Over the past few years, I have attended many vessels as an Accredited Surveyor, and have observed many types of shore connections, some of which were not compliant. I feel it would therefore be beneficial to share some much topical and specific information regarding polarity testing in shore connections gained from many hours of research and reading standards and legislation, and first-hand knowledge as an Electrical Surveyor/Contractor.
In 2017, MSQ released a Marine Information Bulletin with relation to electrical standards and licences for Regulated Ships, and how they now need to comply with AS/NZS 3004: 2014 Electrical installations – Marinas and Boats – Boats.
The term for a regulated ship has been defined in Queensland Legislation “Transport Operations (Marine Safety) Regulation 2016” as Vessels that are not ships, making reference to the Marine Safety (Domestic Commercial Vessel) National Law Regulation 2013 for this definition.
This Regulation identifies that each of the following are a ship:
- dragon boat
NOTE: This legislation has mandated that all ‘recreational ships’ and ‘other Queensland regulated ships’ are to meet these standards.
For single phase shore connections to be safe and compliant, the verification of correct polarity is paramount. Correct polarity is illustrated in Figure 1. The reversal of polarity (Figure 2.), is when the neutral conductor is terminated to where the active conductor is supposed to be. This may seem like a minor problem, as all electrical devices will still operate, and in the event of a short for example will still be live even after turning the “switch” off. Because of this, all switching is in the neutral conductor.
To elaborate further, Figure 1 shows correct polarity, and with the switch open, there is no potential between the load and the earth. Figure 2 shows that incorrect polarity, and with the switch open, there is potential between the load and the earth. Allowing for an increased risk of electrocution, short circuit and/or fire.
Another issue is that of polarity sensitive RCBO devices that are available within Australian. In the event of using this device when the polarity is reversed, these units will likely function as required, and then can be reset. However, irreparable damage can be caused to its operation because of the reversal, and is unlikely to function correctly subsequently, and will not provide any earth leakage
protection (Justice, 2018).
To prevent this reversal of polarity for shore to boat electrical supply as detailed in AS/NZS 3004.2, the following functionalities as listed below, need to be in place to ensure the correct operation of safety devices, and protect the personnel from electrocution and damage to the electrical installation: –
- A circuit breaker operating in all live conductors of the supply, including neutral, and is fitted adjacent to the shore supply inlet on the vessel.
- A test device, connected on the supply side of the vessel’s shore supply circuit breaker to check and visually indicate the polarity of the shore supply in relation to the vessel’s system*.
- An interlocking circuit to ensure the shore power cannot be connected unless the polarity is correct *.
- An indication to show when the shore supply is energised.
- Appropriate switchgear to facilitate the reversal of polarity.
* Except where shore power is supplied to the boat by an on-board isolating transformer or converter with a polarized output.
The Standard also stipulates that instructions for connections of shore power are to be posted at the connection point.
The testing of Polarity is the foundational requirement that all shore connection devises need to address. The AS/NZS 3017:2007 Electrical Installation – Verification Guideline for energised systems, detail testing voltage potential between the active and earthing conductor, with no potential between the neutral and earthing conductor. This is normally achieved by using a multimeter and is a momentary test.
For Vessel shore connections this testing regime requires it to be part of a permanent installation and the need for a Functional Earth. Within AS/NZS 3000:2018 Wiring Rule, 1.4.66 Functional earthing (FE), it states that:
“An earthing arrangement provided to ensure correct operation of electrical equipment or to permit reliable and proper functioning of electrical installations.”
Further details are provided in 5.2.2 Functional Earthing (FE), where it states that:
“Equipment may be required to be connected to the earthing system for purposes of correct operation rather than the safety conditions associated with protective earthing. In such cases, functional earthing conductors are not required to be selected and installed to withstand fault currents or to be identified in the same manner as a protective earthing conductor.”
Examples for FE use.
- connections fitted to certain types of RCDs
- conductors connecting cathodic protection systems
- radio interference suppression
- clean earth
Therefore, a vessel where a permanent Polarity testing arrangement is required, the use of a functional earth is required. However, this test needs to be a momentary test, as Protective earthing conductors shall not normally carry current, so cannot be a permanent connection; (AS/NZS 3000:2018 – Clause 22.214.171.124).
What has been noted by myself over the past few years, is that some shore connection arrangements use a permanent functional earth for testing Polarity, to provide an indication of the correct connection of the conductors.
The below Figure 3., is an extract from an Approved electrical circuit arrangement for a shore connection which is in fact incorrect and not compliant.
The above devise has an appliance inlet, circuit breaker, and polarity indication. The Polarity indication consists of 2 LED lamps connected across the Active/Neutral conductors, with the centre point having a Functional Earth connected to the Protective Earth. As required by the Standard, all functionalities need to be addressed, and as can be seen it only shows 2 out of the 5 have been met.
This polarity indication circuit allows for current to normally be carried in the Protective Earth conductor. The following Figure 4, demonstrates the current path of the above circuit arrangement, for a correct and incorrect polarity within the protective earthing conductor.
This then shows current being carried normally in the Protective Earth conductor, however when compared against the AS/NZS 3000:2018 Clause 126.96.36.199, it fails to meet compliance.
For a Polarity Test to be conducted on an energised system, it is required to allow current to be carried in the Protective Earth conductor. To prevent current being normally carried in the Protective Earth conductor for polarity test, the test needs to be a momentary connection.
The below Figure 5., shows a simple method that the circuit through the Functional Earth needs to make and break to test polarity. This type of circuit arrangement will prevent current being normally carried in the Protective Earth conductor and would then meet compliance.
A further safety consideration should to be given to the installing of a resistor in series with the Functional Earth to limit the current to the Protective Earth conductor in order to protect this circuit (Refer Figure 6.). If the failure of any of the components that lead to a short circuit, the current will be limited by the high resistance. This will reduce the effects of burning/melting, electrical-shock and other hazards to personnel (Michael D. Seal).
From experience, I know that there is a lot of misinformation out there regarding this subject, however the above functional requirements are all necessary to meet compliance to legislation and standards to facilitate the basis for a safe and complaint electrical installation for shore connection devices.