DC Withstand Test and Insulation Resistance Test

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fifty60

fifty60

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I would like to perform a DC withstand test on equipment that will have electronic components without any open contacts in line with the component. For example, I have SSRs and solenoids inside the equipment, but contacts that make/break these components are normally open. These components normally remain off after the on/off switch to the equipment is switched to the on position. Further logic has to be satisfied before the components become energized.

Also on the equipment are limit controllers, PID controllers, an HMI, PLC and a power supply--- these components all normally become energized as soon as the equipment on/off switch is moved to the on position. This means that when I perform the Insulation Resistance and then the Withstand test on the equipment, these components will definitely have the voltage at their input terminals. Granted, the line and neutral feeding the components are shorted together for the testing, so there will not actually be any voltage difference between the line and neutral inputs on the components.

Is it normal to do withstand tests on this type of equipment? I will unplug the equipment and short the line and neutral together on my power cord. I will then apply the test voltage between the shorted line and neutral terminals and the equipment grounding conductor. Should I be concerned about the components that will actually have this voltage connected directly to their input terminals?
 
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I seem to recall that the UL specs that require this actually require that whatever is connected to the line terminals under normal circumstances has to remain connected for the test. The test is a pass/fail on whether a hazard is created, not whether the equipment fails or not.
 
I understand your point. I would prefer that none of the components fail. If I believed that there was a relatively decent chance that a component would fail, I may adjust the timing of my testing. If the line and neutral are shorted together, then 0V should be between the component input terminals right, even if 1000+ voltage is applied between the shorted line/neutral and the equipment grounding conductor? Would this not put any stress whatsoever between the component input terminals, and only between the power cables and ground?
 
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Which means that you may need to write off the item subjected to testing even if it passes.
Big difference between mandatory testing of all units shipped and potentially destructive testing of a sample for listing purposes.

Tapatalk!
 
Imagine a circuit with only a light bulb and a power switch. What would happen if I perform the test with the lightbulb installed. Would I remove the lightbulb before doing the IR and Withstand tests? Would it make more sense to perform the test with the power switch in the off (open) position?
 
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If all you want is to test the power cord and the switch, maybe.
But with the grounded conductor tied to the ungrounded conductor at the test equipment, then the stress on the equipment might actually be lower with the switch closed. :)

Tapatalk!
 
Would you expect any damage to the lightbulb if it were left in the circuit, the switch were closed, and the 1500VDC were applied for an IR test then a Withstand test? I would think that the lightbulb would survive the test and operate normally there after.
 
Would it be correct to say that "For the Hi-pot test to be completely valid, all circuits with contactors would be in the closed position." So any circuit that would normally be open unless closed while the equipment is in normal operation, would need to have the contacts closed. To be valid there should be no open contacts inside of the equipment.
 
With both lines tied together, would there be 0 Volts across the open contacts during the Hi-pot tests? Wouldn't it be ideal to have all contactors closed during the testing?
 
You have a good point there Petersonra. I want to understand exactly how the test is working. A UL inspector can come in and apply 2100VDC to my equipment, so that really only the primary side conductors are being tested. I do not think that this is a very thorough test, or even a correct test, just because it is performed by a UL inspector.

What happens across the open contacts during a Hi-pot test? The voltage between the sides of the contacts should be zero when the hi voltage is applied to both line and neutral. How does this differ from when the contacts are closed and the hi-pot test is performed. Are the conductors even being tested properly if there are open contacts in the circuit.

How is an actual component, lets say a micro plc module, tested by applying 2100VDC to its line and neutral inputs? I'm having a hard time getting a full intuition about what the hi-pot test is doing. I understand what is happening withthe conductors in the system, but am having a hard time with components in the test circuit. There really is not much information online. A lot of redundant and high level information...
 
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I think you are going to have to look in the UL standard and find out just how this test is applied.

It is unlikely a UL inspector is going to perform this test in your shop.

If it is a potentially destructive test, as many UL tests are, it will be performed in one of their labs (or a contract lab) on a sample you provide for this purpose.

If this is a test that is required on each piece produced it is unlikely that UL will require it to be performed in a way that is going to destroy an otherwise satisfactory piece of equipment you made.

See if this helps you any.

http://www.chromausa.com/pdf/app-no...d Compliance for Hipot Testing - 04052013.pdf
 
Yes that is helpful. There is a 230V to 24VDC class 2 power supply in the equipment. I would need to short the output of the power supply together to hopefully not destroy the power supply right?
 
fifty60 said:
Yes that is helpful. There is a 230V to 24VDC class 2 power supply in the equipment. I would need to short the output of the power supply together to hopefully not destroy the power supply right?
Click to expand...

I don't know. It depends on what the UL test procedure says you have to do.

Class 2 power supplies generally require no additional testing in end products.
 
UL is not doing the inspection. This is dielectric testing for a standard that is self declared. My components have all of the approvals that I need to not test. Can I remove the line and neutral from my components, cap them, and then perform the dielectric test on the equipment? This would only stress my wiring, and not the components, which is fine since I have the documentation showing the dielectric tests performed on the components. The standard does not point out whether or not this is acceptable.

I'm trying to not destroy components if at all possible. I have a 230V to 24VDC class II power supply, a pid controller, ssr's, and electromechanical relays. The PID's incorporate triacs for their output switching, and the SSR's are composed of parallell/reverse SCR's. My plan is to remove the line and neutral, and also remove the inputs and outputs from teh PID triacs and the SSR's SCR's and temporarily cap the end of the wires.

I have to perform a dielectric withstand test and an insulation resistance test. I would unwire and cap for each of these tests. Any advice/critique on this approach is definitely appreciated.
 
The standard I am using asks for "no dielectric breakdown", but does not give any specific level of resistance for the insulation. My first time through I received a pass but was reading approximately 2.5MegaOhms. I ran the insulation resistance tests again a few days later, passed again, but was reading approximately 45MegaOhms.

I am testing between the shorted line and neutral and ground pin of the equipment plug. Any advice on how to tell which reading is correct?
 
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The first test (2.5 MegaOhm) I wrapped the IR meter test leads (the alligator clips) with electrical tape. I did this for both the line/neutral and the equipment grounding conductor. The second test (45 MegaOhms) I did not use electrical tap on the test lead alligator clips, I just ensured that the two leads would not come in contact during the test by separating them. Could this have made the difference in my readings?
 
The first test (2.5MegaOhm) was done with the equipment cold. the 2nd test (45MegaOhm) was done after a series of single fault tests--blocking vents one at a time and letting the equipment run for an hour under each single fault. Is there any reasonable explanation other than something being connected wrong to explain the difference in readings? The equipment was connected the same each time.
 
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