hy-pot testing

What potential would be used for a dielectric test on bus work in a

480 VAC MCC?
Reply to
abuse
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Are you doing an AC or DC test? What is the manufactures rating for the buss. Watch out that you do not fry all of the control transformers. I would use

1500 volts and hold for 2 minutes.
Reply to
SQLit

im an electrician and this was a question on a iso certification test. i assume it would be a dc test. thats the normal test we run. many of the questions were very vague such as this and the motor test question. dont shoot the messenger.:)

Reply to
abuse

Was not trying to "shoot the messenger" I like AC tests better cause I can usually do them faster. But you have more potential to hurt equipment and cables if your not careful.

Reply to
SQLit

To preform a megger type time stepped dielectric absorption test I seem to remember that 500V is appropiate.

For a DC HYPOT test on three phase 480v MCC I believe the forumla is: DC hy-pot = (1000V + 2x480 V) x 1.732 =3394.72

Dig around in NFPA70B to confirm as I would since it has been a while here.....

Reply to
softh

thanks thats what i was looking for

Reply to
abuse

i have been told that the "engineering general rule of thumb" is a 6 multiplier which 6*480=2880 would you consider this accurate for the "field"

Reply to
abuse

I would look around in NFPA70B or the IEEE meta document the NFPA adopted its recommendation/requirements from for more details. I am not an engineer, only a rather rusty master electrician who does mostly low voltage controls work these days. I would dig around a little before doing this work, myself. A lot depends on how extensive your test is, I do not know the details on the reason for the test, condition of the MCC, the environment it is located in, the time available to prepare for the test, of how you will isolate the MCC. Be very aware of the possibility of damaging controls on or connected to the MCC and take steps to protect them. Also you must make sure load side equipment is protected.

The higher the test voltage the more likely a failure, and some failures can cause you much grief. Contaminates like carbon, dust, moisture, aresolized residue of oil, smoke etc, inappropriate lubrication or coatings applied to the equipment can cause trace overs. I will caution you to make sure the MCC is VERY clean, and of course dry, before you do the test. If there is carbon tracing in any of the devices it can get onto the load side and damage equipment even with the device open. Plus if you test with the device open you do not get a valid test on the load side of the device. A complete test of the MCC requires one to disconnect the line and load side busses/conductors, and isolate them well. DRY air is the best cleaner in most cases, if the environment has the potential of aresolized compounds there are high dielectric solvents available, but be very studious in how you apply them. Quartz lighting/heaters do a good job of voiding the moisture if enough time is available.

Matt

Reply to
softh

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