Finally, we need to check the dock’s potential.
For this, we’ll move to the shore-power pedestal:
1 With the reference electrode still in the
water, plug the DVOM’s positive lead into
the ground lug on the dock receptacle.
2 Caution: A shock hazard exists. Be sure
you have positively identified the ground
lug at the pedestal, not the hot lead.On
30 amp service, this is typically the notched
or L-shaped lug. On 50 amp service, it is a
shell connection, as shown in the photo.
See the illustrations for other common
shore-power terminal configurations.
3 Most docks will read between –400 mV
and –800 mV. A reading outside that
a basic corrosion survey 113
shell
positive lead
The shell is the ground connection on a typical 50 amp shore-power
receptacle.
100A, 120/240VPin and sleeve
3 pole, 4 wire
50A, 120/240VLocking
3 pole, 4 wire
30A, 120/208V 3ØYLocking
4 pole, 5 wire
100A, 120/208V 3ØYPin and sleeve
4 pole, 5 wire
240 and 208 Volts
Receptacle
Plug
Receptacle
Plug
Receptacle
Plug
Receptacle
Plug
W
G W G
W
G
YX
X
Z
Y
G
Y
X
X
Z
Y W
G
W
X Y
G
W
Y GX
W
Z
Y
X
G
W
Z
Y
X
15A, 120V
Straight blade2 pole, 3 wire
20A, 120V
Straight blade2 pole, 3 wire
20A, 120V
2 pole, 3 wireLocking
30A, 120V
Locking
2 pole, 3 wire
50A, 120V
Locking
2 pole, 3 wire
120 Volts
Receptacle
Plug
Receptacle
Plug
Receptacle
Plug
Receptacle
Plug
Receptacle
Plug
GG
GG
WW
WW
G
W
G
W
G
W
G
W
G W
WG
Dock and shore-cord terminal configurations, from ABYC Standard E-11. (Reprinted with permission from
Boatowner’s Illustrated Electrical Handbook,second edition, by Charlie Wing)