Author: jmsokol
Subject: Important - check this every time you set up
Posted: 20 Aug 2016 at 7:00am
There's a phenomenon I call a Reflected Hot-Skin condition where a Hot-Skin voltage on one RV in a campground can "Reflect" to others in the same loop. But that can only occur if the campground pedestals have an incorrect ground to begin with.
Here's how it works.... Imagine you you have pedestals hooked up on a common feed from the campground's service panel. This is called a "daisy chain" connection. There will be common hot1, hot2, neutral, and ground wires interconnecting all these pedestals. Since the "ground" wire is supposed to be bonded to the service panels Ground-Neutral-Earth connection, any hot-to-chassis current leakage or short inside of a single RV can only go to this "ground" where it will be drained away or trip the RV's circuit breaker. That's exactly how it's all supposed to work. In a properly grounded system it's impossible for any chassis to develop more than a volt or two potential above earth-ground, no matter what kind of other failure occurs.
Now assume there's a break in this pedestal ground wiring on its way back to the service panel's Ground (G-N-E bonding point). Now if one of the RVs develops a short between line-and-chassis the current will have no path to "ground" and it will electrify the entire ground wire interconnecting all the pedestals and RVs together. So anything with a ground wire plugged into one of these pedestals will have its chassis electrified to 120 volts, creating a Hot-Skin condition.
The really dangerous thing about this mis-wiring condition is that because the voltage is feeding into your RV from the ground wire, even shutting off the pedestal or RV circuit breaker can't stop it. And there's no EMS products on the market that can disconnect you from this hot-ground since electrical code does not allow the manufacturer to put a relay contact in the path of the ground wire (officially called the EGC for Equipment Grounding Conductor). However, the EMS will detect the hot-ground condition and shut off your RV's live voltage. So it will appear that you have no AC power from your EMS, while in reality your RV's ground is the only thing electrified.
I've only heard of perhaps half a dozen campgrounds with this non-grounded EGC problem, which allowed a Reflected Hot Skin Condition to occur. While this is a very rare problem, it's still something to be aware of and can easily be detected with a NCVT at any time. If you ever feel a tingle, stop what you're doing and immediately test for a hot-skin voltage. If you do measure one, disconnect from shore power until the problem is resolved.
Subject: Important - check this every time you set up
Posted: 20 Aug 2016 at 7:00am
There's a phenomenon I call a Reflected Hot-Skin condition where a Hot-Skin voltage on one RV in a campground can "Reflect" to others in the same loop. But that can only occur if the campground pedestals have an incorrect ground to begin with.
Here's how it works.... Imagine you you have pedestals hooked up on a common feed from the campground's service panel. This is called a "daisy chain" connection. There will be common hot1, hot2, neutral, and ground wires interconnecting all these pedestals. Since the "ground" wire is supposed to be bonded to the service panels Ground-Neutral-Earth connection, any hot-to-chassis current leakage or short inside of a single RV can only go to this "ground" where it will be drained away or trip the RV's circuit breaker. That's exactly how it's all supposed to work. In a properly grounded system it's impossible for any chassis to develop more than a volt or two potential above earth-ground, no matter what kind of other failure occurs.
Now assume there's a break in this pedestal ground wiring on its way back to the service panel's Ground (G-N-E bonding point). Now if one of the RVs develops a short between line-and-chassis the current will have no path to "ground" and it will electrify the entire ground wire interconnecting all the pedestals and RVs together. So anything with a ground wire plugged into one of these pedestals will have its chassis electrified to 120 volts, creating a Hot-Skin condition.
The really dangerous thing about this mis-wiring condition is that because the voltage is feeding into your RV from the ground wire, even shutting off the pedestal or RV circuit breaker can't stop it. And there's no EMS products on the market that can disconnect you from this hot-ground since electrical code does not allow the manufacturer to put a relay contact in the path of the ground wire (officially called the EGC for Equipment Grounding Conductor). However, the EMS will detect the hot-ground condition and shut off your RV's live voltage. So it will appear that you have no AC power from your EMS, while in reality your RV's ground is the only thing electrified.
I've only heard of perhaps half a dozen campgrounds with this non-grounded EGC problem, which allowed a Reflected Hot Skin Condition to occur. While this is a very rare problem, it's still something to be aware of and can easily be detected with a NCVT at any time. If you ever feel a tingle, stop what you're doing and immediately test for a hot-skin voltage. If you do measure one, disconnect from shore power until the problem is resolved.