Electrical hookup diagnosis

[LHaven]

I have an umpty-amp service box at our main residence. A 60A two-pole breaker feeds underground to a satellite 240V service box 60 yards away at the water well/RV area. The RV outlet out there is 15 yards away from the satellite panel, fed underground with a single pole 30A breaker. This was all there when I bought the property. So far, so good. It's been working fine for both me and other guests for 20 years.

I have a guest with 2005 fiver, 50A, but only one AC, running off a dogbone to the 30A outlet. Big heat wave this week, right now it's 112° and his rig is struggling to maintain 92°. (Yeah, I know the 20° rule, and if that's the entire problem, I guess we're just screwed. But there's more...)

For the past few weeks, his AC has been occasionally popping the breaker, but not at startup, so it doesn't seem to be a problem one could fix with soft-start.

The mobile repairman was out here this morning and told him his AC was in great shape, especially for its age. But he did point out that he was only seeing 112VAC at the rig outlets, and blamed the problem on old wiring in the 15-foot underground feed. Yeah, the wiring (1984 vintage) isn't in NIB shape -- inside the breaker box it shows age-related insulation cracking like the example in the image, though no voids or exposed conductors. I could get it replaced, and I will if it's called for, but I just don't think this is where the problem lies.

With the guest's AC off, I read 120V on both legs. With the guest's AC on, I read roughly 113V on his leg... but 129V on the other leg! At first, I thought this was a problem in the feed from the house, so I swapped the pedestal breaker to the other leg, only to have the problem follow the breaker. (The breaker is less than a month old, because we replaced the old one when it started popping.)

It's one thing to ponder whether his AC should be expected to sink the leg by 8V -- and a scarier thing to ponder why it actually boosts the other leg by 8V. It's like I'm looking at a misbehaving neutral, or bad earthing at the satellite box, or something else unusual and confusing.

Do ACs typically drag down line voltage? Is that degree of sag typical? I don't want to be trying to solve something that's just normal operation.

[MerlinB]

Do you use Facebook? If so, this would be a great question to ask Mike Sokol on the RVelectricity group.

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[flybouy]

Hard to see the attached pic very well but from what I see there I would replace that wiring. That insulation is only going to get worse with age.

At 112 volts the amperage is obviously going to raise but the the question is what's that voltage when it trips? The only way to really know that is to monitor it with a voltage recorder. Given a 15 yr old trailer, high heat and marginal voltage it wouldn't take much of a voltage dip to create problems.

What's the rest of this 60 Amp sub panel feeding? A 2"40 v 60 Amp satellite service"? Are you running a cable company? It's hard to say what's going on with your reported voltage variances as I have no idea what the loads on this branch circuit is, wire size, or any other details.

[LHaven]

The attached pic isn't of my wiring, but the closest image to its aging appearance that I could find on the net. I'd have to have someone in to re-pull underground wiring, and that wouldn't be cheap. I'd rather put that off until it really needed doing. [EDIT: I should add that when I measured the leg voltage it was right off the busbar, so I'm not losing power between the satellite breaker box and the rig. If anything, it acts like resistance in the main 60A feed, and that would probably be big bux to replace.]

The "satellite breaker box" doesn't power satellites. (Ironically, it does indeed power my town's central wireless internet tower, which is up on my windmill, with a 20A circuit -- but it really doesn't draw more than a 100W bulb.) The breaker box powers the RV slot, the well pump (which doesn't run except at night), the booster pump (which has to run any time the water pressure needs boosting), and our automatic gate (which is effectively a 12V battery tender). Of all those things, only the booster pump would put on a significant load, and that would trip the main breaker out there, not the RV slot breaker.

Assume all the wire sizes are to code -- all the ones I added are, and I did have the place inspected when I bought it.

I thought perhaps there might be a neutral problem in his dogbone, but discovered that all ours are the reverse of what he is using (since we don't own 50A rigs), so we didn't have another dogbone to try.

To check, I went out to our own trailer, which is on a different pedestal 10 yards from the main house breaker box. At rest, the rig showed 120V. With the AC running, 115.5, so a 4.5V drop. I'd like to be able to do this same test at a "franchise" RV park to make sure my wiring is not atypical.

[LHaven]

Originally Posted by MerlinB

Do you use Facebook? If so, this would be a great question to ask Mike Sokol on the RVelectricity group.

Would be nice, but FB and I don't mix.

[Gord]

If your guest hasn't done this already it might be an idea to reduce some of the electrical load in the trailer by only using propane for hotwater and putting the fridge on propane as well. This may then allow an increase in voltage which will reduce load on A/C.
If you want to eliminate the wiring from sat building to pedestal as the issue you could maybe temporarily run a #10AWG piece of cable on the ground.

The above are just some ideas that might help to get you through the high heat.

[flybouy]

Three questions I didn't ask last night... How long is your Guest staying?
Do you have a clamp on ac Amp meter available?
What is "umpity-amp" service?
Wire size on that 60 Amp 180 ft run? A simple wire size calculator for a 3% max drop shows a 1 AWG wire size.

[LewisB]

Any chance you have a portable (plug-in) EMS? That would give you a fault code when the power kicks off.

So far as the voltage shift, how are you measuring the voltage? Phase to neutral or phase to ground. I'm no expert, but I'd guess you have undersized and/or old wires and connections that are breaking down under heavy load. That could include shifting the voltage slightly on your neutral wire and making it appear that the other leg is going up (if you are measuring phase to neutral). You might try measuring neutral to ground with no load vs heavy load. That might give you some more info. I'd also go through and tighten all your connections just in case something has worked loose over the years.

