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#101680 - 11/13/02 12:31 AM how to ground this transformer
dtong_ck Offline
Junior Member

Registered: 11/13/02
Posts: 4
Loc: Toronto, Ontario
"....Hi, I am new to this forum and glad to be a member. First of all I have to explain how I usually do when wiring up a step down transformer(600v/120/208v).The transformer is bolted to the floor.I will run the 600v wire (3 hot)to the primary side H1,H2,H3 and the secondary cable(3 hot and a neutral) X0,X1,X2,X3to the panel. Then I will run a bare or green copper wire and connect one end to the building main cold water pipe and the other end to the ground lug (X0)of the transformer. Also the secondary neutral cable is connected to the same ground lug as well.
Now What happen if I have to wire up a transformer that is on wheel and is portable. The reason is that in my factory there are 3phase 30 amp 600v outlet everywhere and we need 120v and 208V power. So the idea is to plug the transformer to the 600v outlet and we have 120/208v power. My question is that how should I ground this setup. There is of course a ground wire from the 600v outlet. Like I mention before I will run a ground wire to the cold water pipe if the transofrmer is in a fixed location. Now since the transformer and panel is portable, All I can do is to connect the ground wire from the outlet to the ground lug in the transformer. And connect the secondary neutral to the same lug. in other words, all ground wires are terminated at the X0 that bond to the frame of the transformer.Is this correct and safe? .."

I am using extra hard usage cable to make a 30amp plug which is wired into a 30A fusible disconnect and from it into the 15kVA transformer. The 120/208V secondary then go to a 150A 3 phase panel.

From the code book, #8 copper shall be used as the ground conductor for the secondary side; however, the ground conductor from the 600v outlet,which I am using for everything, is only #10. Therefore, is it safe? If not,what can I do to make it safe? Thanks in advance.

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2014 / 2011 NEC & Related Books and Study Guides
#101681 - 11/13/02 05:58 AM Re: how to ground this transformer
electric-ed Offline
Member

Registered: 07/08/02
Posts: 184
Loc: Canada
Do I understand that the panel that you intend to supply from this "portable transformer" is also portable?

Did you get some kind of special permission for this. It sounds to me like a code violation. I will have to do some research and get back here later.

Ed

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#101682 - 11/13/02 09:56 PM Re: how to ground this transformer
dtong_ck Offline
Junior Member

Registered: 11/13/02
Posts: 4
Loc: Toronto, Ontario
yes, the panel, disconnect and the transformer are all installed in a cart so that it can be pushed to whereever that it is needed. I should mention also that the conductors size are ok, it is the grounding part that I have question. No, i have not gotten any permission, it is my assistant general manager want this to be done. If I can find out it is a violation of the code,then i can refuse to do it.Thanks.

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#101683 - 11/14/02 09:53 AM Re: how to ground this transformer
electric-ed Offline
Member

Registered: 07/08/02
Posts: 184
Loc: Canada
In my opinion this portable unit that you are describing would be classed as equipment, and would be required to be tested and approved (listed) by CSA, UL, or some other certification agency.

Don't forget liability and insurance issues.

Ed

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#101684 - 11/14/02 09:54 PM Re: how to ground this transformer
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
It is conceivable that the assembly could be constructed with listed/labeled components, and prior to energization [besides the equipment-grounding conductor carried with the ungrounded 600V supply conductors] could conceivably be tied to "nearest effectively ground building steel"—similar to a fixed installation. It is likely that the grounding lead could be treated effectively the same as the grounding connection of a 600V portable welder.

For that purpose, what about using 6AWG welding cable with an rugged, attached portable clamp, like http://www.thermadyne.com/evolution/bigimage.asp?div=twe&pdtid=285 for secondary and enclosure grounding? As an alternative to extending 208/120V from a remote location, I believe it could function as a safer arrangement.

As an alternate to a 2-winding transformer, if it could be assured to be served from a 4-wire 600Y/347V circuit, an autotransformer arrangement may be practical, obviating the need for the secondary grounding as with a separately derived system. Using an otherwise-rated set of 240/120V transformers with a stock 5% tap, the two-winding 228:120V ratio could be configured as a set of 347:120V autotransformers.

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#101685 - 11/14/02 09:59 PM Re: how to ground this transformer
dtong_ck Offline
Junior Member

Registered: 11/13/02
Posts: 4
Loc: Toronto, Ontario
Yes, I agree 100% with you ED. The equipment has to be inspected. By the way,could you please refresh me about what is the purpose of the grounding cable from the X0 to the main service grounding electrode in the self learning module that I had downloaded. Module 405 page 5 of 6 item 9. I know it is for safety and for CEC. What I mean is in theory? Thank.

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#101686 - 11/14/02 10:11 PM Re: how to ground this transformer
dtong_ck Offline
Junior Member

Registered: 11/13/02
Posts: 4
Loc: Toronto, Ontario
Thank Bjarney. It is a good suggestion as to use a clamp for the secondary grounding conductor and I think it will serve the same like a fix installation. The reason I use the 600v/120/208v transformer is because we had it already. The management will not spend money to buy an autotransformer.

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