From the title of your post, 277/480v delta, this is not a delta connection. Back feeding, you mention the 277/480v side? Confusion here could lead to a wiring issue. Help us understand what you really have.
Reversing transformers
- Thread starter sparkey1003
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From the title of your post, 277/480v delta, this is not a delta connection. Back feeding, you mention the 277/480v side? Confusion here could lead to a wiring issue. Help us understand what you really have.
If your service is 120/208 1? 3-wire, you need to feed the low voltage side.
Is this a 3? or 1? transformer? Nameplate data exactly as written would be helpful...
fdt1973
Member
- Location
- Bayonne, NJ, USA
Reversing transformers
OK: maybe I didn't explain myself correctly
My service is 120/208v 3 phase
My heaters are 480 volt 3 phase
The name plates has been worn off with the exception of the 9.3 amps that they say they pull
and I know they are 480v because they were wired that way to a 3 pole 480v 20 amp breaker.
they were given to me so I was the one who uninstalled them.
I have a working step up 30 kva transformer 120/208 to 277/480 I connected it is connected
and I am getting 480 at the secondary which would regularly be the primary due to the fact
that it is backfed. I also read 480v at the heaters but they only warm up a little.
My question should have been:
? Could it be that the heaters are bad and simply dont heat well anymore. This is my original assesment.
but since this is the first time I have backfed a transformer I was hoping someone can enlighten me if they think my problem is being caused by something else that I am not aware of. No breakers are tripping and I have the right voltage at the heaters. I am pretty sure that they are faulty but I want and second opinion before I went and spent $1500.00 on (2) new heaters. I live in jersey and it's going to get cold here soon I am trying to beat the weather. thanks for your responses.
OK: maybe I didn't explain myself correctly
My service is 120/208v 3 phase
My heaters are 480 volt 3 phase
The name plates has been worn off with the exception of the 9.3 amps that they say they pull
and I know they are 480v because they were wired that way to a 3 pole 480v 20 amp breaker.
they were given to me so I was the one who uninstalled them.
I have a working step up 30 kva transformer 120/208 to 277/480 I connected it is connected
and I am getting 480 at the secondary which would regularly be the primary due to the fact
that it is backfed. I also read 480v at the heaters but they only warm up a little.
My question should have been:
? Could it be that the heaters are bad and simply dont heat well anymore. This is my original assesment.
but since this is the first time I have backfed a transformer I was hoping someone can enlighten me if they think my problem is being caused by something else that I am not aware of. No breakers are tripping and I have the right voltage at the heaters. I am pretty sure that they are faulty but I want and second opinion before I went and spent $1500.00 on (2) new heaters. I live in jersey and it's going to get cold here soon I am trying to beat the weather. thanks for your responses.
Measuring 480 at the heaters while they only get slightly warm is a good sign the heaters are bad.
Did you measure current?
kwired
Electron manager
- Location
- NE Nebraska
Possibility - multiple element heating unit, only one (or any thing less than all) element is working. Does not have to be bad elements, could be bad contactor, loose connections, open high limit(s), etc.
Back to post #41. Some forced air unit heaters do require 277/480v. (not sure if yours do) If you are back feeding a delta x wye xfmr, you would not have a neu. (277v) connection. It would be rare to actually have a Y x Y xfmr as you suggest, common for utility use, not secondary distribution. Do you have 4-wires terminated at the heaters and if so, what? This may not have anything to do with the poor output of the heaters (it may) but I'm just questioning the proper wiring.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Usually on the ones that do require a neutral, its the fan thats 277, since the OP's fan is running, I wouldn't think this is the case. This must be a relatively small heater, the last one I hooked up required a 60 amp circuit. Must be an old vestibule heater out of a store? Since it is three phase, and heating elements are single phase, you probably have only one or two heating elements working. a quick check with a ammeter will verify this. Being so small, I would not believe the elements are staged.
