Designer69
Senior Member
I never really brushed up on megger testing of control wiring and don't know much about it.
Do you megger control wires?
- Thread starter Designer69
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zog
Senior Member
- Location
- Charlotte, NC
Horrible thumbrule to use, i see that posted here often and it is too much for control wring and not enough for anything else. Please follow a standard, any standard, ANSI, NETA, IEEE, etc..
zog
Senior Member
- Location
- Charlotte, NC
Per ANSI and NETA specs"Perform insulation-resistance tests on all control wiring with respect to ground. Applied potential shall be 500 volts dc for 300 volt rated cable and 1000 volts dc for 600 volt rated cable. Test duration shall be one minute. For units with solid-state components, follow manufacturer?s recommendation."
And..."Insulation-resistance values for control wiring shall be a minimum of 2.0 megohms."
Note of caution, you can easily cook electronic controls doing this so you have to knwo what you are testing.
Also, I am assuming by "control wiring" you mean the same as I do and NETA does, what exactly arre you calling "control wiring"?, so I can be sure we are all talking about the same thing.
Meggar control wires??
Meggar control wires??
I did process automation upgrades and new installations in factories and process plants for years and NEVER Meg'd control wires. With motor loads you experience an inrush of way over the wire and short circuit interrupting so meg'ing is a good idea as any insulation damage or flaw will eventually weaken and go. I have never meg'd control wires as the amp load is so low, ie a pneumatic valve only draws the current necessary to activate and hold the solenoid and the indicators are only contacts. You have to be careful with a meggar as it can cost a lot of money if you make a mistake. I'm not sure what type of control wires you are referring to though, but have never since 1985 meg'd control wiring.
Meggar control wires??
I did process automation upgrades and new installations in factories and process plants for years and NEVER Meg'd control wires. With motor loads you experience an inrush of way over the wire and short circuit interrupting so meg'ing is a good idea as any insulation damage or flaw will eventually weaken and go. I have never meg'd control wires as the amp load is so low, ie a pneumatic valve only draws the current necessary to activate and hold the solenoid and the indicators are only contacts. You have to be careful with a meggar as it can cost a lot of money if you make a mistake. I'm not sure what type of control wires you are referring to though, but have never since 1985 meg'd control wiring.
STHOMAS
Member
- Location
- North County San Diego
Isn't is true that there should be no electrical/electronic components connected to the wiring that is to be megger tested?
With fire alarm installs, we ALWAYS megger test ALL wiring prior to installing any control device/appliance. This is to assure no parts are detroyed, as well as assuring total resistance of the wire is in fact wire only and no devices are installed creating additional resistance.
Mr. Wizard
Senior Member
- Location
- Texas
I've never megged a LV control wire. I always check continuity between wires and to ground and resistance between wires and to ground. I've been involved in process controls and automation for nearly 10 years, and my methods have yet to fail me.
jcole
Senior Member
- Location
- Lawrenceburg, Kentucky
The only time I meg is for troubleshooting purposes or for PM schedule on motors. I never understood megging new low voltage installs. Medium voltage I could see reasoning. How many contractors out there would relplace cables if they measure below 2Mohms but didnt trip OC device. Not many.
As for control wiring why would you unless you were having a problem? If I was having a problem I could probaly find it with my DMM instead.
As for control wiring why would you unless you were having a problem? If I was having a problem I could probaly find it with my DMM instead.
Does that apply to control wiring only, or for all cable rated 300v/600v.
Could you direct me to your source,or maybe site a section or article #, somthing I could present to my foreman.
I have been told that we(my boss) do(es) not meg our 600v wire at 1000v because it is in excess of the insulation rating.
zog
Senior Member
- Location
- Charlotte, NC
NETA/ANSI MTS or ATS 2007
Ummm, thats the whole point. That is a standard test voltage (Minimum actually) for not only ANSI.NETA but several IEEE and NEMA references, depends on the equipment.
zog
Senior Member
- Location
- Charlotte, NC
Yes, you usually only make that mistake once, per employer anyhow.
zog
Senior Member
- Location
- Charlotte, NC
Some specs require it, those are the ones tested by certified testing companies.
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