This is the fourth article in a series looking at the requirements of Section 710 of BS 7671 for electrical installations in medical locations.
NICEIC Technical Team | .
This article in particular focuses on the requirements for inspection and testing in such medical locations.
This article focuses on the requirements for inspection and testing at various stages during the life cycle of the electrical installation in a medical location.
The process for the initial inspection and testing of a medical location is fundamentally no different to that required in any other installation in terms of procedural methods and the need for dates and results of each verification to be recorded.
For every new installation, addition or alteration, BS 7671 requires inspection and testing be carried out during the construction and on its completion, before being put into service to verify, as far as is reasonably practicable, that the requirements of BS 7671 have been met (134.2.1; 641.1).
As such, the tests described in regulations 643.2 to 643.11, where relevant and appropriate for the installation being tested, shall be carried out (643.1).
Regulation 710.514.9.1 requires that all information pertaining to the electrical installation, including records, drawings, wiring diagrams and documentation relating to any modifications for the medical location, shall be provided. The electrical contractor must therefore ensure that the results of each verification are recorded (710.641).
Regulation 642.3 gives a list for the minimum inspection checks that should be carried out where relevant. The regulation also makes reference to the particular requirements of Part 7 of BS 7671 for special installations or locations, including those of Section 710 for medical locations, which must be taken into account during the verification process.
The specific items to be inspected for a medical location will include, for example, methods of protection against electric shock with respect to both the general requirements of Chapter 41 and the additional requirements of regulation Group 710.41, including the requirements for verification of the resistance of supplementary protective equipotential bonding conductors (710.641 (iii)).
As with many electrical installations, there may be a significant time interval between the initial installation of conductors and the final commissioning or handover of the installation. However, damage to installation wiring may have occurred during this time, when, for example, cables are plastered over and flooring and suspended ceilings are installed.
In such cases, this will necessitate repeating a test previously carried out. It is not acceptable to rely solely on test results obtained at an earlier stage of the installation process, although the results may of course be used to demonstrate where damage has occurred after the initial testing.
In addition to the general requirements of Chapter 64, regulation 710.641 requires that, both prior to commissioning and after alterations or repairs and before recommissioning, the following tests shall be carried out:
i. Complete functional tests of the insulation monitoring devices (IMD) associated with the medical IT system including insulation failure, transformer high temperature, overload, discontinuity and operation of audible/visual alarms.
ii. Measurements of no-load leakage current of circuits supplied by the medical IT transformer, including the leakage current of the enclosure, in a Group 2 location (710.411.6 and 710.512.1.1 indent (i)).
iii. Measurements to verify that the resistance of the supplementary equipotential bonding does not exceed the limits given in 710.415.2.2, such that in Group 1 and 2 medical locations:
As discussed previously in Issue 229 of Connections, in a TN and TT system, the conventional touch voltage of 50 V is reduced to a value of 25 V AC or 60 V DC in group 1 and 2 medical locations. As such, protective equipotential bonding conductors are required to equalise the potential difference and limit the magnitude of touch voltages during a fault. Bonding conductors are used, and typically arranged in radial circuits and connected independently to the Equipotential Bonding Busbar (EBB), in conjunction with circuit protective conductors for the particular circuit, connected at the local distribution board.
To meet the requirements of 710.641 (iii) the value of measured resistance1 between the EBB and each relevant point within the group 1 and 2 locations must be verified to ensure that the results obtained do not exceed those stated in 710.415.2.2, as shown in Fig 1.
Fig 1 Testing between exposed-conductive-parts and extraneous-conductive-parts in a medical location
A schedule of test data must be recorded for the supplementary protective equipotential bonding system. Such information, based on the format given in 710.514.9.1(vii), should include data relating to the measured value of resistance between connected items within the patient environment, and the cross-sectional area (csa) of protective equipotential bonding conductors. Due to limited space on the standard forms, this data may be recorded on a separate document and appended to the Electrical Installation Certificate (EIC).
Test results may be influenced by parallel paths, it may therefore be necessary to disconnect one end of the protective conductor when performing the test.
Note: The above tests are in addition to those required by Chapter 64 of BS 7671, the supporting information given in Health Technical Memorandum HTM 06-01: Electrical Services Supply and Distribution, and the HTM 06-02: Electrical Safety Guidance for Low Voltage Systems, published by the Department of Health.
Equivalent guidance documents are also available for the devolved nations (710.641).
Any periodic inspection and testing is subject to the requirements of Chapter 65 of BS 7671, as for any other installation (135.1 and 710.651). Although BS 7671 does not state which tests or the sequence for testing that form part of a periodic inspection, regulation 651.2 does state that the periodic inspection shall be supplemented by appropriate testing and measurements from Chapter 64.
The person(s) responsible for the initial installation design of the medical location is required to specify the interval for the first periodic inspection. Similarly, where an alteration or addition is made to an existing installation, information relating to the subsequent periodic inspection should be recorded in the EIC (644.4).
Table 1 gives recommendations for the interval to the first periodic inspection of a medical location and is partially reproduced from Table 3.2 in IET GN3.
