Insulation Resistance for LV System

That all depends on what you are doing. If you are trying to directly measure the reverse bias current of a diode that is rated at 5 E-9 A at 75V then all other current paths must be at least ten times higher in resistance or 10*75V/5 E-9 A= 150 Gohms= 150 E 9 Ohms.

Am applying 500 Volts for the system. In this case what will be the acceptable criteria for IR value?

If you're going to play "twenty questions" with us, you have to answer the questions truthfully and accurately. 500 Volts is neither a Low Voltage (LV) system or a standard power distribution voltage.

Follow the wiring standards for your location. Since you do not know these standards (if you did, you wouldn't ask) you should stop working on lethal voltages. You need somebody qualified to work and design a system with lethal voltages to examine your system. Hire an electrician licensed to work in your area. The life you save may not be your own.

redfred - maybe he is one of the 10 types of people in the world . . . .

in many countries LV systems are distribution systems with voltages including 230, 415, 500, 690, 750 and sometimes even 1100 . . .

so i suggest we get into the next round of 20s with the assumption that 500 for the question is LV . . .

now what about the insulation resistance?

the acceptable insulation resistance depends on what you are insulating and why . . . the actual value depends on how the system is wired . . .

please remember that even systems with "good" DC resistance for insulation are often potentially unsafe because of capacitance between conductors and ground to conductors . . . consider also effects of static on surfaces on insulation, creep, humidity and a whole host of factors that affect insulation performance . . .

Sigh.

You're correct that I am flying a little bit off the handle. I do get tired of people coming here seemingly seeking help by using an ill defined acronym and then switching to mean something all together different. If you feel willing to play the prepubescent game of twenty questions with this individual, go right ahead.

From my experiences here when a laymen asks a nebulous question with only one parameter of many needed to answer the question, they either rise to fill in the parameters they thought were insignificant or in this case change the information they've given because they don't know what they are talking about.

I disagree with your comment that 500 volts could be considered by a layman as a low voltage. According to Wikipedia (a volatile but convenient reference) the world wide mains power distribution used in most residences is 240V or less. Therefore 500V is a higher common voltage used by individuals and not a lower voltage.

i did not refer to any layman.

however i did mention that in different countries the parlance / jargon differs . . . .

i add that i understand and empathize with you in many ways . . . maybe because a resident of Mumbai can easily appreciate where a NYer comes from being two cities that never sleep and all that . . . all the best!

In power distribution, voltages up to 600 (or maybe even 1000 or so) are considered low voltage (perhaps depending on jurisdiction). And yet one sees "Danger: High Voltage" stickers on systems over 120V. The terminology seems not to be well standardized across all contexts.

We are using single phase 230V and three phase 415V Low voltage system supply, 50HZ system. am in UAE, In order to do Insulation resistance test our practice is to apply 500V DC.

Perhaps you mean meggering with a 500V DC megger. This is one quick test with portable equipment...

There are also HV tests (hipot) one at power frequency (usually 2.5kV) and an impulse test at up to 12kV. Please check the standards.

Insulation resistance is measured using a 500V DC calibrated Megger.

IR Test carried out between phases,phase-neutral, neutral-earth, phase earth should have insulation resistance greater than 999 Mega ohm . Dielectric test is usually carried out using a 2.5kVAC calibrated High Voltage Test Kit.

999MΩ is higher than I have ever heard, except maybe for extra high voltages.

the megger reading that indicates greater than 999 mega ohm is a perfectly insulated wire. A reading below 1 mega ohm indicates a problem with the wire.if reading range is in-between these two resistances ,then it generally operates with no problems to the electrical circuit.

Nothing is perfect.

Please refer to BS 7671 Inspection and testing section. You will find answers for your query.

Rgds