Parasites: Is Your Shore Line Overloaded?

Have you noticed lately when you’ve unplugged your ambulance if the shore line connection felt a little warm?

If so, you have a serious problem. And if not, you still need to take a look at how much is connected to that essential element of your vehicle’s response-readiness.

When ambulance manufacturers first started equipping their products with shore line connections in the early 1970s, standard recreational vehicle hardware was equal to the task. About all we needed was something that could accommodate trickle-chargers for the system battery, a suction device and maybe a handy-talkie. All that amounted to a total draw of less than 500 watts. A 15-amp residential lighting circuit could easily handle a 500-watt load, and nobody really worried about it.

But times have changed. Today, your shore line is connected to a slew of parasitic loads, including at least a 10-amp charger for the chassis batteries. Add to that the chargers for the self-powered cot and a hydroelectric loading system, the suction device, the monitor-defibrillator, possibly a fridge and maybe a block heater—it all adds up.

Next time you remove the shoreline from its receptacle and it seems warm when you touch it, you can bet money it’s delivering current in excess of its capacity. This could mean it contains one or more conductors that are damaged, or are simply too small for the loads to which they’re connected. It could mean one or both of its ends are worn out. Or, it could mean the shore line receptacle on the vehicle needs to be replaced.

Look for your ambulance’s 110-volt circuit breaker; it should look like a toggle switch. (You need to know where it is and how to reset it.) There should be a number on the visible part of the breaker, typically a 15 or a 20. That number indicates the maximum amount of 110-volt current the breaker will handle before it trips. In either case, the constant-duty rating for your shoreline amounts to less than half of the breaker’s trip limit.

Next, examine the power cord you normally plug into your ambulance. A safe power cord should be firmly attached to its plugs at both ends. It should also be permanently labeled every three or four feet with the kind of wire it contains. A cord that handles a maximum of 15 amps should be labeled 14-3 AWG (indicating three 14-gauge wires.) A cord that handles a maximum of 20 amps should say 12-3 AWG (meaning three 12-gauge wires.) A 12-gauge cord protected by a 20-amp breaker in your station and a 20-amp breaker in your ambulance would be optimal.

Any ambulance that’s plugged into and unplugged from a shore line system even just five times a day should probably have its shore line receptacle replaced once a year. The same is true for the female end of the power cord. Why?

Every time you plug your shore line into its receptacle, the two ends arc slightly. That arcing causes some metal transfer, which amounts to minor damage. Plug the line in 2,000 times and unplug it 2,000 more times, and eventually the electrical contact between the female cord end and the receptacle’s recessed male plug becomes less and less reliable. Power cords also get wet sometimes, and they get run over by vehicles that weigh in excess of five tons. Make it a personal habit to inspect the cord and receptacle every time you connect or disconnect them. (Habits are reliable, even when we’re really tired.)

Always be alert for a warm cord; it’s never OK. Sorry, I know you’ve disciplined yourself to avoid both of those words—and suspect people who overuse them—but a warm power cord relates to your vehicle’s electrical system like non-pleuritic chest pain relates to your coronary arteries. You deserve to know as much about both as you possibly can. And you should.

As for how much current your shoreline is handling, there’s a simple, home-made tool you or your shift supervisor can use to keep an eye on that. Best of all, it’s cheap. You could make it yourself, but it should probably come from your agency’s fleet maintenance folks instead. The following suggestions are meant for them.

Cut two or three feet off of the female end of a power cord that’s being used as a shoreline. (Let’s call that short section a pigtail.) Install a new, good-quality 20-Amp female cord end (Hubbell’s a top brand) on the cut end of the remaining shoreline, and put it back into service.

The pigtail should resemble a three-foot extension cord with the male end cut off. Strip three or four inches of the jacket off of the cut end. There should now be white, black and green insulated conductors and some fiber packing strips sticking out of the end of the jacket. Cut the packing strips, but not the conductors.

Four inches or so from the cut end of the remaining jacket, cut the jacket again. This time remove a one-inch section of the jacket, like a window – revealing the three conductors and three pieces of fiber padding material. Exercise care not to nick or cut anything but the jacket. To do that, bend the cord firmly and touch the jacket lightly on the outer, stretched side of the its bend with a very sharp knife. Be patient, and let the blade separate the stretched jacket material. Rotate the pigtail radially, and extend the cut several times until the jacket has been completely “circumcised,” twice. Don’t remove the four-inch section of intact jacket, but do remove the one-inch section.  

Use a cotter pin puller or a pair of needle-nosed pliers to grasp the black conductor and pull about three inches of it backwards to form an exposed, insulated loop outside the jacket. Use several layers of high-quality electrical tape (like 3M) to reseal the missing section of jacket, but leave the loop exposed. Cut all three exposed conductors to the same length, strip their ends, and install a new, good-quality female cord end. The result should be a three-foot extension cord with 110V male and female ends on it, and a loop of insulated black conductor protruding from a one-inch section where you’ve removed the protective jacket.

Depending on your preference, provide the finished product along with an inexpensive clamp-on, inductance-reading AC ammeter to each station or to each of your shift supervisors and instruct them in its use. (Or, restrict it to use by fleet staff.)

To read a vehicle’s shoreline current, make sure its engine is not running and the key is not in the ignition switch. (That ensures the inverter isn’t supplying any AC power.) Clamp the AC ammeter through the loop protruding from the pigtail, choose a scale that will give you a readable range (say, between 20 and 60 amps,) and record the reading.

If all of the batteries are fully charged, including the chassis batteries, a normal reading might be less than two amps. But if either or both of the chassis batteries need replacement, their reduced resistance would draw the battery charger’s maximum rated output plus other loads – perhaps a total of more than 10 amps at 110 volts AC.

That’s too much, and it should get your attention.

Thom Dick retired in March of 2014 after a 44-year career in EMS as an EMT, paramedic and quality manager. He was an electrician prior to applying for his first position as an ambulance attendant in 1970.