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3 phase 575v delta
2

3 phase 575v delta

3 phase 575v delta

(OP)
we need to safely and temporarially ground 1 phase of a 3 phase system to check and train on using ground fault/detector system how could we do this
thks

RE: 3 phase 575v delta

Is this an ungrounded system? If so, be aware that a second ground will cause heavy fault currents and dangerous arcing. As per Murphy's law, it is a possibility that the testing and training may introduce a second ground with disasterous consequences for the trainees.
That said and at your peril, ground with a resistance that will limit the ground current to an amp or so.
A tip to separate the pros from the geniuses. Replace a ground detector lamp with a burned out lamp. If you have a more sophisticated ground detection system, arrange for it to give an indication of a false ground condition. Your electricians will get a real workout for two or three days. They will become much more familiar with your system. They will hopefully get some practice with working together and logical thought.
Not fair? Life isn't fair. The first time I saw an electrician spend three days looking for a ground when the problem was a burned out lamp, I could only think;
"Thank God that wasn't me!"
A very often made assumption is that all indicators and instruments are working properly. It is very time consuming and frustrating when that assumption turns out to be false.
BUT.
If you have a grounded system, you can usually find a ground quickly by the smoke and loud noise, and the holes burned in the metal work. No need for much training.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: 3 phase 575v delta

As Waross said, uses a resistor, make sure it is enclosed and is rated for the full current and power.

Here's what my co-workers did years ago prior to knowledge about arc flash.  Connect the resistor through a fused contactor with a remote control circuit, like an MCC bucket. Verify there are no existing ground faults by checking the phase-to-ground voltages just prior to the test.  Clear the area around the resistor and MCC and remotely actuate the contactor.    

Depending on the sensitivity of the detection system, you may need to size the resistor for 10-20 amps. 600V/20A = 30 ohms. Watts = 30x20x20= 12,000 watt. (Assumes a fault occurs on other phase).

We used heater elements connected in series.  Once we used coils of #14 wire about 3 ohms/1000 feet. Three 1,000 foot reels in series were about 10 ohms on a 480/277 V system for a 30 A fault. We only ran the test for a few seconds. Do not use wire on metal reels.

I like Waross's idea of faking it!
 

RE: 3 phase 575v delta

(OP)
thks, we have 575v delta ungrounded system, yes we know we can't leave it grd. for long but another grd. could come system at anytime that's why we need to know abount what size resistor/watt also our detector usually pulses about 4 amps more than grd. in checking mode thks again

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