Up until 1986, miners relied on canaries to alert them if dangerous gases were present underground. These little yellow birds, which are particularly susceptible to the odorless and colorless gas carbon monoxide, were carried deep underground in small cages. At the first sign of distress from the canary, a miner would know to leave the shaft as quickly as possible. This warning alarm was vital to a miner’s safety and well-being.

Today, we use the “canary in the coal mine” analogy when referring to any signal that failure is forthcoming. In the case of utilities, understanding when failure is imminent is critical. Whether it’s analyzing overloaded transformers, performing regular line maintenance, or having a regimented vegetation management program, utilities understand all too well the consequences of waiting too long before taking action.  

However, sometimes understanding when there is a problem is not as straightforward as observing a canary in a cage. How do you know when it’s the right time to move from a Power Line Carrier (PLC) network to RF wireless?  Based on conversations with several co-ops that have experienced a PLC system failing first-hand, here are three warning signals that might help you before it’s too late.

How do you know when it’s the right time to move from a Power Line Carrier (PLC) network to RF wireless?

1) Increase in Manual Meter Reads

The original business case for first-gen PLC systems was based around operational efficiency.  If you could stop sending meter readers out in the field, you’d save a substantial amount of money on labor costs. Despite the best intentions of these original systems, there were always a few meters that needed to be read manually. Often these were at the end of the line, where signal strength was starting to fail and installing a signal booster was not a fiscally smart option.

Read Interval Success

Determining an acceptable read rate success is highly dependent upon the utility. What’s ok for one co-op, might not be the same for another. For instance, one midwestern coop with approximately 23,000 endpoints, started to see their read rate success head the wrong direction. When healthy, they had approximately 200 meters that needed to be manually read—which equates to a 99% success rate. For this co-op, a 99% rate was an acceptable number that fit their expectations. However, that number started to change and not in a good way. As PLC systemic issues arose, before long they were manually reading over 2,000 meters a month—a 91% success rate. This was not acceptable.

At that point, it was starting to adversely affect operations and the pocketbook. Keeping detailed records of manual meter read numbers will let you see trends before they get out of hand.

2) Equipment Failure

Periodic maintenance and replacement of electrical equipment is a fact of life.  Whether we are talking about protection and control equipment at a substation or your own personal cell phone, everything has an expected life span. And, this life expectancy can vary greatly depending on operating conditions, upkeep and environmental factors. Transformers, transmission lines, substation equipment, and smart meters are all expected to last a certain number of years before replacement.

So when fail frequencies of your PLC equipment increases—pay attention

So when fail frequencies of your PLC equipment increases—pay attention. Coupling capacitors are a common point of failure for first-generation PLC systems. Used in conjunction with line traps, these coupling capacitors are crucial to transmitting communication signals along transmission lines. When these start to fail, it’s a definite red flag. To add insult to injury, there is often a long lead time to get replacements from some vendors. It’s not uncommon to find co-ops searching for used coupling capacitors to backfill the demand for failed units. 

3) Peer Pressure

This is by far the hardest warning signal to decipher. As co-workers attend industry conferences, read trade journals, and talk to peers at other utilities the grumbling begins. It becomes apparent very quickly, that by using a wireless RF system and having access to reliable 15-minute meter data, are a big part of grid modernization. There is a level of grid visibility and control not present in most legacy PLC systems.

This level of advanced grid insight is what gets engineers excited. Being able to monitor and regulate voltage levels with bellwether meters to lessening the impact of an outage by rerouting power with distribution automation, is intriguing to them. Utility workers are loyal to the co-op and to their members.  They like to be able to save the co-op money during peak load events and provide faster restoral of power to members during extreme weather events. 

Transitioning from PLC to Next-Gen AMI

Key considerations when migrating away from a power line carrier system.

Modernize your grid

Listen carefully to your team and you might start to notice an undercurrent of wanting more. It’s not quite jealousy, but there is a desire for simply…more. More data. More visibility. More control.


If you are starting to read more meters manually, have an uncommon number of PLC equipment failures, or if co-workers are talking about unavailable smart grid capabilities, it’s time to think about a change. It’s difficult to truly quantify the “canary in the coal mine” for PLC systems, but a good first step is to keep detailed records and listen to your peers at the co-op.

Please share your stories about how to see a PLC system failure before it happens in the comments section below.