240 volt GFI protection 1

[paull]

I need help wiring an electrical test station. This test station is used to test an commercial wet/dry vacuum system, in an industrial, production enviorement.
here's what i have;
i have 208 volts comming into my test box from a gfi breaker in the wall, (2 hots, a neutral, and a ground) a Staco, model #2520, Series Variable Transformer. I need this variable voltage control because we manufacture both 110vac and 220vac models. The problem lies here, because we test in a wet enviorment, i need to inexpensively GFI protect the operator. The Staco schematic only shows a the use of the 2 hots, where does the neutral go? Staco tech sup. says leave the neutral hanging, and the operator will still be protected, is this true? i have also seen these little pigtails with a gfi on them, but not in a 240 volt model will this work?....any sources on them? any help will be appreciated. thanks.

 

[peterb]

Assuming that your 208V supply is really one phase of a 208/120V supply - which is consistent with the 2 hot leads + neutral + ground, then the answer may be very simply that you don't need the variable transformer. The supply should give 208V between hot leads and 120V between each hot lead and neutral. I strongly suggest that you try this and simply wire two separate outlets for 120V and 208V in your test station.
If the supply is different from what I have assumed and you do in fact need the transformer, then you will still be protected by the upstream GFI breaker, as this operates on the principle of current balance between the phase and neutral leads. If there is a ground fault, some current will return to the source by the external ground path instead of via the circuit wiring - this unbalance is what the GFI reacts to.

 

[paull]

i guess i should of been a little clearer, we do need the transformer, because we do test other machines at this test station. were we vary the output voltage from 90vac to 240vac. and you are correct, that i do have one phase of a 208/120v supply.
so since i do need the the transformer, will i be safe by leaving the nuetral wire un-connected?....and one more related question, i have been told that, (by not that reliable of a source) that since i have a transformer between the breaker and the testbox. that the transformer in the test box is acting like a "new service". and anything downsteam of that transformer is NOT gfi protected?....sorry to be a pain, but production.

 

[jbartos]

Suggestion: There appears to be the safety factor of utmost concern. It will be better to have a licensed electrical contractor to inspect and correct the installation as the electrical safety code requires. This way the electrical contractor will assume full safety responsibility for the installation and functioning. The public forum cannot deliver what appears to be needed since the exact circuitry and equipment parameters are not available.

 

[rlaft]

I would like to find out who makes GFI's for voltages different than 120 vac. I need one for 80 vac.

 

[don01]

If when you say GFI you are refering to what we call an Earth leakage or Core balance relay then it stands to reason that the protection will hold true if you run the supply thru a variac but even that has to be qualified by how the connections are (No need for nuetral????? that's really scary and totally prohibited in Australia.)

BUT PLEASE AS JBARTOS HAS SAID THIS REALLY SOUNDS LIKE YOU NEED TO GET A QUALIFIED AND REPUTABLE CONTRACTOR IN> he could set you up a system that is safe and easy to use for not much more than you will spend in your own time and labour. And you may save some after its done thru the ease of having a dedicated set up. - I put a star on Jbartos for saying it.

If you are concerned about different voltage ratings then contact your electrical wholesaler after all if you buy anything then you have to go to him.



Regards Don