480 Equipment ground
- Thread starter jc7299
- Start date
- Status
- Location
- Bremerton, Washington
Re: 480 Equipment ground
This has come up many times before.I maintain its only allowed if the transformer marked as being suitable for being reversed or backfed. Step up transformers are available and there is a reason why
Regarding your question on grounding:
Step down transformer is delta wye connected, the common of the transformer being the neutral or gronding point.
When you backfed a transformer, it becomes wye delta. Section 250.20 does not require this secondary to be grounded, but optionally can, you would corner ground it. The problem with a corner ground 480 delat is the voltage to ground is 480 not 277, so a ground fault is far more destructive.
My recommendation is to use a listed step up transformer, esp if you don't understand how and what a corner ground transformer is.
This has come up many times before.I maintain its only allowed if the transformer marked as being suitable for being reversed or backfed. Step up transformers are available and there is a reason why
Regarding your question on grounding:
Step down transformer is delta wye connected, the common of the transformer being the neutral or gronding point.
When you backfed a transformer, it becomes wye delta. Section 250.20 does not require this secondary to be grounded, but optionally can, you would corner ground it. The problem with a corner ground 480 delat is the voltage to ground is 480 not 277, so a ground fault is far more destructive.
My recommendation is to use a listed step up transformer, esp if you don't understand how and what a corner ground transformer is.
Re: 480 Equipment ground
I agree that a step up transformer is the way to go but unfortunately I was given this Hammond transformer to do the job and the the?bosses don't want to spend the money, what I'm worried about is someone being in contact with the machine when a fault occurs.
p.s.
I really don't like to do work like this it sounds unsafe.
I agree that a step up transformer is the way to go but unfortunately I was given this Hammond transformer to do the job and the the?bosses don't want to spend the money, what I'm worried about is someone being in contact with the machine when a fault occurs.
p.s.
I really don't like to do work like this it sounds unsafe.
- Location
- Massachusetts
Re: 480 Equipment ground
You ground a phase of the transformer and treat it more or less like a neutral.
As Tom pointed out it the transformers output will need to be corner grounded delta.
You ground a phase of the transformer and treat it more or less like a neutral.
As Tom pointed out it the transformers output will need to be corner grounded delta.
- Location
- Massachusetts
pierre
Senior Member
- Location
- Westchester County, New York
Re: 480 Equipment ground
As far as listing is concerned, some manufacturers have transformers that are not to be backfed, and are listed and labeled as such. Otherwise if the transformer is not listed as such I can see it being done.
As far as listing is concerned, some manufacturers have transformers that are not to be backfed, and are listed and labeled as such. Otherwise if the transformer is not listed as such I can see it being done.
- Location
- Massachusetts
Re: 480 Equipment ground
Most that I can remember are labeled high voltage low voltage, not primary and secondary.
Are we sure of that or just assuming?
Most that I can remember are labeled high voltage low voltage, not primary and secondary.
Re: 480 Equipment ground
jc, i understand you not wanting to disappoint your boss and all, but hooking up a transformer to be run as step up, when it is rated for step down, does not fall into the line of electrician. this is something that a EE should lay out. (if it can be done safely)
you are taking huge risks. I cannot say that i have not done it.. i can say that it was completely engineered..
sometimes your own saftey, and confidence in your installations needs to take precident over pleasing the boss.
jc, i understand you not wanting to disappoint your boss and all, but hooking up a transformer to be run as step up, when it is rated for step down, does not fall into the line of electrician. this is something that a EE should lay out. (if it can be done safely)
you are taking huge risks. I cannot say that i have not done it.. i can say that it was completely engineered..
sometimes your own saftey, and confidence in your installations needs to take precident over pleasing the boss.
- Location
- Massachusetts
Re: 480 Equipment ground
Are you familiar with wiring a typical Wye transformer with an XO?
If you are you will now put that to work with one of the "H" terminals.
Pick H1, H2 or H3 and bond it to ground just like you would normally do with XO. That is now a grounded conductor requiring all the normal grounded conductor rules... white, no fuses etc.
By the way, the XO in your set up will remain unconnected to anything.
Are you familiar with wiring a typical Wye transformer with an XO?
If you are you will now put that to work with one of the "H" terminals.
Pick H1, H2 or H3 and bond it to ground just like you would normally do with XO. That is now a grounded conductor requiring all the normal grounded conductor rules... white, no fuses etc.