My feeling about this is to take the whole thing to the scrap yard and forget it....
WHen you talk about heaters, are you talking about just heating elements?
You should have some idea about the wattage of these things because of the amperage draw, and the area you are trying to heat, yet you report that the heaters are only warm, and don't seem to recognize the need to check the amperage, or consider the expected resistance of the heaters. I can't imagine that you have a safe installation there.
I also can't imagine these heaters being economical to operate.
WHen you talk about heaters, are you talking about just heating elements?
You should have some idea about the wattage of these things because of the amperage draw, and the area you are trying to heat, yet you report that the heaters are only warm, and don't seem to recognize the need to check the amperage, or consider the expected resistance of the heaters. I can't imagine that you have a safe installation there.
I also can't imagine these heaters being economical to operate.
kwired
Electron manager
- Location
- NE Nebraska
That entirely depends on what his electric energy rates are. Some places electricity is competitive with other energy sources, some users get better rates than other users on same utility because of other reasons. Rates are lower where I live in winter months to encourage more usage because summer months is when the system is loaded the most.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
reversing xformer
reversing xformer
As noted previously, this reversing xformer subject comes up often. IMO, while it can be done properly, my experience tells me that is rarely the case. Over the years I have run accross these installs numerous times and rarely found it to be correctly done. Oddly enough, I just came accross yet another one yesterday while looking at another issue on a site. Of course it was also improperly installed. Some years back I had an improperly reversed xformer on a site that we maintained that I decided to issue a letter stating my concerns to manager of a county owned facility. He in turn sent it to the AHJ which responded that this is done all the time, not a problem, the electrician doesn't know what he is talking, etc. About a year later, due to the right sequence of events, it failed and had a small fire. Now that I am older and wiser, unless I'm asked to check these for proper installation, I just ignore it to avoid the drama.
Even if properly done IMO there are too many negative issues such as no 277 volt, you need to corner ground which gives 480 volt ground and you need single phase gear for the corner ground which leads to confusion in say a light commercial setting.
I just don't know why people do this when all the xformer manufacturers list a 208 delta X 277/480 Y unit. Sure, they cost a little more as they are not made in volume. I just believe this is a better practice.
reversing xformer
As noted previously, this reversing xformer subject comes up often. IMO, while it can be done properly, my experience tells me that is rarely the case. Over the years I have run accross these installs numerous times and rarely found it to be correctly done. Oddly enough, I just came accross yet another one yesterday while looking at another issue on a site. Of course it was also improperly installed. Some years back I had an improperly reversed xformer on a site that we maintained that I decided to issue a letter stating my concerns to manager of a county owned facility. He in turn sent it to the AHJ which responded that this is done all the time, not a problem, the electrician doesn't know what he is talking, etc. About a year later, due to the right sequence of events, it failed and had a small fire. Now that I am older and wiser, unless I'm asked to check these for proper installation, I just ignore it to avoid the drama.
Even if properly done IMO there are too many negative issues such as no 277 volt, you need to corner ground which gives 480 volt ground and you need single phase gear for the corner ground which leads to confusion in say a light commercial setting.
I just don't know why people do this when all the xformer manufacturers list a 208 delta X 277/480 Y unit. Sure, they cost a little more as they are not made in volume. I just believe this is a better practice.
kwired
Electron manager
- Location
- NE Nebraska
You can not use fuses in the grounded phase, you can however use a 3 pole circuit breaker include the grounded phase through the breaker. See 240.22(1). You must still run a separate equipment grounding conductor, the grounded phase is treated just like a neutral in a system with a neutral - once you are past the system bonding jumper separate the grounded from the grounding conductors.
Most times when people are asking about doing this they are mostly interested in supplying a single piece of equipment and having 277 volts available is not important or necessary. Chances are they have little or no extra capacity to power anything besides the original intended load anyway.
The only thing dangerous about corner grounded systems is when someone messes with it that does not understand it.
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