any reason why not to use stinger leg?

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postgenerate

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I would like to remove load from my A and B phases. I have an oportunity to use the stinger leg to Neutral or to A or B to run a single phase AC compressor. My current configuration is 3 phase 200A delta service.

I have
Voltage A to N = 120V
Voltage B to N = 120V
Voltage C to N = 208V
Voltage A to B = 240V (currently connected to unit)
Voltage C to A or B = 240V

My most desired connection is C to N as this will eliminate the entire load from my 120V lines. I understand I need a 250V i.e. not 120/250V breaker. Is there any reason why this configuration is ill advised?

A lessor desired but still better connection is C to A or B. as this will drop half the load but has the advantages it gives me 240V.

Suggestions?

Thanks!
 
infinity said:
Can you buy a single pole CB that will be rated to work on 208 volts?
Click to expand...

Yes, I have found relatively expensive single pole CBs rated at "straight 240" that should work. And I have double pole CBs rated the same way that could give me the C to A or B connection at 240V.
 
As you have already discovered; A-C and B-C will give you the same voltage (240 volt) as A-B. Each of these combinations are "single phase".

But C-N will not run an Air Conditioner. The voltage is unstable, and as Infinity pointed out, the single pole breakers for that panel are rated 120 volt.

This type of question comes about because your panel is full, or full except for a few empty C spaces. That being the case, an upgrade is in order. It could be as simple as adding a "sub panel".
 
postgenerate said:
...My most desired connection is C to N as this will eliminate the entire load from my 120V lines. ...
Click to expand...
I don't think that connection reduces any load on the A - B transformer coil. To get current out of the C - N connection, the curent through the N has to go through either A - N coil or the B - N coil.

Maybe it's time to get a 3phase 208 transformer.

carl
 
postgenerate said:
Yes, I have found relatively expensive single pole CBs rated at "straight 240" that should work. And I have double pole CBs rated the same way that could give me the C to A or B connection at 240V.
Click to expand...

So, what you are saying is: You have found a single pole breaker that is rated 240 volts that is listed for your panel, and you are going to use it C-N, even though as an EE you should know better than to do so. You just want US to tell you why you shouldn't. Is that it? :confused:
 
I doubt very much that a panel served with delta high leg is going to accomodate a single pole breaker that is rated for 208 or higher. I think I can safely say that they don't exist that way in the field. I defy anyone to show me a link to the contrary that shows such a single pole breaker that will fit in panels that are already installed for the typical delta service.
 
Everybody, Thanks.

You are right, I cannot find a single pole breaker for this particular panel. That rules out the C-A or C-B 208-N connection. My AC compressor will work at 208V at a few amps higher. but because of the lack of availability of the breaker, and the instability the voltage, and the higher current, this is clearly not an answer.

And yes I know that a C-N connection will not reduce my transformer load. Selfishly I was only trying to spread the load across the 200A main fuses since the stinger was little used. and of course the neutral is not fused.

Also, It is not that the panel is full. I actually have space. I was calculating the load according to the NEC guidance and found that I was at 225A for a 200A panel.

So, my solution so far is to use the A-C connection for 2 wire 240V for 1 5 ton AC unit and the B-C connection for another 240V 2-wire 5-ton AC unit. I cannot find any reason why these AC units will have trouble with a 208 to GND potential. Would you consider any non 3-phase application of the stinger leg unstable (even the line to line connection)? Advice is always good, thanks. And sorry for the duplicate posts. --Tom
 
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high leg

high leg

sidebar question: why is "C" the "high" leg ??
 
C phase ?

C phase ?

I believe not only is it "not the norm", it's a violation of 408.3 (E). As I recall, eons ago "C" was the high leg. Perhaps the Murray panel is old, but I'm suprised to see it as a requirement on any recently produced panel.
 
augie47 said:
I believe not only is it "not the norm", it's a violation of 408.3 (E). As I recall, eons ago "C" was the high leg. Perhaps the Murray panel is old, but I'm suprised to see it as a requirement on any recently produced panel.
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Augie, Yes. B phase is the Hi leg per 408.3(E) But I think some POCO's require C phase as The "Bastard" leg as we call it, at the meter. Geesh! I hope to heavens I did not offend anyone by saying "Bastard"....or "Heavens".
 
dcspector said:
Augie, Yes. B phase is the Hi leg per 408.3(E) But I think some POCO's require C phase as The "Bastard" leg as we call it, at the meter. Geesh! I hope to heavens I did not offend anyone by saying "Bastard"....or "Heavens".
Click to expand...

thats the way it is here. all the wild leg transformers are c phase they are all 20 plus years old.
 
dcspector said:
Augie, Yes. B phase is the Hi leg per 408.3(E) But I think some POCO's require C phase as The "Bastard" leg as we call it, at the meter. Geesh! I hope to heavens I did not offend anyone by saying "Bastard"....or "Heavens".
Click to expand...
It can be C phase in the meter, but has to be B phase in the panel.
 
Minuteman said:
As you have already discovered; A-C and B-C will give you the same voltage (240 volt) as A-B. Each of these combinations are "single phase".

But C-N will not run an Air Conditioner. The voltage is unstable, and as Infinity pointed out, the single pole breakers for that panel are rated 120 volt.

This type of question comes about because your panel is full, or full except for a few empty C spaces. That being the case, an upgrade is in order. It could be as simple as adding a "sub panel".
Click to expand...

Hey I have a question. What makes the stinger leg unstable? Is it deemed unstable because the voltage fluctuates? If so, is that due to other loads cycling on and off on the other two ungrounded phases?

:confused:
 
Luketrician said:
Hey I have a question. What makes the stinger leg unstable?
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I think that this is a myth. I have recorded many of these services for other purposes, and have not identified any marked instability in the high leg.
 
High legs around here seems to be 190 something.

Would the unit even run like this (High leg and neutral)?
 
220/221 said:
High legs around here seems to be 190 something.

Would the unit even run like this (High leg and neutral)?
Click to expand...
I was working on a Carrier unit on Monday, and it had a voltage range of 190-254 on the dataplate. Never saw one with that big of a range before.
 
So...if the unit said 200 volts would it matter if they were grounded or ungrounded conductors?

Not codewise but would it function?
 
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