By the way, the XO in your set up will remain unconnected to anything.
- Location
- Massachusetts
- Location
- Massachusetts
Re: 480 Equipment ground
At the same time they tell you just how to do it and the issues that may come up.
Re: 480 Equipment ground
so buy one of the step up transformers, and use the correct eqipmet for the correct job....
or get engineering support for the hook up from an EE or sq d...
why are electricians unwilling to ask for help from engineers.....????? I know they can be long winded, but they usually have one or two good sentences worth listening to in thier hour long disertations....
so buy one of the step up transformers, and use the correct eqipmet for the correct job....
or get engineering support for the hook up from an EE or sq d...
why are electricians unwilling to ask for help from engineers.....????? I know they can be long winded, but they usually have one or two good sentences worth listening to in thier hour long disertations....
- Location
- Massachusetts
Re: 480 Equipment ground
I have back fed transformers to provide temp 480 on some jobs. It is not rocket science, it's just a transformer.
Too each their own, I am a Yankee and we are know for being frugal.
I am not afraid to ask for help from anyone. At the same time if I had a customer that owned a step down and asked me if I could use it for step up I would give it a try after explaining to the customer that it may not be the best solution.
I have back fed transformers to provide temp 480 on some jobs. It is not rocket science, it's just a transformer.
Too each their own, I am a Yankee and we are know for being frugal.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: 480 Equipment ground
The NEC allows both grounded and ungrounded delta distribution systems. One is not inherently more dangerous than the other. Electricians need to be trained to work on both.
I have designed many backfeed transformer arrangements and in each case attention had to be paid to all of the concerns mentioned in Square D's FAQ. Note: that all though Square D does not recommend backfeeding they do not advise against it either. They do not even threaten warranty problems like they do with classified breakers.
For transformer secondaries connected in delta, I recommend a grounded B phase arrangement when multiple pieces of equipment will be fed (i.e a panelboard) and suggest ungrounded (with a listed audible annunciator) when feeding a single item (like a machining center).
The NEC allows both grounded and ungrounded delta distribution systems. One is not inherently more dangerous than the other. Electricians need to be trained to work on both.
I have designed many backfeed transformer arrangements and in each case attention had to be paid to all of the concerns mentioned in Square D's FAQ. Note: that all though Square D does not recommend backfeeding they do not advise against it either. They do not even threaten warranty problems like they do with classified breakers.
For transformer secondaries connected in delta, I recommend a grounded B phase arrangement when multiple pieces of equipment will be fed (i.e a panelboard) and suggest ungrounded (with a listed audible annunciator) when feeding a single item (like a machining center).
Re: 480 Equipment ground
I have contacted a EE and now waiting for feedback from him , and I'm difinetly not afraid of upsetting my bosses I don't like this set up anymore than any of you guys me and the boss have been arguing for over a week now I thought i would see if anyone else felt like I did. or if I was wrong it been known to happen.
I been thinking of telling him he can do this one on his own .but thanks again for all the info I've learned alot.
I have contacted a EE and now waiting for feedback from him , and I'm difinetly not afraid of upsetting my bosses I don't like this set up anymore than any of you guys me and the boss have been arguing for over a week now I thought i would see if anyone else felt like I did. or if I was wrong it been known to happen.
I been thinking of telling him he can do this one on his own .but thanks again for all the info I've learned alot.
- Location
- Massachusetts
Re: 480 Equipment ground
IMO In the interest of ease of maintenance and safety (of the workers who are not trained for ungrounded systems) to have a single piece of equipment fed by an ungrounded system in a building that is predominately supplied by grounded systems is just asking for trouble.
The only reason I can see for using an ungrounded system is for continuation of service.
Is a single milling machine put out of service reason enough to have an electrical 'oddity'?
I of course agree the NEC allows both, very few electricians are trained to work on or have experience with (intentionally) ungrounded systems.
IMO In the interest of ease of maintenance and safety (of the workers who are not trained for ungrounded systems) to have a single piece of equipment fed by an ungrounded system in a building that is predominately supplied by grounded systems is just asking for trouble.
The only reason I can see for using an ungrounded system is for continuation of service.
Is a single milling machine put out of service reason enough to have an electrical 'oddity'?
- Location
- Illinois
- Occupation
- retired electrician
Re: 480 Equipment ground
Bob,
Don
Bob,
And these same electricians that don't know about ungrounded systems would understand a corner grounded delta system????
Don
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