Date (Y-M-D): 1989-05-08
Subject: Grounding Safety in drydock
Shipowners, Masters and Drydock Managers are reminded of the need to ensure that a vessel's metallic hull or in the case of a non-metallic hull, the continuous ground conductor, is solidly grounded immediately upon entering a drydock or whenever the vessel's hull is out of the water and shore power is brought onboard.
Metallic hulled vessels utilizing an alternating current three phase four wire system or a single phase three wire system, each with a solidly grounded neutral and a one to one ratio shore power isolating transformer, are particularly vulnerable to accidents in drydock whenever shore power is brought onboard if the frame of the isolating transformer is insulated from the hull. The ground conductor brought onboard is usually one of the conductors of the multi-conductor shore power cable and could be connected to the frame of the transformer. Because the frame of the transformer may be insulated from the vessel's hull, the shore ground conductor may not effectively ground the vessel's hull. If a fault occurred within the shore power isolating transformer which caused a live conductor to touch the vessel's hull, the hull would probably have a potential difference between it and the shore ground. Persons working on scaffolds or under the vessel who come in contact with "shore ground" at the same time touching the vessel's hull could suffer a serious injury from a fall or serious electric shock or both. The ground conductor, therefore, must be solidly attached to the vessel's hull as well as the frame of the transformer.
Non-metallic hulled vessels, with an alternating current electrical system having a solidly grounded neutral, also pose a risk to personnel when the vessel is out the of water and shore power is energized. If a shore power isolating transformer is fitted, then a somewhat similar situation to that of the metallic hulled vessel exists. If a fault occured, with a live conductor touching the continuous ground conductor, persons working under the vessel who came in contact with "shore ground" and the vessel's copper ground plate could also suffer a serious injury. In this situation, the shore ground conductor must be solidly attached to the continuous ground conductor or to the copper ground plate fixed to the vessel's hull.
Vessel's which do not have solidly grounded neutral systems should also have a shore ground conductor solidly ground to the hull each time shore power is energized.
Special care should also be exercised when shore power is connected through step-up or step-down transformers to ensure that the transformer frame as well as the metallic hull are solidly grounded.
Care should be taken whenever the vessel is out of the water and shore power is brought onboard to ensure that personnel are not permitted to work under the vessel, aloft in masts and rigging and over the vessel's side until the shore ground conductor is solidly grounded to the hull or the continous ground conductor.
Keywords: Questions concerning this bulletin should be addressed to:
2. Shore Power
3. Isolating Transformer
Tower C, Place de Ville
11th Floor, 330 Sparks Street
Ottawa, Ontario K1A 0N8
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