When megg. a cable [600V] in the absence of manufacturer data what is the recommended test value? In looking at ANSI/NETA ATS-2009 the table indicates 100mg. When a cable was tested [part of a splice to existing cable] it tested in the giga range, when it was tested complete from one end to the other [approx. 500'] thru four splices with the breaker at each end open it tested in the 30mg range, it was cold during the test [approx. 3 degree F] looking at the temp. de-rating tables it appears that the 30mg would be acceptable. However what would account for such a drop from the first reading to the overall complete circuit reading??? curious???
Megger ?
- Thread starter Mike01
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big john
Senior Member
- Location
- Portland, ME
100M is the industry standard minimum for new installations in the absence of manufacturer's specs.
The values you give are not acceptable if this is a new commission. Insulation resistance deteriorates in the presence of heat, not cold. So in your case the fact that it's cold means you should've gotten much higher values, and you appear to be correcting them in the wrong direction.
What type of cabling is this? Hold old and in what environment was the circuit where you installed this? I assume you tested at 1kV? How were the cable ends cleaned/isolated?
Your cumulative leakage would go up because you increase the size of the circuit. You said you did a 1 minute test, what was the DAR?
The values you give are not acceptable if this is a new commission. Insulation resistance deteriorates in the presence of heat, not cold. So in your case the fact that it's cold means you should've gotten much higher values, and you appear to be correcting them in the wrong direction.
What type of cabling is this? Hold old and in what environment was the circuit where you installed this? I assume you tested at 1kV? How were the cable ends cleaned/isolated?
Your cumulative leakage would go up because you increase the size of the circuit. You said you did a 1 minute test, what was the DAR?
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike01...
Adding to Big John's excellent point ... it is possible to predict IR value at operating temperature, if environmental condfitions, i.e., temperature and Relative-Humidity, are known at time insulation was tested!
Regards, Phil Corso
Adding to Big John's excellent point ... it is possible to predict IR value at operating temperature, if environmental condfitions, i.e., temperature and Relative-Humidity, are known at time insulation was tested!
Regards, Phil Corso
- Location
- Placerville, CA, USA
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- Retired PV System Designer
Unless one component of the measured resistance is from a fault rather than intact insulation....
Tony S
Senior Member
- Location
- Resting under the Major Oak UK
Could I ask how long you?re holding the test for? A long run will take a while to charge and give stable readings.
Some of the more expensive Meggers have a timed function.
Some of the more expensive Meggers have a timed function.
zog
Senior Member
- Location
- Charlotte, NC
Correction factor at 5 degrees F is 0.5 so your 30M is really more like 15M.
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Zog,
IEEE Std-142-2000, 'warns' about deriving a Polarization Index (1-minute to 10-minute IR-ratio) without knowledge of RH!
Phil Corso
IEEE Std-142-2000, 'warns' about deriving a Polarization Index (1-minute to 10-minute IR-ratio) without knowledge of RH!
Phil Corso
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Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike01,
Were the spliced section(s) the same-size and length(s) as the original length that measured in the G-Ohm range?
Phil Corso
Were the spliced section(s) the same-size and length(s) as the original length that measured in the G-Ohm range?
Phil Corso
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike01,
Were the spliced section(s) the same-size and length(s) as the original length that measured in the G-Ohm range?
Woull you like a testing method to solve your dilema?
Phil Corso
Were the spliced section(s) the same-size and length(s) as the original length that measured in the G-Ohm range?
Woull you like a testing method to solve your dilema?
Phil Corso
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Mike01,
I meant a very simple method!
Phil
I meant a very simple method!
Phil
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