Dear Mike,
It may be best to check pedestal voltage under load before plugging in. Is there an easy way to do this? —Don/Piano-tuna
Dear Don,
That’s a great idea, but likely beyond the scope of most RV owners. That’s because meaningful load testing can be time-consuming and complicated.
The basics
There are at least two different types of load testing – static and dynamic – with the static load test being the gold standard. A static load test works by applying a specific/heavy current load over an extended period of time, typically minutes. A dynamic load test applies a very short pulse of current, which typically lasts only a fraction of a second, maybe a line cycle or two.
Static Load Tests
To perform a static load test on a budget, you can utilize something like a half-dozen 1200 to 1800 watt space heaters or hair dryers, or even a bank of incandescent light bulbs. I performed this type of load test for many years, and it can tell you a lot about the condition of the wiring – but getting a bunch of space heaters running at the same time is a bit cumbersome.
What I currently use for static load testing is much more elegant: an Avtron K490 10kW load bank which is switchable between 120 and 240 volts and can apply the load in 1,000 watt increments up to 10,000 watts via front panel switches. It has a bank of cooling fans that sounds like a swarm of angry bees and a big relay to apply the load via a single master switch.
Price of a purpose-built load bank like this one is around $3,000 to $4,000, so only someone doing power diagnostics like me would ever own one. It’s also heavy to haul around, and requires custom-built power cables that can carry a full 80+ amp load without overheating.
Finally, when gathering field measurements with a static load bank it’s possible to create hazardous situations, and there are some calculations involved to interpret the results. So I’ll save static load testing for the advanced education area in RVelectricity.com.
Dynamic Load Tests
The second type is a dynamic (or impulse) load test using a Ground Loop Impedance Tester such as the SureTest Circuit Analyzer or Amprobe INSP-3. These work by applying a single pulse of 5 to 15 amperes, which will load and measure the electrical circuit just enough to predict the actual voltage drop at the outlet under 15- or 20-amp loads. You can then extrapolate these 20-amp results by 150% or 250% to predict voltage drops under 30- or 50-amp loads.
While less complicated and inexpensive compared to a high-wattage static load bank, cost of a Ground Loop Tester is still a lot more than a DMM (Digital Multi-Meter), costing around $200 to $300, plus the price of a few custom breakout cables for the 50-amp outlet. While this type of load test is quick and safe to perform, it’s still more money and complexity than most casual users will commit to.
However, I think that campgrounds should perform a dynamic load test on ALL pedestal outlets at least once a season as a part of routine maintenance. Since a lot of electrical inspectors use this type of tester already, I’ll include Ground Loop Impedance Testers in the Intermediate area of RVelectricity very soon. Lots to do…
Yeah, sometimes a simple question requires a complex answer. But properly testing a large power distribution system like a campground isn’t quick or easy, which is perhaps why it gets messed up so often. Hope this helps provide some insight into what goes into deep level power testing. Much more on this topic later, but for now that’s the basics.
See you next time, and let’s play safe out there….
Mike Sokol is an electrical and professional sound expert with 40 years in the industry. His excellent book RV Electrical Safety is available at Amazon.com.
##RVT859
You’re right: after investing in a good quality digital multimeter (with DC current), I’m not ready to invest more in a Ground Loop Impedance Tester, but I have added one to my Amazon “Wish List”. ?
This year’s travel season (May-October) has taken us to many parks, and we’ve only had two (so far) that have failed our real life load tests.
At one, voltage was only 115VAC at rest but dropped below 108VAC and our Progressive Industries unit cut off power when usage on Leg 1 exceeded 33A. We used manual load shedding (turn off the AquaHot electric when using the microwave) to get through.
At the second, the PI unit cut out at an even lower 18A, so we basically couldn’t run much at all. If we had been there longer, I probably would have needed the generator at times.
As expected, both parks said it must be our rig, as they “never had a problem before”.
I often respond to that line of ignorance by saying “…and I’m immortal, because I’ve never died BEFORE…”
Mike Campgrounds not doing a thorough job not the only problem . Ignorant campers that pull plugs out of a hot line and leave circuit breaker on don’t help the situation. Unfortunately there are more of them then I can count.
Charles, you are correct. Hot-plugging shore power cords under load will certainly lead to future connection problems. I think the only way to resolve this issue is through education of the public and campgrounds, as well as proper maintenance. But anything that takes additional time or money is a tough sell.
Not your job although on the other hand a throw away from RVTravel for campgrounds to give customers upon arrival might do some good and advertise the newsletter at same time
Charles, Chuck and I have talked about doing exactly that, and we’re currently looking for a sponsor that could pay to have a few hundred thousand of these safety guides printed and shipped to campgrounds around the country to hand out. However, we also have to get the campgrounds to agree on the idea of handing them out. Much more to work on.
Sounds good to me. Good Luck
Just create a nice pdf file that can be printed in b/W that has a place for the campground to put their contact info and email it to the campgrounds periodically with updates. Also make it available to your svp members for distribution.
Yes, that’s a good idea and I’ll put it on my to-do list.
Last week I hit a site that was 112V no-load, 108V just charging batteries, and I demo’d the unusabilty to management with a 1000W heater pulling the pedestal down to 90s… Worst voltage drops I’ve ever seen, but manager insisted its the utility”s failure instead of their distribution. *sigh*
Yup, you can do a lot of load testing with a space heater or hair dryer. I’ve used 1,000 watt PAR lights for many years to test stage power.