Megging an existing older feeder busway - HELP!

[MPdesign]

For an existing older busway (70's, I-Line, 3,000A) that feeds floor to floor from the main to one mechanical panel up many floors, I would like to test the insulation for safety's sake.

I believe that I can de-energize the building, turn off the breaker feeding the busway, turn off all breakers in the mechanical panel, and then megger to the busway to recheck the insulation.

Is there a problem with doing this or doing it in this way? The busway is bolted to bus in the gear - it does not have taps.

Your help is greatly appreciated!

Cheers,
Joe

P.S.
I am not the guy who will be doing the megging, I am the guy who is determining the best way to test the busway - so please don't think that I am going to go and do this myself and get hurt (that is what I would I would think if I read this..)

 

[petersonra]

why do you think it needs doing?

is there some indication it has issues?

are you having problems of some sort?

is it just old and you want to do it so you feel better about it?

 

[MPdesign]

The bus has had hot spots for many years (10+), not so hot as to be outside of manufacturer's specs, but for enough years that I want to ensure the integrity of the insulation - just in case there were some transient very hot spots - that occurred outside of testing.

 

[petersonra]

hot spots?

I am almost afraid to ask but what do you mean by "hot spots"?

and how do you know about them? another question I am almost afraid to ask.

 

[MPdesign]

Infra-red testing over the past 15 years. The readings have decreased over the past 15 years because of efficiency upgrades. I really cannot post all of the details. What are your thoughts on the megging?

 

[don_resqcapt19]

It is unlikely that megging will reveal anything related to hot spots. It will, if done correctly, tell you something about the condition of the insulation, but without previous baseline testing, it won't tell you much, unless the readings are not acceptable.

 

[MPdesign]

That is all that I am really looking for, I am trying to ensure that the insulation integrity is good and not deteriorating. I do not think it will, but I want to ensure that it does not fail.

I am looking at the hot spots separately, this is just pertaining to how can I ensure the insulation integrity.

Is there a problem with doing this - or is there a problem doing it in this way?

I want to ensure that readings are acceptable now - and create a new baseline for future review.

 

[ATSman]

My first thoughts are hot spots caused by loose connections not insulation breakdown. Your statement that the heat has decreased over the years due to more efficiency indicates that the load current has decreased; Less current = less heat due to P= I squared R.
A more useful test in this case would be a Ductor (low resistance) Test using an instrument like a Biddle DLRO test set. During this test the duct is isolated, the 2 bus phases are shorted at one end and the measurement is taken at the other end. A-B, B-C & C-A. The resistance values are compared and should be fairly close together. After evaluation of the readings then corrective action can be taken.
Are the section connections readily accessible? With some of the older bus duct, covers have to be removed to get to the connections for torquing. Some newer stuff have insulated bolts and are designed to be torqued hot........... although I wouldn't :happyno:
Good luck

 

[MPdesign]

The hot spots are a separate issue. I am aware of the problem with the hot spots and what is causing them.

Separately from that - I just want to make sure it doesn't blow up next week on my watch by testing the insulation resistance...

So a "Ductor" test is recommended instead of a Meggar test to make sure it doesn't short out?

Is that correct? Sq D appears to recommend a megger test. This ductor test sounds very similar to the megger test.

My questions was:
Do I have to completely isolate the bolted busway before the test or is it OK to just shut down the breaker feeding it - and turn off all of the breakers in the panel that it feeds?

There have been questions raised about unbolting and rebolting the busway from the older gear bus because when you do that, dust flies, possible metal shavings move, and reseating it could be an issue if there is some type of pitting.

Thank you all for your help. I appreciate your concern about the hot spots but "right now" I am just trying to find out about megging (and now Ductor testing). I will start a separate thread or discuss the hot spots once the original issue is settled.

You have all been very helpful and I appreciate your help!

 

[weressl]

The hot spots are a separate issue. I am aware of the problem with the hot spots and what is causing them.

Separately from that - I just want to make sure it doesn't blow up next week on my watch by testing the insulation resistance...

So a "Ductor" test is recommended instead of a Meggar test to make sure it doesn't short out?

Is that correct? Sq D appears to recommend a megger test. This ductor test sounds very similar to the megger test.

My questions was:
Do I have to completely isolate the bolted busway before the test or is it OK to just shut down the breaker feeding it - and turn off all of the breakers in the panel that it feeds?

There have been questions raised about unbolting and rebolting the busway from the older gear bus because when you do that, dust flies, possible metal shavings move, and reseating it could be an issue if there is some type of pitting.

Thank you all for your help. I appreciate your concern about the hot spots but "right now" I am just trying to find out about megging (and now Ductor testing). I will start a separate thread or discuss the hot spots once the original issue is settled.

You have all been very helpful and I appreciate your help!

Would you just change the oil in your car when you have a misfiring engine?

 

[MPdesign]

Gentlemen,
I came here looking for help because I know that this forum has been respected, by me, for 15 years.

Mike Holt is respected and trusted.

I know that the best and most knowledgeable in the industry are here.

I have a question.

I swear that I will further discuss the hot spots but first can anyone please just tell me what I asked.

Please show me the respect of answering my question.

 

[weressl]

The hot spots are a separate issue. I am aware of the problem with the hot spots and what is causing them.

Separately from that - I just want to make sure it doesn't blow up next week on my watch by testing the insulation resistance...

So a "Ductor" test is recommended instead of a Meggar test to make sure it doesn't short out?

Is that correct? Sq D appears to recommend a megger test. This ductor test sounds very similar to the megger test.

My questions was:
Do I have to completely isolate the bolted busway before the test or is it OK to just shut down the breaker feeding it - and turn off all of the breakers in the panel that it feeds?

There have been questions raised about unbolting and rebolting the busway from the older gear bus because when you do that, dust flies, possible metal shavings move, and reseating it could be an issue if there is some type of pitting.

Thank you all for your help. I appreciate your concern about the hot spots but "right now" I am just trying to find out about megging (and now Ductor testing). I will start a separate thread or discuss the hot spots once the original issue is settled.

You have all been very helpful and I appreciate your help!

1. Follow the manufacturers instructions for testing.
2. Clean and remove debris and then isolate the bus duct on both ends.
3. Megger the bus to the manufacturers specification.
4. I would recommend a PI(Polarization Index) test as well.
5. Following manufacturers instructions remove covers, clean and check torque values at all current carrying and mechanical support/bracing connections.

 

[eHunter]

1. Follow the manufacturers instructions for testing.
2. Clean and remove debris and then isolate the bus duct on both ends.
3. Megger the bus to the manufacturers specification.
4. I would recommend a PI(Polarization Index) test as well.
5. Following manufacturers instructions remove covers, clean and check torque values at all current carrying and mechanical support/bracing connections.

+1
3a. While the buses are isolated, take the relatively small amount of time, short at the far end, perform Ductor tests with DLRO on all bus bars and establish baseline values and create permanent records.
6. Visually inspect for any damage or deterioration.