4F5: AC Metering
Between the AC and DC
circuit breaker panels is a panel
with two digital meters. The left
one is for AC, the right for DC.
The following applies to the left
hand, AC Meter.
Voltage:
Press “V” to read
voltage; pressing repeatedly cycles you through line 1 and line 2 voltages. When connected to
shore power or with the generator running, you should have between 110 and 130 volts, 105
volts minimum. When connected to 30-amp shore power you should not turn on too many
breakers, lest the load exceed 30 amps; with the generator, do not exceed 90 amps.
Current:
Press “A” to read current; pressing repeatedly cycles you though the load on Line 1 and
Line 2 amperages.
Line Frequency:
Press “Hz” to read frequency of each line. This should always be “60".
Is it 110 or 120? The fact is, these voltages are “arbitrary” values! It depends upon the
shore-side utility or boat generator settings, as well as the amount of load on the cable or
generator. In the “real world”, it doesn’t matter as long as it’s at least 105 volts but not more
than 130!
4F6: AC Reverse Polarity
Although we tend to think of AC Electricity as having only two
conductors, it actually has three. One of these is called “neutral”; one is
“hot”; and one is “ground”, that is, it is supposed to be the same as the
water around the boat and the earth ashore.
The vessel and many of its appliances rely upon these
connections having the correct “polarity”, or relationship to one another
and the earth; this is essential to be sure that users of AC equipment do
not get a shock when touching and AC equipment.
Now in a house ashore, it’s easy: We don’t “plug in” the house,
for it stays connected to the utility company all the time! But in a boat
when in the harbor, we do plug in using our Shore Power cords (and
sometimes using extension cords). If the outlet to which we plug our cord, or if the cord itself is
mis-wired, then these connections can become mixed up, and then there is a significant chance
of getting a shock or just as bad, a chance that running gear outside the boat will be subject to
rapid corrosion, because the boat is immersed in sea water, a good conductor of electricity.
Metering panel. Left meter is AC, right is DC. In center are line monitors for the two AC circuits.
Circuit Status Indicators
Section 4F: Electrical Systems, AC 4.13
