Carbon Monitoring

Carbon Monitoring Defined

By Gary McCreadie

I used to be a second or third yr apprentice working for a really educated boss and enterprise proprietor.  On the time, he simply occurred to be the dispatcher, which was bitter candy.  The bitter half, properly, he was one arduous ass dude that didn’t assume twice about putting in a brand new opening in your again aspect.  The candy, after the blood stopped dripping out of your anus, he was the very best tech assist I’ve ever had.  

I arrived to a name at a sewage remedy plant, from what I bear in mind it was a ten ton Provider rooftop unit with no cooling.  The fuses had been blown, after I changed them and turned on the ability, they immediately blew once more.  I referred to as my boss and let him know what was occurring, he requested me a query, he mentioned, “are the contactors all black and lined in carbon?”  Sure, sure they had been, how did he know that?  He defined that what I used to be was carbon monitoring…From that time on, I by no means forgot and have declared struggle on this phenomenon.  I’ll get to how and why this occurs in a minute, however let me end the remainder of the service name.  I went out and picked up two new contactors, changed them, cleaned up all wiring and cleaned {the electrical} cupboard of remaining carbon.  Changed the fuses as soon as once more and all was good on the earth.  So how did my boss know?  Expertise of being in the identical place, that is how.  A place I’ve now been in lots of occasions myself…Which I’m now sharing with you.   

So what’s carbon monitoring?  When a contactor is de-energized and pulls away, there’s an arc that’s created, a bi-product from the recent electrical arc is carbon.  Carbon collects and builds on the contactor over time.  If sufficient carbon is allowed to construct it could actually create a path throughout energy legs or to the panel that the contactor is mounted to, which is grounded.  This path is taken into account to be a brief, what occurs when energy is shorted to floor or throughout energy legs?  Growth goes the dynamite…That’s what occurs.  One thing to bear in mind although, I’ve by no means encountered blown fuses from carbon monitoring from a unit put in indoors.  Why, it doesn’t rain inside.  What I imply by that’s, out of doors models are uncovered to the weather.  On a moist day, when moisture content material is excessive within the air, that moisture embeds itself throughout the carbon monitor making a conductive path.  Mud can even contribute to this problem, as an example, if a unit electrical panel is below a detrimental because of the blower fan, mud may be pulled into the cupboard and create the identical consequence.  

Here’s what I’ve realized to do once I encounter a blown predominant.  Shut off the native disconnect after which visually examine the road aspect of all contactors throughout the machine.  Test for seen indicators of carbon tracks and examine the highest terminals on every contactor for indicators of melting, the warmth generated by the brief will generally barely expend the road aspect of the contactor, see under photographs.  I additionally use a megohmmeter to examine for carbon monitoring if a visible examine doesn’t reveal something.  Disconnect all wiring from the contactor, place one lead of the megger on the contactor line aspect terminal and the opposite result in floor.  A studying of something below 20 megohms must be thought-about a path to floor.  

On this picture you may see the melted terminal that was brought on by mud construct up over time that created a path to floor.

This picture is a detailed up of the above picture exhibiting the again aspect the contactor

With a purpose to keep away from carbon monitoring, visible inspections are key.  Changing contactors and cleansing up wiring and cupboard base plates can go alongside manner in avoiding service calls and hold you busy on the similar time.  

Try the hyperlink to my YouTube channel for extra ideas, tips, and troubleshooting movies and take a look at the The HVAC Know It All podcast right here or in your favorite podcast app.  Comfortable HVACing…

Gary McCreadie