Megger or Replace cable

[FaradayFF]

Hi folks,

We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.

Thanks,
EE

 

[Coppersmith]

Hi folks,

We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.

My gut says replace it but you will need to do a cost benefit analysis to get a definitive answer that question i.e. [cost to replace cable] vs. [cost to test cable] + [cost to replace cable] x odds it has failed stated as a decimal from .00 to 1.00.

Make sure you take all the labor and material costs into account for an accurate analysis. (Including the difficulty of running the cable.)

You could also do nothing and replace it when it fails. This might be the least expensive solution if downtime is allowed.

 

[ptonsparky]

We did a sound analysis of feeders for some pellet mills. I had the CEO listen as I bent the wires in a gutter. The sound of the old rubber insulation cracking was enough. It most likely would have passed a megger test as the area was dry and they had had no issues.

 

[zbang]

I had the CEO listen as I bent the wires in a gutter. The sound of the old rubber insulation cracking was enough. It most likely would have passed a megger test as the area was dry and they had had no issues.

And they might meg out fine until they're being bent around to connect the new compressor. If it's a fairly easy pull, I'd just replace them.

What size are we talking about? Heck of a difference between replacing 10g and 2g.

 

[sameguy]

In a nuke you megger new wire.

 

[Coppersmith]

In a nuke you megger new wire.

Not only nukes. I've seen many new switchgear installs get megged. Last thing you want is all that new equipment blowing up due to a bad conductor.

 

[RichB]

Not only nukes. I've seen many new switchgear installs get megged. Last thing you want is all that new equipment blowing up due to a bad conductor.

It is in our spec to meg all new circuit conductors--Done that all my career--just makes sense--only takes seconds to meg a conductor

 

[ptonsparky]

Hi folks,

We're replacing a low voltage air compressor that has been in service for around 50 years at an industrial plant. Would you recommend megger testing the feed or pulling a new cable? The distance is about 70 feet from MCC to the unit.

Thanks,
EE

Define low voltage. What HP?

 

[FaradayFF]

20 HP unit.

 

[ptonsparky]

20 HP unit.

That's #8 at 480v. It cost more to talk about it than pull new wire. Depending on what your work procedures are, of course. Is there easily scheduled down time?

 

[iceworm]

pt -
Yep, and #10CU are enough

20HP
27A x 1.25 = 34A
310.15.b >> #10CU, 75C >> 35A

 

[FaradayFF]

Well,

These are actually 208Volts motors. The cables are installed in a dry environment, so I think we'll just end up megger them.

Thanks to all who responded.