changed to 800A @ 480. Don't know why, lighting is all 120, no elevators, no big 3 phase motors. The only thing not 208/120 is the 150 PTAC air conditioners.
The snag was the 150 PTACs that were imported were not rated for 277. The change in service voltage must have happened after the project started.
Thanks to all for the responses
Carnak, these may be something to discuss with an inspector or electrical engineer. [Make some money in the process.] I didn’t mean to throw a wrench in the gears for you.
I came across the 150V-to-ground restriction on some 1ø 230V ducted-package air conditioners that prevented them for being 'staggered' across a building-service high leg of a 240V system.
A weird irony about 240V 1-pole breakers is that 277V 1-pole breakers are available, but I don’t know if that’s in the cards for your hotel project.
The change to 480Y/277V may have been for the utility’s lack of a 208Y/120V transformer that would handle the connected load. 208V3ø@1200A is ~432kVA. It could be that a reasonable upper limit for 208V service from the local utility was something like 225 or 300kVA. {Offhand, 480V3ø@800A is ~665kVA.}
. Rectifiers came from the UK, and 416 was within tolerance of the 380V the British rectifers were designed for
If the rectifiers actually carried a nominal 380V rating, then it's likely they were intended for the Continental European (or perhaps Irish) market rather than British.
Since standardization of supplies in the early 1970s, British devices are generally rated 415V. Prior to that, most apparatus was rated 440V to cover the highest nominal system in use (250/433V).
Carnak,
What is your concern with opening the neutral with the hot on a branch ckt?
240.22 seems to permit it.
redsy,
How would opening the grounded conductor help? The breaker would still have to be rated 240 and not 120/240.
Don
Don,
It would be easier to obtain a 2-pole, 240 volt breaker than it would be a single-pole, 240 volt breaker (does such an animal exist?).
Carnak,
I thought that this was the original concern of this post??
240 volt CBs are available, although they cost a bit more.
[This message has been edited by Redsy (edited 08-07-2003).]
Update
The 416V transformers feed GE panel boards rated for 480/277. The single pole breakers are rated for 277V.
My concern here was I have never seen an air conditioning unit fed with a 240 hot and a neutral. The PTACs are all by GE so I have a call in to them.
A majority of the PTACs have been in service since 1989,so I am really wondering if I have been worried about nothing.
Wouldn't most American 240V A/C units (at least those intended for commercial use) be listed for more than 150V to ground?
They would need to be so rated for operation on a 240V corner-grounded delta supply, or if one side were connected to the high leg (208V) of a 4-wire delta.
PTAC- something to the effect of "Packaged Terminal Air Conditioner", the through-the-wall units you see in a lot of motels.
I think my concern boils down to does a motor 'care' how it is getting its power as long as the voltage, phase and frequency are correct.
It looks like the answer is no, the motor does not care.
I asked the manufacturer's engineer, and he spent a couple hours going through the NEC and could find nothing wrong.
The 150 to ground issue is not a problem with 3 phase equipment in a building powered by 240 open delta.