However, when making the recommendation of the interval, the person compiling the EIC should take into account, amongst other things, Note 1 to regulation 710.651, which recommends inspections:
a) Annually – complete functional tests of the IMDs associated with the medical IT system, including insulation failure, transformer high temperature, overload, discontinuity and operation of audible/visual alarms.
b) Annually - measurements to verify that the resistance of the supplementary protective equipotential bonding does not exceed the limits given in regulation 710.415.2.2 and recorded in the format given in 710.514.9.1 (vii).
c) Three-yearly-measurements of leakage current of output circuits and of the enclosure of the medical IT transformers in no-load condition (710.512.1.1 (i)).
With regard to indents (i) and (iii), the testing of such systems should be carried out either by the IT system manufacturer or those with specific knowledge of medical IT systems.
Note 2 to regulation 710.651 advises that supporting information on periodic inspection and testing is given in the Health Technical Memorandum 06-01: Electrical Services Supply and Distribution. Client or local health authority requirements, if any, may also apply (see Note 6 to 710.1).
Contractors undertaking work in such types of medical locations must be competent and have sufficient knowledge, training and experience to carry out the necessary work in a safe and effective manner.
Useful links:
https://www.england.nhs.uk/publication/electrical-safety-guidance-for-low-voltage-systems-htm-06-02/
https://www.nss.nhs.scot/publications/electrical-services-supply-and-distribution-shtm-06-01/
https://nwssp.nhs.wales/ourservices/specialist-estates-services/publications-and-information/welsh-health-technical-memoranda-whtms-health-technical-memoranda-htms/
1Where a TT system earthing arrangement is employed, a satisfactory value of resistance for the electrode will also be required.
Introduction
The first article in Issue 227 of Connections looked at the scope of Section 710, and described the system of grouping and how the system classification for safety service supplies, given in Section 560, is applied to a medical location. The second article, in Issue 228, considered the fundamentals of the medical IT system as a means to provide a reliable source of supply and the third article, in Issue 229, considered the requirements for shock protection.This article focuses on the requirements for inspection and testing at various stages during the life cycle of the electrical installation in a medical location.
Initial verification
Verification of new work shall be made by one or more skilled persons competent in such work (641.6). This would require any such competent person(s) to have sufficient training, knowledge and experience working in medical locations to undertake the initial verification effectively and safely.The process for the initial inspection and testing of a medical location is fundamentally no different to that required in any other installation in terms of procedural methods and the need for dates and results of each verification to be recorded.
For every new installation, addition or alteration, BS 7671 requires inspection and testing be carried out during the construction and on its completion, before being put into service to verify, as far as is reasonably practicable, that the requirements of BS 7671 have been met (134.2.1; 641.1).
As such, the tests described in regulations 643.2 to 643.11, where relevant and appropriate for the installation being tested, shall be carried out (643.1).
Regulation 710.514.9.1 requires that all information pertaining to the electrical installation, including records, drawings, wiring diagrams and documentation relating to any modifications for the medical location, shall be provided. The electrical contractor must therefore ensure that the results of each verification are recorded (710.641).
Inspection
The objective of the initial inspection is to verify that the installed electrical equipment (excluding ME equipment), and including wiring systems:- complies with the requirements of Section 511 (Compliance with Standards)
- is correctly selected and erected in accordance with BS 7671 while taking account of manufacturers’ instructions
- is not visibly damaged or defective in a way that would impair safety (642.2).
Regulation 642.3 gives a list for the minimum inspection checks that should be carried out where relevant. The regulation also makes reference to the particular requirements of Part 7 of BS 7671 for special installations or locations, including those of Section 710 for medical locations, which must be taken into account during the verification process.
The specific items to be inspected for a medical location will include, for example, methods of protection against electric shock with respect to both the general requirements of Chapter 41 and the additional requirements of regulation Group 710.41, including the requirements for verification of the resistance of supplementary protective equipotential bonding conductors (710.641 (iii)).
Testing
The general requirements of Part 6 of BS 7671 apply to testing in medical locations as much as any other type of installation. The sequence of tests and how they are performed also remains the same.As with many electrical installations, there may be a significant time interval between the initial installation of conductors and the final commissioning or handover of the installation. However, damage to installation wiring may have occurred during this time, when, for example, cables are plastered over and flooring and suspended ceilings are installed.
In such cases, this will necessitate repeating a test previously carried out. It is not acceptable to rely solely on test results obtained at an earlier stage of the installation process, although the results may of course be used to demonstrate where damage has occurred after the initial testing.
