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ground fault indication

ground fault indication

ground fault indication

(OP)
I want to stepup voltage from 120/208V system to 600V to operate milling machine and will require ground fault indicating lamps (3). Commercially available devices seem expensive, does anyone have a more reasonable method that is acceptable to inspection? Is simply 3 transformer type pilot lights good enough?

RE: ground fault indication

Sounds reasonable to me, but the only one who could really answer that would be your inspector.  

RE: ground fault indication


The lamps may do the job.  They need to be large enough to offset capacitive charging current in the 600V system.  What is the anticipated transformer kVA rating?   

{Aside — In NEC regions, if the transformer is 3-wire ∆-∆, the 208V overcurrent protection can also provide overcurrent protection of the 600V winding.}
  

RE: ground fault indication

(OP)
Thanks peebee & busbar. The trans will be 30 KVA

RE: ground fault indication


At 30kVA, the ungrounded-system charging current will be fairly low—ROUGHLY 30mA.  [One amp/MVA rule of thumb for low-voltage ungrounded systems.]
  
For novelty, if the powered equipment would work OK at nominally 624 volts, one could conceivably use 1ø transformers with 600V-rated insulation {most UL506 units seem to be.}

Three 240:120V transformers could be configured in a wye-autotransformer arrangement for ~360V ø-n.  For three 1ø transformers, all X2s connect to 208V neutral—each X1 connects to a 208V phase and respective transformer H1—with 624V 3ø on the three H2 leads.  The “600V” neutral would be solidly grounded by default through the 208Y/120V 4-wire system.  Taps may could be used for voltage adjustment.  Smaller units with 240 x 480 Volts – 120/240 Volts • 2 – 2.5% FCAN + 2 – 2.5% FCBN Taps are catalog items.
  

RE: ground fault indication

(OP)
Interesting idea busbar,although I already have a  3 Ph.,
30 Kva,600-120/208 V transformer.Are you suggesting that this alternate method would not require the use of indicating lamps due to the "600 V neutral" connection?

RE: ground fault indication

Presuming that there is a control circuit, then it should not operate Ungrounded.  If supplied by transformer, then neutral must be grounded.  And, if grounded, then, ground-fault lamps are useless.

RE: ground fault indication

I disagree with you, Shortstub.  I do think grounding is a good idea, but it's not strictly required by NEC.  See NEC 250.20(B).  

RE: ground fault indication


mcfluffie, if the 600V system is solidly grounded, as would be the case with an autotransformer, then a ground fault would rightly operate an overcurrent device on “first fault,” and the lamps would be of no use as mentioned by Shortstub.  

If the subject transformer is 600∆-208Y, in a stepup mode leave the XO connection floating.
  

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