I’ve a customer that experiences annual failures of his electric hot water heater. Everything has been checked aside of evaluating the quality of the ground rod. The local power supplier used to provide this service, but does not any longer. I’ve Googled sources for rental of the instrumentation to evaluate the ground rod, without success. Any advice is welcome. Thanks.
I’m not sure yet about evaluating the quality of a ground rod–I’m still looking, however, I can tell you that in order to be maximally effective a ground rod must penetrate the water table. In most areas, an 8-foot rod is sufficient, though in some cases a longer rod may be needed.
Generally, most utilities, for their own grounding purposes (for lightning protection on transmission lines, etc.) specify resistance not to exceed 25 ohms. To get this they will drive multiple ground rods, connected in parallel.
In regards the water heater; I don’t know that the ground itself is the problem as most electric water heaters are 240 volts and don’t require a neutral (just a tank ground for protection) so, unless they are having some kind of cathodic problem, i’d look elsewhere. The single most common cause of premature heater element failure is low water level. First off, do both elements fail at the same time or does the top element fail more often? If it’s just the top element there may be some type of siphoning problem that will expose the top element; try a check valve on the intake side. Scale build-up can also cause problems. If you do suspect some type of power quality problem, have your customer ask the utility to install a recording voltmeter (RVM). This is actually a pretty common request to make of a utility when power quality issues are suspected. The information the utility gains from this will indicate over/under voltage problems as well as fluctuating voltages.
Sorry, that’s the best i can come up with given the information provided. If you can explain the nature of the failure, i might think of something else.
This is a small (12 gallon) 120 VAC unit for a commercial occupancy. Elements do not fail-the failure is at the jacket, which leads me back to thinking that it is being used as it’s own sacrificial anode. The last unit lasted just shy of 1 year, and the customer tells me this is typical. Oddly enough, I have another customer in the same industrial park, 500 yards away, who has replaced his heater once in 15 years, the only difference I can see being his interior plumbing is CPVC, effectively isolating the heater.
Can you install insulating unions on the heater’s input and output connections. That would provide the same effect as the client with the CPVC lines would it not?
The OP made me think megger, I believe that’s was a term used to describe the tester for ground systems, anyhow… here’s a link to a rental site for a Digital Megger Ground Continuity Earth Tester. Fully automatic, four terminal instrument suitable for the testing of ground electrodes and measuring Ground Resistivity. Four ranges covering measurements from 10mOhms to 20kOhms
Ahh crap, and on preview, what GaryM said. They are required around here.
Yes, the megger is a tool used to evaluate soil resistance. My father could have gotten one for me if he still worked for PECo, but he has retired. PECo was the utility I contacted in an attempt to resolve the issue.
Yes-I’ve thought about dielectric unions. In PECo’s service territory they are not required. I was surprised when doing a service ampacity upgrade in Hanover, PA, that the inspector noted my bonding jumper from cold water to gas line and advised me to remove it. Although required by NFPA 70, aka NEC, MetEd/GPU does not use dielectric unions on their gas lines at metering locations, and bonding causes their piping to become a sacrificial anode.
I’ll look into the megger rental, and many thanks to the posters. If this thread is still alive, I’ll post results.