Published to Technical Construction Files on Nov 26, 2015
This document has been produced by Spiers Engineering Safety as a guide to our clients for evidencing the design of electrical circuit. It summarises the design process implied by BS EN 60204-1 and can be used in conjunction with it. Compliance with this document DOES NOT GIVE A PRESUMPTION OF CONFORMITY as it is not a harmonised standard.
Post installation electrical safety tests shall be completed in all cases regardless of calculations made during the design of the system in order to verify ‘as installed’ conditions, unless it is not reasonably practicable to do so. In this case please provide a justification/explanation for why it is not reasonably practicable to complete any applicable tests and what alternative actions have been taken to verify electrical safety.
BS EN 60204-1:2006+A1:2009, 18 Verification
The extent of verification will be given in the dedicated product standard for a particular machine. Where there is no dedicated product standard for the machine, the verifications shall always include the items a), b) and f) and may include one or more of the items c) to e):
a) verification that the electrical equipment complies with its technical documentation;
b) in case of protection against indirect contact by automatic disconnection, conditions for protection by automatic disconnection shall be verified according to 18.2;
c) insulation resistance test (see 18.3);
d) voltage test (see 18.4);
e) protection against residual voltage (see 18.5);
f) functional tests (see 18.6).
Please provide a response to the following questions including calculations where applicable for inclusion in the technical file.
1) Taking in to account the following notes from EN60204, is it suitable in this case to verify Zs by calculation using a Ze value provided by the client and the impedance of the line/cpc conductors based on CSA and length?
BS EN 60204-1:2006+A1:2009
A.4 Verification of conditions for protection by automatic disconnection of the supply
Where the calculations of the fault loop impedance or of the resistance of the protective conductors are available and when the arrangement of the installations permits the verification of the length and cross-sectional area of the conductors, verification of the continuity of the protective conductors may replace the measurement.
If yes, please continue….
If no, please provide the assumptions made in the selection and arrangement of the protective devices and the values (actual calculated values, not those identified in EN 60204 as maximum values) that you, the designer, would expect to achieve in order that this can be verified upon installation. Where measured values are not substantially the same as those intended by the designer then further investigation is required.
2) List all circuits within this panel
3) For each circuit, identify the methods used and in what areas of the machine, for protection against electric shock
4) List the part number and breaking capacity of the protective devices used for each circuit.
5) What is the Zs value for each circuit (by calculation)? Where can this be found?
6) In order to demonstrate that thermal resistivity changes have been taken in to account, for each circuit, does calculation show that Zs is less than or equal to 2/3 of U/I.
7) Where, for any circuit, the answer to (6) is no, then provide evidence of a satisfactory outcome of a more precise assessment in line with IEC 60364-6:2006
8) What is the worst case prospective fault current (by calculation) for each circuit and is the protective device suitable?
9) What is the disconnection time for each circuit (by calculation) and is it acceptable?
Note: for TN systems when the equipment is class 1 hand held or portable equipment and the equipment is supplied either through socket-outlets or directly without socket-outlets then the disconnection time is < 5s as per the table below
10) For each circuit, where disconnection times are not achieved in (9), do you, the designer, intend to provide supplementary bonding to ensure that a touch voltage does not exceed 50V?
11) For each circuit, where supplementary bonding is used for protection against electric shock, what is the Rpe required to limit the touch voltage to 50V.
12) Are all cables used manufactured to an applicable standard. Example standards as follows: Note: Where others standards are used, not listed below, please provide further details.
BS 6004, BS 6231, BS 6500, BS 7211, BS 5467, BS 6724, BS 6622, BS 7629
13) For each circuit, give details of any derating of current carrying capacity of conductors/cables after taking account of installation methods, environmental factors (temperature) and multi core cables. This information will include:
14) For each circuit, please give details of the co-ordination between conductors and protective devices providing overload protection. This will include:
15) For each circuit, is the relationship Ib ≤ In ≤ Iz achieved?
16) For each circuit, is the current carrying capacity (Iz) at least 1.45 times the min. current to operate the protective device (I2) ? to evidence that overload protective devices will protect cables and satisfy the 2 following conditions;
Ib ≤ In ≤ Iz
I2 ≤ 1,45 x Iz
Ib is the current for which the circuit is designed;
Iz is the effective current-carrying capacity, in amperes, of the cable for continuous service
according to Table 6 for the particular installation conditions:
In is the nominal current of the protective device;
NOTE 1 For adjustable protective devices, the nominal current In is the current setting selected.
I2 is the minimum current ensuring effective operation of the protective device within a
specified time (for example 1 h for protective devices up to 63 A).
This guidance is for electrical equipment (machines), erected and connected on site, where the continuity of the protective bonding circuits has not been confirmed following erection and connection on site. In this case for each circuit the following test shall be complete and documented:
Note: The scheme of inspection for Test 1 will be detailed in the report available for audit. This will include or make reference to the expected resistance values based on the design calculations which will be available for audit.
Note 2: Low resistance connections between conductive parts shall be achieved by earth bonding straps unless the connection is verified by test between each adjacent conductive part in the electrical path to the MET (earth bar).
Note 3: The low resistance measured shall be in the expected range according to the length, the cross sectional area and the material of the equivalent protective bonding conductor for the least favourable relevant circuit.