I’m talking about how much time is spent in front of open live electrical systems, in what is commonly referred to as the “Danger Zone.” I have seen quite a few beginning thermagraphers spend entirely too much time trying to get the image “just right” with perfect level and span to highlight the anomaly.
I understand why, it’s how they were taught in a classroom setting, which is great! They remember what was taught in class and are trying to get the perfect image. But, in the field. you need to realize that exposure to the live system needs to be minimized.
How is that accomplished? Well, remember back to your level one training. What are the three things that cannot be changed after an image is saved?
- Focus
- Range
- Perspective
Does that ring any bells? It should! Ok, here is what I have done in the past to decrease my time in the “Danger Zone.”
I set my span just a little over (2-3°C) the warmest item in the equipment to be inspected, and little (2-3°C) under the coolest item. After three to four items, an average will be apparent.
Now the tricky part, what are our items of interest? The coil of the starter? Not really, those are normally the hottest thing in the enclosure (MCC) in a normal operating condition. Relays? Again, not really – they contain coils which will heat up as they are being used. How about control transformers? Again, not really – they are coils. So, do you see a trend here? What is left? All of the “connection” points, you would be surprised how many there are.
Let us walk through a typical MCC bucket. We will follow the power train – the point where the conductors come through the back wall of the bucket from the buss stab (the connection from the buss bars to the bucket). As we follow the flow of power, we’re looking for a difference between the phases at that point, by difference I mean contrast in the image on the view screen (not temperature at this point). If the level and span are good, any hot conductor will look different just by the color or shade.
Now we can move to the connections at the top (line side) of the disconnecting device (typically a knife switch or breaker) down to the switch its self (knife switch pivot point). Next is the line side of the fuses (if equipped) and load side of the fuses (fuse holders and the conductor connection points) following the conductors to the line side of the starter or contactor. Remember, all we are looking for at this point is a difference in color or shades NOT temperatures. We can move onto the starter coil next (remember what we said about coils?) but what we need to look at are the conductor connections at the coil. But, skip it for now because of the span and level changes that would be required to view these connections.
The overloads are next, skip these also for now just like the coils. We move on to the load side of the overloads, here we need to compare the conductors and the connection points of those conductors. Don’t forget the control wiring terminal strip! If this is the last connection contained in the enclosure, we can now reset the level and span to view those hotter items, the overloads and the connections of the starter coil and the control transformer.
During this whole description of the inspection we have not even looked at temperature. If there were any anomalies (differences in shade or color) we just save the image with the three “cannot change items” referred to earlier, correct them, and do the analysis in the software, in the comfort of your office or hotel room, not in front of the live equipment.
It may be that during the analysis you determine the anomaly is not at a point to where it needs to be reported (by your Standard Operating Procedures, SOP) or written practice. Those images can either be deleted or saved and not included in the report. For example, I have saved 50 images in the field and only used 15 of those in a report. I saved time in the field opting to go through the images in the comfort of my hotel instead of in an MCC room with an air temperature between 85°F-100°F.
With enough practice and experience you can cut your exposure time down to just seconds instead of minutes for each MCC bucket.