wnjj wrote:
Bobbo wrote:
DrewE wrote:
Bobbo wrote:
wnjj wrote:
The other thing that can fry stuff in a RV is a standard 4-pin 50A connection with an open neutral. That can cause half of the devices in your RV to see much higher than 120V and why many suggest installing some kind of protection system.
Yes, an open neutral on a 50 amp rig will fry stuff. However, it doesn't fry just half of the stuff, it fries everything. Since there is no NEUTRAL, everything sees the full 240v. Fortunately, an open NEUTRAL is rare.
Everything doesn't see 240V, not at the same time. The 240V is split between the two legs; the one with the higher load and hence lower impedance sees proportionally more of the voltage, and the one with the lower load sees less voltage. In theory, if the legs were perfectly balanced, there would be no change in their voltage and no problems at all; indeed, in that situation, there is no neutral current, so it's effectively an open circuit anyhow. The legs are not perfectly balanced in normal cases, though, and how far out of balance they are can change rather rapidly and spectacularly if devices are damaged and become open circuits (or short circuits, followed by their circuit breaker tripping, making an open circuit).
A broken neutral is indeed very bad news. It does not, however, lead to 240V at all the outlets and loads.
Agreed that all items don't see 240v AT THE SAME TIME. However, when leg 1 sees 240v and blows out its 120v items, they stop pulling power and leg 2 now sees the 240v. So, saying they don't see 240v AT THE SAME TIME is accurate. It is milliseconds between the two.
When the fried items “blow” and stop pulling power, the circuit is now open and nothing sees any or voltage. The L1 and L2 loads are in series so when one side loses all of its devices and there’s no neutral, there is isn’t a complete circuit.
The more heavily loaded side pulls down below 120v and the other side goes up. As items blow open, the mismatch is greater until the lightest loaded side goes open circuit. The heavily loaded side will never see more than 120v.
You are correct, if you assume that everything, literally EVERYTHING, on the dead leg blows. If anything, anything at all, keeps pulling current, the other leg does see 240v. A lot of stuff that plugs in, in this day and age, are rated for 100v to 240v and 50hz to 60hz. Those items will keep pulling current. I don't think it is safe to assume that the first leg will completely blow out and the second leg will be saved. But, I don't usually deal in absolutes. It seems much safer to me to say everything in the RV is at risk than to say that half of the RV will be safe. It may, or it may not be.