In addition to the general requirements of Chapter 64, regulation 710.641 requires that, both prior to commissioning and after alterations or repairs and before recommissioning, the following tests shall be carried out:
i. Complete functional tests of the insulation monitoring devices (IMD) associated with the medical IT system including insulation failure, transformer high temperature, overload, discontinuity and operation of audible/visual alarms.
ii. Measurements of no-load leakage current of circuits supplied by the medical IT transformer, including the leakage current of the enclosure, in a Group 2 location (710.411.6 and 710.512.1.1 indent (i)).
iii. Measurements to verify that the resistance of the supplementary equipotential bonding does not exceed the limits given in 710.415.2.2, such that in Group 1 and 2 medical locations:
- The resistance of protective conductors between the earth terminal of any socket-outlet or fixed equipment and any exposed-conductive-part and/or extraneous-conductive-part shall be such that the touch voltages 25 V AC or 60 V DC are not exceeded (710.411.3.2.5), and
- The measured resistance between the earth terminal of any socket-outlet or fixed equipment and any extraneous-conductive-part shall not exceed 0.2 Ω (see Fig 1).
As discussed previously in Issue 229 of Connections, in a TN and TT system, the conventional touch voltage of 50 V is reduced to a value of 25 V AC or 60 V DC in group 1 and 2 medical locations. As such, protective equipotential bonding conductors are required to equalise the potential difference and limit the magnitude of touch voltages during a fault. Bonding conductors are used, and typically arranged in radial circuits and connected independently to the Equipotential Bonding Busbar (EBB), in conjunction with circuit protective conductors for the particular circuit, connected at the local distribution board.
To meet the requirements of 710.641 (iii) the value of measured resistance1 between the EBB and each relevant point within the group 1 and 2 locations must be verified to ensure that the results obtained do not exceed those stated in 710.415.2.2, as shown in Fig 1.
Fig 1 Testing between exposed-conductive-parts and extraneous-conductive-parts in a medical location
A schedule of test data must be recorded for the supplementary protective equipotential bonding system. Such information, based on the format given in 710.514.9.1(vii), should include data relating to the measured value of resistance between connected items within the patient environment, and the cross-sectional area (csa) of protective equipotential bonding conductors. Due to limited space on the standard forms, this data may be recorded on a separate document and appended to the Electrical Installation Certificate (EIC).
Test results may be influenced by parallel paths, it may therefore be necessary to disconnect one end of the protective conductor when performing the test.
Note: The above tests are in addition to those required by Chapter 64 of BS 7671, the supporting information given in Health Technical Memorandum HTM 06-01: Electrical Services Supply and Distribution, and the HTM 06-02: Electrical Safety Guidance for Low Voltage Systems, published by the Department of Health.
Equivalent guidance documents are also available for the devolved nations (710.641).
Periodic verification
Persons undertaking the periodic inspection, testing and reporting in a medical location should have above-average knowledge and experience of working in such types of environments to enable them to safely and accurately assess the condition of the existing installation.Any periodic inspection and testing is subject to the requirements of Chapter 65 of BS 7671, as for any other installation (135.1 and 710.651). Although BS 7671 does not state which tests or the sequence for testing that form part of a periodic inspection, regulation 651.2 does state that the periodic inspection shall be supplemented by appropriate testing and measurements from Chapter 64.
The person(s) responsible for the initial installation design of the medical location is required to specify the interval for the first periodic inspection. Similarly, where an alteration or addition is made to an existing installation, information relating to the subsequent periodic inspection should be recorded in the EIC (644.4).
Table 1 gives recommendations for the interval to the first periodic inspection of a medical location and is partially reproduced from Table 3.2 in IET GN3.
However, when making the recommendation of the interval, the person compiling the EIC should take into account, amongst other things, Note 1 to regulation 710.651, which recommends inspections:
a) Annually – complete functional tests of the IMDs associated with the medical IT system, including insulation failure, transformer high temperature, overload, discontinuity and operation of audible/visual alarms.
b) Annually - measurements to verify that the resistance of the supplementary protective equipotential bonding does not exceed the limits given in regulation 710.415.2.2 and recorded in the format given in 710.514.9.1 (vii).
c) Three-yearly-measurements of leakage current of output circuits and of the enclosure of the medical IT transformers in no-load condition (710.512.1.1 (i)).
With regard to indents (i) and (iii), the testing of such systems should be carried out either by the IT system manufacturer or those with specific knowledge of medical IT systems.
Note 2 to regulation 710.651 advises that supporting information on periodic inspection and testing is given in the Health Technical Memorandum 06-01: Electrical Services Supply and Distribution. Client or local health authority requirements, if any, may also apply (see Note 6 to 710.1).
Summary
Although the general requirements for inspection and testing have been considered at the various stages throughout the life cycle of a medical location, this article in particular, has focused on both the additional requirements in Section 710 for initial verification (710.641) and those for periodic inspection and testing (710.65).Contractors undertaking work in such types of medical locations must be competent and have sufficient knowledge, training and experience to carry out the necessary work in a safe and effective manner.
Useful links:
https://www.england.nhs.uk/publication/electrical-safety-guidance-for-low-voltage-systems-htm-06-02/
https://www.nss.nhs.scot/publications/electrical-services-supply-and-distribution-shtm-06-01/
https://nwssp.nhs.wales/ourservices/specialist-estates-services/publications-and-information/welsh-health-technical-memoranda-whtms-health-technical-memoranda-htms/
1Where a TT system earthing arrangement is employed, a satisfactory value of resistance for the electrode will also be required.