There's no such thing as "a 20º rule". It is quite possible to cool a trailer to say 35º below ambient. It's a simple issue of heat loss vs cooling capacity. To get it cooler, you will need more AC units.

Good luck with the trouble shooting!

[JRTJH]

My thought, for what it's worth, based on the description of how things are "wired and protected by satellite boxes and breakers"..

Have you considered the voltage drop on the "ENTIRE" circuit when the booster pump turns on? Sounds to me like the "voltage down/amps up" that occurs when the boost pump turns on would lower the voltage to everything on the entire system. If the RV air conditioner is on, then as the voltage drops, it will increase amperage to the circuit breakers both in the trailer, at the camper plug in and those that are also on the boost pump draw.

[Gord]

Another considerations is where your system ground rods are located. There should only be one set very close to the main service entry. Additional grounds rods installed in the system or sub panels that still have the neutral to ground bonding screw installed will lead to ground loops under load conditions and will cause odd things to happen with voltages.

[LHaven]

Lots of questions to answer…

My guest is here indefinitely.

I do have my father's analog Bakelite Amprobe clamper which I can drag out as I need it. I will add that since the 30A breaker is new (weeks), and it does occasionally pop every few days, we know my guest does draw over 30A on occasion. But I don't have anything that can record and keep a history, only stuff I have to watch as things happen.

My property's main breaker is a Bryant BJ2200B, marked 10,000 amps AIC and no other marking . The net informs me it is a 200A breaker, which is smaller than I thought it was. It isn't tripping, in any case.

I don't know what the gauge is that feeds the satellite panel. Everything is black and rubberized, so there isn't any printing to help. I'd have to mike the conductor at the main panel (assuming that would accurately tell me anything), which would leave my guest powerless for a span.

I don't have a portable EMS.

I measured the voltage shift between each busbar connection in the satellite box and the ground bus. I think the ground bus is also the neutral bus in this box, but I'd have to go back out there when it's light to make sure.

First time I read it, I didn't understand the question about the booster pump, but now I do: if it turns on, it lowers the box voltage, which raises the current on the guest circuit and pops the breaker. I'll ask my guest to check whether the booster pump happens to be running when his breaker pops.

As for the ground rods, I don't know where they are or why. I avoid the whole grounding issue like the plague because to me it's "any way a bug." I have to assume the electrical inspector certified it was done the "right" way.

[bobbecky]

You mentioned that when the load pulls down the voltage on one leg, the voltage goes up on the other leg. This is likely caused by a bad neutral connection. In an extreme bad or open neutral situation, you can get an extreme swing in voltage from one leg to the other. I would be checking all the connections, especially the neutral connections all the way back to the main panel. If all those look good, this can also be caused by a problem with the utility service coming from their transformer. I’m a retired lineman, and have witnessed as much as an 80 volt swing from one leg to the other, and this will cause serious damage to everything connected.

[flybouy]

Love the old RS-1 Ampobe.
In reviewing the post I have a couple of recommendations/thoughts. I see a couple of viable scenarios playing out.

As yourself what's changed, what happened before the issue started. If the issue started when your "guest" arrived then that's where I'd look first. As your "guest" may be there for an extended stay then you need to find out sooner, not later. It's quite common for folks that don't understand the need for electrical power management to forget, plug in a curling iron and then when it trips the breaker deny that they did anything for fear of "getting into trouble" or they don't want to upset you. If that's what's going on then the recent heat wave and lowered voltage would exacerbated the issue.

The other possibility is that the amperage draw was on the hairy edge and the recent brown out pushed it over the edge. This could be a result of "booster pump" (is that w well pump or water booster pump?) could be aging and drawing higher amps, could be a neutral issue, or several other things. Without a baseline amp reading when the voltage is "normal" it's hard to tell.

First I'd start a journal on when this happens, i.e. time of day, what activity is going on like electric cloths dryer running, the washing machine running, is someone taking a shower, what are the conditions in the camper (any switches for electric water heater or fridge electric turned on or did the occupant just toast a bagel or make coffee? After a couple of entries look to see if there are any patterns that show up.

I would start by having everything running as it normally would be and check the amperage on both lines that feed the main panel. If there is a large disparity between L1 and L2 then check the individual circuits and record the breaker # and amp reading. If there is a load imbalance you may need to move a circuit from side to the other.

These are just educated guesses as I'm not there to see or test anything. The recent lower voltage during the heatwave has exposed an "achilles heel" which could be a blessing in disguise if it ends up exposing a potentialy dangerous condition like failed insulation on wiring.

Hope this helps.

[DucBill]

LHAVEN you've been given some excellent TS info having worked for utility for 31 yrs you should be able to get your utility to send out a Field Service Representatitive or testman to verify your problem is not utility service related. FWIW I have a Fuzion 375 with 2 ACs that I have added Micro Aire soft starters that allows me to run from 30amp service but I have to switch the water heater and refrigerator on to LP and open brkr on converter (solar charging batteries) and tell DW not to use microwave or hairdryer with both AC on. My PI EMS has interrupted when we have accidently exceeded 30a and voltage dropped below 103vac. It's great to be able to use 30a site when 50a sites aren't available even when heat is on. Good luck with your electrical issues, work safely as electricity always takes the path of least resistance don't let it be through you.